CA1329957C - Process for removing metal contaminants from liquids and slurries - Google Patents
Process for removing metal contaminants from liquids and slurriesInfo
- Publication number
- CA1329957C CA1329957C CA000565562A CA565562A CA1329957C CA 1329957 C CA1329957 C CA 1329957C CA 000565562 A CA000565562 A CA 000565562A CA 565562 A CA565562 A CA 565562A CA 1329957 C CA1329957 C CA 1329957C
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- Prior art keywords
- reducing bacteria
- culturing
- sludge
- sulfate
- bacteria
- Prior art date
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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
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
- C22B3/18—Extraction of metal compounds from ores or concentrates by wet processes with the aid of microorganisms or enzymes, e.g. bacteria or algae
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Microbiology (AREA)
- Environmental & Geological Engineering (AREA)
- Hydrology & Water Resources (AREA)
- Water Supply & Treatment (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Biodiversity & Conservation Biology (AREA)
- Molecular Biology (AREA)
- Biochemistry (AREA)
- Biotechnology (AREA)
- Health & Medical Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
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- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Purification Treatments By Anaerobic Or Anaerobic And Aerobic Bacteria Or Animals (AREA)
- Removal Of Specific Substances (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A process for removing dissolved metal contaminants from liquids and slurries which comprises:
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions to produce insoluble metal sulfide; and (ii) recovering the insoluble metal sulfides;
wherein the reducing bacteria is capable of causing reduction of sulfate to sulfide.
A process for removing dissolved metal contaminants from liquids and slurries which comprises:
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions to produce insoluble metal sulfide; and (ii) recovering the insoluble metal sulfides;
wherein the reducing bacteria is capable of causing reduction of sulfate to sulfide.
Description
~ 132~57 This invention relates to e~traction of metals from liquids and slurries. More specifically, it relates to a process for removal of metal contaminants from sewage sludges and industrial wastewaters utilizing microbial activity.
Sewage treatment plants, as commonly operated in municipal facilities, treat aqueous sewage affluent microbially to produce an aqueous sewage sludge. The water is separated from the sludge in a clean enough form for discharge to receiving waters. The sludge undergoes biological decomposition and/or concentration. The sludge so produced is commonly rich in phosphorus, nitrogen and organic nutrient materials so that it is attractive for use as a soil conditioner in agricultural ~ertilizer. In fact, spreading of sewage sludge on agricultural land is an attractive sludge disposal option because it co~lbines beneficial reuse and disposal of the sludge at the same time.
If, however, sewage sludge is to be put to such use, it needs to have a low metal content to minimize the health hazard associated with metal up-take by plants and its subsequen-t accumulation in the food chain.
To date, no satisfactory commercial method for removing heavy metals from sewage sludge has been developed. Attempts have been made to remove heavy metal from sewage sludge using acid treatment but the cost o~ such treatment is excessive because of the large amounts of acids required. In addition, at the end of such treatment large amounts of lime are needed to raise the pH of the sludge to neutral.
-.
':
` ~ 132~7 Further, industrial wastewaters, such as those fromelectro-plating industries, are usually laden with heavy metals which renders these wastewatsrs unacceptable for either reuse or discharge to the environment. To date, there is no satisfactory and economical method for removing heavy metals from these wastewaters. Currently these metals are usually removed by chemical precipitation - often with lime - a costly process.
It is an object of the present invention to provide a process for reducing the content of heavy metals in liquids and slurries.
Further, it is another object of the present invention to provide a process for reducing the content of heavy metals in sewage sludge.
Still further, it is another object of the present invention to provide a process fox reducing the amounts of heavy metals from industrial wastewaters.
Accordingly, in a broad aspect, the present invention provides a process for removing dissolved metal contaminants from liquids and slurries which comprises:
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions in the waste water to produce insoluble metal sulfides from the soluble metal ions; and ~, .
;
.
.
_ 3 13~99~7 (ii) recovering the insoluble metal sulfides;
wherein the reducing baateria is capable of causing reduction of sulphate to sulfide.
The liquid or slurry so treated may be feedstock or waste water from a variety of different sources such as mill effluents, mine drainage, electroplating, steel, pulp and paper industries, and the like. In one particular ambodiment, the liquid or slurry is that which forms part of, or is separated from, sewage sludge, Thus, in another aspect, the present invention provides a process for removing metal contaminants from sewage sludge which comprises:
(i) culturing at least one oxidizing bacteria in the presence of the sewage sludge under acidic conditions to produce a sludge comprising soluble metal ions;
~il) separating the soluble metal ions;
(iii) culturing at least one reducing bacteria in tha presence of the soluble metal ions to produce insolubla metal sulfides, and (iv) reaovering the insoluble metal sulfides;
;:
, ~ ~ 4 ~L3299~7 wherein the oxidizing bacteria is capable of causing oxidation of ferrous ion to ferric ion and/or oxidation of sulphur/sulfide to sulphate during culturing thereof, and the reducing bacteria is capable of causing recluction of sulphate to sul~ide during the culturing thereof.
In yet another aspect, the present invention provides a process for recovering metal contaminants from wastewater comprising soluble metal ions in an aqueous solution, the process comprising:
(i) culturing at least one reducing bacteria in the solution capable of causing the reduction of sulfate to sulfide to produce insoluble metal sulfide from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution sufficient amounts of sources of carbon, sulfate and nutrients to culture the reducing bacteria.
In yet another aspect, the present invention provides a process for recovering copper, nickel and zinc from wastewater from electroplating processes, said wastewater comprising soluble metal ions sele~ted from copper, nickel and zinc in an aqueous solution, the process comprising:
~ i) culturing at least one sulfate reducing bacteria selected ~rom the group of Desulfovibrio, Desulfobacter and Desulfotomaculum to produce insoluble metal sulfides from said f ~
, .~, . ..
- 4a - 13299~7 soluble metal ion~; ~nd (ii) recovering he insoluble ~etal sulfides;
wherein the step of culturing includes addlng to the solution a food processing waste containing suf~icient amounts of carbon, sulfate and nutrients to culture the sulfate reducing bacteria.
Figure 1 ls a schematic of an embodiment of th~
process of the present inventlon.
In one aspect of th0 proces~ of the present lnventlon, solubillzatlon of metals from sewa~e sludge is accomplished by b~cterial oxldation rather than chemical acldlflcatlon of the slud~e. A system of blological oxidatlon or ~bacter1al leachlng~
is employed in whlch lron or sulphur oxid~zlng bacteria are used as blologlcal cataly~t to stimulate oxidation of lnsoluble metals to soluble matal lon under a favourable pH enYiron~ent~
Most of the heavy ~etals tn se~age sludge are associated with the solid frac~lon. The inorganic metal pr~cipltates are the predominant form, although organometal complexation ls also slgniflcan~. Hydrogen sulflde is generated durlng ~he lnltl~l sludge dlgestlon, whi~h reaot~ with metals present to form insoluble 0ets~ ~ulfid0~ ~hich preolpltate lnto the solld fractionO Thus, the heavy metal~ ln sludge are predominantly or ~ubstantlally present as thelr insoluble sulfldes. In order to remove heavy metals from the ~ludge, the motals ~ave to be ~olublllzed.
~ 7 The solubility of metals in sludge is governed in part by pH. Other important factors therein include the oxidation reduction potential (ORP) of the sludge, the concentration of the metals and the ligands (negative ions or uncharged molecules) and the chemical e~uilibria between the constituents.
As desaribed above, during digestion of the sludge, most metals form simple substantially insoluble compounds.
Raising of the ORP of the sludge at suitable pH shifts the chemical equilibria in favour of metallic ion formation and hence, solubilization of the metal for removal from the sludge.
In the bacterial leaching process, metals are solubilized and dissolved from insoluble masses either directly by metabolism of micro-organisms or indirectly by the products of their metabolism. In ths direct mechanism, the leaching bacteria attack mineral sulfides directly by enzymatic actions and the metals become solubilized because of the oxidation of mineral sulfides, thus:
bacteria MS ~ 202 ~~~> MSO4 in which M repressnts any bivalent metal.
In the indirect machanism, ferrous ion is used as an intermediary. The bacteria first cause oxida-tion of ferrous ion . . , ~ .
: : ~
" - 6 - 1 3~?~
to ferric ion. Then the ferric ion, being an oxidizing agent, oxidizes other metals and liberates them into solution, thus:
oxidizing bacteria Fe2~ ----_______> Fe3~
4 Fe3~ + 2MS + 2H20 + 32 ------> 2M2 ~ + 4 Fe2 ' + H2 S4 Th~se reactions occur cyclically with more and more oxidation and solubilization of divalent metals. Sulfuric acid generation is beneficial to the process.
The preferred oxidizing bacterial cultures for use in the sewage sludge treatment embodiment of the present invention are chemolithotrophic bacteria which are capable of causing oxidation of ferrous ion to ferric ion (Fe2~ ---> Fe3~) and/or oxidation of sulphur/sulphide to sulphate during their growth~
Preferred oxidizing bacteria cause both oxida~ions. Specific examples of suitable known species of bacteria for use in the present invention are Thiobaccillus ferrooxidans, Thiobaccillus thio-oxidans, Thiobaccillus thioparus, Thiobaccillus concretivorous, Thiobaccillus organoparus, Sulfolobus acidocaldarius, Sulfobolus brierleyi, Le~tospirillium ferrooxidans, and Thermothrix thiopara. Of these the most important and most preferred are T. ferrooxidans and T.
thiooxidans especially a mixed culture of both these organisms.
T. ferrooxidans and T. thiooxidans are both known and used in the bacterial leaching of mineral ores. For use in the present invention these organisms undergo aerobic growth and require .
, '. ' ~ ' ~ ,, ' ' . ' ~L 3 ~ 7 carbon dioxide, o~ygen, mineral salts, reduced iron and sulphur and an acidic pH for growth. Carbon dioxide serves as a sole carbon source. Energy is obtained from oxidation of ferrous ion, elemental sulphur, and reduced inorganic sulphur.
The pH of the sludge during the first s-tep of the treatment process of the present invention should be acidic, i.e.
less than 7, preerably less than 5 and most preferably in the range from about pH 2 to about p~ 4.5. This is suitably arranged by appropriate acidification of the sludge with mineral acid preferably sulfuric acid prlor to bacterial addition. The sludge is aerated during the bacterial leaching process to ensure aerobic bacterial growth. Culturing suitably takes place for at least two days, preferably from about 10 to 15 days. The temperature of the process is not critical within relatively wide limits and is suitably in the 5C to 40C preferably 15C to 25C
approximate range~
The solubilized metal ions are then removed from the sludge in the form of an a~ueous solution. The method of such removal is not particularly limited; however, in a preferred embodiment the solubilized metal ions are removed in the form of an aqueous solution by using a combination of gravity thickening followed by centriugation. The use of gravity thickening prior to centrifugation results in a reduced volume of sludge to be centrifuged. Commercially available full scale centrifuges can provide a G range of up to 2,000 G. Preferably, the gravity thiakened sludge is subjected to at leas-t 1,200 G.
' `' ' ,~. ' ,: , . ~ .
- 8 _ 132~3~
After removal in tha form of an aqueous solution, the solubilized metals are then subjected to bacterial reduction to insolubilize them. The system of biological reduction employed in this step of the process utilizes sulphur reduclng bacteria as biological catalysts and results in the reduction of soluble metal ions to insoluble metals or metal compounds in a favourable pH environment.
The metal laden leachate produced from the first step of the sludge treatment process of the present invention must be processed further to reduce the metal concentration to acceptable levels prior to disposal or reuse. After separation soluble metal residues may be precipitated by reduction of mineral sulfates, thus:
reducing M2~ ~ sa _ > MS
bacteria where solubilized metal ions M2~ react with sulfides S2- to form insoluble MS precipitates.
The reducing bacteria suitable for use in the second step of the process of the present invention are dissimilatory sulphate reducing bacteria which are capable of causing reduction of sulphate to sulphide. The preferred species of reducing bacteria for use in the process of the present invention are species of the genera Desulfovibrio, Desulfobacter, ' ..
- ~3~9~7 Desulfococcus, Desulfobulbus, Desulfosarcina, Desulfonema and Desulfotomaculum, and most preferably Desulfovibrio, Desulfobacter and Desulf tomaculum.
The pH of the metal laden leachate during the bacterial reduction process of the present invention should be greater than 5, pre~erably greater than 6, and most preferably in the range from about pH 6.5 to about pH 8. This may be suitably achieved by treating the metal laden leachate with lime prior to the addition of the reducing bacteria. Such treatment with lime may result in precipitation of a small amount of some metals which may be allowed to settle and then be removed.
Among the metals which can be solubilized and removed in the process of the present invention are most of those commonly found to be associated with sludge solids including cadmium, copper, iron, lead, nickel, zinc, arsenic, cobalt, chromium, mercury, molybdenum and selenium. The process is most effective for the removal of cadmium, copper, nickel, and zinc metals. Perhaps the most troublesome metal in this regard because of its propensity for assimilation into plants and hence entry into the food chain is cadmium. The procass of the present invention is particularly suitable for use in removing cadmium.
An advantage of the process described herein is that it may be used in either a batch or continuous mode. Preferably, the present process is used in a continuous mode.
.
' --` 13299~7 The invention is further illustrated in the following specific non-limiting examples.
EXAMPLE 1. PREPARATION AND ACCLIMATION OF OXIDIZING BACTERIAL
CULTURE - ~-Thiobacillus ferrooxidans used in the leaching experiments were first isolated from acid mins water and subsequently grown on a special iron o~idizing medium ("Standard Methods for the examination of Water and Wastewater"; 1980; 15th ed.; American Public Health Association). The final pH of the medium was 3.0, and the cultura was incubated aerobically at 20 C. Growth was monitored by measuring the formation of ferric oxide by adding 1 mL of the aulture to 1 mL of 2 N hydrochloric acid and measuring spectrophotometrically the resultant yellow orange ferric chloride complex (Schnaitman, C. A.; Journal of Bacteriology, 99, pg. 552).
Since the bacteria were isolated from acid mine water, acclimation to anaerobic sludge was needed. This was carried out by adding 10 mL of an anaerobically digested sludge to 500 mL of the bacterial culture each day over a one week period. The sludge was obtained from the Humber Wa~tewater Treatment Plant, Metropolitan, Toronto.
`; ' ~ ' ``;
32~7 EXAMPLE 2. SLUDGE TREATM~NT EXPERIMENTS
Referring now to the Figure, the anaerobically digested primary sludge obtained from Example 1 above was introduced into a sludge holding tank 1 wherein it was acidified with sulphuric acid to pH 4. From the holding tank, -the acidified sludge was fed to a leaching tank 2 wherein it was subjected to oxidative bacterial leaching under the following conditions:
i) pH = 3 ii) aeration = 50 cm3 of air/L of sludge iii) leaching time = 10 days;
iv) sludge solids concentration = 3%; and v) initial T. ferrooxidans inoculum of 5 x 106 cells/mL of sludge.
The leached sludge was then transferred to a sludge settling tank 3, wherein it was thickened to a solids content of about 6~ at a sludge detention time of about 12 hours. Overflow from the sludge settling tank which comprised metal laden leachate was transferred to a holding tank 5 by gravity.
Underflow from the sludge settling tank was transferred to a centrifuge 4 wherein it was de-watared to a solids content of about 20% by cantrification at 1200G. The centrate was returned to the leachate holding tank 5. The metal laden supernatant was transferred from the holding tank 5 to a mixing tank 6 where it was treated with lime to a pH of about 6.5 which resulted in precipitation of a small amount of metalO The precipitated metal ,~ ; ' ` :
- . .
1329~7 was allowed to settle and then removed for disposal. The precipitate-free and pH adjus-ted supernatant was then transferred to the anaerobic filter station 7. The anaerobic filtar station 7 comprised two upflow anaerobic filters which were run in parallel. Each of the anaerobic filters contained an appropriate reducing bacteria. Plastic bio-rings with a porosity of about 90% were used as the filter media.
The sludge used in this study has good soil conditioning and fsrtilizing potential because it contains significant amounts of organic matter and plant nutrients. On a dry weight basis the volatile solids, total nitrogen, phosphorus and potassium content of the sludge were 55~, 5%, 3~, and 1%, respectively. However, the sludge prior to sub~ection to the bacterial leaching process was not acceptable for land utilization because of its high concentration of heavy metals.
The average concentrations of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) ~n the digested sludge before oxidative bacterial leaching are shown in Table l. Treatment of the digested sludge in the oxidative bacterial leaching unit resulted in metal solubilization of the sludge. The average concentrations of metal in the leached sludge are also shown in Table 1 and are much lower than those for the digested sludge.
The metal solubilization efficiencies are summarized in Table l.
Each of Zn, Ni and Cd showed a hi~h degree of solubilization (>
75~); Cu was less readily solubilized because of its a~finity for organic matter.
' . ~. , - 13 - 13~9~
It is worth noting -that the sludge traatment experiments of this example ware conducted in a continuous manner for a period of 60 days.
T~BLE 1 Average Average conc. (mg/L) in conc. (mg/L) in sludge before sludge af~er Solubiliza~ion Metal leaching eaching efficiency (%) Cd 225 56 75 Cu 1830 976 47 Ni 510 151 70 Zn 10088 1852 87 Analysis of the nutrient content of the sludge after oxidative baaterial leaching indicated that the organic matter nitrogen (N3, phosphorus (P) and potassium (K) were conserved.
The N-P-K concentrations in the leached sludge were comparable to the N-P-K content before leaching. Thus, the potential of the sludge as a plant fertilizer material is not adversely affected by the bacterial leaching.
The effluent rom the anaerobic filter station was :~
then analyzed for metal content, tha results of which ara provided in Table 2. The overall matal removal efficiency of the ,~ . , .
` --" 132~7 anaerobic filter was very high (> 85~) for all four metals (Cd, Cu, Ni and Zn).
Average Average conc. (mg/L) in conc. (~g/L) i~
leachate before leachate after Me~al removal Metal filtration filtr~tion _ efficiency (%) Cd 2.7 0.1 96 Cu 3.5 0.4 89 Ni 10.6 0.6 94 Zn 183.4 24.6 87 Two tests were carried out to confirm the occurrence of microbial sulphate reduction. The first test performed on the filter oontents involved bacterial enumeration by pour plate technique and indicated that sulphate reducing bacteria were present and active. The number of sulphate reducing bacteria was 9 x 106/mg of filter solids. The second test involved measuring -the sulphide concentration of the anaerobic filter influent and effluent as well as the filter contents. The results showed that while the influent contained no sulphide the effluent contained about 10 mg/L of soluble sulphide. As for the filter solids, insoluble sulfides constituted about 5% of the fixed solids.
Thus, the process of the present invention may be used to remove metal contaminants from sewage sludge, and subsequently to remove the metal from the sludge superna-tant. After ~ 329~7 neutralization with lime, the substantially metal free sludge solids can -then be applied on agricultural lands. Moreover, the small amounts of residual metals in the sludge are strongly complexed with organic matter and are therefore unlikely to be taken up by plants in any significant amount.
EXAMPLE 3. INDUSTRIAL WASTEWATER TREATMENT EXPERIMENTS
In a series of experiments, a sample of industrial wastewater, specifically electroplating waste, was treated to remove heavy metal contaminants. Specifically, the wastewater was passed through an anaerobic filter which had been seeded with anaerobically digested sludge which contained sulphate reducing bacteria. A food processing waste was used as a source of carbon, sulphate and nutrients for the sulphate reduoing bacteria.
Content in Content in Removal Metal Influent, mg/L Efflue~t, mg/L Efficiency (%) Cu 7.28 0.04 99.5 Ni 17.50 0.08 99.5 Zn 28.20 0.02 99.9 ~ -The anaerobic filter provided 16 hours detention for the mixture of electroplating and food processing wastes, with the entire system operating continuously. The results in Table 3 indicate that Cu, Ni and Zn were removed at efficiencies greater , 1 32~7 than 99% using the process disclosed herein. Thus, it is within the scope of the present invention to remove and recover metals from industrial wastewaters such as those from electroplating industries. The metal free liguid waste and the plating materials could then be reused thus providing a more economical method than is now available for waste disposa:l and metal recovery in the plating industry.
. .
: . .
. - .
.
Sewage treatment plants, as commonly operated in municipal facilities, treat aqueous sewage affluent microbially to produce an aqueous sewage sludge. The water is separated from the sludge in a clean enough form for discharge to receiving waters. The sludge undergoes biological decomposition and/or concentration. The sludge so produced is commonly rich in phosphorus, nitrogen and organic nutrient materials so that it is attractive for use as a soil conditioner in agricultural ~ertilizer. In fact, spreading of sewage sludge on agricultural land is an attractive sludge disposal option because it co~lbines beneficial reuse and disposal of the sludge at the same time.
If, however, sewage sludge is to be put to such use, it needs to have a low metal content to minimize the health hazard associated with metal up-take by plants and its subsequen-t accumulation in the food chain.
To date, no satisfactory commercial method for removing heavy metals from sewage sludge has been developed. Attempts have been made to remove heavy metal from sewage sludge using acid treatment but the cost o~ such treatment is excessive because of the large amounts of acids required. In addition, at the end of such treatment large amounts of lime are needed to raise the pH of the sludge to neutral.
-.
':
` ~ 132~7 Further, industrial wastewaters, such as those fromelectro-plating industries, are usually laden with heavy metals which renders these wastewatsrs unacceptable for either reuse or discharge to the environment. To date, there is no satisfactory and economical method for removing heavy metals from these wastewaters. Currently these metals are usually removed by chemical precipitation - often with lime - a costly process.
It is an object of the present invention to provide a process for reducing the content of heavy metals in liquids and slurries.
Further, it is another object of the present invention to provide a process for reducing the content of heavy metals in sewage sludge.
Still further, it is another object of the present invention to provide a process fox reducing the amounts of heavy metals from industrial wastewaters.
Accordingly, in a broad aspect, the present invention provides a process for removing dissolved metal contaminants from liquids and slurries which comprises:
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions in the waste water to produce insoluble metal sulfides from the soluble metal ions; and ~, .
;
.
.
_ 3 13~99~7 (ii) recovering the insoluble metal sulfides;
wherein the reducing baateria is capable of causing reduction of sulphate to sulfide.
The liquid or slurry so treated may be feedstock or waste water from a variety of different sources such as mill effluents, mine drainage, electroplating, steel, pulp and paper industries, and the like. In one particular ambodiment, the liquid or slurry is that which forms part of, or is separated from, sewage sludge, Thus, in another aspect, the present invention provides a process for removing metal contaminants from sewage sludge which comprises:
(i) culturing at least one oxidizing bacteria in the presence of the sewage sludge under acidic conditions to produce a sludge comprising soluble metal ions;
~il) separating the soluble metal ions;
(iii) culturing at least one reducing bacteria in tha presence of the soluble metal ions to produce insolubla metal sulfides, and (iv) reaovering the insoluble metal sulfides;
;:
, ~ ~ 4 ~L3299~7 wherein the oxidizing bacteria is capable of causing oxidation of ferrous ion to ferric ion and/or oxidation of sulphur/sulfide to sulphate during culturing thereof, and the reducing bacteria is capable of causing recluction of sulphate to sul~ide during the culturing thereof.
In yet another aspect, the present invention provides a process for recovering metal contaminants from wastewater comprising soluble metal ions in an aqueous solution, the process comprising:
(i) culturing at least one reducing bacteria in the solution capable of causing the reduction of sulfate to sulfide to produce insoluble metal sulfide from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution sufficient amounts of sources of carbon, sulfate and nutrients to culture the reducing bacteria.
In yet another aspect, the present invention provides a process for recovering copper, nickel and zinc from wastewater from electroplating processes, said wastewater comprising soluble metal ions sele~ted from copper, nickel and zinc in an aqueous solution, the process comprising:
~ i) culturing at least one sulfate reducing bacteria selected ~rom the group of Desulfovibrio, Desulfobacter and Desulfotomaculum to produce insoluble metal sulfides from said f ~
, .~, . ..
- 4a - 13299~7 soluble metal ion~; ~nd (ii) recovering he insoluble ~etal sulfides;
wherein the step of culturing includes addlng to the solution a food processing waste containing suf~icient amounts of carbon, sulfate and nutrients to culture the sulfate reducing bacteria.
Figure 1 ls a schematic of an embodiment of th~
process of the present inventlon.
In one aspect of th0 proces~ of the present lnventlon, solubillzatlon of metals from sewa~e sludge is accomplished by b~cterial oxldation rather than chemical acldlflcatlon of the slud~e. A system of blological oxidatlon or ~bacter1al leachlng~
is employed in whlch lron or sulphur oxid~zlng bacteria are used as blologlcal cataly~t to stimulate oxidation of lnsoluble metals to soluble matal lon under a favourable pH enYiron~ent~
Most of the heavy ~etals tn se~age sludge are associated with the solid frac~lon. The inorganic metal pr~cipltates are the predominant form, although organometal complexation ls also slgniflcan~. Hydrogen sulflde is generated durlng ~he lnltl~l sludge dlgestlon, whi~h reaot~ with metals present to form insoluble 0ets~ ~ulfid0~ ~hich preolpltate lnto the solld fractionO Thus, the heavy metal~ ln sludge are predominantly or ~ubstantlally present as thelr insoluble sulfldes. In order to remove heavy metals from the ~ludge, the motals ~ave to be ~olublllzed.
~ 7 The solubility of metals in sludge is governed in part by pH. Other important factors therein include the oxidation reduction potential (ORP) of the sludge, the concentration of the metals and the ligands (negative ions or uncharged molecules) and the chemical e~uilibria between the constituents.
As desaribed above, during digestion of the sludge, most metals form simple substantially insoluble compounds.
Raising of the ORP of the sludge at suitable pH shifts the chemical equilibria in favour of metallic ion formation and hence, solubilization of the metal for removal from the sludge.
In the bacterial leaching process, metals are solubilized and dissolved from insoluble masses either directly by metabolism of micro-organisms or indirectly by the products of their metabolism. In ths direct mechanism, the leaching bacteria attack mineral sulfides directly by enzymatic actions and the metals become solubilized because of the oxidation of mineral sulfides, thus:
bacteria MS ~ 202 ~~~> MSO4 in which M repressnts any bivalent metal.
In the indirect machanism, ferrous ion is used as an intermediary. The bacteria first cause oxida-tion of ferrous ion . . , ~ .
: : ~
" - 6 - 1 3~?~
to ferric ion. Then the ferric ion, being an oxidizing agent, oxidizes other metals and liberates them into solution, thus:
oxidizing bacteria Fe2~ ----_______> Fe3~
4 Fe3~ + 2MS + 2H20 + 32 ------> 2M2 ~ + 4 Fe2 ' + H2 S4 Th~se reactions occur cyclically with more and more oxidation and solubilization of divalent metals. Sulfuric acid generation is beneficial to the process.
The preferred oxidizing bacterial cultures for use in the sewage sludge treatment embodiment of the present invention are chemolithotrophic bacteria which are capable of causing oxidation of ferrous ion to ferric ion (Fe2~ ---> Fe3~) and/or oxidation of sulphur/sulphide to sulphate during their growth~
Preferred oxidizing bacteria cause both oxida~ions. Specific examples of suitable known species of bacteria for use in the present invention are Thiobaccillus ferrooxidans, Thiobaccillus thio-oxidans, Thiobaccillus thioparus, Thiobaccillus concretivorous, Thiobaccillus organoparus, Sulfolobus acidocaldarius, Sulfobolus brierleyi, Le~tospirillium ferrooxidans, and Thermothrix thiopara. Of these the most important and most preferred are T. ferrooxidans and T.
thiooxidans especially a mixed culture of both these organisms.
T. ferrooxidans and T. thiooxidans are both known and used in the bacterial leaching of mineral ores. For use in the present invention these organisms undergo aerobic growth and require .
, '. ' ~ ' ~ ,, ' ' . ' ~L 3 ~ 7 carbon dioxide, o~ygen, mineral salts, reduced iron and sulphur and an acidic pH for growth. Carbon dioxide serves as a sole carbon source. Energy is obtained from oxidation of ferrous ion, elemental sulphur, and reduced inorganic sulphur.
The pH of the sludge during the first s-tep of the treatment process of the present invention should be acidic, i.e.
less than 7, preerably less than 5 and most preferably in the range from about pH 2 to about p~ 4.5. This is suitably arranged by appropriate acidification of the sludge with mineral acid preferably sulfuric acid prlor to bacterial addition. The sludge is aerated during the bacterial leaching process to ensure aerobic bacterial growth. Culturing suitably takes place for at least two days, preferably from about 10 to 15 days. The temperature of the process is not critical within relatively wide limits and is suitably in the 5C to 40C preferably 15C to 25C
approximate range~
The solubilized metal ions are then removed from the sludge in the form of an a~ueous solution. The method of such removal is not particularly limited; however, in a preferred embodiment the solubilized metal ions are removed in the form of an aqueous solution by using a combination of gravity thickening followed by centriugation. The use of gravity thickening prior to centrifugation results in a reduced volume of sludge to be centrifuged. Commercially available full scale centrifuges can provide a G range of up to 2,000 G. Preferably, the gravity thiakened sludge is subjected to at leas-t 1,200 G.
' `' ' ,~. ' ,: , . ~ .
- 8 _ 132~3~
After removal in tha form of an aqueous solution, the solubilized metals are then subjected to bacterial reduction to insolubilize them. The system of biological reduction employed in this step of the process utilizes sulphur reduclng bacteria as biological catalysts and results in the reduction of soluble metal ions to insoluble metals or metal compounds in a favourable pH environment.
The metal laden leachate produced from the first step of the sludge treatment process of the present invention must be processed further to reduce the metal concentration to acceptable levels prior to disposal or reuse. After separation soluble metal residues may be precipitated by reduction of mineral sulfates, thus:
reducing M2~ ~ sa _ > MS
bacteria where solubilized metal ions M2~ react with sulfides S2- to form insoluble MS precipitates.
The reducing bacteria suitable for use in the second step of the process of the present invention are dissimilatory sulphate reducing bacteria which are capable of causing reduction of sulphate to sulphide. The preferred species of reducing bacteria for use in the process of the present invention are species of the genera Desulfovibrio, Desulfobacter, ' ..
- ~3~9~7 Desulfococcus, Desulfobulbus, Desulfosarcina, Desulfonema and Desulfotomaculum, and most preferably Desulfovibrio, Desulfobacter and Desulf tomaculum.
The pH of the metal laden leachate during the bacterial reduction process of the present invention should be greater than 5, pre~erably greater than 6, and most preferably in the range from about pH 6.5 to about pH 8. This may be suitably achieved by treating the metal laden leachate with lime prior to the addition of the reducing bacteria. Such treatment with lime may result in precipitation of a small amount of some metals which may be allowed to settle and then be removed.
Among the metals which can be solubilized and removed in the process of the present invention are most of those commonly found to be associated with sludge solids including cadmium, copper, iron, lead, nickel, zinc, arsenic, cobalt, chromium, mercury, molybdenum and selenium. The process is most effective for the removal of cadmium, copper, nickel, and zinc metals. Perhaps the most troublesome metal in this regard because of its propensity for assimilation into plants and hence entry into the food chain is cadmium. The procass of the present invention is particularly suitable for use in removing cadmium.
An advantage of the process described herein is that it may be used in either a batch or continuous mode. Preferably, the present process is used in a continuous mode.
.
' --` 13299~7 The invention is further illustrated in the following specific non-limiting examples.
EXAMPLE 1. PREPARATION AND ACCLIMATION OF OXIDIZING BACTERIAL
CULTURE - ~-Thiobacillus ferrooxidans used in the leaching experiments were first isolated from acid mins water and subsequently grown on a special iron o~idizing medium ("Standard Methods for the examination of Water and Wastewater"; 1980; 15th ed.; American Public Health Association). The final pH of the medium was 3.0, and the cultura was incubated aerobically at 20 C. Growth was monitored by measuring the formation of ferric oxide by adding 1 mL of the aulture to 1 mL of 2 N hydrochloric acid and measuring spectrophotometrically the resultant yellow orange ferric chloride complex (Schnaitman, C. A.; Journal of Bacteriology, 99, pg. 552).
Since the bacteria were isolated from acid mine water, acclimation to anaerobic sludge was needed. This was carried out by adding 10 mL of an anaerobically digested sludge to 500 mL of the bacterial culture each day over a one week period. The sludge was obtained from the Humber Wa~tewater Treatment Plant, Metropolitan, Toronto.
`; ' ~ ' ``;
32~7 EXAMPLE 2. SLUDGE TREATM~NT EXPERIMENTS
Referring now to the Figure, the anaerobically digested primary sludge obtained from Example 1 above was introduced into a sludge holding tank 1 wherein it was acidified with sulphuric acid to pH 4. From the holding tank, -the acidified sludge was fed to a leaching tank 2 wherein it was subjected to oxidative bacterial leaching under the following conditions:
i) pH = 3 ii) aeration = 50 cm3 of air/L of sludge iii) leaching time = 10 days;
iv) sludge solids concentration = 3%; and v) initial T. ferrooxidans inoculum of 5 x 106 cells/mL of sludge.
The leached sludge was then transferred to a sludge settling tank 3, wherein it was thickened to a solids content of about 6~ at a sludge detention time of about 12 hours. Overflow from the sludge settling tank which comprised metal laden leachate was transferred to a holding tank 5 by gravity.
Underflow from the sludge settling tank was transferred to a centrifuge 4 wherein it was de-watared to a solids content of about 20% by cantrification at 1200G. The centrate was returned to the leachate holding tank 5. The metal laden supernatant was transferred from the holding tank 5 to a mixing tank 6 where it was treated with lime to a pH of about 6.5 which resulted in precipitation of a small amount of metalO The precipitated metal ,~ ; ' ` :
- . .
1329~7 was allowed to settle and then removed for disposal. The precipitate-free and pH adjus-ted supernatant was then transferred to the anaerobic filter station 7. The anaerobic filtar station 7 comprised two upflow anaerobic filters which were run in parallel. Each of the anaerobic filters contained an appropriate reducing bacteria. Plastic bio-rings with a porosity of about 90% were used as the filter media.
The sludge used in this study has good soil conditioning and fsrtilizing potential because it contains significant amounts of organic matter and plant nutrients. On a dry weight basis the volatile solids, total nitrogen, phosphorus and potassium content of the sludge were 55~, 5%, 3~, and 1%, respectively. However, the sludge prior to sub~ection to the bacterial leaching process was not acceptable for land utilization because of its high concentration of heavy metals.
The average concentrations of cadmium (Cd), copper (Cu), nickel (Ni) and zinc (Zn) ~n the digested sludge before oxidative bacterial leaching are shown in Table l. Treatment of the digested sludge in the oxidative bacterial leaching unit resulted in metal solubilization of the sludge. The average concentrations of metal in the leached sludge are also shown in Table 1 and are much lower than those for the digested sludge.
The metal solubilization efficiencies are summarized in Table l.
Each of Zn, Ni and Cd showed a hi~h degree of solubilization (>
75~); Cu was less readily solubilized because of its a~finity for organic matter.
' . ~. , - 13 - 13~9~
It is worth noting -that the sludge traatment experiments of this example ware conducted in a continuous manner for a period of 60 days.
T~BLE 1 Average Average conc. (mg/L) in conc. (mg/L) in sludge before sludge af~er Solubiliza~ion Metal leaching eaching efficiency (%) Cd 225 56 75 Cu 1830 976 47 Ni 510 151 70 Zn 10088 1852 87 Analysis of the nutrient content of the sludge after oxidative baaterial leaching indicated that the organic matter nitrogen (N3, phosphorus (P) and potassium (K) were conserved.
The N-P-K concentrations in the leached sludge were comparable to the N-P-K content before leaching. Thus, the potential of the sludge as a plant fertilizer material is not adversely affected by the bacterial leaching.
The effluent rom the anaerobic filter station was :~
then analyzed for metal content, tha results of which ara provided in Table 2. The overall matal removal efficiency of the ,~ . , .
` --" 132~7 anaerobic filter was very high (> 85~) for all four metals (Cd, Cu, Ni and Zn).
Average Average conc. (mg/L) in conc. (~g/L) i~
leachate before leachate after Me~al removal Metal filtration filtr~tion _ efficiency (%) Cd 2.7 0.1 96 Cu 3.5 0.4 89 Ni 10.6 0.6 94 Zn 183.4 24.6 87 Two tests were carried out to confirm the occurrence of microbial sulphate reduction. The first test performed on the filter oontents involved bacterial enumeration by pour plate technique and indicated that sulphate reducing bacteria were present and active. The number of sulphate reducing bacteria was 9 x 106/mg of filter solids. The second test involved measuring -the sulphide concentration of the anaerobic filter influent and effluent as well as the filter contents. The results showed that while the influent contained no sulphide the effluent contained about 10 mg/L of soluble sulphide. As for the filter solids, insoluble sulfides constituted about 5% of the fixed solids.
Thus, the process of the present invention may be used to remove metal contaminants from sewage sludge, and subsequently to remove the metal from the sludge superna-tant. After ~ 329~7 neutralization with lime, the substantially metal free sludge solids can -then be applied on agricultural lands. Moreover, the small amounts of residual metals in the sludge are strongly complexed with organic matter and are therefore unlikely to be taken up by plants in any significant amount.
EXAMPLE 3. INDUSTRIAL WASTEWATER TREATMENT EXPERIMENTS
In a series of experiments, a sample of industrial wastewater, specifically electroplating waste, was treated to remove heavy metal contaminants. Specifically, the wastewater was passed through an anaerobic filter which had been seeded with anaerobically digested sludge which contained sulphate reducing bacteria. A food processing waste was used as a source of carbon, sulphate and nutrients for the sulphate reduoing bacteria.
Content in Content in Removal Metal Influent, mg/L Efflue~t, mg/L Efficiency (%) Cu 7.28 0.04 99.5 Ni 17.50 0.08 99.5 Zn 28.20 0.02 99.9 ~ -The anaerobic filter provided 16 hours detention for the mixture of electroplating and food processing wastes, with the entire system operating continuously. The results in Table 3 indicate that Cu, Ni and Zn were removed at efficiencies greater , 1 32~7 than 99% using the process disclosed herein. Thus, it is within the scope of the present invention to remove and recover metals from industrial wastewaters such as those from electroplating industries. The metal free liguid waste and the plating materials could then be reused thus providing a more economical method than is now available for waste disposa:l and metal recovery in the plating industry.
. .
: . .
. - .
.
Claims (16)
1. A process for removing dissolved metal contaminants from liquids and slurries which comprises:
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions in said liquids and slurries to produce insoluble metal sulfide from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the reducing bacteria is capable of causing reduction of sulfate to sulfide.
(i) culturing at least one reducing bacteria in a solution comprising soluble metal ions in said liquids and slurries to produce insoluble metal sulfide from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the reducing bacteria is capable of causing reduction of sulfate to sulfide.
2. The process of Claim 1 wherein said reducing bacteria is selected from the group comprising Desulfovibrio, Desulfobacter, Desulfococcus, Desulfobulbus, Delsulfosarcina, Desulfonema and Desulfotomaculum.
3. The process of Claim 1 wherein said reducing bacteria is selected from Desulfobacter, Desulfovibrio and Desulfotomaculum.
4. A process for removing metal contaminants from sewage sludge which comprises:
(i) culturing at least one oxidizing bacteria in the presence of the sewage sludge under acidic conditions to produce a sludge comprising soluble metal ions;
(ii) separating the soluble metal ions;
(iii) culturing at least one reducing bacteria in the presence of said soluble metal ions to produce insoluble metal sulfides; and (iv) recovering said insoluble metal sulfides;
wherein said oxidizing bacteria is capable of causing oxidation of ferrous ion to ferric ion and/or oxidation of sulfur/sulfide to sulfate during culturing thereof, and said reducing bacteria is capable of causing reduction of sulfate to sulfide during the culturing thereof.
(i) culturing at least one oxidizing bacteria in the presence of the sewage sludge under acidic conditions to produce a sludge comprising soluble metal ions;
(ii) separating the soluble metal ions;
(iii) culturing at least one reducing bacteria in the presence of said soluble metal ions to produce insoluble metal sulfides; and (iv) recovering said insoluble metal sulfides;
wherein said oxidizing bacteria is capable of causing oxidation of ferrous ion to ferric ion and/or oxidation of sulfur/sulfide to sulfate during culturing thereof, and said reducing bacteria is capable of causing reduction of sulfate to sulfide during the culturing thereof.
5. The process of Claim 4, wherein said oxidizing bacteria is selected from the group comprising Thiobaccillus ferrooxidans, Thiobaccillus thio-oxidans, Thiobaccillus thioparus, Thiobaccillus concretivorous, Thiobaccillus organoparus, Sulfolobus acidocaldarius, Sulfobolus brierleyi, Leptospirillium ferrooxidans, and Thermothrix thiopara.
6. The process of Claim 4, wherein said oxidizing bacteria is selected from the group comprising T. ferrooxidans and T.
thiooxidans.
thiooxidans.
7. The process of Claim 4, wherein said reducing bacteria is selected from the group comprising Desulfovibrio, Desulfobacter, Desulfococcus, Desulfobulbus, Delsulfosarcina, Desulfonema and Desulfotomaculum.
8. The process of Claim 4, wherein said reducing bacteria is selected from Desulfobacter, Desulfovibrio and Desulfotomaculum.
9. A process for recovering copper, nickel and zinc from wastewater from electroplating processes, said wastewater comprising soluble metal ions selected from copper, nickel and zinc in an aqueous solution, the process comprising:
(i) culturing at least one sulfate reducing bacteria selected from the group of Desulfovibrio, Desulfobacter and Desulfotomaculum to produce insoluble metal sulfides from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution a food processing waste containing sufficient amounts of carbon, sulfate and nutrients to culture the sulfate reducing bacteria.
(i) culturing at least one sulfate reducing bacteria selected from the group of Desulfovibrio, Desulfobacter and Desulfotomaculum to produce insoluble metal sulfides from said soluble metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution a food processing waste containing sufficient amounts of carbon, sulfate and nutrients to culture the sulfate reducing bacteria.
10. A process for recovering metal contaminants from wastewater comprising soluble metal ions in an aqueous solution, the process comprising:
(i) culturing at least one reducing bacteria in the solution capable of causing the reduction of sulfate to sulfide to produce insoluble metal sulfide from said solubla metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution sufficient amounts of sources of carbon, sulfate and nutrients to culture the reducing bacteria.
(i) culturing at least one reducing bacteria in the solution capable of causing the reduction of sulfate to sulfide to produce insoluble metal sulfide from said solubla metal ions; and (ii) recovering the insoluble metal sulfides;
wherein the step of culturing includes adding to the solution sufficient amounts of sources of carbon, sulfate and nutrients to culture the reducing bacteria.
11. The process of Claim 10 wherein said reducing bacteria is selected from the group comprising pesulfovibrio, Desulfobacter, Desulfococcus, Desulfobulbus, Desulfosarcina, Desulfonema and Desulfotomaculum.
12. The process of Claim 11 wherein said reducing bacteria is selected from Desulfobacter, Desulfovibrio and Desulfotomaculum.
13. The process of Claim 10 wherein said wastewater is selected from the group comprising mine drainage, wastewater from electroplating processes, wastewater from steel processing and manufacturing processes, and wastewater from pulp and paper manufacturing processes.
14. The process of any one of Claims 1 to 8 and 10 to 13 wherein said metal contaminants are selected from the group comprising cadmium, copper, iron, lead, nickel, zinc, arsenic, cobalt, chromium, mercury, molybdenum and selenium.
15. The process of Claim 14 wherein said metal contaminants are selected from the group comprising cadmium, copper, nickel and zinc.
16. The process of Claim 1 wherein said liquids and slurries comprise leachate produced in the bacterial leaching of sewage sludge.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000565562A CA1329957C (en) | 1988-04-29 | 1988-04-29 | Process for removing metal contaminants from liquids and slurries |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000565562A CA1329957C (en) | 1988-04-29 | 1988-04-29 | Process for removing metal contaminants from liquids and slurries |
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| CA1329957C true CA1329957C (en) | 1994-05-31 |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103193316A (en) * | 2013-04-15 | 2013-07-10 | 北京工业大学 | Method for biologically treating cadmium-containing wastewater |
| WO2015048919A1 (en) * | 2013-10-04 | 2015-04-09 | Universidad De Santiago De Chile | Method and composition for the bioremoval of sulfates, using a bacterial consortium |
| CN107244789A (en) * | 2017-06-09 | 2017-10-13 | 李超 | A kind of bioleaching system and the method for sludge treatment using the system |
| CN113149345A (en) * | 2021-03-31 | 2021-07-23 | 衡阳师范学院 | Wastewater treatment apparatus and wastewater treatment method |
-
1988
- 1988-04-29 CA CA000565562A patent/CA1329957C/en not_active Expired - Fee Related
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103193316A (en) * | 2013-04-15 | 2013-07-10 | 北京工业大学 | Method for biologically treating cadmium-containing wastewater |
| CN103193316B (en) * | 2013-04-15 | 2014-09-10 | 北京工业大学 | Method for biologically treating cadmium-containing wastewater |
| WO2015048919A1 (en) * | 2013-10-04 | 2015-04-09 | Universidad De Santiago De Chile | Method and composition for the bioremoval of sulfates, using a bacterial consortium |
| CN107244789A (en) * | 2017-06-09 | 2017-10-13 | 李超 | A kind of bioleaching system and the method for sludge treatment using the system |
| CN113149345A (en) * | 2021-03-31 | 2021-07-23 | 衡阳师范学院 | Wastewater treatment apparatus and wastewater treatment method |
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