CA2511091C - Electrochemical stabilization and preconditioning process for municipal and industrial sludge - Google Patents

Abstract

Preconditioning process for sludge characterised in that it includes the following steps: acidifying the sludge so as to obtain a pH between about 3.5 and 5, to generate acidified sludge; electrolysing the acidified sludge in an electrolytic cell including electrodes of which at least one is an anode and one a cathode, the cell capable of generating an oxidising bactericide in situ, selected among hypochlorous acid and persulfuric acid, to generate electrolysed sludge, the electrolysed sludge having higher drainage properties and stability than the sludge.

Description

i, TITLE
[0001] ELECTROCHEMICAL PACKAGING METHOD AND
STABILIZATION OF MUNICIPAL AND INDUSTRIAL PURIFICATION SLUDGE
FIELD OF THE INVENTION

The present invention relates to an electrochemical process of conditioning and stabilization and municipal sewage sludge and industrial. This process allows a significant reduction of the indicators of pathogens and odors. This process also improves significantly the characteristics of sludge dewaterability thus favoring the increase of their dryness during their mechanical dehydration.
PRIOR ART

[0003] The treatment of municipal and industrial wastewater results in increasing production of sewage sludge. These various sludge obviously be eliminated by minimizing risks to human health and ecosystems. The the most commonly used methods of removing this biomass are agricultural landfilling, landfill and incineration. The final disposition These releases are subject to various technical and economic.

[0004] Incineration and burial, although sometimes necessary, allow that sludge removal without taking advantage of their physical properties and chemical. In addition, the difficulty of dehydrating in a very perFormant way the sewage sludge is a major obstacle to the disposal of sludge by burial or incineration. The scarcity of landfills sanitary (higher acceptance costs) and the very high costs inherent in incineration In recent years, sludge has increased the attractiveness of of the sludge as agricultural or silvicultural fertilizers.

4,

(0005) The agricultural valorization of sludge is the preferred option by authorities and it is widely practiced around the world. On time 30 to 40% of the world's wastewater sludge is currently used for soil fertilization. The integration of efficient processes of stabilization sludge in municipal and industrial wastewater treatment plants would to increase the possibilities of agricultural valorization of sludge Wastewater.

(0006) In addition, the use of a stabilization process also improve the sludge dewatering capacity would be desirable, holding account of the difficulties associated with this stage of sludge treatment treatment.
Thus, the conditioning of sewage sludge before dewatering mechanics is usually carried out by adding flocculant (polymer organic). However, mechanical dewatering of biological sludge conditioned remains difficult, so that the final dryness of the sludge dehydrated remains low and therefore generates transportation and disposition by significant application, burial, or incineration.

(0007) Stabilization of sludge in treatment plants is carried out usually by biological processes of aerobic or anaerobic digestion.
The aerobic digestion is a sludge stabilization technique used especially in small and medium-sized wastewater treatment plants. Stabilization by aerobic digestion is feasible on secondary sludge or sludge mixed (primary and secondary). The high energy cost associated with aeration of the Sludge is a factor limiting the use of this technology. When digestion aerobic bacteria metabolize organic matter solubilized in carbon dioxide, water and new bacterial cells. When the Soluble organic matter is depleted, bacterial cells die and thus release intracellular nutrients that serve as food at other organizations. The rate of mineralization of sludge depends mainly of residence time, temperature, as well as age of introduced sludge.
A
residence time of 14 to 20 days is usually required for a stabilization adequate biomass.

i,

Anaerobic digestion is also among the most commonly used methods.
used for the stabilization of municipal sewage sludge.
The use of the anaerobic digestion for the stabilization of sewage sludge dates back to many decades. In fact, methane fermentation has a very great power of cell biodestruction. It allows the elimination of a significant amount of organic materials. Anaerobic digestion of sludge has three stages:
at) during the first stage, the complex organic compounds of the part solid sludge undergoes transformation into complex organic compounds soluble; b) after this solubilization, the complex organic molecules are converted into volatile fatty acids, simpler compounds, by microorganisms anaerobic; c) the last step of the series reaction is mineralization volatile fatty acids to methane, carbon dioxide and sulfide hydrogen. In operation at most facilities municipal, the three stages of methane fermentation occur simultaneously in a closed digester. The sludge retention time is of the order of 30 days.

Both sludge treatment techniques, namely aerobic digestion and anaerobic, require the installation of large size digesters, what entails high capitalization costs. Moreover, the implantation of such systems in already operational stations may be difficult to achieve considering little space available. It must also be considered that the application of these sludge treatments do not improve their ability to be dehydrated and can even have an opposite effect.

When cost reduction is a priority objective, the power of fermentable sludge may be reduced, at least temporarily, by the alone addition of chemical reagents in combination or not with a treatment thermal.
The supply of lime can be carried out on liquid sludge or sludge dried. To obtain adequate disinfection power, sludge have to brought to pH 12 for at least two hours and preferably during 24 hours.
hours. The reduced cost of lime, its alkalinity and its favorable effect on the physical structure of the sludge make it the most used reagent. This latest does not increase the amount of biodegradable organic material contained in the sludge. A fermentation recovery is possible if the subsequent evolution of the conditions of the environment allows it. Another disadvantage of this technique is that the mass of sludge is not reduced, but at contrary, is increased as a result of the addition of alkaline agents. It is also necessary report that application of limed sludge on agricultural land is not desirable in areas where the soils are alkaline, as is the case, for example, in a much of the west of the American continent.

Chemical fixation is a process for the alkaline stabilization of sludge who transforms sludge into an inert product, which can be used for fill of land on the surface or for application on land. During the chemical fixation, a series of chemical reactions take place by combining the sludge dehydrated with chemical reagents, which allows obtaining a solid stable from the chemical, biological and physical point of view. The final product is almost odorless and virtually free of pathogenic microorganisms. Of more, the metals initially present in the sludge are fixed in the solid got.
Two chemical fixing processes have been patented (US Pat.
4,853,208 and 6,248,148) and marketed: Chem-x and N-Viro Soil. The process Chem-fix uses Portland cement and sodium silicate to produce a soil synthetic based sludge. The N-Viro Soil process uses lime and the cement dust as chemical additives. The N-Viro Soil process can also use fly ash and lime dust. Although these chemical stabilization techniques can be solutions alternatives promising, economic and technical constraints restrict, at right now, the use of these technologies. In addition, it should be noted that application These treatments do not improve the dehydration capacity of sludge.

Faced with the difficulty of dewatering sludge and sewage sludge problems related to the use of the usual sludge digestion processes, various processes combined chemical and thermal stabilization and pre-conditioning sludge have been developed in recent years. However, these p. , processes remain mostly too expensive to be widely used in municipal and industrial wastewater treatment plants.

Thermal stabilization, also known as wet combustion, consists of heat the sludge in the presence of air under very high pressure (up to 20 MPa and more) in order to achieve a thorough oxidation of the material organic, simultaneously with the physical transformation of colloidal materials (Dollerer and Wilderer, Wat. Sci. Technol., 1993, 28 (1), 243-248; Karlsson and Goransson, Wat.
Sci. Technol., 1993, 27 (5/6), 449-456). This stabilization technology serves also to the thermal conditioning of sludge. The sludge thus treated can, in fact, be filtered easily, with the achievement of a dryness of cakes between 40 and 70%. A process of oxidation under pressure (22 MPa) and high temperature (374 ° C) has also been proposed for waste treatment biological (Modell, Technological Materials, 1993, 8 (7/8), 131).

Another proposed approach consists in the strong hydrolysis of the material organic sludge by a heat treatment (150 to 160 ° C) in acid medium (pH 1 to 2) (Everett, Wat Res., 1974, 8, 899-906). This treatment allows a approximately 90% reduction in suspended solids important filterability of unhydrolyzed sludge. After treatment, sludge and the hydrolyzate are neutralized by the addition of lime, which leads to the production an inorganic sludge containing the extracted heavy metals, a sludge organic valorizable by soil amendment, and a strongly liquid fraction loaded in organic matter which has returned to the top of the processing chain of sludge.

The increase in the temperature of the sludge leads to a transformation irreversible of its physical structure, especially if they contain a strong proportion organic and colloidal materials. During heating, the gels colloidal are eliminated and the particulate hydrophilicity decreases sharply. The temperature of heater used for thermal conditioning varies between 150 and 200 ° C and the weather cooking time between 30 and 60 minutes, depending on the type of sludge and filterability desired. This i treatment mode is applicable on all predominantly sludge organic and allows to obtain relatively stable performances compared to chemical conditioning. In addition, this treatment allows a thickening important and fast sludge after cooking with obtaining sludge decanted at more than 120 g MES / L and even, in some cases, more than 200 g MES / L. The sludge structure is improved so that filtration without reagents is always possible. In fact, very strong dryness of filter cakes press are affected (> 50% ST) with thermal conditioning. It is also necessary hold account that the sludge thus conditioned is sterilized, therefore free from pathogenic microorganisms. The association of anaerobic sludge digestion and thermal conditioning is one of the most interesting sectors, because she allows the optimal reuse of biogas (methane). The implantation of However, thermal conditioning requires a costly investment in comparison to chemical conditioning. In addition, this heat treatment leads to the production of filtrate heavily loaded with organic matter and nitrogen ammonia which must be recycled at the head of the treatment plant. of the measures of Special prevention must also be taken to limit the disadvantages caused by the production of odors: thickener coverage and basins of retention, limitation of the purges of cooking reactors and deodorization of the air in the main speakers (cooking, thickening, dehydration).

Fujiyasu et al. (Canadian Patent No. 1,074,925) have, for their part, on point a method of chemical conditioning of biological sludge comprising a addition of 0.5% to 30% of hydrogen peroxide and the addition of a metal ion trivalent (or more), at a rate of 0.1% to 10% with respect to the mass of sludge dry.
This process also includes adjusting the pH of the sludge during the treatment at values between 4 and 9. This conditioning process, by adding of Inorganic products, however, does not include a subsequent stage of flocculation of sludge by addition of organic polymers prior to mechanical dehydration. However, the dehydration of biological sludge on equipment such as pressure band filters, requires the formation of large flocs, which requires the addition of organic polymers. The conditions of treatment proposed by Fujiyasu et al. including the addition of concentrations p ~

high levels of hydrogen peroxide and a trivalent ion make sure to make very difficult the subsequent use of an organic polymer.

Various electrochemical processes have also been proposed for the decontamination and conditioning of biological sludge (original municipal and Industrial). For example, Held and Chauhan (Canadian Patent Application No.
2.382.357) describe a method using electric discharges (fields pulsed electric power) at high voltages (15,000 to 100 OOOV). These sudden variations in electric fields affect bacterial cells in causing physiological disturbances, thus causing a release of the liquid inter and intracellular, which reduces to about 50% (w / w) the mass of sludge generated after mechanical dewatering of sludge. The best yields of this system (pulsed electric fields) are obtained by imposing high energies of about 100 J / mL or 400 kWh / tbs for sludge initials with a total solids concentration of 6%. The method of treatment sludge developed by Held and Chauhan, certainly improves the dryness of the sludge, but it remains ineffective for the elimination of odors foul.
Indeed, the only imposition of pulsed electric field does not necessarily induce a oxidation of malodorous compounds (propionic acid, butyric acid and sulfide of hydrogen), which compounds are commonly present in sludge treatment. In addition, this technique requires very sophisticated for the imposition of a pulsed electric field and therefore very expensive, which could limit its scope of application and its industrial development.

Ishigaki (Canadian Patent No. 1,334,658) has developed a cell electrolytic system for the treatment of sewage sludge, which is equipped a a multitude of flat electrodes placed in parallel (anodes and cathodes) and individually connected to the current generator capable of delivering a voltage ranging between 1.5 and 20 V. Electrodes of iron (anode) and steel stainless (cathode) are arranged so that an anode is immediately followed a cathode with a relatively small electrode distance (15 mm).
This process induces transformation of hydrophilic particulate substances (organic and inorganic) in hydrophobic substances, which allows i, improve the filterability of biosolids during mechanical filtration.
Another particularity of the method developed by Ishigaki, lies in the fact that within the electrolytic cell, there is a predefined area located in the vicinity of each electrode and inside which circulates an ascending current (or flow) sludge treated (thin layer of treated sludge), allowing regular removal the accumulation of gas bubbles (notably 02 and H2) and flocs located between the electrodes and on the surface thereof. This has the advantage on the one hand, to avoid congestion of the electrodes and, on the other hand, to improve the sludge electrodes in view of the physical and effective transformation of sludge by oxidation, reduction and neutralization.

The processes developed by Held and Chauhan (Canadian patent application No. 2,382,357) and Ishigaki (Canadian Patent No. 1,334,658) do not mention of the presence of a bactericidal oxidant whose action could be prolonged in the sludge at the outlet of the electrolyser (residual effect). The residual effect of the oxidant would ensure a more or less long term stability of sludge processed and dried. In fact, in most wastewater treatment plants, sludge dehydrated are initially stacked and stored at room temperature before any final disposal (landfilling, spreading or incineration). In particular, in the method developed by Held and Chauhan (patent application No. 2,382,357), even though bacterial cells have been physiologically disturbed by application of a pulsed electric field, they On the other hand, they are able to reactivate when they find themselves in a more favorable environment (in the absence, in particular, of a disruptive effect:
field electric). A bacterial reviviscence could thus be observed during the period of storage of the sludge and consequently, to cause nuisance olfactory effects induced by malodorous organic and inorganic compounds.

The object of the present invention is to propose an original method of electrochemical treatment of sewage sludge to avoid certain disadvantages of the methods of the prior art.

4, SUMMARY OF THE INVENTION

The method of the present invention aims to effectively oxidize the seeds pathogens and at the same time reduce the unpleasant odors of sludge purification while improving their filterability (increase in dryness).

More particularly, the invention relates to a treatment method of the sewage sludge including pathogens and molecules generating foul smells, characterized in that the sludge is subjected to brought to a pH of less than about 5.0 and greater than about 3.5 in the presence or not a support electrolyte, in a reactor comprising at least one anode and a cathode and subjected to an electrochemical reaction in such a way that the bacteria and malodorous compounds are reduced, and in that dehydrated more efficiently the sludge thus treated. Once the treatment electrochemical sludge can be flocculated with a flocculant a mechanical dewatering (eg press belt filter, filter press trays centrifuge, screw press, etc.). Dehydrated sludge can be stored for a relatively long period (2 to 3 weeks) before any disposition final (burial, spreading or incineration). The present invention enables advantageously to generate in situ a long-lasting bactericidal oxidant life which can furthermore provide a residual effect, namely, which avoids or of to slow down the possible recontamination of the treated sludge.

The term "sewage sludge" refers here to sludge from the treatment wastewater from domestic, municipal or industrial sources, including the primary sludge, secondary (biological) sludge, mixed sludge (mix of primary and secondary sludge), domestic sludge, municipal sludge, the paper mill sludge, refinery sludge, agro-food sludge, the sludge from septic tanks, lagoon sludge, de-inking sludge and a combination of two or more of these types of sludge. According to some modes specific embodiments of the present invention, the sludge has a concentration initial in total solids optimally varying between about 5 and about 50 g / L.
For total solids concentrations above 50 g / L, agitation Sludge mechanics becomes very difficult. For solid concentrations totals less than 5 μL, the effluent usually does not contain enough solid to obtain a dryness of acceptable dehydrated sludge.

The term "carrier electrolyte" refers here to an inorganic salt capable of increase in-situ production of an oxidant and improve conductivity of the sludge. Without limiting the previous definition, and according to production of the present invention, the carrier electrolyte is a salt of chloride or a sulphate salt. In particular, the chloride salts can be chosen among the NaCl, CaCl2, MgCl2, NH4Cl, KCl and FeCl3, whereas sulphates may be selected from Na2SO4, (NH4) 2SO4, CaSO4 and MgSO4.

The term "stabilization" refers here to the treatment that makes it possible to slow down proliferation of pathogens and foul odors in sludge following their conditioning and dehydration.

The term "flocculating agent" refers here to any agent capable of promoting the aggregation of suspended solids in sludge. Without limiting this definition, agents such as organic polymers can be used in the of the present invention.

The term "conditioning" refers here to the treatment applied to sludge before the flocculation step.

When referring herein to an interval, the term "
about "
always applies to both ends of the interval.
ACIDIFICATION

The acidification of the sludge can be carried out for example with acid sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, used acid or combination of two or more of these acids. Sulfuric acid with cause its significantly lower cost. In the case of the process operated in two phases (acidification and addition of successive ions), the initial acidification sludge, before the addition of chloride ions is usually carried out at a pH of enter about 3.5 and about 5.0. Less acidification of the sludge (pH>
5.0) night to in situ production of HCIO or H2S208 and cause a loss of effectiveness level of destruction of pathogen indicators (faecal coliforms and total) and transforming the hydrophilic particles into hydrophobic particles.
On the on the other hand, more pronounced acidification of the sludge (pH <3.5) causes a premature corrosion of dewatering equipment and rise significantly the cost of chemicals. Also, an acidification pronounced sludge is conducive to the formation of organochlorine compounds.
OXIDIZING AGENT

The use of a source of chloride or sulfate ions allows a go, to improve the conductivity (support electrolyte) of the sludge and, on the other hand, enrich chloride ion sludge required for the production of the oxidant (HCIO) or (H2S208). Chloride or sulphate ions can be added to the sludge if the used sludge does not contain enough to generate enough oxidizing agent.
Oxidation reactions

The anodic oxidation of chloride ions to gaseous chlorine is followed by her disproportionation in solution and leads to the formation of hypochlorous acid (HCIO), which reaction is favorable in slightly acidic medium (3.5 <pH <5.0).
The hydrolysis of chlorine is very fast, in a few seconds, so well that sludge is not treated with C12 but rather with HCIO.

We can schematize the reactions according to the following equations - at the anode + 7 Cl - - ~ CI Z + 2e -- in solution Clz + 2H20 r ~ HCIO + Cl- + H30 +

[0033] It is also possible to envisage a dissociation reaction of acid hypochlorous as HClO + H20 p Cl0- + H30 +

The last reaction leads to the formation of the hypochlorite ion (CIO).
) who is also a bactericidal oxidant but less effective than hypochlorous acid (HClO). It has been noted that, in general, molecular oxidants are more bactericidal than ionic oxidants. Indeed, the compounds Molecular molecules are very often very easily membranes bacterial as the ions.

The anodic oxidation of sulfate ions leads to the formation of acid persulfuric (H2S208) following the reactions - at the anode 2S04z- - ~ SzOg- + 2e-- in solution SZOg- + 2H + ~ HZS20 $

The anodic oxidation of the sulfate ions can be followed by hydrolysis of persulfuric acid formed and leads to the formation of molecular oxygen (02), or mono-persulfuric acid (H2SO5) or hydrogen peroxide (H2O2), which reagents are formed especially at temperatures above 60 ° C.

BOY WUT , The decomposition reactions of persulfuric acid can be schematised according to the following equations HZSZO $ + HZO - ~ 2504- + 4H + + ~ OZ
HzSzO $ + H20 ~ HZSOS + S04- + 2H +
S HZSOS + HZO - ~ H202 + S04- + 2H +

If we compare the bactericidal power of oxidants (H2S208, 02, H2S05 and H202) formed during the electrolysis of sludges containing sulphate ions, acid Persulfuric acid is the most effective oxidant, followed by mono-persulfuric acid and hydrogen peroxide, which are more oxidizing than oxygen molecular.

When sodium chloride or sodium sulfate is used, it is is at a concentration that is optimally smaller than about 10 g / L of sludge of the of this concentration, the dryness obtained is less good. Indeed, in presence of a large concentration of chloride or sulphate salts, the residual concentration of oxidizing agent generated is important, which can react with the flocculant thus preventing effective sludge flocculation.
PEROXIDE

During the electrolysis of sludge in the presence of sulfate ions, an addition of hydrogen peroxide at concentrations ranging from 0.2 to 0.3 g H202 / L
can be desirable to accelerate the kinetics of disinfection and deodorization of sludge.
ELECTROLYSIS

The electrochemical treatment according to the present invention increases the dryness sludge, destroys pathogens and reduces foul odors.
Increasing the dryness of sludge

The increase in dryness is due to three main factors

An action induced by the electric field: the presence of the field electric is favorable to the setting in movement of the colloidal particles, contributing so to aggregation or coagulation thereof. Also, the sudden variation of the field electric by a rapid passage from the anode to the cathode disturbs so physiological bacterial cells, followed by a release of the liquid inter and intra favorable for increasing the dryness of the sludge.

Direct oxidation at the anode and indirect solution (by generation of HCIO or H2S208) soluble organic compounds bound to colloidal and preventing the destabilization of the latter. Direct action and indirect Hydrophilic particulate matter is conducive to better aggregation of colloidal particles and dewatering of the treated sludge.

Direct oxidation at the anode and indirectly (by generation of HCIO or H2S20 $) bacterial cells causes release of the inter and intra cellular. The release of this liquid is favorable to the reduction of mass of sludge generated, so to a better dryness after dewatering sludge.
Effect on pathoenes

The standards relating to the maximum concentration of pathogens that the Sludge intended for spreading varies from one jurisdiction to another. Thus, sludge intended for spreading must contain a maximum of 1000 (MPN) coliforms faeces (Escherichia cols) per gram of dry matter (Criterion P1 -Government of Quebec, 2004). The reduction of pathogen also has as advantage of reducing foul odors during storage.

Electrolysis according to the present invention acts at three levels on the cell bacterial

[0047] a) a direct electrochemical action by oxidation at the anode. This oxidation deactivates bacteria (physiological disturbance) by oxidizing inclusions cytoplasmic membrane proteins consisting predominantly of phospholipids and protecting the bacteria;

B) an action induced by the electric field. The sudden variation of field electric by a rapid passage from the anode to the cathode also disturbs of physiological way the bacterial cells;

C) an indirect complementary electrochemical action by generation in situ hypochlorous acid or persulfuric acid. Hypochlorous acid or formed persulfuric can permanently destroy bacteria beforehand deactivated at the anode and thus prolong the microbicidal effect at the outlet of the electrolyser, especially during the storage of dewatered sludge.
Reduction of odors

[0050] The malodorous compounds (propionic acid, butyric acid, sulfide hydrogen, etc.) are directly oxidized at the anode and indirectly oxidized in solution with hypochlorous acid or persulfuric acid.

During electrolysis, it is desirable for an operation optimal, generate hypochlorous acid concentrations in such a way as to obtain a residual concentration of HCIO varying between approximately 0.02 and 0.7 g / L in the sludge in order to obtain an optimal effect of sludge disinfection (ex.
removal E, fecal and total coliforms), effective odor control, and a significant improvement in sludge dewaterability.

Electrolysis of the sludge carried out in such a way as to obtain a Residual HCIO concentration greater than 0.7 g / L results in important operations and generates a great hydrolysis of the material organic sludge, which generally results in a significant and desired concentration of organic matter in solution in the filtrates or supernatants during sludge dewatering. Also, a strong concentration of HCIO is likely to lead to the formation of organochlorine compounds in the treated sludge.

Preliminary tests can be performed to verify the residual concentration of oxidant generated. The reading of the conductivity can also give clues as to whether or not to add supporting electrolyte.
TEMPERATURE OF ELECTROLYSIS

The electrochemical reaction is carried out by imposing an intensity of current and electrical conductivity (usually between 0.8 and 10.2 mS / cm 2) so as to obtain a sludge temperature of between 10 and 60 ° C, preferably between about 20 and about 40 ° C and without outside of heat, the electrochemical reaction itself being exothermic. Like this at mentioned in the description of the prior art (Everett, Wat Res., 1974, 8, 899-906), an increase in temperature leads to a transformation of the physical structure of sludge, which induces a decrease in hydrophilicity particulate, which is conducive to better dewatering of sludge.
As well, an increase in temperature has the effect of increasing the speeds of chemical and biochemical reaction. The threshold of 60 ° C minimizes the decomposition reactions of persulfuric acid leading to formation less reactive transient species. In fact, during electrolysis, a spontaneous and progressive increase in temperature is observed. This increase in temperature is all the more important as the intensity of current increases while electrical conductivity decreases. It is therefore possible to increase the temperature of the sludge by increasing the intensity and to make it decrease by increasing the amount of chloride or sulphate ions.
INTENSITY AND DURATION OF ELECTROLYSIS

(0055) The current applied is partly a function of the duration of electrolysis. These parameters must be adapted according to the nature of the sludge to be treated.
We note, however, that short-term electrolysis with weak currents allows to obtain a better faradic yield for the in situ production of hypochlorous acid, but at the expense of chemical efficiency (ie oxidizing agent relative to the amount of chloride or sulfate ions in the sludge treat). In an industrial application, it is appropriate to adapt the parameters of this process according to the degree of contamination of the sludge (pathogenic germs, malodorous compounds) and total solids concentration. During the treatment, the intensity of the current is generally between 2 and 15A, which correspond to an anodic current density varying between 1.2 and 8.8 A / dm 2. The duration of the electrochemical reaction is usually between about 10 and 120 minutes.
REACTOR OR ELECTROCHEMICAL CELL

The terms "electrochemical reactor" and "electrochemical cell"
are used here indistinctly. The electrolytic cell is undivided (ie she does not have a membrane or partition separating the electrodes (anodes and cathodes) consists of at least one insoluble anode and cathode, the number of electrodes varying according to the volume or the capacity of the reactor used.
In this cell, the oxidation of chloride ions or sulphate ions into acid hypochlorous (HCIO) or persulfuric acid (H2S208) and the oxidation of organic compounds are preferentially carried out on the oxidation of water in oxygen. Without limiting the generality of the foregoing, the cell includes a anode with insoluble electrodes (catalytic electrodes) known as a strong surge in oxygen.

According to a variant of the process, the anode can be in the form of expanded metal cylinder of titanium coated with ruthenium oxide or oxide iridium (Ti / RuO 2 or Ti / IrO 2) and the cathode can be in the form of expanded metal cylinder, for example titanium (Ti). These electrodes (anode and cathode) are of appropriate mesh so as to avoid the obstruction of here treatment. For example, the anode and the cathode may have characteristics of following stitches: length LD = 12 mm; width AU = 6 mm and width of the slot N = 4 mm. These parameters can be determined precisely by the skilled in the art depending on the characteristics of the sludge to be treated. The Figure 1 presents a schematic view of the electrode mesh structure up to be used.

Such expanded metal electrodes provide good performance mechanical, a large exchange surface with respect to the solid electrodes and constitute, good promoters of turbulence, thus avoiding, on the one hand, avoiding the adsorption of gas bubbles on the electrodes and on the other hand, to increase the electrode-sludge transfer coefficient.

According to preferred embodiments, the electrodes are in the form of of expanded metal. This electrode configuration provides good performance mechanical, a large exchange surface with respect to solid electrodes and is a good promoter of turbulence to increase the coefficient of transfer to the electrode-slurry interface. This electrode structure is advantageous relative to that of the solid electrodes, which structure does not allow to induce a turbulent effect in the vicinity of the electrodes, which could lead to congestion of the electrodes.

By way of illustration, Figure 2 attached to this description describes a view schematic diagram of an electrochemical reactor for carrying out the process of treatment according to a specific embodiment of the invention. According to this Figure, the cylindrical reactor (1) is equipped with a mechanical stirrer (3) operated by a motor (4). The anode (5) is an expanded metal cylinder arranged coaxially +, around the stirrer (3) and the cathode (6) is placed coaxially with the agitator around of it so that the surface of the cathode is large area by compared to that of the anode. The anode and the cathode are connected to a generator of direct current (7). The agitator is a metal rod provided with a propeller and completely covered with PVC or Teflon plastic, so as to avoid a polarization of the rod and a disturbance of the electrochemical reaction. The distance inter-electrode is between about 1 and about 5 cm.

According to another variant of the process (see FIG. 3), the reactor is under cylindrical form (1) consisting of volume electrodes. The anode (2) can be present in circular form of expanded metal of titanium coated with oxide of ruthenium or iridium oxide (Ti / RuO 2 or Ti / IrO 2) and the cathode (3) can be present in circular form of expanded metal, for example titanium (Ti) or stainless steel (stainless steel). The electrolytic cell consists of a series electrodes (anodes and cathodes) placed in a stable and horizontal position and individually connected to the current generator. The electrodes are arranged (in parallel) so that an anode is immediately followed a cathode with an inter-electrode distance that can vary between approximately 1 and about 5 cm. In continuous mode, the cell is fed from the bottom (4) upwards (8) to ugly a pump (5) and the sludge successively pass through the anode and the cathode.
of the plates (10) of PVC perforated with holes (distributors), placed at the entrance and to the electrolyser outlet make it possible to ensure a distribution of the sludge on all the surface of the electrodes. A pump (7) with high flow ensures recirculation a part of the sludge (having passed through the cell) to ensure agitation sufficient to inside the electrolytic cell. A vent system (9) attached to a funnel (11) allows the evacuation of gases. Untreated raw sludge is stored in a tank (6). Treated sludge is transported to the injection site of polymer (12).

According to another variant of the process, the reactor can be in the form of parallelepipedic, consisting of voluminal electrodes. The anode can be present in rectangular expanded metal form of titanium coated with oxide of ruthenium or iridium oxide (Ti / RuO 2 or Ti / IrO 2) and the cathode may be form ~. . ..

rectangular expanded metal, for example titanium (Ti) or steel stainless (Stainless steel). The electrolytic cell thus consists of a set electrode placed in parallel (anodes and cathodes) and individually connected to the power generator. The electrodes are arranged so that a anode immediately followed by a cathode with an inter-electrode distance up vary between about 1 and 5 cm. The electrolytic cell is also equipped a sludge recirculation system (high flow rate) to ensure agitation enough inside this one.
FLOCCULATION

The electrolyzed sludge can then be flocculated by addition.
a flocculating agent. The optimal amount of flocculant can be determined by the observation of the resistance of the flocs and the appearance of the inter-floc liquid by example. Without limiting the generality of the foregoing, the flocculating agent used for the flocculation of treated sludge may be one of the organic polymers conventional employees for flocculation of sludge in water treatment plants waste. By way of examples, mention may be made of cationic polymers or anionic sold under the trademarks PercoIT "" and ZietagT "" by Ciba Company Specialty Chemicals Canada Inc., and LPMT "" by LPM Technologies Inc.
NEUTRALIZATION

(0064) The sludge can also be completely (pH> _ 7) or partially (pH <
7) neutralized by adding an alkaline agent according to the standards to avoid, for example, soil acidification during sludge spreading. This complete or partial neutralization may be done before or immediately after the sludge flocculation phase, or after a storage period for dewatered sludge. The alkaline agent used for neutralize the sludge can be for example lime, hydroxide of sodium, calcium carbonate, ammonium hydroxide, magnesium hydroxide, of the dolomite or an industrial worn base.

It is also possible to mix the sludge having undergone the treatment acid and oxidant with untreated sludge and then flocculate the sludge mixed by addition of a flocculating agent and finally dehydrating these with a usual equipment for mechanical dewatering. This way of doing things is particularly efficient in the case of the acid and oxidizing treatment of sludge biological (secondary sludge), which are then mixed with untreated primary sludge.

The method according to the present invention can advantageously be integrated in sludge treatment chains operating in factories purification without having to make any adjustments to the processing and dewatering of sludge already in place. In addition, the non-polluting appearance of electricity, the ease of automation that it brings, as well as the reduction of volume of equipment are parameters that characterize this invention, compared to the prior art using digesters or reactors important dimensions.

More particularly, according to a specific embodiment of the present The invention relates to a process for conditioning sludge purification device characterized in that it comprises the following steps : acidification of sewage sludge to reach a pH between about 3.5 and about 5 for generate acidified sludge; electrolysis of acidified sludge in a cell electrolytic electrode comprising at least one anode and at least one a cathode, the cell being able to generate in situ a bactericidal oxidant selected among hypochlorous acid and persulfuric acid, to generate sludge electrolyzed, electrolyzed sludge with dehydration and stability higher than sewage sludge. According to a more specific embodiment, the electrolytic cell includes at the anode insoluble electrodes to strong overvoltage of oxygen.

According to another specific embodiment, chloride ions are added to the sludge before electrolysis. According to another specific embodiment, the ions chlorides are added at a concentration ranging from about 0.6 to about 6.0 g CI-/ L.
According to another specific embodiment, chloride ions are added to the sludge and wherein the ions are selected from the group consisting of NaCl, CaCl 2, MgCl 2, of NH4Cl, KCl and FeCl3. According to another specific embodiment, the ions chlorides are added as NaCl at a concentration of at most 10 g NaCl / L.
according to another specific embodiment, the chloride ions are added in the form from NaCI
at a concentration of not more than 8 g NaCl / L.

According to another specific embodiment, sulphate ions and peroxide are added to the sludge before electrolysis. According to another specific embodiment, the sulphate ions are added at a concentration varying between approximately about 6.7 g S042- / L: According to another specific embodiment, the sulphate ions are added sludge and where the ions are selected from the group consisting of Na2SO4, (NH4) 2SO4, CaSO4 and MgSO4. According to another specific embodiment, the ions sulphates are added as Na2SO4 at a concentration varying between about 2.5 and about 10 g Na2SO4 / L and peroxide at a concentration variant between about 0.2 and about 0.3 g H 2 O 2 / L.

According to another specific embodiment, the electrolytic cell works at an intensity varying between about 2 and about 15A, which corresponds to a density anodic current ranging from about 1.2 to about 8.8 A / dm 2. According to one other Specific realization, the electrolytic cell operates at an intensity varying between about 5 and about 10A, which corresponds to anodic current density ranging from 2.9 to about 5.9 A / dm2. According to another embodiment specific, the electrolysis is applied for a duration varying between approximately 10 and approximately 120 minutes. According to another specific embodiment, the electrolysis is applied for a duration varying between approximately 30 and 60 minutes.
According to another specific embodiment, the electrolytic cell is type single cylindrical including concentric electrodes ers metal and disposed such that an anode is immediately followed by a cathode. According to one another specific embodiment, the electrolytic cell is of type single cylindrical ..

comprising a series of circular metal electrodes and placed in position stable and horizontal so that an anode is immediately followed by a cathode. It can also be of parallelepipedal shape comprising a series planar and rectangular electrodes arranged so that an anode is immediately followed by a cathode.
According to another specific embodiment, at least one of the anodes of the cell Electrolytic is made of a material selected from coated titanium ruthenium oxide (Ti / RuO 2), iridium oxide (Ti / 1rO 2), tin oxide (Ti / Sn02) platinum (Ti / Pt), and a combination of these materials, and the at least one cathode is made of a material selected from titanium (Ti), stainless steel (Stainless steel) and a combination of these materials. According to another specific embodiment, the electrodes are expanded metal or solid plates. According to another production Specifically, the electrodes are spaced so as to create a distance between electrode between about 1 and about 5 cm.
According to another variant of the present invention, the acidification of sludge is carried out by adding an inorganic acid chosen from the group consisting of of sulfuric acid, hydrochloric acid, nitric acid, acid phosphoric, a industrial spent acid and a combination of at least two of these acids. according to a Another specific embodiment of the present invention, electrolysis is conducted at a temperature of between about 10 and about 60 ° C
without input outside heat. According to another specific embodiment of the present the invention, the electrolysis is conducted at a temperature of between 20 and about 40 ° C without external heat input. According to another mode specific of Embodiment of the present invention, the electrolyzed sludge is mixed with sewage sludge. According to another specific embodiment of the present In the present invention, the sewage sludge has an initial concentration of solids totals ranging from about 5 to about 50 g / L. According to another specific mode of Embodiment of the present invention, the electrolyzed sludge is flocculated by the addition of a flocculating agent to generate flocculated sludge. According to one other Specific embodiment of the present invention, flocculated sludge are ~.

dried. According to another specific embodiment of the present the electrolyzed sludge is completely (pH7) or partially (pH
<7) neutralized by the addition of an alkaline agent. According to another mode specific of embodiment of the present invention, the dewatered sludge is neutralized by adding an alkaline agent immediately after dehydration. According to one other specific embodiment of the present invention, sludge dried neutralized by addition of an alkaline agent after a period of storage of sludge. According to another specific embodiment of the present invention, the alkaline agent used to neutralize the sludge is chosen from the group composed of lime, sodium hydroxide, calcium carbonate, hydroxide ammonium hydroxide, magnesium hydroxide, dolomite, an industrial worn base and a combination of two or more of these alkaline agents.
According to another specific embodiment, the present invention has the following object a process for conditioning sewage sludge, characterized in that comprises the following steps: acidification of the sewage sludge so as to reach a pH between about 3.5 and about 5 to generate acidified sludge; adding ion selected from the group consisting of chloride ions and sulfate ions; and electrolysis of acidified sludge in an electrolytic cell comprising of the electrodes including at least one anode and at least one cathode, the cell being capable of generating in situ a bactericidal oxidant selected from the acid hypochlorous and persulfuric acid, to generate electrolyzed sludge, sludge electrolyses with dehydration and higher stability than the sludge treatment. According to other specific embodiments of the present invention, the steps of acidification and addition of ions are carried out successively or simultaneously. The method can also be operated in the mode selected from group composed of the cuvée, semi-continuous and continuous modes.
DETAILED DESCRIPTION OF THE INVENTION
The method of the invention makes it possible to significantly improve the dewaterability characteristics of sludge by increasing the dryness of sludge during of their mechanical dehydration.

~ .., _ * ..

In addition, this technology is more efficient than the technologies.
usual mesophilic aerobic or anaerobic digestion for the destruction of indicators bacterial pathogens (> 5 log reduction units).
coliforms feces and total or elimination of more than 99.9%) and thus allows stabilization effective sludge. Finally, the application of this technology does not affect no significantly the nutrient content of sludge dehydrated and significantly reduces the generation of sludge odors.
The in situ generation of an oxidant for the treatment of sludge, gives also a practical advantage to the present invention because it allows a go to overcome the difficulties associated with the transport and handling of product processing by increasing the dryness of the sludge and secondly, it makes it possible to store sludge treated and dehydrated for a long time and without emanation unpleasant odors.
The invention has been described generally, and is now illustrated by nonlimiting examples of embodiment given as an indication.

Treatment of municipal sewage sludge The process according to the invention has been tested on digested sludge from of municipal wastewater treatment. These sludges are generated in reactors sequential biologics (RBS) and are collected at the end of the storage aerobic. The initial total solids concentration of these sludges was 21.6 gL.
The electrochemical reactor used for the tests is shown schematically in FIG.
2. The Cylindrical electrolytic cell made of plexiglass consists of two electrodes concentric and equipped with a propeller stirrer in Teflon "". The cathode is a ElectrolyticaT "brand titanium expanded cylinder, with a radius of 9 cm, height 28 cm, mesh size 9.08 dm2 and empty surface area between the stitches 7.87 dm2.
The centrally located anode surrounding the agitator rod is a cylinder in deployed titanium brand ElectrolyticaT "", radius 5 cm, height 28 cm, area of mesh 5.04 dm2 and empty surface area between the meshes 4.37 dm2. The volume treated . ~. ..,. ..

was 5.0 L and only one third of the active surface of the anode (1.7 dm2 ) and some cathode (3.0 dm2) was immersed in the effluent to be treated.
A series of experiments was carried out at current intensity and temperature variables in batch mode. The prior acidification of the sludge has been carried out by addition of concentrated sulfuric acid (H2SO4, 10 N), or hydrochloric acid concentrated (HCl, 3 N). The sludge was subjected to an electrolysis of 30 min, period during which the sludge was continuously agitated. A
times treated, the sludge was flocculated by addition of an organic polymer cationic sold under the trademark Zetag 7689T "" and sludge was filtered under empty for a period of 10 minutes and under a pressure of 750 mm Hg.
The SV1 filtration unit used in the tests included a pump vacuum, a buchnerT "" and Whatman 934AHT membranes "" (trademark) having a porosity of 1.5 gym. The dryness of the dewatered sludge was subsequently measured after drying of these at 105 ° C for a period of 24 h. The filtrates were preserved for chemical analysis (chemical oxygen demand (COD), ammonia nitrogen (N-NH4) and nitrates / nitrites (N- (NO- / NO2)).
The experimental conditions imposed and the results obtained are shown in Table 1. The data provided in the CONT column correspond to to the results of the control test (without treatment) performed in triplicate and serving as basis of comparison with treated sludge. In Test A, no reagent n / A
was added to sludge before electrolysis, unlike tests B, C and D at Classes of which prior acidification has been carried out, followed or not by the addition of of sodium chloride. Consumptions of chemical reagents are given in kilogram of 100% (pure) products per tonne of dry sludge (tbs). energy consumed during electrolysis is expressed in kilowatt hours per tonne of sludge dry (kWh / tbs).
The final pH values measured during the tests are between 4.53 and 6.81 while final POR values range from -181 to 129 mV. During the trials a sulfuric acid consumption of 14.6 or 27.6 kg H2S04 / tbs was employee.

. ... k ... .. ... .., ".

For hydrochloric acid, a contribution of 31.0 kg / HCl was tested.
On the other hand, an addition of 92.5 kg NaCl / tbs (4.3 g NaCl / L) was made during of the trials.
The optimum polymer dosage for the flocculation of non-sludge treated itself was approximately 1.9 kg / tbs. In comparison, concentrations of 1.4 and 2.3 kg polymer / tbs were required for sludge flocculation processed. As well, energy consumption between 252 and 1480 kWh / tbs was required for the stabilization of sludge.
An average dryness value of 12.5% (w / w) was measured during tested Control (CONT) of dewatering of untreated sludge carried out in triplicate.
The application of the process (tests B, C and D) made it possible to increase the dryness to of the between 14.4 and 23.0%, representing gains of between 1.9 and 10.5 points dryness. This increase in the dryness of dewatered sludge makes it possible to reduce the quantity of sludge generated, ie between 13.3 and 45.8% (w / w). In contrast, a loss dry matter content of 1.2 points was recorded following the application of the done without initial acidification of the sludge, nor prior addition of chlorine sodium. II is It is important to note that in tests B, C and D, the addition of NaCl reagents or HCI has allowed to enrich the sludge in chloride ion, which is favorable to the production in of hypochlorous acid useful for the disinfection and deodorization of sludge and useful as well as the dewaterability of sludge.

+. ... ".

PR-PACKAGING
AND STABILIZATION
electrochemical MIXED DIES RES AROB IES ISSUES N PURATION
ONE WATER
STATIO

MUNICIPAL USES

Parameters Tests CONT ABCD

pH ~ final 6.81 6.81 4.90 4.97 4.53 Final POR (mV) -200 -181 83 81 129 Temperature (C) 25.0 31.0 23.0 29.9 41.2 Intensity (A) 0.0 5.0 5.0 10.0 10.0 Conductivity (mS / cm2) 1.28 1.10 5.63 5.37 3.72 Duration of treatment - 30 30 30 30 (Min) SV1 SV1 SV1 SV1 SV1 filtration unit Consumption (kgltbs) H2S04 0.0 0.0 14.6 27.4 0.0 HCI 0.0 0.0 0.0 0.0 31.0 NaCl 0.0 0.0 92.5 92.5 0.0 Polymer 1,9 2,3 1,4 2,3 1,4 energy (kW / tbs) 0.0 807 257 842 1 480 Fertilizer value COD filtrate (mg / L) 489 417 831 1 280 1 190 N-NH4 filtrate (mg / L) 67.7 61.6 68.5 80.7 85.7 P-P04 filtrate (mg / L) 11.7 6.23 12.8 11.0 14.6 N02 / N03 filtrate (mg / L) 0.19 0.40 0.39 0.15 0.24 dehydration Final Siccit (% w / w) 12.5 11.3 15.7 14.4 23.0 Reduction of mass - -10.2 20.2 13.3 45.8 (%

P / P) SV1: filtration unit 78,5 cm2 under vacuum having a filtering surface of The in situ production of HCIO is also useful for the oxidation of compounds organic dissolved on colloidal materials. HCIO's action on these soluble materials allows better aggregation of colloidal materials and a more efficient dewatering of treated sludge. To this is added a increase of the temperature during the electrolysis, which induces a transformation physical sludge, conducive to better dewatering of sludge. In particular, the better dryness of dewatered sludge (23.0% w / w) recorded during the test D is partly attributed to an appreciable increase in temperature (41.2 ° C).
The preservation of the fertilizing elements of the sludge following the application of the The method was evaluated by measuring the concentration of COD, P-P04, N-NH4 and N- (NO3 / NO2) in the sludge dewatering filtrates. The values measured values show that the application of the process does not induce a loss appreciable the fertilizing value of the sludge, in particular as regards the elements P-P04, N-NH4 and N- (NO- / NO2). On the other hand, the application of the process leads to a increase in initial COD concentration (489 mg / L) to values included between 831 and 1280 mg / L. This increase of the COD in the filtrate of dewatering of treated sludge is mainly attributed to the action of HClO
organic molecules initially bound to the solid fraction of sludge, the treatment time not being long enough to obtain oxidation of these solubilized organic compounds (formation of H20 and release of CO2).
This first series of tests has thus demonstrated that it was possible to efficiently transform the particulate hydrophilic substances of the sludge into hydrophobic substances, which significantly improves the dewatering sludge while maintaining their fertilizing value.
The process was then applied to municipal sludge by injecting this different concentrations of sodium chloride, followed by the dehydration to using a vacuum filtration unit (SV2) having a filtering surface relatively large (compared to the SV1 filtration unit) and equipped with ....., ~ ... ~.,. .. ....

membranes with high porosity. The experimental procedure is succinctly described in Example 2.

Treatment of municipal sewage sludge by varying the amount electrolyte support The average concentration of total solids of municipal sludge used for testing is 22.6 g / L, or 2.3% solids. The process experimental employee is almost identical to the one used in the previous example. PH
initial sludge is adjusted by the addition of sulfuric acid. different concentrations of NaCl (0, 2, 4, 6 and 8 g / L) were added to the sludge to determine the optimal concentration for which better dehydration and best disinfection are obtained. Also, the addition of NaCl makes it possible to improve the conductivity of the reaction medium and thereby reduce the energy consumption.
The sludge is placed in the preceding reactor (FIG. 2), maintained with mechanical stirring and electrolyzed for a period of 60 minutes under a current intensity of 8 OA.
(0091) Subsequent dehydration of the sludge was carried out using a unit vacuum filtration system (SV2) having a filter area of 201 cm 2 and equipped with Whatman membranes (trademark) No. 4 of pore diameter variant between 20 and 25 ~, m. Samples of unfiltered sludge were kept for the measurements of faecal and total coliforms by the technique of the most likely (MPN).
Table 2 presents the experimental conditions used during the trials as well as the main results. The final pH values measured are between 3.85 and 5.10, while the redox potential (POR) values are included between 280 and 635 mV. The sulfuric acid consumptions are 29.2 and 23.3 kgH2S0 ~ / tbs, while a NaCl consumption varying between 88.5 and ., i ...

354 kg NaCl / tbs was also used. In addition, a consumption energy between 644 and 2340 kwh / tbs was required during testing. The contribution of NaCl in sludge (tests F, G, H and I) can reduce the quantity by up to 72%
energy consumed compared to test E during which no additional NaCl has not been performed. Optimal dosages determined by tests Preliminary flocculation was carried out by imposing concentrations variant between 0.5 and 8.0 kg / tbs of polymer for the flocculation of treated sludge and no treated are approximately 2.5 kg / tbs, with the exception of test H during which one concentration of 3.0 kg polymer / tbs was tested.

.A ~ .__ .._. . .., ~~, .._...

AEROBIC DERIVED SLUDGE FROM A WATER PURIFYING STATION
MUNICIPAL WELFARE
Parameters Tests CONT EFGHI

Final pH - 3.85 4.51 4.75 5.10 4.96 Final POR (mV) - 280 405 635 430 480 Temprature (C) 10.0 40.1 27 23 21.5 20.3 Intensity (A) 0.0 8.0 8.0 8.0 8.0 8.0 Conductivity (mS / cm2) 1.6 2.5 5.3 7.8 10.3 14.8 Duration of treatment - 60 60 60 60 60 (Min) HCIO residual 0.0 0.11 0.28 0.39 0.50 0.68 (G / L) SV2 SV2 SV2 SV2 SV2 SV2 filtration unit Consumption (kgltbs) H2S04 0.0 29.2 23.3 23.3 23.3 23.3 NaCI 0.0 0.0 88.5 177 266 354 Polymer 2.5 2.5 2.5 2.5 3.0 2.5 energy (kWh / tbs) 0.0 2340 1250 899 729 644 microorganisms Collar. fcaux (NPP / gbs) 140 885 1 130 133 <1 <1 Collar. totals (NPP / gbs) 355 1,600 2,000 412 _ 115 <1 dehydration Final Siccit (% 25.3 32.4 32.2 34.1 23.5 25.8 w / w) Reduction mass (% - 21.9 21.4 25.9 -7.6 1.9 w / w) SV2: filtration unit a surface under filter empty of 201 having cm2 . ~., _. . ~ .. ~. ~ ....

The average dryness obtained after dehydration of untreated sludge (CONT test) is 25.3%. The application of the process (tests E, F and G) allows to increase the dryness of dewatered sludge between 32.2% and 34.1%, gains from 6.9 to 8.8 dry points. This increase in the dryness of dewatered sludge reduces the amount of sludge generated by 21.4 to 25.9%. On the other hand, the dryness decreases (tests H and I) when the concentration of sodium chloride is set at 266 or 354 kg / tbs. This drop in dryness could be attributed to one residual concentration of relatively high HCIO (0.5 and 0.7 g / L
respectively), which is likely to interfere with the flocculant and avoid thus a good flocculation of sludge. The best dryness of sludge dried (34.2%) is obtained for an optimal sodium chloride concentration of 177 kg NaCl / tbs and a residual concentration of hypochlorous acid of 0.4 g HCI / L.
The disinfecting efficacy of the process was also evaluated.
The application process allows the effective removal of pathogen indicators, by the occurrence of faecal and total coliforms. Thus, concentrations relatively elevated faecal coliforms of 140,000 and 355,000 NPP / gbs were respectively measured in untreated sludge. In comparison, Residual concentrations of lower faecal coliforms 1 NPP / gbs (abatement greater than 5 log units) or between 133 and 1130 MPN / gbs have were measured in the treated sludge. Concentration measures residual total coliforms performed on the treated sludge indicate concentrations less than 1 NNP / gbs (allowance greater than 5 log units) or between 115 and 2,000 NPP / gbs.
In sum, the analysis of all the results presented in the Board 2, shows that Test G would be the optimal test for stabilization and conditioning of municipal sludge studied. This test requires a dose optimum of 177 NaCI kg / tbs, a concentration of 23.3 H2S04 kg / tbs, one dose of 2.5 kg polymer / tbs and energy consumption 899 kwh / tbs. Dryness relatively high of 34.1% (w / w) and an abatement of fecal coliforms and totals up to 3 log units (> 99.9% reduction) were obtained.

...., _ .., .. "~,." ~ _........., .... rt_x ..,, ......

In order to verify the reproducibility of the results obtained following the application of optimal conditions for the treatment of municipal sludge, a third series of tests was carried out according to the procedure described in example 3 next.

Treatment of municipal sewage sludge - audit of the reproducibility of the process Five liters of previously acidified municipal sludge, containing 4 g / L of NaCl (177 kg NaCl / tbs) were electrolyzed in the same apparatus (Figure 2) for 60 minutes under a current intensity of 8 OA. The dehydration subsequent sludge was carried out using a filtration unit under empty (SV2). These electrochemical stabilization tests, followed by flocculation and Sludge dewatering was done in triplicate. Tests of flocculation and dewatering of untreated sludge was also carried out in triplicate and compared to treated sludge. Table 3 compares the conditions experimental and the main results of sludge dewatering.
At the end of the electrochemical treatment, the average pH value of the sludge is 4.81 ~ 0.18 while that of the POR is 437 ~ 33 mV. In the case of untreated sludge an average pH value of 6.81 t 0.15 and a value Mean POR of -115 t 49 mV was measured. Negative values of POR
measured in untreated sludge are characteristic of a very reducer. In comparison, the high POR values measured in sludge treated indicate a highly oxidizing environment favored by in situ production from HCIO
during electrolysis.
The initial average temperature of the sludge was 11.3 t 0.4 ° C, while that of the treated sludge was 26.4 t 1.8 ° C. During the tests, the conductivity of the medium has increased from an average value of 2.3 to 0.7 mS / cm2 (initial sludge) to a final value of 8.2 t 0.4 mS / cm2 (treated sludge). Conductivity of the medium is _. ~ ", ~ .. _ .... ... ~~" .. .. _ ...

so relatively good. Also, an energy consumption of 862 ~ 9 kWh / tbs was required for sludge treatment.
The optimum polymer dosage for non-sludge flocculation treated was approximately 1.9 kg / tbs while an addition of 2.5 kg / tbs a was required for flocculation of treated sludge.

. ~ ..k__ r ..... ~~. ~ ... ... .. * ....._ AEROBIC DERIVED SLUDGE FROM A WATER PURIFYING STATION
MUNICIPAL WELFARE
Parameters Tests e Untreated sludge Processed sludge Final pH 6.35 0.15 4.81 0.18 Final POR (mV) -115 49 437 33 Intensity (A) 0.0 0.0 8.0 0.0 Temperature (C) 11.3 0.4 25.6 1.8 Conductivity (mS / cm2) 2.31 0.69 8.2 0.4 SV2 SV2 filtration unit Consumption (kgltbs) HzS04 0.0 0.0 23.3 0.0 NaCl 0.017017 0 Polymer 1.85 0.00 2.51 0.00 energy (kWh / tbs) 0.0 0.0 862 9 Fertilizer value COD filtrate (mg / L) 902 50 1 400 40 N-NH4 filtrate (mg / L) 76.1 5.3 76.8 1.7 P-P04 filtrate (mg / L) 4.6 1.0 2.6 0.1 K filtrate (mg / L) 94.2 9.5 121 1 Ca filtrate (mg / L) 59.7 2.8 124 2 Mg filtrate (mg / L) 66.6 1.9 97.3 1.2 microorganisms Fcaux coliforms (NPP / gbs) 200,000 21,000 <1 Total coliforms (NPP / gbs) 1,200,000 310,000 26 5 dehydration Final Siccit (% w / w) 23.9 1.3 33.4 1.4 Reduction of mass - 29.3 3.0 (%

w / w) a: triplicate tests SV2: Vacuum filtration unit having a filtering surface of 201 cm2 ~ ..._ ", ~ ... ._ ... ....,. ~. ~ ~ .. ~., [00101] An average dryness value of 23.9 t 1.3% (w / w) was recorded during dewatering tests of untreated sludge. In comparison, the application of electrochemical treatment makes it possible to increase the dryness of sludge to an average value of 33.4 t 1.4% (w / w), a dryness gain of 9.5 points. This increase in dryness results in, on average, a reduction of 29.3 ~ 3.0% in the mass of sludge generated following mechanical dewatering.
The low values of standard deviation calculated for each of the parameters operating procedures, as well as those relating to the estimation of the dryness of sludge dehydrated, testify to the repeatability of the results and the reliability of the process.
On the other hand, the disinfecting power of the process has been evaluated by the measurement after a two-week delay of the germs concentrations indicators of bacterial contamination (faecal and total coliforms) in sludge liquids (processed and untreated). The results obtained show an elimination total faecal coliforms (abatement greater than 5 log units) and one reduction appreciable total coliforms (upper abatement 4 units logarithmic).
The treatment therefore allows effective stabilization of municipal sludge point microbiological view.
[00104] Also, the fertilizing value of the sludges following the application of the process evaluated by measuring nutrient concentrations (COD, P-P04, NOT-NH4, Ca, K and Mg) in the sludge dewatering filtrates. Increases of concentrations of Ca, K and Mg in solution, estimated at 52, 22 and 32% were observed. An increase in organic matter (COD) in solution (estimated at around 35%) was also observed. A fraction of items nutrients (K, Mg and Ca) and organic matter, initially related to Contents insoluble sludge, is put in solution following the application of the process.
In In any case, the application of the process does not result in solubilization considerable of K, Mg, Ca and COD. A significant part of these elements is maintained in the solid fraction of the sludge making them suitable for spreading.

~~ _r ,, .. ~~ _. ._, .. m. . , .._., ....

In particular, the concentrations of NH4 measured in the filtrate of dewatering treated sludge are of the same order of magnitude as those recorded in the dewatering effluent of untreated sludge, then that the P-P04 concentration was reduced by 44% in the dewatering effluent of the treated sludge. This reduction of P-PO 4 in solution is attributed to a coprecipitation of phosphate ions in the solid fraction of the sludge during treatment. In a global way, the application of the method makes it possible to conserve the fertilizing value of sludge.
[00106] The reduction of foul odors of sludge following the application of the The process was also evaluated by a qualitative method of perception smell, based on a scale of 1 (no smell) to 5 (presence smell very unpleasant). To do this, thirteen individuals of sensitivities different have been tested. According to the established scale (1 = no smell, 2 =
smell not unpleasant; 3 = slightly unpleasant smell; 4 = unpleasant smell and 5 = very unpleasant smell), notes were assigned to the samples. At total, 7 samples were presented to the individuals among whom were three treated and dewatered sludge samples, three sludge samples no treated and dehydrated and a sample of black earth (sample control).
The control sample is a sample of black earth sold in the trade for residential growth of plants. This sample control served as a basis comparison with treated and untreated sludge. An average value of 3.8 t 0.8 was attributed to untreated sludge, while a value of 2.3 t 0.8 has been attributed to treated sludge. With regard to the control sample (soil black), a value of 1.2 t 0.4 has been attributed to it.
[00107] The olfactory odor perception being different from an individual to the other, the average obtained for each type of sample might not be representative. However, considering all the results obtained on each sample type as being a statistical population and in admitting that the sampled population follows a normal distribution, it was possible to determine the confidence interval of the true mean (p) with a degree of confidence of ~ .., ~ ..m ~ r. ..._.... , ~., ~ _ ._.__.._ 99%. Thus, the absolute average of the odors emanating from the control sample (Earth black) ranged from 0.92 to 1.54, while the absolute average of odors from treated sludge was between 1.97 and 2.63 and that of non sludge treated was between 3.47 and 4.13. It is important to note that intervals of determined confidences do not intersect. The volunteers therefore noted of the differences in odor intensities for each type of sample (sludge treated untreated sludge, and black earth). Electrochemical treatment induces a noticeable decrease in foul odors.
[00108] The preceding examples relate to the treatment of sludge Municipal. In particular, Example 3 made it possible to check the reproducibility and process reliability on such effluents. The following example 4 demonstrates applicability of the process on secondary sludge from a water treatment plant waste a pulp and paper mill. Operating conditions best determined during the previous tests (in particular as regards the time of treatment, NaCl concentration and current intensity) were directly applied.

Secondary sludge treatment of pulp and paper The initial total solids concentration of the sludge used to the tests was 12.5 g / L, or 1.3% solids. Sludge (5.0 L) initially acidified and containing 4 g / L of NaCl, were placed in the same reactor (described previously, Figure 2) and electrolyzed for a period of 60 minutes under a current intensity of 8 OA. Once treated, the sludge has been flocculated to using an organic polymer sold under the trademark LPM 9511 T "", followed by dehydration using vacuum filtration unit (SV2) described previously. Table 4 compares the operating conditions as well as main results of dewatering tests on treated and non-treated sludge treated made in triplicate. Also shown in this table are the concentrations of nutrients and the residual concentrations of seeds pathogen indicators.

[00110] The average pH and POR values of the treated sludge are respectively at 4.41 t 0.16 and 490 t 113 mV, while average values (pH
and POR) untreated sludge is 6.24 t 0.13 and -117 t respectively mV.
During the tests, an average acid consumption of 13.2 kg of H2S0.4 / tbs was used for sludge acidification. The rise in concentration chloride ions in the sludge (for the production of HCIO) required a supply of 200 kg NaCl / tbs. Also, an average energy consumption of 1100 t 40 kWh / tbs was required during sludge treatment.
[00112] The optimal polymer dosage for non-sludge flocculation treated and treated sludge was identical and was approximately at 3.0 kg / tbs.
[00113] The application of the method allows an effective elimination of pathogen indicators (faecal and total coliforms). So, a concentration of faecal and total coliforms of 216800 NPP / gbs and 284800 NPP / gbs was respectively measured in untreated sludge. In comparison, measures performed on treated sludge samples indicated a concentration residual fecal coliform less than 1 MPN / gbs (greater than log units) and a residual concentration of total coliforms of 18 MPN / gbs (abatement greater than 4 log units).
Measurements of ammoniacal nitrogen (, N-NH4) and phosphate (P-P04) in the dewatering filtrates of treated and untreated sludge show that the application does not solubilize these elements. On the other hand, a increase in the concentration of organic matter (COD) in solution (estimated at approximately 43%) was observed. A fraction of the organic matter initially related to the insoluble matter of the sludge, is put in solution following the application of process.

.... k .. ~~ .. ~. .... w. . , ..... ". ~ .. ~~ A ~ _a ......

SECONDARY SLUDGE FROM A WASTEWATER PURIFYING STATION
FROM A PLANT OF PAPERS AND PAPERS
Parameters Tests a Untreated sludge Processed sludge Final pH 6.24 t 0.13 4.41 0.61 Final POR (mV) -117 53 490 113 Intensity (A) 0.0 t 0.0 8.0 0.0 Temperature (C) 14.3 2.4 26.1 0.5 Conductivity (mS / cm2) 0.93 0.16 7.69 0.22 SV2 SV2 filtration unit Consumption (kgltbs) HZS04 0.0 0.0 13.2 0.0 NaCI 0.0 0.0 200 0 Polymer 3.0 0.0 3.0 0.0 energy (kWh / tbs) 0.0 0.0 1 100 40 Fertilizer value COD filtrate (mg / L) 550 173 970 36 N-NH4 filtrate (mg / L) 45.4 4.9 42.3 1.7 P-P04 filtrate (mg / L) 21.5 1.6 21.9 1.8 microorganisms Fc coliforms (NPP / gbs) 216,800 <1 Total Coliforms (NPP / gbs) 284,800 18 31 dehydration Final Siccit (% w / w) 19.9 0.2 25.3 1.2 Reduction of mass (% - 21.2 3.8 w / w) a: triplicate tests SV2: Vacuum filtration unit having a filtering surface of 201 cm2 (00115) An average value of 19.9% (w / w) was measured during the tests of dewatering of untreated sludge. The application of the process allowed increase the dryness at a value of 25.3% (w / w), a gain of 5.4 dry points.
This increase in the dryness of dewatered sludge reduces by 21.2% the mass sludge produced.
Moreover, the elimination of foul smelling sludge following the application of the process was evaluated by a qualitative method of perception Olfactory. An average value of 4.5 t 0.5 was attributed to non-sludge treated while a value of 2.4 t 0.4 was attributed to the treated sludge. With regard to the black soil sample (control sample), a value of 1.2 t 0.3 him has been awarded.
[00117] As before, confidence intervals containing the absolute average odors perceived by volunteers on each type samples were determined. So, the absolute average of odors from of the control sample (black earth) ranged from 0.90 to 1.40. In comparison, the absolute average odor from treated sludge was between 2.20 and 2.60 and that of untreated sludge was between 4.20 and 4.70. The treatment electrochemical sludge therefore allows a significant reduction of odors foul smelling from untreated sludge.
[00118] Examples 1 to 4 above show that the best stabilization tests (destruction of pathogens and elimination of odors) and dehydration (increased dryness of dewatered sludge) are obtained by addition of chloride ion in the sludge, which reagent is favorable to the in situ production of hypochlorous acid (HCIO) required for disinfection and to the deodorization of these biosolids. Analysis of treated and dehydrated sludge indicates, however, the possibility of generating by-products, such as chloroform (2.8 to 6.7 mg / kg DM), vinyl chloride (41 mg / kg DM), toluene (28.5 mg / kg DM), chlorophenol (2.1 mg / kg DM), dichlorophenol (3.5 mg / kg DM) and trichlorophenols (5.0 mg / kg DM), which are considered to be carcinogens.

-, + ... w._ ...... v4. ~ ".. ~, .. ~~ ....

These by-products are in fact obtained following the reaction of HCIO on some specific organic compounds called precursors (phenols, substances humic and fulvic, etc.) commonly found in wastewater and sludge treatment.
In order to avoid the formation of these toxic byproducts, the NaCl electrolyte can be substituted with Na 2 SO 4. The addition of Na2SO4 reagent allows indeed to enrich the sludge in sulphate ions whose anodic oxidation leads to the formation of persulfate or persulfuric acid (H2S20a), an oxidant bactericidal very powerful able to oxidize organic and inorganic compounds malodorous. Thus, a fifth series of tests was carried out according to the procedure described in Example 5.

Treatment of municipal sewage sludge with a source of sulphate ions title of electrolyte support [00120] Five liters of undigested mixed sludge, previously acidified (35.4 to 44.2 kg H2S0 ~ / tbs) and containing 2.5 to 10 g / L Na2SO4 (74.5 to 298 kg) Na2S0 ~ / tbs) were electrolyzed in the same reactor (previously described, Figure 2) for a period of 60 minutes under a current intensity of 8 OA.
A concentration of hydrogen peroxide of 0.2 and 0.3 g / L (5.70 and 9.51 kg H202 / tbs respectively) has been necessary in some cases to improve process performance. Initial concentration of total sludge solids used for testing was 33.6 g / L, or 3.4% solids. Once processed, sludge was flocculated using an organic polymer sold under the brand name of Percol 789T "", while the untreated sludge was flocculated at ugly of a polymer sold under the trademark Percol 757T "". The dehydration Subsequent sludge was carried out using a filtration unit under empty (SV2). These electrochemical stabilization tests, followed by flocculation and Sludge dewatering was performed and compared to untreated sludge.
The Table 5 compares the experimental conditions and the main results of sludge dewatering.

NON-DIGERATED MIXED SLUDGE OF A WATER PURIFYING STATION
MUNICIPAL WELFARE
Parameters Tests CONT JKLM
Final pH 5.4 4.17 4.03 4.12 4.11 Final POR (mV) -138 -70 -55 -35 -22 Temprature (C) 10.2 23.7 24.3 27.3 22 Intensity (A) 0.0 8.0 8.0 8.0 8.0 Conductivity (mS / cm 2) 0.8 6.5 6.3 4.7 10.2 Hard treatment 0.0 60 60 60 60 (Min) SV2 SV2 SV2 SV2 SV2 filtration unit Consumption (kgltbs) HzS04 0.0 36.3 41.7 35.4 44.2 Na2S04 0.0 149 149 74.5 298 HZOZ 0.0 5.7 0.0 9.51 0.0 Polymer 5,0 4,5 4,5 4,5 3,7 energy (kWhltbs) 0.0 586 532 708 422 Fertilizer value COD filtrate (mg / L) 2850 3480 3253 3481 3269 N-NH4 filtrate (mg / L) 182 191 181 178 185 P-P04 filtrate (mg / L) 53.0 63 120 32 174 microorganisms Coliforms fcaux 9.2 x 105 271 271 271 536 (CFU / 100 mL) Total coliforms 1.61 x 536 13095 271 5655 10 ' (CFU / 100 mL) dehydration Final Siccit (% 21.6 28.1 24.9 26.4 22.4 w / w) Rduct. mass (% 23.3 13.2 18.2 3.7 w / w) SV2: vacuum filtration unit having a filter surface of 201 cm2 The final pH of the treated sludge is between 4.03 and 4.17, then that the final POR values are between -70 and -22 mV. In the case untreated sludge, average pH values of 5.36 t 0.07 and -138 t 14 mV were measured.

.._ ~. ~ ..N. ~ __ .. ~. ..._.... "__ .. ~~~~ .....

The initial average temperature of the sludge was 10.2 t 1.7 ° C, then that treated sludge ranged from 22 to 27 ° C. During the tests, conductivity of the medium increased from an average value of 0.8 t 0.1 mS / cm 2 (sludge initials) to a final value of between 4.7 and 10.2 mS / cm 2 (treated sludge). The Conductivity of the medium is therefore relatively good. Also, a consumption energy consumption between 422 and 708 kWh / tbs was required for the stabilization of sludge. Energy consumption is even lower than the electrical conductivity increases.
The optimum polymer dosage for non-sludge flocculation treated was approximately 5.0 kg / tbs. In comparison, concentrations of 3.7 and 4.5 kg polymer / tbs were required for the flocculation treated sludge.
An average dryness value of 21.6% (w / w) was measured during the control test (CONT) for dehydration of untreated sludge carried out in triplicate. The application of the electrochemical process (tests J, K, L and M) has allowed to increase dryness to between 22.4% and 28.1% (w / w), either gains from 0.8 to 6.5 dry points. This increase in sludge dryness dehydrated reduces the amount of sludge generated, between 3.7 and 23.3% (w / w).
The disinfecting efficacy of the process was also evaluated by the measuring bacterial indicator bacteria concentrations (faecal and total coliforms) in liquid sludge (treated and non-treated).
treated). The The results obtained show an effective elimination of these indicators of pathogens. Thus, relatively high concentrations of coliforms fecal and total of 9.2 x 105 and 1.6 x 10 'CFU / g bs were respectively measured in untreated sludge. In comparison, residual concentrations of faecal coliforms between 271 and 536 CFU / g bs (> 99.0% reduction of faecal coliforms) were measured in the treated sludge. The measures of Residual concentrations of total coliforms made on sludge treated _. ~. ~~., w ... ~ .. ~,. ~ ._,. _. ~ .. "P .. .. _.._ indicate concentrations between 536 and 13 095 CFU / g bs (> 99.9%) of reduction of total coliforms).
On the other hand, the fertilizing value of the sludge following the application of process was evaluated by measuring nutrient concentrations (COD, P-P04 and N-NH4) in the sludge dewatering filtrates. Except of the concentration of P-P04 measured in tests K and M, all settings recorded shows that the application of the process does not induce a loss considerable the fertilizing value of the sludge. For example, an increase in concentration of COD between 12 and 18% and a slight increase in N-NH4 between 1.6 and 5%
were measured following the application of electrochemical treatment. In particular In test L, a decrease in the concentration of P-P04 in the filtrate of dewatering of treated sludge was recorded. A non negligible nutrients is therefore maintained in the solid fraction of sludge processed.
[00127] In sum, the analysis of all the results presented in Table 5 shows that the L-test would be the optimal test for stabilization and the conditioning of municipal sludge studied. This test requires a dose optimum of 74.5 kg Na2SOa / tbs, a concentration of 35.4 kg H2S0 ~ / tbs, a concentration of 9.51 kg H202 / tbs and a dose of 4.5 kg polymer / tbs. A
energy consumption of 708 kWh / tbs is also required for the electrochemical treatment of sludge. Relatively high dryness of 26.4 (w / w) and a fecal and total coliform abatement of up to 4 units logarithmic (> 99.9% coliform reduction) are obtained.
[00128] The concentration of organic pollutants in the treated sludge from the optimal test L was analyzed and compared to untreated sludge.
The The main organic contaminants found in these sludges are grouped together Table 6.

. ~. ~ .a,., .. ~ .. ~ ....,. . ... "

TABLE 6 CONCENTRATIONS OF TRIHALOMETHANES (THM), HYDROCARBONS
MONOCYCLIC AROMATICS (HAM) AND COMPOUNDS
PHNOLIQUES

IN THE CHILDREN
LIQUID SLUDGE
NON-TREATS AND TREATIES, MEASURES WHEN APPLYING OPTIMAL CONDITIONS
OF

TREATMENT OF RES SLUDGE
MIXED NON-DIG

Organic Pollutants Units Sludge Sludge untreated milked Trihalomthanes (THM) Vinyl chloride wg / L <8 <8 Dichloromthane wg / L <200 <200 Chloroform ~ g / L 54 22 Carbon tetrachloride ~ g / L <4 <4 1,12,2-Ttrachlorothane ~ g / L <20 <20 Bromoform ~ g / L <4.0 <4.0 Aromatic hydrocarbons monocyclic (HAM) Benzene ~ g / L <8.0 <8.0 Tolune ~ g / L 10000 1400 Chlorobenzene ~ g / L <8 <8 thylbenzene ~ g / L <4 15 Styrene ~ g / L <4.0 <4.0 1,3,5-trimethylbenzene ~ gIL 5.2 <4.0 1,2,4-trimethylbenzene ~ g / L 16 <4.0 1,3-dichlorobenzene ~ g / L <4 <4 1,4-dichlorobenzene ug / L 26 5.5 Phnolic compositions Phnol ~ gIL 130 53 o-crsol ~ g / L 23 160 m-crsol ~ g / L 13 53 p-crsol ~ g / L 2200 770 2-chlorophnol ~ g / L <7.0 <5.0 3-chlorophnol ~ g / L <7.0 <50 4-chlorophnol ~ g / L <1.0 1.8 2,4 and 2,5 Dichlorophnol ~ g / L <10.0 <7.0 3,5-Dichlorophnol ~ g / L <7.0 <5.0 2,3-Dichlorophnol wg / L <5.0 <5.0 2,4,5-Trichlorophnol ~ g / L <5.0 <4.0 2,3,4-Trichlorophnol ~ g / L <4.0 <3.0 3,4,5-Trichlorophnol ~ g / L <5.0 <4.0 2,3,4,5-Ttrachlorophnolwg / L <4.0 <3.0 Pentachlorophnol ~ g / L <4.0 <3.0 _. ~ ...:. ~~. ~ ... ~ ..., .. ~. ...... .. ~ ~ ~ ._ w..m ._.._.

[00129] The concentrations of trihalomethanes (THM) measured in the treated and untreated sludge were mostly below of detection, with the exception of chloroform. A concentration of 54 ~ g / L was recorded in untreated sludge compared to 22 ~, g / L measured in treated sludge, a reduction of more than 50% chloroform.
In the case of monocyclic aromatic hydrocarbons, the highest concentration measured in untreated sludge was 10,000 ~, g / L of toluene, compared to 1,400 μg / L recorded in the treated sludge, be one 86% removal of toluene during treatment.
Furthermore, the analysis of phenolic compounds in sludge initial (untreated sludge) indicates a concentration of 130 pg / L of phenol and a concentration of 2,236 ~ g / L of cresol (o-cresol, m-cresol and p-cresol). In comparison, the application of electrochemical treatment reduces the concentration of phenol and cresol at 53 wg / L ( a 59% phenol reduction) and 963 μg / L (57% reduction in cresol).
Ultimately, the proposed electrochemical treatment makes it possible to to stabilize the sludge from the microbiological point of view, to increase the dryness sludge dehydrated and retain the fertilizing value of the sludge while favoring significant elimination of organic pollutants.

Claims (35)

1. Process for conditioning sewage sludge characterized in that it comprises:
(a) an acidification of the sewage sludge so as to reach a pH between about 3.5 and about 5 to generate acidified sludge;
b) electrolysis of acidified sludge in a cell electrolytic device comprising electrodes of which at least one anode and at least one cathode, in order to generate in situ hypochlorous acid or persulfuric acid as bactericidal oxidant, to generate electrolyzed sludge;
and c) flocculation of the electrolyzed sludge by the addition of a flocculating agent for generating flocculated sludge, flocculated sludge with dehydration and stability higher than sewage sludge. The method of claim 1, wherein the cell electrolytic system includes insoluble electrodes with high voltage at the anode oxygen. The method of claim 1 or 2, wherein Chloride ions are added to the sludge before electrolysis. 4. The process according to claim 3, wherein the ions chlorides are added at a concentration varying between approximately about 6.0 g Cl- / L. The method of claim 3 or 4, wherein the Chloride ions are added as NaCl, CaCl 2, MgCl 2, NH 4 Cl, KCl or FeCl3. The method of claim 3, wherein the ions chlorides are added as NaCl at a concentration of not more than 10 g NaCl / L. The method of claim 3, wherein the ions chlorides are added as NaCl at a concentration of not more than 8 g NaCl / L. The method of claim 1 or 2, wherein Sulphate ions and peroxide are added to the sludge before electrolysis. The method of claim 8, wherein the ions sulphates are added at a concentration varying between approximately 6.7 g SO4 2- / L. The method of claim 8 or 9, wherein the sulfate ions are added as Na2SO4, (NH4) 2SO4, CaSO4 or MgSO4. The method of claim 8, wherein the ions sulphates are added as Na2SO4 at a concentration varying between about 2.5 and about 10 g Na2SO4 / L and peroxide at a concentration ranging from about 0.2 to about 0.3 g H2O2 / L. 12. Process according to any one of claims 1 to 11, in which the electrolytic cell operates at a varying intensity between about 2 and about 15A, which corresponds to a current density anodic ranging from about 1.2 to about 8.8 A / dm 2. 13. Process according to any one of claims 1 to 11, in which the electrolytic cell operates at a varying intensity between about 5 and about 10A, which corresponds to a current density anodic ranging from 2.9 to about 5.9 A / dm2. 14. Process according to any one of claims 1 to 13, in which the electrolysis is applied for a duration varying between about 10 and about 120 minutes. 15. Process according to any one of claims 1 to 13, in which the electrolysis is applied for a duration varying between about 30 and 60 minutes. 16. Process according to any one of claims 1 to 15, in which the electrolytic cell is of a single cylindrical type comprising concentric metal electrodes and arranged in such a way an anode is immediately followed by a cathode. 17. Process according to any one of claims 1 to 15, in which the electrolytic cell is of a single cylindrical type comprising a series of circular metal electrodes and placed in position stable and horizontal so that an anode is immediately followed of a cathode. 18. Process according to any one of claims 1 to 15, in which the electrolytic cell is of parallelepipedal shape comprising a series of flat and rectangular electrodes arranged such so that an anode is immediately followed by a cathode. 19. Process according to any one of claims 1 to 18, wherein the at least one anode is made of coated titanium ruthenium oxide (Ti / RuO2), iridium oxide (Ti / IrO2), tin oxide (Ti / SnO2), platinum (Ti / Pt), or a combination of these materials, and minus one cathode is made of titanium (Ti), stainless steel (stainless steel) or in a combination of these materials. 20. Process according to any one of claims 1 to 19, wherein the electrodes are of expanded metal. 21. Process according to any one of claims 1 to 20, wherein the electrodes are spaced apart to create a distance inter-electrode of between about 1 and about 5 cm. 22. Process according to any one of claims 1 to 21, in which the acidification of the sludge is carried out by adding acid sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, a industrial spent acid or a combination of at least two of these acids. 23. Process according to any one of claims 1 to 22, in which the electrolysis is carried out at a temperature between about 10 ° C and about 60 ° C without external heat input. 24. Process according to any one of claims 1 to 22, in which the electrolysis is carried out at a temperature between about 20 ° C and about 40 ° C without external heat input. 25. Process according to any one of claims 1 to 24, in which the electrolyzed sludge is mixed with sludge treatment. 26. Process according to any one of claims 1 to 25, in which the sewage sludge has an initial concentration of solid totals ranging from about 5 to about 50 g / L. 27. Method according to any one of claims 1 to 26, wherein the flocculated sludge is dehydrated. 28. Process according to any one of claims 1 to 26, wherein the electrolyzed sludge is completely (pH> = 7) or partially (pH <7) neutralized by the addition of an alkaline agent. The method of claim 27, wherein the sludge dehydrated are neutralized by addition of an alkaline agent immediately after dehydration. 30. The method of claim 27, wherein the sludge dehydrated are neutralized by the addition of an alkaline agent after sludge storage period. 31. Method according to any one of claims 28 to 30, wherein the alkaline agent used to neutralize the sludge is from lime, sodium hydroxide, calcium carbonate, hydroxide Ammonium hydroxide, magnesium hydroxide, dolomite, a spent base industrial or a combination of two or more of these alkaline agents. 32. Process for conditioning sewage sludge characterized in that it comprises:
(a) an acidification of the sewage sludge so as to reach a pH between about 3.5 and about 5 to generate sludge acidified;
b) an addition of chloride ions or sulphate ions;

c) electrolysis of acidified sludge in a cell electrolytic electrode comprising at least one anode and at least one minus one cathode, in order to generate in situ hypochlorous acid or persulfuric acid as a bactericidal oxidant, to generate sludge electrolyzed; and d) flocculation of the electrolyzed sludge by the addition of a flocculating agent for generating flocculated sludge, flocculated sludge with dehydration and stability higher than sewage sludge. The method of claim 32, wherein the steps acidification and addition of ions are carried out successively. 34. The method of claim 32, wherein the steps acidification and addition of ions are carried out simultaneously. 35. Process according to any one of claims 1 to 34, operated in cuvée, semi-continuous or continuous mode.