Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F3/00—Biological treatment of water, waste water, or sewage
  • C02F3/34—Biological treatment of water, waste water, or sewage characterised by the microorganisms used
  • C02F3/345—Biological treatment of water, waste water, or sewage characterised by the microorganisms used for biological oxidation or reduction of sulfur compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/004—Sludge detoxification
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F9/00—Multistage treatment of water, waste water or sewage
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/722—Oxidation by peroxides
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/78—Treatment of water, waste water, or sewage by oxidation with ozone
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2303/00—Specific treatment goals
  • C02F2303/04—Disinfection

Definitions

• the present invention relates to a method for decontaminating sewage sludge such as municipal sewage sludge.
• the technology makes it possible to considerably reduce the toxic metal contents in the sludge and, in so doing, to preserve its fertilizing properties, to destroy the pathogenic germs which they contain and to significantly reduce the production of odors during their handling during or after treatment.
• the sludge from the wastewater which can be treated by the process of the present invention includes sludge of primary, secondary, digested aerobic or anaerobic type, lagoons or septic tanks.
• Incineration and landfill are conventional methods of sludge disposal.
• the increase in volumes of sludge to be disposed of and the scarcity of places of disposal, as well as growing social opposition to these methods of disposal, tend to favor methods of recovery, in particular as agricultural or forestry fertilizers.
• Agricultural recycling of sludge the preferred option by government authorities, is increasingly practiced around the world. In the United States, in 1976, this practice was used for the disposal of 26% of sewage sludge produced by municipalities. In 1990, it increased to 33% of the total volume of sludge produced. In Europe in general, around 37% of the sludge is used in agriculture. In the United Kingdom, more than 51% of the sludge produced is used for this purpose, while almost 40% are disposed of in this way in Japan. In Canada, 29% of the estimated total volume of municipal sludge is deposited on agricultural land.
• cadmium is a particularly feared element since the symptoms of its phytotoxicity appear at concentrations almost 10 times higher than those where the symptoms of its zootoxicity appear.
• excessive absorption of cadmium causes its accumulation in the kidneys and liver, causing histological and functional damage.
• the biological effects of cadmium also include interference with fundamental enzymatic systems, such as oxidative phosphorylase, by blocking thiol groups, as well as interference with the synthesis of nucleic acids.
• Cadmium also has certain cardiotoxic properties.
• Lead is also an element which has a higher zootoxicity potential than that of phytotoxicity.
• toxic metals such as Al, As, Sb, Be, Bi, Cd, Hg,
• inorganic acids alone does not allow effective solubilization of copper and lead, despite considerable acidification of the sludge, i.e., at a pH of the order of pH 1.5.
• the solubility of metals in sludge is affected mainly by the pH, but also by other equally important factors which must be taken into account, such as the redox potential of the medium, the concentration of metals and ligands, eg anions and uncharged molecules, and the chemical balance between the constituents.
• the solubilization of copper and lead in the sludge requires a significant increase in the redox potential, which cannot be obtained quickly by chemical oxidation during the aeration of the sludge.
• the large quantities of acid required to dissolve the metals make these techniques unattractive economically.
• the process described in US 5,051,191 comprises a very significant acidification of the sludge (pH 1.0 to 2.0) by the addition of sulfuric or hydrochloric acid, coupled with a supply of oxidizing agent in the form of ferric salts (sulfate or chloride) at a concentration varying between 0.5 and 3.0 g Fe 3+ / L (sulfate or chloride) and the addition of a regenerating agent oxidizing agent such as hydrogen peroxide, sodium or calcium hypochlorite, compressed air, oxygen, ozone, sulfur dioxide, chlorine or chlorine compounds.
• a treatment period of 10 to 30 minutes is sufficient with this technology for an adequate solubilization of heavy metals.
• the decontamination chain also includes a step of conditioning the sludge by flocculation with a cationic or anionic polymer, followed by dewatering the sludge on a vacuum drum filter with washing of the decontaminated sludge.
• Tests for separation of metals by centrifugation have also been carried out. Two successive centrifugation stages allow the metals to be concentrated in a pellet. The metal concentrations found in the pellet are between 60 and 73% for cadmium, nickel, chromium, copper and zinc, while this process does not allow lead to be extracted. This technique presents problems in terms of recovery and recovery of solids, since sludge reduced to metals constitutes only 23% of the volume of total sludge.
• a technology developed by INRS consists of a bioleaching process for heavy metals using ferrous sulfate.
• the process is used for the decontamination of sewage sludge that has previously undergone a microbiological stabilization step by aerobic or anaerobic digestion.
• the reaction time in the bioreactor varies between 1 and 2 days depending on the operating mode and the specific sludge to be treated.
• An addition of ferrous sulfate is necessary as a source of energy substrate.
• the acidity conditions thus created and the increase in the oxidizing conditions of the medium during the oxidation of the ferrous ion to ferric ion, allow significant solubilization of the toxic metals found in the sludge.
• the present invention relates to a hybrid chemical and biological process for decontamination of sewage sludge containing heavy metals and pathogenic microorganisms, comprising the following steps:
• the sludge is acidified to a pH varying from 2 to 3 and maintained at a redox potential greater than +400 mV.
• the process can be carried out in cuvée, semi-continuous and continuous mode.
• the xiviant solution comprises an inorganic acid such as sulfuric acid, hydrochloric acid and their mixtures, and an oxidizing agent.
• the xiviant solution may also include a precursor of an oxidizing agent, so that the oxidizing agent can be generated in situ.
• ferrous sulfate in the presence of native bacterial flora from the sludge is converted to ferric sulfate, which acts as an oxidizing agent. This biological oxidation is carried out by a culture of Thiobacillus ferrooxidans present in the native biomass of the sludge or by the addition in the mixture of collection strains.
• Figure 1 illustrates a decontamination chain according to an embodiment of the invention in which the xiviant solution is added directly to the sludge;
• Figure 2 illustrates a decontamination chain according to a second embodiment of the invention in which the hexiviant solution of ferric sulfate is produced externally, followed by the addition of sulfuric acid and an oxidizing agent;
• Figure 3 illustrates a decontamination chain according to a third embodiment of the invention in which the production of ferric sulfate takes place directly in the sludge, followed by the addition of the oxidizing agent.
• the process of the present invention represents an important evolution compared to the current processes, since it makes it possible to take advantage of the advantages of the biological processes like the low cost in chemical products, and of chemical processes like the less investment attributable to a short time treatment, reaction stability, better control of inputs, resistance to variations in process operating conditions such as temperature, the presence of aggressive chemical reagents, ionic strength, etc.
• the present process can advantageously compete with the current sludge treatment chains, which only allow a relative microbiological stabilization of the sludge, without allowing the extraction of toxic metals.
• the leaching of metals can be accomplished in 3 distinct variants from each other.
• the leaching is accomplished by the direct addition to the sludge of a hixiviant solution composed of an inorganic acid, preferably sulfuric acid or hydrochloric acid, with at least less an oxidizing agent, preferably ferric chloride, ferric sulfate, hydrogen peroxide, ozone, potassium permanganate etc.
• a hixiviant solution composed of an inorganic acid, preferably sulfuric acid or hydrochloric acid, with at least less an oxidizing agent, preferably ferric chloride, ferric sulfate, hydrogen peroxide, ozone, potassium permanganate etc.
• the sludge must be maintained at a pH preferably between 2.0 and 3.0 by adding the acid, but must not drop below a value of 2, since this would cause dissolution or undesirable degradation of the fertilizing elements. contained in the sludge.
• the oxidizing agent is added if necessary so as to keep the sludge at an oxidation-reduction potential (POR) greater than 400 mV.
• the oxidizing agent allows on the one hand to accelerate the solubilization of metals by an increase in oxidizing conditions and, on the other hand, to significantly reduce the dissolution of nutrients or fertilizers such as phosphorus and nitrogen .
• the simultaneous addition of the acid and the oxidizing agent also makes it possible to substantially reduce the odors emanating from the sewage sludge, while causing the destruction of pathogenic germs (bacterial indicators).
• a hydraulic retention time of between 0.5 and 6 hours is preferable for dissolving metals and stabilizing the biomass.
• the dissolution of the metals present in the sludge is carried out by the addition of an hexiviant solution containing the oxidizing agent and acid, the xiviant solution being produced in a bioreactor by the biological oxidation of ferrous iron to ferric iron.
• This xiviant solution thus makes it possible to lower the pH and increase the redox potential of the sludge under conditions suitable for dissolving metals toxic.
• Sulfuric acid and another oxidizing agent such as hydrogen peroxide can be added directly to the sludge with the Hexiviant solution produced by the bioreactor to adjust the solubilization conditions of the metals and help reduce the release of odors.
• the pH of the sludge is preferably maintained between 2.0 and 3.0 but must not at any time fall below a value of 2.0, while the redox potential preferentially remains above 400 mV.
• a hydraulic retention time of between 0.5 and 6 hours is preferable for the operation of this step.
• the step of dissolving the metals can also be carried out producing the oxidizing agent, in this case ferric sulfate, directly in the sludge.
• the oxidation of the iron (FeSO 4 , 7H 2 O) added to the sludge is carried out by the native bacterial flora which includes, for example, Thiobacillus ferrooxidans, capable of oxidizing the ferrous ion to ferric ion.
• the same pH conditions as in the other two alternatives mentioned above should prevail.
• the reaction time in the bioreactor is between 1 and 2 days depending on the operating mode and the specific sludge to be treated.
• Iron oxidation can also be accelerated by adding a culture of Thiobacillus ferrooxidans, or other ferrous ion oxidizing microorganisms, added directly to the sludge to reduce the residence time of the sludge in the bioreactor and promote system stability.
• the hydraulic retention time of the sludge must be adjusted so as to maintain a POR greater than 400 mV in the sludge.
• an oxidizing agent such as hydrogen peroxide, or a nitrate salt can be added in a subsequent step at a concentration sufficient to reduce residual odors in an adjacent reactor.
• the addition of peroxide can be carried out at the end of the treatment period in the bioreactor.
• the various variants of the metal dissolution step described above can be carried out in cuvée, semi-continuous or continuous mode of operation.
• the preferred type of reactor used for this step is a mechanically agitated or aerated tank, although other reactor configurations may just as well be used.
• a solids content of sludge between 30 and 40 g / L represents the optimal range of operation for this technology.
• any person skilled in the art will be able to adapt said content according to the processing capacity of the station's equipment.
• the previously mentioned hexiviant solution preferably consists of a very concentrated solution of ferric sulfate in a strongly acid medium, i.e., pH preferably between 1.0 and 2.5.
• This solution is generated by the biological oxidation of ferrous sulfate, and can be carried out in cuvée, semi-continuous and continuous mode, in a stirred and aerated tank type reactor.
• Other types of reactors could be used to increase the kinetics of ferrous sulphate oxidation, in particular the use of immobilized cell bioreactors, such as rotary biological disks with PVC support, or percolation columns with polyurethane foam support, ion exchange resins, glass beads or activated carbon particles.
• the reaction pH must be adjusted so as to allow adequate kinetics of the oxidation of ferrous iron and avoid precipitation of the ferric iron produced. Although a pH between 1.0 and 2.5 allows the production of ferric iron, it is preferable to maintain the pH below a value of 1.8 in order to minimize, or even eliminate the significant precipitation of iron in the bioreactor.
• the pH maintained in the reactor can also be adjusted so that the xiviant solution produced alone is sufficient to reduce the pH of the sludge to the desirable level, ie, greater than 2.0, and preferably between 2.0 and 3.0, without having to add additional sulfuric acid or any other acid mentioned above.
• the concentration of substrate ie ferrous sulphate, must be as high as possible in order to minimize the amount of xiviant solution to be added to the sludge and thus, to minimize the size of the bioreactor required for the oxidation of iron.
• Substrate contents between 10 and 30 g Fe 2+ / L are preferable for the stage of production of the xiviant solution.
• the iron oxidation bioreactor It is also suggested to operate the iron oxidation bioreactor with a hydraulic retention time preferably between 12 and 36 hours. Using a immobilized cell bioreactor, a shorter retention time, on the order of 6 to 6 p.m. is usually sufficient.
• the hydraulic retention time (TRH) and the substrate concentration used are the two important parameters for the sizing of the bioreactor.
• the iron oxidation bioreactor would be of a size equal to 24 m 3 for a hydraulic retention time of 24 hours (iron oxidation yield of 90%, concentration of substrate of 15 g Fe 2 7L, final contents of ferric iron 0.8 g / L in the sludge treatment tank, safety factor of 20%).
• the iron oxidation bioreactor can be kept at room temperature.
• the aeration rate of the bioreactor is preferably adjusted so as to maintain a concentration of dissolved oxygen greater than 1 mg / L.
• the cultures of bacteria oxidizing the ferrous ion can be prepared from the native biomass of the sludge or from collection strains which are previously added to the mixture.
• the proportion of the final dewatering filtrate used for the operation of the iron oxidation bioreactor should be of the order of 5 to 10%.
• the sludge in the reactor After treating the sludge in the reactor, the latter is conditioned by the addition of a commercial flocculant such as a cationic or anionic organic polymer.
• a commercial flocculant such as a cationic or anionic organic polymer.
• flocculants are well known to the person skilled in the art.
• a coagulant aid in certain cases greatly improves the quality of sludge flocculation.
• preferred coagulants which have been successfully tested under these conditions are clays, such as bentonite, or also ferrocyanide salts such as potassium or sodium ferrocyanide.
• the sludge is then dehydrated on a unit of plate filter presses. Other methods of mechanical dehydration, such as press belt filters, centrifuges or rotary presses, can also be used.
• the dewatered sludge is finally neutralized near the point of neutrality (pH s 7) or, for certain specific applications, at a higher pH, by adding a base, such as quicklime (CaO), inert lime (Ca (OH) 2 ), agricultural lime (CaCO 3 ) or dolomitic lime (CaO - MgO mixture), and transported by truck to the place of spreading.
• a base such as quicklime (CaO), inert lime (Ca (OH) 2 ), agricultural lime (CaCO 3 ) or dolomitic lime (CaO - MgO mixture
• Complementary sludge drying and granulation, composting or formulation and agglomeration processes including the addition of chemicals or organic fertilizers to the agglomerated sludge for specific fertilization applications can also be applied to decontaminated sludge before their valorization either in agriculture, forestry, horticulture, crops in greenhouses or outside greenhouses of vegetables or fruits, the rehabilitation of grounds, or the constitution and the maintenance of lawns.
• Decontaminated sludge can also be mixed with other organic materials such as peat, compost, manure, etc., before being recycled.
• the acidic leachate containing the metals is neutralized at a basic pH, preferably between 7 and 10, by adding a solution of a basic compound such as saturated lime, sodium hydroxide, calcium carbonate, bicarbonate sodium, ammonium hydroxide and magnesium hydroxide. Mixtures of bases can also be used, as well as certain precipitating agents, such as trimercapto-s-triazine.
• the leachate is subsequently left to settle until a metallic mud is obtained.
• An optional addition of polyelectrolyte makes it possible, in certain cases, to increase the precipitation yields of metals. This last residue is initially dehydrated on a filter press unit, then dried in air or in a dryer before being transported to a hazardous waste disposal site. Other mechanical dehydration methods can also be used, including press belt filters, centrifuges and rotary presses.
• the process of the present invention allows efficient removal of heavy metals. Indeed, copper and zinc removal yields of between 70 and 90% are observed, while for manganese, a percentage of extraction between 75 and 95% is easily reached.
• the other heavy metals such as cadmium and nickel are also dissolved when they are present in the sludge.
• the process can also be operated adequately under the various climatic conditions encountered in North America or Europe.
• the destruction performance of the bacterial and viral indicators of the process is clearly superior to that achieved with conventional aerobic and anaerobic digestion processes.
• the present process results in a significant reduction in the production of unpleasant odors in the sludge produced compared to the raw sludge.
• the chemical characterization of the sludge treated by the present decontamination process indicates that the decontaminated sludge has a fertilizing value comparable to that of sludge digested by conventional aerobic route.
• decontamination according to the process of the invention leads to appreciable enrichment of the iron and sulfur sludges.
• Greenhouse studies on barley with sludge decontaminated by the process of the invention using ferrous sulfate as an oxidizing agent have shown that the sludge retains a good fertilizing value and that it does not cause environmental or agronomic problems. In fact, these tests indicated that the recovery potential of sludge thus decontaminated is higher than that of most conventional sludge.
• the agricultural spreading of decontaminated sludge could be of particular interest, with regard to the nutritive sulfur requirements of plant crops. It should also be noted in this regard that an appreciable portion of the agricultural land found throughout the world has sulfur deficiencies.
• the process of the present invention can be implemented and permanently integrated in the wastewater or sludge treatment chains, or even installed on mobile platforms for the occasional treatment of sewage sludge. Additional upgrading processes, such as advanced dehydration, thermal drying in the cold or in the open air, enhancement by addition of potash, dolomite, or other organic or inorganic fertilizers, a mixture with other biomass, etc., can be added downstream of the sludge dewatering step in the complete decontamination chain.
• Additional upgrading processes such as advanced dehydration, thermal drying in the cold or in the open air, enhancement by addition of potash, dolomite, or other organic or inorganic fertilizers, a mixture with other biomass, etc.
• the process of the present invention has been tested for the treatment of physico-chemical sludges generated during the treatment of municipal wastewater using ferric chloride.
• a total of 47 tests were carried out in the cuvée operating mode.
• a volume of 143 m 3 of sludge having an average total solid content of 29.3 g / L was treated using a leaching step by direct addition to the sludge of sulfuric acid and hydrogen peroxide as oxidizing agent .
• PH conditions varying between 2.0 and 2.6 were used, while the redox potential was adjusted between 400 and 500 mV during these tests, with leaching times varying between 1 and 4 hours .
• ammonium (NH 4 ) measurements show that the application of conditions according to the process of the present invention has little effect on the concentrations of ammoniacal nitrogen in solution during the treatment.
• the average concentration of soluble NH 4 measured in the leached sludge is lower (147 ⁇ 74 mg / L) than that obtained for the initial sludge (268 ⁇ 125 mg / L).
• measurements of the total nitrogen content in the sludge demonstrate that the leached and dehydrated sludge contains as much total nitrogen (2.97 ⁇ 0.54% w / w) as the untreated sludge (2.26 ⁇ 0.78% w / p).
• DOC dissolved organic carbon
• the technique used to quantify the reduction in odors following the application of the process consists in measuring the flow of odor emitted by the sludge.
• the odor flux is defined as the odor flow per unit area.
• Odor flow samples were taken using an Odoflux TM flow chamber. This flow chamber makes it possible to quantify the flow of odor emitted on the surface of the sludge. It thus becomes possible to compare precisely and repeatedly the surface emission of the different types of sludge on the same basis.
• a volume of around 70 liters of sludge was used for sampling. The sludge was placed in a plastic tank 76 cm in diameter, with a sludge thickness of 10 cm.
• the flow chamber was deposited on the sludge and then inserted at a depth of 5 cm.
• the odor samples were kept in Tedlar TM bags for transport to the laboratory.
• the samples taken were analyzed to obtain olfactometric measurements by dynamic dilution to the olfactory perception threshold according to standard ASTM E679-91.
• the perception threshold is defined as the rate of dilution with clean air for which 50% of a jury charged with scent perceive or do not perceive the odor.
• the odor perception threshold is equivalent to 1 uo / m 3 .
• the number of dilutions of the odor mixture necessary to obtain 1 uo / m 3 indicates the concentration of "odor" in odor unit per cubic meter of air (uo / m 3 ).
• the results demonstrate an appreciable suppression of odors for dehydrated and decontaminated sludge compared to non-decontaminated sludge (> 97%).
• a high removal efficiency of odors were obtained for liquid leached sludge (> 93%), compared to untreated liquid sludge taken from a mixing tank.
• the decontamination and stabilization process has been tested for the treatment of biological sludge from the treatment of municipal wastewater. During this work, a total of 4 tests were completed in the cuvée operating mode. A volume of 16 m 3 of sludge having an average total solid content of 20.5 g / L was treated using a leaching step by direct addition to the sludge of sulfuric acid and ferric chloride as an oxidizing agent. PH conditions varying between 2.0 and 2.5 were used, while the oxidation-reduction potential was adjusted between 400 and 490 mV during the tests, with leaching times between 1 and 4 hours.

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• 1999
  • 1999-08-03 CA CA002279525A patent/CA2279525A1/fr not_active Abandoned
• 2000
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