CN111517606B - Method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point - Google Patents
Method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point Download PDFInfo
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- 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
- C02F11/02—Biological treatment
- C02F11/04—Anaerobic treatment; Production of methane by such processes
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- 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
- C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
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- 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
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- 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
- C02F1/42—Treatment of water, waste water, or sewage by ion-exchange
- C02F2001/425—Treatment of water, waste water, or sewage by ion-exchange using cation exchangers
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- Y02E50/00—Technologies for the production of fuel of non-fossil origin
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Abstract
The invention provides a method for strengthening anaerobic digestion of sludge by utilizing acid fermentation of kitchen waste based on isoelectric points, which comprises the following steps: carrying out anaerobic fermentation on the kitchen waste to produce acid, so as to obtain kitchen waste fermentation acid production liquid; concentrating and enriching the kitchen waste fermentation acid production liquid, and respectively collecting fermentation acid production supernatant and fermentation residues; conditioning the sludge to the isoelectric point of the sludge by using fermented acid-producing supernatant; performing solid-liquid separation on the conditioned sludge, and respectively collecting a first supernatant and sludge sediments; adjusting the first supernatant by using alkali liquor, performing centrifugal treatment, and respectively collecting a second supernatant and a metal deposit; treating the second supernatant with cation exchange resin, and collecting filtrate; mixing and stirring fermentation residues, sludge sediments and filtrate to obtain a mixture; carrying out anaerobic digestion, and collecting biogas and biogas residues; according to the invention, the kitchen waste fermentation acid-producing liquid is used for providing exogenous hydrogen protons to remove heavy metals in the sludge, so that the kitchen waste is effectively treated while the sludge recycling is enhanced.
Description
Technical Field
The invention belongs to the technical field of recycling treatment of perishable organic wastes such as sludge and the like, and particularly relates to a method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric points.
Background
Currently, with the widespread use of the activated sludge process in sewage treatment plants, large amounts of waste activated sludge are produced. The waste activated sludge contains a large amount of perishable organic matters and heavy metals, and serious secondary pollution may be caused if the waste activated sludge is not treated in time. The anaerobic digestion technology can reduce the pollution of sludge to the environment and recover energy, and is considered to be a sludge treatment technology with great potential. However, the long anaerobic digestion period of the sludge (more than 30 days), the low methane yield per organic matter (VS) (180-220mL/g VS) and the low degradation degree of the organic matter (only 30-40% of VS can be removed) greatly limit the popularization and application of the anaerobic digestion technology of the sludge. Meanwhile, with the increase of population and the development of economy, the yield of the kitchen waste is increased day by day. The conventional landfill will inevitably cause serious environmental pollution, and thus, the proper disposal of the kitchen garbage is urgent.
The existing patent technologies mainly improve the hydrolysis degree of sludge organic matters by directly pretreating sludge, such as hydrothermal pretreatment, ultrasonic pretreatment, alkali pretreatment, and high-pressure homogeneous pretreatment, for example: the patent with the publication number of CN108217933A discloses an internal circulation mixing device of a two-phase anaerobic digester for efficiently promoting acid production, the patent with the publication number of CN106365373A discloses a method and equipment for treating anaerobic digestion liquid of municipal sludge, the patent with the publication number of CN106929410A discloses an acid production phase reactor for two-phase anaerobic digestion of municipal solid waste, the patent with the publication number of CN108821531A discloses a method for synergistic anaerobic treatment of municipal sludge and kitchen waste through hot alkali pretreatment, the patent with the publication number of CN109250879A discloses a method for improving sludge fuel through hydrothermal reaction atmosphere, and the like.
Researches find that the isoelectric pretreatment of the sludge can effectively improve the anaerobic digestion efficiency of the sludge, remove heavy metals in the sludge and be beneficial to land utilization of biogas residues after anaerobic digestion of the sludge. However, the isoelectric point of the sludge is acidic (pH value is 3.5-4.5), and exogenous hydrogen protons are required to be added, so that the development of the pretreatment technology is limited. In recent years, acid fermentation treatment of kitchen waste is widely popularized due to the fact that the acid fermentation treatment of the kitchen waste becomes a green sustainable treatment mode. The pH value of the kitchen waste fermentation acid production liquid can be reduced to below 3, which provides possibility for adjusting the pH value of the sludge.
Disclosure of Invention
In order to improve the anaerobic digestion efficiency of the sludge, the kitchen waste and other perishable organic wastes, the invention provides a method for strengthening anaerobic co-digestion by utilizing kitchen waste acid fermentation based on the isoelectric point of the sludge. The method can enhance anaerobic biological conversion efficiency of sludge organic matters based on isoelectric point pretreatment, provides exogenous hydrogen protons to remove heavy metals in sludge by utilizing kitchen waste fermentation acid-producing liquid, and effectively disposes the kitchen waste while enhancing sludge recycling.
In order to achieve the above purpose, the solution of the invention is as follows:
a method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) carrying out medium-temperature or high-temperature anaerobic fermentation on the kitchen waste to produce acid for 1-8 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid to ensure that the pH value is less than 3, and respectively collecting fermentation acid production supernatant and fermentation residues;
(3) regulating the pH value of the sludge to the isoelectric point of the sludge by using fermented acid-producing supernatant, and stirring simultaneously;
(4) carrying out solid-liquid separation on the sludge conditioned in the step (3), and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0-11.0 by using alkali liquor, performing centrifugal treatment according to the solubility product of metal hydroxide, and respectively collecting a second supernatant and a metal deposit;
(6) treating the second supernatant obtained in the step (5) by 2-6BV of cation exchange resin, and collecting filtrate;
(7) regenerating the cation exchange resin in the step (6) by hydrochloric acid and sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 6.0-8.0, and stirring to obtain a mixture;
(9) and (3) carrying out medium-temperature, transition-temperature or high-temperature anaerobic digestion on the mixture obtained in the step (8) for 5-14 days, and collecting biogas and biogas residues, wherein the biogas can be used for power generation, and the biogas residues for removing heavy metals can be directly used for improving the land.
Further, in the step (1), the kitchen waste is pretreated before anaerobic fermentation for acid production, wherein the pretreatment comprises a thermal hydrolysis method, a stirring and crushing method, a proton regulation method and an enzymatic reaction method.
Further, in the step (1), the medium temperature is 30-40 ℃ and the high temperature is 50-60 ℃.
Further, in the step (3), the pH value of the sludge is 3.5-4.5; the stirring speed is 200-800rpm, and the stirring time is 2-8 h.
Further, in the step (4), the rotation speed at the time of solid-liquid separation is 8000-12000 rpm.
Further, in the step (5), the alkali liquor is selected from more than one of sodium hydroxide, sodium carbonate, sodium bicarbonate and potassium hydroxide; the concentration of the alkali liquor is 2-8 mol/L.
Further, in the step (5), the rotation speed of the centrifugation is 6000-10000 rpm.
Further, in the step (6), the cation exchange resin is a sodium type cation exchange resin.
Specifically, the sodium cation exchange resin is selected from one or more of sodium macroporous strong-acid styrene cation exchange resin, sodium macroporous strong-acid acrylic cation exchange resin, sodium macroporous weak-acid styrene cation exchange resin, sodium macroporous weak-acid acrylic cation exchange resin, sodium gel strong-acid styrene cation exchange resin, sodium gel strong-acid acrylic cation exchange resin, sodium gel weak-acid styrene cation exchange resin and sodium gel weak-acid acrylic cation exchange resin.
Further, in the step (7), the concentration of hydrochloric acid is 1-4mol/L, and the concentration of sodium hydroxide is 1-4 mol/L.
Further, in the step (8), the stirring time is 1-3 h.
Further, in the step (9), the medium temperature is 30-40 ℃, the transition temperature is 40-50 ℃, and the high temperature is 50-60 ℃.
Due to the adoption of the scheme, the invention has the beneficial effects that:
firstly, the method for strengthening sludge recycling by utilizing acid fermentation of kitchen waste based on the isoelectric point of sludge, which is adopted by the invention, enables acid fermentation liquor generated by pre-fermentation of the kitchen waste to be used as a proton regulator for conditioning the sludge, so that the semi-rigid structure of the sludge is damaged, and the dissolution and hydrolysis of sludge organic matters in the anaerobic digestion process are increased. The kitchen waste pre-fermentation residues are rich in acidifying bacteria, conditioned sludge organic matters are easy to dissolve out and hydrolyze in the anaerobic digestion process, residues generated by pre-fermentation are mixed with sludge conditioned by acid fermentation liquor, and anaerobic bioconversion of the sludge organic matters to produce methane can be improved. In addition, because the pH value of the isoelectric point of the sludge is lower than 4.5, part of heavy metals (> 50%) in the sludge can be transferred from a solid phase to a liquid phase, and after solid-liquid separation, the heavy metals dissolved in the supernatant can be effectively recovered by carrying out cation exchange and multi-stage chemical precipitation on the supernatant, so that the recovery of the heavy metals is realized. In the process, solid-liquid micro-interfaces in the kitchen waste and the sludge are fully updated, and meanwhile, the sludge without heavy metals, the kitchen fermentation liquor and the biogas residues after residue mixing and anaerobic digestion can be directly used for improving the land.
Secondly, the longest period of anaerobic digestion of the sludge is only 14 days, the unit organic matter methane yield is improved by 30-40%, the degradation rate of organic matters of the sludge is improved by 20-50%, and the anaerobic digestion efficiency of the sludge is greatly improved, so that the method has an obvious effect, the kitchen waste is treated while the sludge is treated, heavy metals in the sludge are removed while the kitchen waste is treated, the anaerobic digestion efficiency of the sludge is enhanced, and therefore biogas residues generated by anaerobic digestion can be directly used for improving soil, and the method has an important significance for improving the comprehensive resource utilization of perishable organic wastes.
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FIG. 1 is a schematic flow chart of the method for enhancing anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point.
Detailed Description
The invention provides a method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric points.
As shown in figure 1, the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) carrying out medium-temperature or high-temperature anaerobic fermentation on a proper amount of kitchen waste to produce acid for 1-8 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid to ensure that the pH value is less than 3, and respectively collecting fermentation acid production supernatant and fermentation residues;
(3) regulating the pH value of a proper amount of sludge to the isoelectric point of the sludge by using fermented acid-producing supernatant, and stirring simultaneously;
(4) carrying out solid-liquid separation on the sludge conditioned in the step (3), and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0-11.0 by using alkali liquor, classifying and recovering metals according to the solubility of metal hydroxides, performing centrifugal treatment, and respectively collecting a second supernatant and a metal deposit;
(6) treating the second supernatant obtained in the step (5) by 2-6BV of cation exchange resin, and collecting filtrate;
(7) regenerating the cation exchange resin in the step (6) by hydrochloric acid and sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 6.0-8.0, and stirring to obtain a mixture;
(9) and (3) carrying out medium-temperature, transition-temperature or high-temperature anaerobic digestion on the mixture obtained in the step (8) for 5-14 days, and collecting biogas and biogas residues, wherein the biogas can be used for power generation, and the biogas residues for removing heavy metals can be directly used for improving the land.
In the step (1), a proper amount of the kitchen waste can be determined according to the fermentation acid-producing liquid enriched as required, and meanwhile, the physical, chemical and biological pretreatment before the anaerobic fermentation acid-producing of the kitchen waste is included.
Specifically, the acid production by anaerobic fermentation of the kitchen waste comprises pretreatment of the kitchen waste, wherein the pretreatment comprises a thermal hydrolysis method, a stirring and crushing method, a proton regulation and control method and an enzymatic reaction method.
In the step (1), the medium temperature is 30-40 ℃ and the high temperature is 50-60 ℃.
In the step (2), the concentration and enrichment of the acid generating solution by fermenting the kitchen waste can be realized by centrifugation at 10000-.
In the step (3), when the pH value of the sludge is regulated, the sludge can be determined according to the dosage of the subsequent anaerobic digestion of the sludge, but the maximum quantity is not higher than the quantity of the kitchen waste used for fermenting and producing acid.
In the step (3), the pH value of the sludge is 3.5-4.5; the stirring speed is 200-800rpm, and the stirring time is 2-8 h.
In the step (4), the rotation speed at the time of solid-liquid separation is 8000- & ltSUB & gt 12000 rpm.
In the step (5), the alkali liquor is selected from more than one of sodium hydroxide, sodium carbonate, sodium bicarbonate and potassium hydroxide; the concentration of the alkali liquor is 2-8 mol/L.
In step (5), the rotation speed of the centrifugation is 6000-10000 rpm.
In the step (6), the cation exchange resin is a sodium type cation exchange resin.
Specifically, the sodium cation exchange resin is selected from one or more of sodium macroporous strong-acid styrene cation exchange resin, sodium macroporous strong-acid acrylic cation exchange resin, sodium macroporous weak-acid styrene cation exchange resin, sodium macroporous weak-acid acrylic cation exchange resin, sodium gel strong-acid styrene cation exchange resin, sodium gel strong-acid acrylic cation exchange resin, sodium gel weak-acid styrene cation exchange resin and sodium gel weak-acid acrylic cation exchange resin.
In step (7), the heavy metal is recovered from the regenerated liquid, and the metal is recovered by classification according to the solubility of the metal hydroxide in reference to step (5).
In the step (7), the concentration of the hydrochloric acid is 1-4mol/L, and the concentration of the sodium hydroxide is 1-4 mol/L.
In the step (8), the stirring time is 1-3 h.
In the step (9), the medium temperature is 30-40 ℃, the transition temperature is 40-50 ℃, and the high temperature is 50-60 ℃.
The present invention will be further described with reference to the following examples.
The sludge used in the examples is sludge from a sewage treatment plant in Shanghai city (VS is 55.8-70.1%, and TS is 2.1-8.2%), the kitchen waste is from a college dining hall in Shanghai (VS is 87.4-95.5%, and TS is 10.5-12.1%), the main components are rice, vegetables, meat, eggs, etc., and the inoculation sludge in anaerobic digestion is sludge discharged from a semicontinuous anaerobic reactor (VS is 37.5-48.7%, and TS is 2.6-5.1%).
Example 1:
the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) after 500g of kitchen waste is subjected to thermal hydrolysis pretreatment, performing high-temperature (55 ℃) anaerobic fermentation for producing acid for 4 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid in the step (1) to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of 500g of sludge to the isoelectric point (the pH value is 4.2) of the sludge by using the fermentation acid-production supernatant in the step (2), and stirring for 4 hours at the rotating speed of 400 rpm;
(4) performing solid-liquid separation on the sludge conditioned in the step (3) at the rotating speed of 10000rpm, and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0, 6.0, 8.0, 9.0, 10.0 and 11.0 respectively by using 4mol/L sodium hydroxide, grading and recovering metals according to the solubility integral of the metal hydroxides, centrifuging at the rotating speed of 8000rpm, and collecting a second supernatant and a metal deposit respectively;
(6) treating the second supernatant obtained in the step (5) by 4BV of sodium type macroporous strong acid styrene cation exchange resin, and collecting filtrate;
(7) regenerating the sodium macroporous strong-acid styrene cation exchange resin in the step (6) by 1mol/L hydrochloric acid and 1mol/L sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 7.0, and stirring for 2 hours to obtain a mixture;
(9) and (3) performing high-temperature (55 ℃) anaerobic digestion on the mixture (namely the perishable organic wastes) in the step (8) for 10 days, and collecting biogas and biogas residues.
The results show that the sludge treated by the method of the embodiment has the heavy metal removal rate of about 45 percent, the unit organic matter methane yield is increased by 32 percent, and the organic matter degradation rate of the sludge is increased by 40 percent.
Example 2:
the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) after 500g of kitchen waste is subjected to thermal hydrolysis pretreatment, performing high-temperature (55 ℃) anaerobic fermentation for producing acid for 3 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid in the step (1) to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of 500g of sludge to the isoelectric point (the pH value is 3.8) of the sludge by using the fermentation acid-production supernatant obtained in the step (2), and stirring for 3 hours at the rotating speed of 600 rpm;
(4) performing solid-liquid separation on the sludge conditioned in the step (3) at the rotating speed of 10000rpm, and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0, 6.0, 8.0, 9.0, 10.0 and 11.0 respectively by using 4mol/L sodium hydroxide, grading and recovering metals according to the solubility integral of the metal hydroxides, centrifuging at the rotating speed of 6000rpm, and collecting a second supernatant and a metal deposit respectively;
(6) treating the second supernatant obtained in the step (5) by 4BV of sodium type macroporous weakly acidic styrene cation exchange resin, and collecting filtrate;
(7) regenerating the sodium type macroporous weakly acidic styrene cation exchange resin in the step (6) by 1mol/L hydrochloric acid and 1mol/L sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 7.0, and stirring for 3 hours to obtain a mixture;
(9) and (3) carrying out medium-temperature (37 ℃) anaerobic digestion on the mixture (namely the perishable organic wastes) in the step (8) for 14 days, and collecting methane and biogas residues.
The results show that the sludge treated by the method of the embodiment has the heavy metal removal rate of about 43 percent, the unit organic matter methane yield is increased by 30 percent, and the organic matter degradation rate of the sludge is increased by 36 percent.
Example 3:
the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) after 500g of kitchen waste is subjected to thermal hydrolysis pretreatment, performing high-temperature (55 ℃) anaerobic fermentation to produce acid for 6 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid in the step (1) to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of 400g of sludge to the isoelectric point (the pH value is 4.1) of the sludge by using the fermentation acid-production supernatant in the step (2), and stirring for 6 hours at the rotating speed of 800 rpm;
(4) performing solid-liquid separation on the sludge conditioned in the step (3) at the rotating speed of 10000rpm, and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0, 6.0, 8.0, 9.0, 10.0 and 11.0 respectively by using 4mol/L sodium hydroxide, grading and recovering metals according to the solubility integral of the metal hydroxides, centrifuging at the rotating speed of 8000rpm, and collecting a second supernatant and a metal deposit respectively;
(6) treating the second supernatant obtained in the step (5) by using 4BV sodium type macroporous weak acid acrylic acid cation exchange resin, and collecting filtrate;
(7) regenerating the sodium type macroporous weakly acidic acrylic cation exchange resin in the step (6) by 1mol/L hydrochloric acid and 1mol/L sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 7.0, and stirring for 2 hours to obtain a mixture;
(9) and (3) carrying out anaerobic digestion on the mixture (namely the perishable organic wastes) in the step (8) for 10 days at a transition temperature (42 ℃), and collecting biogas and biogas residues.
The results show that the sludge treated by the method of the embodiment has the heavy metal removal rate of about 49 percent, the unit organic matter methane yield is increased by 35 percent, and the organic matter degradation rate of the sludge is increased by 46 percent.
Example 4:
the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) carrying out thermal hydrolysis pretreatment on 600g of kitchen waste, and carrying out medium-temperature (37 ℃) anaerobic fermentation for producing acid for 8 days to obtain kitchen waste fermentation acid-producing liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid in the step (1) to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of 500g of sludge to the isoelectric point (the pH value is 3.8) of the sludge by using the fermentation acid-production supernatant in the step (2), and stirring for 2 hours at the rotating speed of 200 rpm;
(4) carrying out solid-liquid separation on the sludge conditioned in the step (3) at the rotating speed of 12000rpm, and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to be 4.0, 6.0, 8.0, 9.0, 10.0 and 11.0 respectively by using 6mol/L sodium hydroxide, classifying and recovering metals according to the solubility of the metal hydroxides, centrifuging at the rotating speed of 10000rpm, and collecting a second supernatant and a metal deposit respectively;
(6) treating the second supernatant obtained in the step (5) by 5BV of sodium type gel strong-acid styrene cation exchange resin, and collecting filtrate;
(7) regenerating the sodium type gel strong-acidity styrene cation exchange resin in the step (6) by using 1mol/L hydrochloric acid and 1mol/L sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 7.0, and stirring for 3 hours to obtain a mixture;
(9) and (3) carrying out medium-temperature (37 ℃) anaerobic digestion on the mixture (namely the perishable organic wastes) in the step (8) for 14 days, and collecting methane and biogas residues.
The results show that the sludge treated by the method of the embodiment has the heavy metal removal rate of about 50 percent, the unit organic matter methane yield is increased by 33 percent, and the organic matter degradation rate of the sludge is increased by 42 percent.
Example 5:
the method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point comprises the following steps:
(1) carrying out thermal hydrolysis pretreatment on 700g of kitchen waste, and carrying out high-temperature (55 ℃) anaerobic fermentation for producing acid for 5 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid in the step (1) to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of 500g of sludge to the isoelectric point (the pH value is 4.3) of the sludge by using the fermentation acid-production supernatant obtained in the step (2), and stirring for 5 hours at the rotating speed of 600 rpm;
(4) carrying out solid-liquid separation on the sludge conditioned in the step (3) at the rotating speed of 12000rpm, and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0, 6.0, 8.0, 9.0, 10.0 and 11.0 respectively by using 3mol/L sodium hydroxide, classifying and recovering metals according to the solubility of the metal hydroxides, centrifuging at the rotating speed of 10000rpm, and collecting a second supernatant and a metal deposit respectively;
(6) treating the second supernatant obtained in the step (5) by 4BV of sodium type gel weakly acidic styrene cation exchange resin, and collecting filtrate;
(7) regenerating the sodium type gel weak-acidic styrene cation exchange resin in the step (6) by 2mol/L hydrochloric acid and 2mol/L sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 7.0, and stirring for 3 hours to obtain a mixture;
(9) and (3) performing high-temperature (55 ℃) anaerobic digestion on the mixture (namely the perishable organic wastes) in the step (8) for 10 days, and collecting biogas and biogas residues.
The results show that the sludge treated by the method of the embodiment has the heavy metal removal rate of about 53 percent, the unit organic matter methane yield is increased by 40 percent, and the organic matter degradation rate of the sludge is increased by 50 percent.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. It will be readily apparent to those skilled in the art that various modifications to these embodiments and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments. Those skilled in the art should appreciate that many modifications and variations are possible in light of the above teaching without departing from the scope of the invention.
Claims (9)
1. A method for strengthening anaerobic co-digestion by utilizing acid fermentation of kitchen waste based on sludge isoelectric point is characterized by comprising the following steps: which comprises the following steps:
(1) carrying out medium-temperature or high-temperature anaerobic fermentation on the kitchen waste to produce acid for 1-8 days to obtain kitchen waste fermentation acid production liquid;
(2) concentrating and enriching the kitchen waste fermentation acid production liquid to enable the pH value of the kitchen waste fermentation acid production liquid to be less than 3, and respectively collecting fermentation acid production supernate and fermentation residues;
(3) regulating the pH value of the sludge to the isoelectric point of the sludge by using the fermented acid-producing supernatant, and stirring simultaneously;
(4) carrying out solid-liquid separation on the sludge conditioned in the step (3), and respectively collecting a first supernatant and sludge sediments;
(5) adjusting the pH value of the first supernatant in the step (4) to 4.0-11.0 by using alkali liquor, performing centrifugal treatment according to the solubility product of metal hydroxide, and respectively collecting a second supernatant and a metal deposit;
(6) treating the second supernatant obtained in the step (5) by 2-6BV of cation exchange resin, and collecting filtrate;
(7) regenerating the cation exchange resin in the step (6) by hydrochloric acid and sodium hydroxide, and recovering heavy metal by using the regenerated liquid;
(8) mixing the fermentation residues in the step (2), the sludge sediment in the step (4) and the filtrate in the step (6) to ensure that the pH value of the system is 6.0-8.0, and stirring to obtain a mixture;
(9) carrying out medium-temperature, transition-temperature or high-temperature anaerobic digestion on the mixture obtained in the step (8) for 5-14 days, and collecting biogas and biogas residues;
in the step (1), the medium temperature is 30-40 ℃, and the high temperature is 50-60 ℃;
in the step (6), the cation exchange resin is a sodium type cation exchange resin;
in the step (9), the medium temperature is 30-40 ℃, the transition temperature is 40-50 ℃, and the high temperature is 50-60 ℃.
2. The method of claim 1, wherein: in the step (1), the kitchen waste is pretreated before anaerobic fermentation and acid production, and the pretreatment comprises a thermal hydrolysis method, a stirring and crushing method, a proton regulation and control method and an enzymatic reaction method.
3. The method of claim 1, wherein: in the step (3), the pH value of the sludge is 3.5-4.5; the rotation speed of the stirring is 200-800rpm, and the stirring time is 2-8 h.
4. The method of claim 1, wherein: in the step (4), the rotation speed during the solid-liquid separation is 8000- & ltSUB & gt 12000 rpm.
5. The method of claim 1, wherein: in the step (5), the alkali liquor is selected from more than one of sodium hydroxide, sodium carbonate, sodium bicarbonate and potassium hydroxide; the concentration of the alkali liquor is 2-8 mol/L.
6. The method of claim 1, wherein: in the step (5), the rotation speed of the centrifugation is 6000-10000 rpm.
7. The method of claim 1, wherein: the sodium cation exchange resin is selected from more than one of sodium macroporous strong-acid styrene cation exchange resin, sodium macroporous strong-acid acrylic cation exchange resin, sodium macroporous weak-acid styrene cation exchange resin, sodium macroporous weak-acid acrylic cation exchange resin, sodium gel strong-acid styrene cation exchange resin, sodium gel strong-acid acrylic cation exchange resin, sodium gel weak-acid styrene cation exchange resin and sodium gel weak-acid acrylic cation exchange resin.
8. The method of claim 1, wherein: in the step (7), the concentration of the hydrochloric acid is 1-4mol/L, and the concentration of the sodium hydroxide is 1-4 mol/L.
9. The method of claim 1, wherein: in the step (8), the stirring time is 1-3 h.
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