CA2472879A1 - Electrochemical stabilization and preconditioning process for municipal and industrial sludge - Google Patents

Abstract

A method for electrochemical treatment of pre-dewatering packaging of sewage sludge, characterized in that it comprises the following steps: acidification of the sludge so as to reach a pH sufficiently high to avoid corrosion and low enough to significantly reduce the indicators pathogens; treating acidified sludge in an electrolytic cell capable of generating a bactericidal oxidant in situ at a concentration sufficiently high to disinfect the sludge and low enough to prevent the formation of organochlorine compounds in the sludge; electrolysing the sludge for a period of time sufficient to stabilize the sludge and improve dewaterability.

Description

TITLE
Electrochemical process for stabilizing and pre-conditioning municipal and industrial sewage sludge FIELD OF THE INVENTION
The present invention relates to an electrochemical process of stabilization and pre-conditioning of municipal sewage sludge and industrial. This process allows a significant reduction of the indicators of pathogens and odors. This process also improves significantly the dewaterability characteristics of sludge in raising the dryness of sludge during mechanical dewatering.
PRIOR ART
Municipal and industrial wastewater treatment 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.
Incineration and landfilling, although sometimes necessary, allow sludge removal without taking advantage of their properties physical and chemical. In addition, the difficulty of dehydrating in a very performance of sewage sludge is a major obstacle to disposition sludge by landfill or incineration. The scarcity of sites sanitary landfill (higher acceptance costs) and the high costs high inherent to the incineration of sludge have increased in recent years, the attractiveness of using sludge as agricultural fertilizer or forestry.
The agricultural valorization of the sludge is the option preferred by the governmental authorities and is widely practiced around the world.
AT
Currently, 30 to 40% of sewage sludge produced in the world are used for soil fertilization. Process integration performing sludge stabilization in municipal wastewater treatment plants and industrial would increase the possibilities of recovery of waste sludge of Wastewater.
In addition, the use of a stabilization process also improve the sludge dewatering capacity would desirable, taking into account the difficulties associated with this stage of sludge treatment treatment. Thus, the conditioning of sewage sludge before their Mechanical dehydration is usually done by adding flocculant (organic polymer). However, mechanical dewatering of biological sludge so conditioned remains difficult, so that the final dryness of the sludge dehydrated remains low and therefore generates transportation and disposition appreciable.
The stabilization of sludge in the 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.
Anaerobic digestion is also one of the most effective methods commonly used for the stabilization of municipal sewage sludge.
The use of anaerobic digestion for sludge stabilization purification goes back several decades. In fact, methane fermentation has a very great

2 cell biodestruction power. It allows the elimination of a quantity important organic matter. Anaerobic sludge digestion involves three stages: a) during the first stage, organic compounds complex of the solid part of the sludge undergo a transformation into organic soluble complexes; b) after this solubilization, the organic molecules Complexes are converted into volatile fatty acids, simpler compounds, by of the anaerobic microorganisms; (c) the last stage of the series reaction is the complete mineralization of volatile fatty acids to methane, carbon and hydrogen sulfide. In operation of most amenities Municipalities, the three stages of methane fermentation occur simultaneously in a closed digester. The sludge retention time is the order of 30 days.
Both sludge treatment techniques, ie aerobic digestion and anaerobic, require the installation of size digesters important, this which results in high capitalization costs. In addition, the implementation of such systems in already operational stations may be difficult feasible given the limited space available. It must also be considered that the application of these treatments on the sludge does not improve their capacity to be dehydrated and may even have the opposite effect.
When the reduction of the investment amount is a goal priority, the fermentable power of sludge can be reduced, at least temporarily, by the mere addition of chemical reagents in combination or no with a heat treatment. The supply of lime can be carried out on sludge liquids or on dewatered sludge. To obtain a power of disinfection the sludge should be brought to pH 12 for at least two hours and preferably for 24 hours. The reduced cost of lime, its alkalinity and his favorable effect on the physical structure of the sludge make it the most reactive used.
This last technique does not modify the quantity of organic matter biodegradable contained in the sludge. A fermentation recovery is therefore possible if the subsequent evolution of the conditions of the environment allows it. A
other disadvantage of this technique is that the mass of sludge is not reduced, But on the contrary, it is increased as a result of the addition of alkaline agents.
It takes

3 also point out that the application on agricultural lands of sludge limed is not not desirable where soils are alkaline, as is the case, for example, in much of the west of the American continent.
Chemical fixation is an alkaline sludge stabilization process which converts the sludge into an inert product, which can be used to the 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 problems related to the use of the usual sludge digestion processes, various combined chemical and thermal stabilization processes and conditioning sludge has been developed in recent years.
However, these processes remain for the most part too expensive to be employees commonly used in municipal and industrial wastewater treatment plants.
Thermal stabilization, also known as wet combustion, consists heat sludge air, very high pressure in sub (up to 20 MPa and more) in order to achieve oxidation grows from the the one organic, simultaneously 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 technology of stabilization is also used for thermal conditioning of sludge. Sludge thus treated can indeed be filtered easily, with the obtaining dryness cakes between 40 and 70%. A pressure oxidation process (22 MPa) and at high temperature (374 ° C) was also proposed for the treatment of biological waste (Modell, Mater Techno, 1993, 8 (7/8), 131).
Another proposed approach is the strong hydrolysis of the organic matter from sludge by heat treatment (150 to 160 ° C) in the middle acid (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 of the temperature of the sludge leads to a irreversible transformation of its physical structure, especially if they contain a high proportion of organic and colloidal materials. During heating, the gels Colloidal particles are eliminated and particulate hydrophilicity decreases sharply. The heating temperature used for thermal conditioning varies enter 150 and 200 ° C and the cooking time between 30 and 60 minutes, depending on the type of mud and the desired filterability. This method of treatment is applicable to all sludge to predominance and allows for relatively high performance stable compared to the chemical conditioning. Moreover, this treatment allows a large and rapid thickening of sludge after cooking with obtaining sludge decanted above 120 g MES / L and even, in some cases, over 200 boy Wut MY / L. The structure of the sludge is improved so that a filtration without bring reagents is always possible. In fact, very strong dryness filter cakes-press are reached (> 50% ST) with thermal conditioning. It must also take into account that the sludge thus conditioned is sterilized, therefore

5 free of pathogenic microorganisms. The association of anaerobic digestion of the sludge and thermal conditioning is one of the most interesting, because it allows the optimal reuse of biogas (methane). Implantation from the pre-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, developed a process for the chemical conditioning of biological sludge comprising a contribution of 0.5% to 30% of hydrogen peroxide and the addition of an ion metallic 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 press belt filters, however, requires the training large flakes, which requires the addition of organic polymers. The conditions of treatment proposed by Fujiyasu et al. including the addition of concentrations 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

6 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 kWhltbs 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 nauseating odors.
In indeed, the imposition of a pulsed electric field alone does not necessarily a oxidation of malodorous compounds (propionic acids, butyric acid and hydrogen sulphide), 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) 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 range between 1.5 and 20 V. The electrodes are arranged such kind an anode is immediately followed by a cathode with an inter relatively weak electrode (15 mm). This process induces the transformation of hydrophilic particulate substances (organic and inorganic) in substances which improves the filterability of the biosolids during of the mechanical filtration. Another peculiarity 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 within which circulates current (or flow) ascending treated sludge (thin layer of treated sludge), allowing to regularly eliminate the accumulation of gas bubbles (in particular 02 and H2) and of flocs located between the electrodes and on the surface thereof. This has for advantage on the one hand, to avoid congestion of the electrodes and, on the other hand, to improve sludge-electrode exchanges for the physical and effective transformation of sludge by oxidation, reduction and neutralization.

7 The processes developed by Held and Chauhan (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 extend in the sludge at the outlet of the electrolyser (residual effect). The effect remnant of the oxidant would ensure a more or less long-term stability of sludge treated and dehydrated. Indeed, in most treatment plants, the Dehydrated sludge is initially stacked and stored at room temperature before any final disposal (landfill, land application or incineration).
In particular, in the method developed by Held and Chauhan (application for Canadian Patent 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 sludge storage period and, as a result, lead to odor nuisance induced by organic and inorganic compounds malodorous.
The object of the present invention is to propose an original method Electrochemical treatment of sewage sludge to avoid some disadvantages of the methods of the prior art.
According to some specific embodiments, the method aims to to quantitatively oxidize pathogenic germs and simultaneously reduce odor nauseating while improving sludge filterability (increase in dryness).
SUMMARY OF THE INVENTION
The proposed process applies equally well to secondary sludge (organic) and mixed (mixture of primary and secondary sludge), of origin municipal and industrial, optimally in a moderately acidic environment (pH
less than 5.0 and greater than 3.5). Once the electrochemical treatment realized, the sludge is flocculated with a flocculating agent followed by dehydration mechanical (eg pressure band filter, plate filter, centrifuge, screw press, etc.). Dehydrated sludge can be stored during a

8 relatively long period (2 to 3 weeks) before any final disposition (burial, spreading or incineration). The present invention enables advantageously to generate in situ a long-lasting bactericidal oxidant life which can furthermore ensure a residual effect, namely, which avoids the possible recontamination of the treated sludge.
The invention relates first of all to a method for the treatment of sludge, including sludge from municipal wastewater treatment and sludge from pulp and paper manufacturing industries, including seeds pathogens and odor-generating molecules, characterized in that said sludge is subjected to a pH of less than 5.0 and optimally greater than 3.5 in the presence or absence of a supporting electrolyte, in a reactor comprising at least one anode and one cathode and subjected to electrochemical reaction in such a way that bacteria and compounds malodorants are reduced, and that dehydrates more effectively said sludge thus treated.
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. In In particular, these chloride salts may be chosen from NaCl, CaCl2, the MgCl2, NH4Cl, KCl and FeCl3.
According to a specific embodiment of the present invention, the process relates to electrochemical conditioning treatment pre-dehydration of sewage sludge characterized in that it comprises the following steps acidification of the sludge so as to reach a pH high enough to to avoid corrosion and low enough to significantly reduce indicators of pathogens; treatment of acidified sludge in an electrolytic cell able to generate in situ a bactericidal oxidant in a sufficient concentration high to disinfect the sludge and low enough to prevent the formation of organochlorine compounds in sludge; electrolyze the sludge during a period sufficient time to stabilize the sludge and improve their dehydrability.

9 According to another specific embodiment, the present invention object a process for stabilization and conditioning of sewage sludge, characterized in that a) the sludge is acidified in such a way as to obtain acidified sludge;
having a pH optimally between 3.5 and 5.0;
b) optionally added to the acidified sludge, ions chlorides at a concentration ranging from 0.6 to 6.0 g CI-iL per examples form of sodium chloride (1 to 10 g NaCl / L), if the sludge used does not not enough;
c) the acidified sludge is treated in an electrolytic cell operating at an intensity varying between 2 and 15A, which is capable of generate in situ a bactericidal oxidant, in this case the hypochlorous acid used for the treatment of sludge in such a quantity as to obtain a concentration residual varying between 0.02 and 0.7 g HCIO / L;
d) the intensity of the current is imposed during a period of time sufficient, usually between 10 and 120 minutes, to stabilize sludge and improve their dehydration;
e) the stabilized sludge is flocculated by addition of a flocculating agent; and f) the flocculated sludge is dehydrated.
Steps (a), (b) and (c) of the method according to this embodiment of the invention may be carried out in one, two or three phases of which can be easily operated in the cuvée, semi-continued or continuous.
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 method, according to a specific embodiment of the present The invention relates to the electrochemical treatment of sewage sludge containing pathogenic germs, malodorous compounds and substances hydrophilic particulates, in particular municipal sewage sludge and of the sewage sludge from the pulp and paper industry, characterized in this said sludge is fed to a pH of less than 5.0 and greater than 3.5 in presence or absence of a supporting electrolyte, in a reactor comprising at least an anode and a cathode and subjected to an electrochemical reaction of such bacteria and malodorous compounds should be removed, and this that said sludge thus treated is more effectively dehydrated. According to one fashion more specific embodiment of the present invention, said reactor is type single cylinder comprising concentric metal electrodes and disposed such that an anode is immediately followed by a cathode. According to one alternative embodiment of the present invention, said reactor is type single cylinder comprising a series of circular electrodes (anodes and cathodes) made of metal and placed in a stable and horizontal position way an anode is immediately followed by a cathode. According to an alternative mode of embodiment of the present invention, said reactor is shaped cuboid comprising a series of planar and rectangular electrodes (anode and cathodes) arranged so that an anode is immediately followed by a cathode.
According to another more specific embodiment of the present invention, the anodes are made of a material selected from coated titanium oxide ruthenium (Ti / RuO 2), iridium oxide (Ti / IrO 2), tin oxide (Ti / SnO 2) or platinum (Ti / Pt), and the cathodes are made of titanium (Ti) or steel stainless (Stainless steel). According to another more specific embodiment of the present invention, the electrodes are expanded metal or solid plates. According to another fashion specific embodiment of the present invention, the distance between electrode is between about 1 and about 5 cm. According to another specific mode of embodiment of the present invention, the acidification of the sludge is carried out by adding of an inorganic acid selected from the group consisting of sulfuric, hydrochloric, nitric and phosphoric acid, an industrial waste acid and a combination of two or more of the above acids. According to another specific mode of Embodiment of the present invention, a support electrolyte is used.
According to some Specific embodiments of the invention, the electrolyte is chosen among the group consisting of sodium chloride, CaCl 2, MgCl 2, NH 4 Cl, KCl and FeCl3. When sodium chloride is used, it is used at a concentration more only about 10 glL of sludge. According to another specific mode of realisation of the present invention, the intensity of the current imposed in the reactor electrochemical varies between 2 and 15A.
According to another specific embodiment of the present invention, the sludge treatment time is between about 10 and about 120 minutes. According to another specific embodiment of the present invention, the Electrochemical oxidation reaction is conducted at a temperature comprised enter about 10 and about 60 ° C, preferably between about 20 and about 40 ° C and this, without external heat input, the electrochemical reaction being itself exothermic. According to other specific embodiments of the present the method is operated in batch mode, or semi-continuous or continuous mode.
according to other specific embodiments of the present invention, prior to their Dehydration, the treated sludge is mixed with untreated sludge.
According to other specific embodiments of the present invention, the sludge have an initial concentration in total solids ranging from approximately 5 to about 50 g / L. According to other specific embodiments of the present invention, the sludge is selected from the group consisting of primary sludge, sludge secondary, mixed 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 mud. According to other modes specific embodiments of the present invention, the treated sludge can be completely (pH Z 7) or partially (pH <7) neutralized by the addition of a alkaline agent. According to other specific embodiments of the present the treated sludge, neutralized or not, is flocculated by the addition of a organic polymer before dehydration. According to other specific modes of embodiment of the present invention, the treated and dehydrated sludge is neutralized by the addition of an alkaline agent immediately, or after period sludge storage. According to other specific embodiments of the In the present invention, the alkaline agent used to neutralize sludge is selected among the group consisting of lime, sodium hydroxide, carbonate of Calcium, ammonium hydroxide, magnesium hydroxide, dolomite, based industrial waste and a combination of two or more of these alkaline agents.
according to other specific embodiments of the present invention, sludge processed and dehydrated can be stored for a period of time enter approximately 1 and 6 months without emanation of foul odors.
DETAILED DESCRIPTION OF THE INVENTION
The process consists of a sludge treatment by a reaction electrochemically in an optimally moderately acidic medium (3,5 <pH <5.0), performed in a reactor capable of generating in situ an oxidant (HCIO) in presence of chloride ions added or already present in the sewage sludge.
acidification sludge is preferably carried out with sulfuric acid. The number of HCIO generated varies with the intensity of the imposed current, the time of imposition of current and the concentration of chloride ions in solution. Chloride ions are added to sludge if the sludge used does not contain enough sludge.
These ions are injected as sodium chloride in concentrations variant between 1 and 10 g NaCl / L sludge. During electrolysis, chloride ions are oxidized to hypochlorous acid, so as to obtain a concentration residual of HCIO varying between 0.02 and 0.7 g / L in the treated sludge. The addition of acid inorganic (such as H2SO4) and optionally chloride ions, may be done simultaneously, ie in a single phase, or in two phases, either a initial acidification of the sludge, followed by the addition of chloride ions.
The acidification of the sludge can be carried out for example with sulfuric, hydrochloric, nitric, phosphoric acid or a spent acid. We uses preferably sulfuric acid. In the case of the process operated in two phases, the initial acidification of the sludge, before the addition of chloride ions is carried out usually at a pH between 3.5 and 5.0. Less acidification sludge (pH> 5.0) causes a loss of efficiency at the level of destruction of pathogen indicators (faecal and total coliforms). On the other side, more acidification of sludge (pH <3.5) causes a corrosion premature dehydration equipment and dramatically increases the cost in chemicals. Also, a pronounced acidification of sludge is favorable to the formation of organochlorine compounds.
The use of an inorganic salt such as sodium chloride allows on the one hand, to improve the conductivity (support electrolyte) of the sludge and, else on the other hand, to enrich the sludge with chloride ions necessary for the production of oxidant (HClO). 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 a slightly acid 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 HClO.
We can schematize the reactions according to the following equations - at the anode CI - - CI Z + 2e -- in solution CIZ + 2Hz0 p HClO + Cl- + H30 ' It is also possible to envisage a dissociation reaction of hypochlorous acid such as HClO + Hz0 r ~ Cl0- + H30 +
The last reaction leads to the formation of the hypochlorite ion (CIO-) which is also a bactericidal oxidant but less effective than the acid hypochlorous (HCIO). It has been noted that, in general, oxidants Molecular molecules are more bactericidal than ionic oxidants. Indeed, molecular compounds very generally cross much more easily the bacterial membranes as the ions.

Therefore, according to a specific embodiment of the invention, the sludge is acidified to the optimum pH (3.5 <pH <5.0) with acid sulfuric in order to generate mainly the molecular form of the oxidant (HCIO) following anodic oxidation of chloride ions.
During electrolysis, it is desirable, for optimal operation generate hypochlorous acid concentrations, so 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 fecal and total coliforms), effective odor control, and a significant improvement in sludge dewaterability.
Sludge electrolysis 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.
The treated sludge is then flocculated by adding an agent flocculant. Use of a moderately acidic pH, less than 5.0 and greater than 3.5, does not require sludge neutralization before their flocculation by addition of polymers and subsequently their mechanical dehydration at using a filter press, press belt filter, centrifuge, press rotary, screw press, etc.
According to a specific embodiment, the flocculating agent used for the flocculation of treated sludge is one of the usual organic polymers employees for the flocculation of sludge in sewage treatment plants. AT
title examples are cationic or anionic polymers sold under the Trademarks PercoITM and ZietagT "'by Ciba Specialties Company Chemicals Canada Inc., and LPMT "'by LPM Technologies Inc. In addition, the dehydration of slightly acidic sludge helps to store sludge during a long period of time without having recovered the putrescibility of the sludge.
Optionally, the sludge can also be completely (pH> _ 7) or partially (pH <7) neutralized by the addition of an alkaline agent before the sentence flocculation of sludge. Complete or partial neutralization of sludge can also be immediately performed after dehydration, or after a storage period of 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 sludge that has been subjected to acid and oxidizing treatment with untreated sludge, then flocculate sludge mixed by adding a flocculant and finally dehydrating these with standard mechanical dewatering equipment. 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. In general, however, the process can to be used for the treatment of various types of sludge from waters household, municipal or industrial waste (primary, secondary Mixed media, paper mills, refineries, agro-food, septic tanks, lagoons, deinking, etc.).
The electrolytic cell, non-compartmentalized consists of minus an insoluble anode and cathode. Preferably, an anode is used at strong oxygen surge so that ion oxidation chlorides Hypochlorous acid (HCIO) is preferentially carried out on the oxidation of water in oxygen.
The process according to the present invention acts at three levels on bacterial cells a) a direct electrochemical action by oxidation at the anode. This oxidation deactivates bacteria (physiological disturbance) by oxidizing protein inclusions of the cytoplasmic membrane consisting predominantly of phospholipids and protecting the bacteria;
b) action induced by the electric field. The sudden variation of electric field by rapid passage from the anode to the disturbed cathode also physiologically bacterial cells;
c) indirect electrochemical action indirect by generation in situ hypochlorous acid. Hypochlorous acid formed helps to destroy bacteria previously deactivated at the anode and, extend thus the microbicidal effect at the outlet of the electrolyser, especially when storage of dewatered sludge.
According to another advantageous aspect of the present invention, the reactor Electrochemical allows to oxidize directly to the anode and in solution (by action of hypochlorous acid) soluble organic compounds bound to colloidal and prevent the destabilization of the latter. Direct action and indirect effect on hydrophilic particulate matter is favorable to a best aggregation of colloidal particles and effective dewatering of sludge processed. In comparison with the known prior art, the present invention present so an electrolytic cell particularly favorable to the conditioning of sludge treatment.
The malodorous compounds (propionic acid, butyric acid, hydrogen sulfide etc.) are directly oxidized at the anode and indirectly oxidised in solution with hypochlorous acid.
According to a specific variant, the electrochemical reaction is at a temperature between about 20 and 60 ° C and advantageously between 20 and 40 ° C without external heat input. The reaction electrochemical being itself exothermic. During electrolysis, a spontaneous increase and progressive temperature is observed. As mentioned in the description of the prior art (Everett, Wat Res., 1974, 8, 899-906), a increase in temperature leads to a transformation of the structure physical sludge, which induces a decrease in hydrophilicity particulate, this which is favorable to better dewatering of sludge. Also, a increase of temperature increases the rate of chemical reaction and Biochemical.
According to a variant of the process, the anode can be under the Expanded metal cylinder shape of titanium coated with ruthenium oxide or iridium oxide (Ti / RuO 2 or Ti / 1rO 2) and the cathode may be form 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 solid electrodes and constitute, in fact, good promoters of turbulence thus allowing a go, to avoid the adsorption of gas bubbles on the electrodes and on the other hand, to increase the electrode-sludge transfer coefficient. One of the methods according to a Specific embodiment of the present invention therefore uses a configuration electrode different from that described in the prior art, which uses of the flat and solid electrodes (Canadian Patent No. 1,334,658).
The applied current is partly a function of the duration of the electrolysis.
These parameters must be adapted according to the nature of the sludge treat.
It should be noted, however, that short-lived electrolysis with currents low allows to obtain a better faradic yield for the in situ production of hypochlorous acid, but at the expense of chemical efficiency. In industrial application, the parameters of this process should be adapted in depending on the degree of contamination of the sludge (pathogenic germs, compounds malodorous) and concentration in total solids. During treatment, intensity current is generally between 2 and 15A and the duration of the reaction electrochemical is usually between about 10 and 120 minutes.

By way of illustration, Figure 2 attached to this description describes a schematic view of an electrochemical reactor for carrying out the processing method according to a specific embodiment of the invention.
according to this Figure, the reactor (1) cylindrical (2), is provided with a stirrer mechanical (3) powered by a motor (4). The anode (5) is an expanded metal cylinder willing coaxially around the stirrer and the cathode (6) is placed coaxially with agitator around it so that the surface of the cathode is of large area compared to that of the anode. The anode and the cathode are connected to a DC generator (7). The agitator is a metal rod equipped with a propeller and completely covered with PVC or Teflon plastic, so that to avoid polarization of the stem and a disturbance of the reaction electrochemical. The inter-electrode distance is between about 1 and 5 cm. Note that when refers in the present at an interval, the term "about" always applies to two ends of the gap.
According to another variant of the process (see FIG. 3), the reactor can be in cylindrical form (1), consisting of volume electrodes. The anode (2) can be in a circular form made of expanded titanium metal of oxide 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 about 1 and 5 cm. In continuous mode, the cell is powered from the bottom (4) up (8) using 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.
The present invention relates, according to a specific mode of embodiment, a method that can advantageously be integrated into the chains of treatment of sludge in operation without having to modify major. In addition, the non-polluting aspect of electricity, the ease automation that it brings, as well as the reduction of the volume of equipment are settings which characterize the present invention, compared to the prior art using large scale digesters or reactors. Also, generation in of an oxidant for the treatment of sludge, also gives an advantage practice of the present invention, because it allows on the one hand to free oneself of the difficulties with the transport and handling of the product on the other hand, she allows to store treated and dehydrated sludge for a long time period and this, without emanating unpleasant odors.
The method according to the invention can be integrated into the chains sludge treatment plants in operation in wastewater treatment plants, without having to make adjustments to the processing and dehydration of sludge already in place. The method makes it possible to significantly improve dewaterability characteristics of sludge by increasing the dryness of sludge during of their mechanical dehydration. In addition, this technology is more performing that the usual technologies of aerobic or anaerobic digestion mesophilic for destruction of bacterial indicators of pathogens (> 5 units logarithmic reduction of faecal and total coliforms or elimination of more than 99.9%) and thus allows effective stabilization of sludge. Finally, the application of this technology does not significantly affect the content of elements fertilizers dewatered sludge and can significantly reduce the generation smells of sludge.
The invention has been described generally, and is now illustrated by (non-limiting) examples of implementation given for information only.
Example 1: Treatment of municipal sewage sludge The process according to the invention has been tested on sewage sludge from municipal wastewater treatment. The initial concentration solid total sludge was 21.6 g / L. The electrochemical reactor used for the The tests are shown schematically in Figure 2. The cylindrical electrolytic cell, in Plexiglas, consists of two concentric electrodes and equipped with a agitator to TeflonT "propellers. The cathode is a cylinder made of titanium Mark Electrolytic "", radius 9 cm, height 28 cm, mesh area 9.08 dm2 and area of empty surface between the meshes 7,87 dmz. Anode placed in the center, surrounding the rod of the agitator, is a cylinder in rolled titanium brand Electrolytica "", of radius 5 cm, height 28 cm, mesh area 5,04 dm2 and surface area empty between the meshes 4.37 dm2. The volume treated was 5.0 L and only one third of the active area of the anode (0.191 dm2) and the cathode (0.344 dm2) was immersed in the effluent to be treated.
A series of experiments was carried out at current intensity and variable temperature in batch mode. The prior acidification of sludge has been by addition of concentrated sulfuric acid (H2SO4, 10 N), or acid concentrated hydrochloric acid (HCl, 3N). Sludge has been subjected to electrolysis 30 min period during which the sludge has been continuously agitated.
Once treated, the sludge was flocculated by adding a polymer organic cationic sold under the trademark Zetag 7689T "" and the sludge was filtered under vacuum for a period of 10 minutes and under a pressure of 750 mm Hg. The SV1 filter unit used in the tests included a pump Vacuum, Buchner and Whatman Membranes 934AHT "" (Trademark) having a porosity of 1.5 wm. The dryness of dewatered sludge was by after measured after drying of these at 105 ° C for a period of 24 h.
The The filtrates have been stored for chemical analyzes (chemical oxygen (COD), ammoniacal 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 the final POR values are between -181 and 129 mV. then of the tests, a sulfuric acid consumption of 14.6 or 27.6 kg H2S0 ~ ltbs was employee. For hydrochloric acid, a contribution of 31.0 kg / HCl was summer tested. On the other hand, an addition of 92.5 kg NaCl / tbs (4.3 g NaCl / L) was performed during tests.
Optimum polymer dosage for non-sludge flocculation treated was approximately 1.9 kg / tbs. In comparison, concentrations of 1.4 and 2.3 kg polymer / tbs were required for the flocculation treated sludge. Also, energy consumption varies between 252 and 1480 kWh / tbs was required for sludge stabilization.
An average dryness value of 12.5 ° 10 (w / w) was measured during of the control test (CONT) for dehydration of untreated sludge carried out in triplicate. The application of the process (tests B, C and D) increased dryness to values between 14.4% and 23.0%, representing gains of 1.9 to 10.5 points of 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 necessary for the disinfection and deodorization of sludge.

Table 1 Pre-conditioning and electrochemical stabilization tests sludge from a municipal wastewater treatment plant Parameters Tests CONT ABCD
Final pH 6.81 6.81 4.90 4.97 4.53 Final POR (mV) -200 -181 63 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 (mglL) 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 (%

w / w) SV1: Vacuum filtration unit having a filter surface of 78.5 cm2 In situ production of HCIO is also useful for the oxidation of dissolved organic compounds attached to colloidal materials. The action of HClO
on these soluble materials allows a better aggregation of materials colloidal and more efficient dewatering of the treated sludge. To this is added a increase in temperature during electrolysis, which induces a physical transformation of sludge, favorable to better dehydration of the sludge. In particular, the better dryness of dewatered sludge (23.0% plp) recorded in test D is partly attributed to an increase appreciable temperature (41.2 ° C).
The conservation of the nutrients of sludge following the application of the process was evaluated by measuring the concentration of COD, of P-PO4, N-NH4 and N- (NO- / NO2) in the dehydration filtrates of sludge. The measured values show that the application of the process does not induce a appreciable loss of the fertilising value of the sludge, particularly as regards concerned the elements P-PO4, N-NH4 and N- (NO3 / NO2). On the other hand, the application of process lead to an increase in the initial concentration of COD (489 mg / L) at values between 831 and 1280 mg / L. This increase in 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 shown 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 injecting this time, different concentrations of sodium chloride, followed of the dehydration using a vacuum filtration unit (SV2) having a area relatively large filter (compared to SV1 filtration unit ) and equipped with high porosity membranes. The experimental procedure is briefly described in Example 2.
Example 2: Treatment of municipal sewage sludge Average total solids concentration of municipal sludge used for testing is 22.6 glL, or 2.3% solids. The process experimental used is almost identical to that used in the example previous.
The initial pH of the 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 of determine the optimal concentration for which better dehydration and better disinfection are obtained. Also, adding NaCI allows improve the conductivity of the reaction medium and thus reduce the consumption Energy.
The sludge is placed in the previous reactor (Figure 2), kept mechanically stirred and electrolyzed for a period of 60 minutes under a current intensity of 8 OA.
Subsequent dewatering of the sludge was done using of a vacuum filtration unit (SV2) having a filter surface of 201 cm2 and equipped with Whatman membranes (trademark) No. 4 diameter of pores ranging between 20 and 25 ~, m. Samples of unfiltered sludge summer preserved for measurements of faecal and total coliforms by the technique of Most Probable Number (MPN).
Table 2 presents the experimental conditions used during tests, as well as the main results. The final pH values measured are enter 3.85 and 5.10, while the redox potential (POR) values are 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 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 2s NaCl has not been performed. Optimum dosages for sludge flocculation treated and untreated are approximately 2.5 kg / kg, with the exception of test H at during which a concentration of 3.0 kg polymer / tbs was tested.

Table 2 Pre-conditioning and electrochemical stabilization tests of sludge purification station municipal wastewater 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 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) 140 000 885 1 130 133 <1 <1 Collar. totals (NPPlgbs) 355,000 1,600 2,000 412 115 <1 dehydration Final Siccit (% 25.3 32.4 32.2 34.1 23.5 25.8 w / w) Mass reduction - 21.9 21.4 25.9 -7.6 1.9 (%

w / w) SV2: filter unit a surface vacuum filtering of 201 cm2 The average dryness obtained after dewatering non-sludge treated (CONT test) is 25.3%. The application of the process (tests E, F and BOY WUT) makes it possible to increase the dryness of dewatered sludge between 32.2 and 34.1%, either gains from 6.9 to 8.8 dry points. This increase in sludge dryness Dehydrated reduces the amount of sludge generated from 21.4 to 25.9%.
In However, the dryness decreases (tests H and I) when the concentration of the chloride of sodium is fixed at 266 or 354 kg / tbs. This drop in dryness could be attributed to a relatively high residual HCIO concentration (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 HCIOIL.
The disinfecting efficacy of the process has also been evaluated.
The application of the method allows an effective elimination of the indicators of pathogens, in this case faecal and total coliforms. Thus, relatively high concentrations of fecal and total coliforms of 140,000 and 355,000 NPP / gbs were measured in untreated sludge, respectively.
In comparison, residual concentrations of internal faecal coliforms 1 MPN / gbs (allowance greater than 5 log units) or between and 1,130 MPN / gbs were measured in the treated sludge. The measures of Residual concentrations of total coliforms made on sludge treated indicate concentrations below 1 NNP / gbs (above 5 logarithmic units) or between 115 and 2,000 NPP / gbs.
In sum, the analysis of all the results presented in the Table 2 shows that Test G would be the optimal test for stabilization and the conditioning of municipal sludge studied. This test requires a dose optimum of 177 NaCI kg / tbs, a concentration of 23.3 H2SOa 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.

In order to verify the reproducibility of the results obtained the application of the optimal conditions of treatment of municipal sludge, a third series of tests was carried out according to the procedure described in example 3 next.
Example 3: Treatment of municipal sewage sludge Five liters of previously acidified municipal sludge, containing 4 μL 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 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 the production of HCIO
in situ during electrolysis.
The initial average sludge temperature was 11.3 ~ 0.4 ° C, so that of the treated sludge was 26.4 t 1.8 ° C. During the tests, the conductivity of medium increased from an average value of 2.3 to 0.7 mS / cm 2 (sludge initials) to a final value of 8.2 t 0.4 mS / cm 2 (treated sludge). The conductivity of the middle east so relatively good. Also, an energy consumption of 862 ~ 9 kWh / tbs was required for sludge treatment.

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.

Table 3 Pre-conditioning and electrochemical stabilization tests sludge from a municipal wastewater treatment plant Parameters Tests a Untreated sludge Processed sludge Final pH 6.35 t 0.15 4.81 0.18 Final POR (mV) -115 49,437 t 33 Intensity (A) 0.0 0.0 8.0 0.0 Temperature (C) 11.3 0.4 25.6 t 1.8 Conductivity (mS / cm2) 2.31 0.69 8.2 0.4 SV2 SV2 filtration unit Consumption (kg / tbs) H2S04 0.0 t 0.0 23.3 0.0 NaCl 0.017017 0 Polymer 1.85 f 0.00 2.51 0.00 energy (kWh / tbs) 0.0 t 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 (mglL) 59.7 2.8 124 2 Mg filtrate (mg / L) 66.6 1.9 97.3 t 1.2 microorganisms Fcaux coliforms (NPP / gbs) 200,000 21,000 <1 Total Coliforms (NPP / gbs) 1,200,000 310,000 26 t 5 dehydration Final Siccit (% w / w) 23.9 t 1.3 33.4 1.4 Reduction of mass - 29.3 3.0 (%

P / P) a: triplicate tests SV2: Vacuum filtration unit having a filtering surface of 201 cm2 An average dryness value of 23.9 t 1.3% (w / w) was recorded dehydration 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.
Low standard deviation values calculated for each parameter 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 measuring bacterial indicator bacteria concentrations (faecal and total coliforms) in liquid sludge (treated and non-treated).
treated). The results obtained show complete elimination of faecal coliforms (abatement greater than 5 log units) and an appreciable reduction in coliforms totals (upper allowance 4 log units). The treatment allows therefore effective stabilization of municipal sludge from the point of view Microbiological.
Also, the fertilizing value of the sludge following the application of the process has 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.
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.
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 ~ 0.8 was attributed to untreated sludge, while a value of 2.3 ~ 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.
The odor perception is different from one person to another, 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 (~) with a degree of confidence of 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.
The preceding examples relate to sludge treatment 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.
Example 4 Treatment of Secondary Sludges of Pulp and Paper The initial total solids concentration of the sludge used for 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, monitoring 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.
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 ~ 0.13 and -117 t respectively.
mV.
During tests, an average acid consumption of 13.2 kg of H2S04 / tbs was required for sludge acidification. The rise in concentration of chloride ions in sludge (for the production of HCIO) a need a contribution of 200 kg NaCl / tbs. Also, energy consumption average of 1100 t 40 kWh / tbs was required during sludge treatment.
Optimum polymer dosage for non-sludge flocculation treated and treated sludge was identical and was approximately at 3.0 kg / tbs.
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, fes 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.

Table 4 Pre-Conditioning and Electrochemical Stabilization Tests of sludge from a wastewater treatment plant of a pulp and paper Parameters Tests e Untreated mud Treated mud Final pH 6.24 t 0.13 4.41 t 0.61 Final POR (mV) -117 53 490 113 Intensity (A) 0.0 0.0 8.0 t 0.0 Temperature (C) 14.3 2.4 26.1 0.5 Conductivity (mS / cm2) 0.93 t 0.16 7.69 0.22 SV2 SV2 filtration unit Consumption (kgltbs) H2S04 0.0 0.0 13.2 0.0 NaCl 0.0 t 0.0 200 t 0 Polymer 3.0 t 0.0 3.0 0.0 energy (kWh / tbs) 0.0 f 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 (NPPlgbs) 284,800 18 31 dehydration Final Siccit (% w / w) 19.9 0.2 25.3 1.2 Reduction of mass - 21.2 3.8 (%

plp) a: triplicate tests SV2: Vacuum filtration unit having a filtering surface of 201 cm2 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 ° l0 (w / w), a gain of 5.4 points dryness. This increase in the dryness of dewatered sludge reduces by 21.2% the mass sludge produced.
In addition, 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.
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.

Claims

Embodiments of the invention, about which a right exclusive ownership or privilege is claimed, are defined as follows : 1. Electrochemical conditioning treatment method dewatering of sewage sludge characterized in that it comprises the steps following:
acidification of sludge so as to reach a pH sufficiently high to avoid corrosion and low enough to reduce significantly pathogen indicators;
treatment of acidified sludge in a capable electrolytic cell to generate in situ a bactericidal oxidant in a sufficient concentration high to disinfect the sludge and low enough to prevent the formation of organochlorine compounds in sludge;
electrolyze the sludge for a period of time sufficient to stabilize sludge and improve dehydration.