Method for increasing methane yield of anaerobic digestion sludge based on polyaluminum chloride (PAC)

Abstract

The invention provides a method for reducing the toxicity of nano-zinc oxide in anaerobic digestion sludge, and particularly relates to a method for reducing nano-zinc oxide (nZnO) in sludge by using polyaluminum chloride (PAC). According to the method, different doses of PAC are added to be mixed with the sludge containing nano zinc oxide, the adsorption capacity of the sludge is enhanced, the toxic action of nZnO on microorganisms is reduced, then Zn < 2 + > release is delayed and reduced, the detoxification effect on the sludge microorganisms is achieved, the anaerobic digestion performance is improved, and the yield of methane polluted by an anaerobic system is increased. The method has the advantages of easily available raw materials, low operation cost and the like, and provides technical support and guidance for promoting the progress of a sludge anaerobic digestion technology.

Description

(I) Technical field

[0001] The invention belongs to the technical field of environmental protection of new pollutants, and specifically relates to a method for utilizing polyaluminium chloride (PAC) to reduce the toxicity of nano zinc oxide (nZnO) and thereby increase the methane yield of anaerobic digestion sludge. (II) Background technology

[0002] Most nanomaterials lack effective disposal methods, which inevitably causes them to enter the water and soil environment, destroy the ecosystem, and directly or indirectly endanger human health. After the sewage containing nanomaterials enters the sewage treatment plant, the general sewage treatment plant can effectively remove more than 95% of the nanoparticles in the wastewater, causing them to accumulate in the sludge, but how to dispose of these residual sludges that may contain a large amount of nanomaterials has become a thorny problem. Sludge anaerobic digestion uses functional anaerobic microorganisms to decompose organic matter in the sludge and simultaneously produce biogas, which can also achieve energy recovery and reuse. One of the difficulties faced by sludge anaerobic digestion technology comes from the negative impact of new pollutants on the anaerobic digestion process of sludge, including methanogens, hydrolytic bacteria and acid-producing bacteria.

[0003] Nano zinc oxide (nZnO) has high biological toxicity and high detection rate. After being released into the environment, it is eventually collected in domestic sewage or industrial wastewater due to its bioavailability, and enters the municipal sewage treatment plant (WWTP) through the urban sewage system. As the final link of sludge treatment, the sludge anaerobic digester therefore contains the highest concentration of nano zinc oxide. It can be seen that the concentration of nZnO in sludge will increase rapidly with the expansion and application of nanomaterials in the future, and then have a toxic effect on the microorganisms in anaerobic sludge. Therefore, how to combine the improvement of anaerobic sludge methane production and develop a pharmaceutical-based regulation technology that can circumvent the microbial toxicity of nZnO is the key to improving the applicability of anaerobic sludge digestion in the future.

[0004] Polyalumina, commonly known as basic aluminum chloride, is produced by partial hydrolysis of an acidic AlCl3 solution in a specific reactor. 3+ ), dimers (such as Al2(OH)2 4+ ), trimer (such as Al3(OH)4 5+ ) and inert macropolymers. It is a water-soluble inorganic high molecular polymer formed by multi-nuclear hydroxyl complexes, which has the ability to adsorb, condense and precipitate impurities in water. In addition, PAC can also adsorb and complex harmful ions in water, and is widely used in domestic water treatment, some industrial wastewater containing anions and cations, and sludge conditioning and dehydration. Therefore, according to the properties of PAC, anaerobic sludge cultivation is expected to reduce the toxic effects of nZnO in sludge. (III) Summary of the invention

[0005] The object of the present invention is to provide a method for reducing the toxic effect of nZnO in anaerobic digestion sludge and increasing methane production. The method can enhance the adsorption capacity of the sludge by adding polyaluminium chloride to the sludge, cooperate with the sludge to remove Zn2+, reduce the toxic effect of nZnO on microorganisms, and increase methane production.

[0006] The technical solution of the present invention is: a method for increasing the methane yield of anaerobic digestion sludge based on polyaluminium chloride (PAC), comprising the following steps:

[0007] (1) Preparation of nZnO suspension: Dissolve nZnO in ultrapure water, stir well, and then ultrasonically crush.

[0008] (2) Equipment construction for anaerobic digestion of sludge: The anaerobic digestion experiment of sludge was completed using a fully automatic methane potential test system. The entire system was fully sealed to ensure an anaerobic environment. The experimental parameters (such as the time and speed of mechanical stirring) could be set and controlled by a connected computer. Using synthetic wastewater as the substrate, the process of sludge containing nZnO and coagulant entering the anaerobic digestion tank of the sludge treatment plant for anaerobic digestion of sludge was simulated.

[0009] (3) Establishment of sludge anaerobic digestion system: It is composed of sludge, buffer, substrate and other components. The substrate includes trace elements, glucose, nutrient broth and yeast extract; the other components, including PAC and nano zinc oxide, are all in solid form.

[0010] (4) Gas production measurement: A pulse meter is installed in the measuring device. When CH4 enters the measuring device, it is divided into bubbles of certain size. By recording and calculating the number of bubbles, the real-time sludge anaerobic digestion methane production curve and rate curve are obtained.

[0011] (IV) Beneficial effects

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] (1) The present invention provides a method for reducing the toxicity of nano zinc oxide in anaerobic digestion sludge. After adding PAC, the precipitation and encapsulation of nZnO are enhanced, thereby delaying and reducing the toxicity of Zn 2+ The release of nZnO reduces the inhibition of nZnO on the sludge, thereby detoxifying the sludge microorganisms, improving the anaerobic digestion performance, and increasing the production of contaminated methane in the anaerobic system.

[0014] (2) The present invention has the advantages of easy availability of raw materials, low operating costs and obvious effects, and provides technical support and guidance for promoting the advancement of sludge anaerobic digestion technology. (V) Description of the drawings

[0015] Figure 1The gas production performance of anaerobic digestion under nZnO stress under different concentrations of PAC of the present invention is shown in FIG. (VI) Specific implementation methods

[0016] The specific implementation modes of the present invention will be further described in detail below with reference to the accompanying drawings.

[0017] In this experiment, anaerobic sludge was selected from the anaerobic digestion reactor of a sludge treatment plant in Tianjin. The treatment process used by the plant is "high-concentration and high-efficiency anaerobic digestion + plate and frame high-pressure diaphragm dehydration + drying", and the sludge treatment capacity is 800t / d (based on a moisture content of 80%), which is converted into a dry sludge treatment capacity of 160t / d, and the temperature is 35±2℃.

[0018] (1) Dissolve nZnO in ultrapure water, stir evenly, and then ultrasonically disrupt for 30 min. The power of the ultrasonic cell disruptor is set to 97.5 W, and the concentration of nano zinc oxide is 10000 mg / kg TS. Add it into a 400 ml brown glass bottle.

[0019] (2) The reaction was carried out in a closed brown glass bottle, 30.0 g TS / L of sludge was added to mix into sludge under the toxicity stress of nano zinc oxide, and then PAC with concentrations of 5, 10, 20 and 30 mg / g TS and 2.0 g / L of corresponding substrates (including trace elements, glucose, nutrient broth and yeast extract, etc.) and 1.0 g / L NaHCO3 buffer and other components were added to the sludge containing nano zinc oxide, mixed evenly, and the detoxification effect was achieved using a fully automatic methane potential test reactor. The other components, including PAC and nano zinc oxide, were all in solid form.

[0020] (3) Before operation, nitrogen was introduced into the reaction bottle for 4 min to drive out oxygen, and the operating temperature of the sludge anaerobic digestion reactor was maintained at 35±2℃.

[0021] (4) Good nutritional conditions are ensured by the equipped stirring motor. The CO2 fixed unit is equipped with a 3M NaOH solution (containing 0.5% phenolphthalein) to absorb acidic gases such as CO2 and H2S produced during anaerobic digestion, thereby ensuring that the gas entering the host measurement volume is CH4. A pulse meter is installed in the measuring device. When CH4 enters the measuring device, it is divided into bubbles of a certain size. By recording and calculating the number of bubbles, the real-time sludge anaerobic digestion methane production curve and rate curve are obtained.

[0022] (5) Based on the measured gas production and the corresponding formula, a graph of methane production of sludge under nano-zinc oxide stress at different concentrations of PAC was drawn.

[0023] (6) According to the evaluation scheme of the present invention, Figure 1The figure shows the effect of PAC on the 24h gas production of anaerobic digestion of sludge under nZnO stress. Under nZnO stress, the sludge gas production was significantly inhibited (p>0.05). After adding 0-30mg Al / gTSPAC, the gas production showed an increasing trend with the increase of PAC dosage, but at 24h, all groups were lower than the blank group. After 24h, the cumulative methane production of the blank group was 237.8mL, which decreased to 149.2mL under single nZnO stress, while the methane production in the nZnO+PAC sludge system increased by 24.2-58.1mL compared with single nZnO, indicating that nZnO and PAC in the composite system have an antagonistic effect on sludge gas production, that is, PAC has a regulatory effect on the microbial toxicity caused by nZnO.

[0024] In summary, the coagulant PAC has a certain detoxification effect on the stress of high concentration nZnO, and the detoxification effect gradually increases with the increase of PAC concentration. It should be understood that the embodiments and examples discussed here are only for illustration, and can be improved or changed for those skilled in the art, and all these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for increasing methane production from anaerobic digestion sludge based on polyaluminium chloride (PAC), characterized in that The following steps are involved: 1) Construction of sludge anaerobic digestion equipment; the sludge anaerobic digestion experiment is completed using a fully automatic methane potential test system. The entire system is fully sealed to ensure an anaerobic environment, and the experimental parameters can be set and controlled by a connected computer. Using synthetic wastewater as a substrate, simulate the process of sludge containing nZnO and coagulants entering the anaerobic digestion tank of the sludge treatment plant for sludge anaerobic digestion. 2) Establishment of sludge anaerobic digestion system; dissolve nZnO in ultrapure water, stir evenly, ultrasonically disrupt for 30 minutes, set the power of ultrasonic cell disruptor to 97.5W, and add nano zinc oxide concentration to 10000mg / kg TS, add to 400ml brown glass bottle, and then add reagents and substrates to the sludge containing nano zinc oxide. The specific configuration is: composed of sludge, buffer, substrate and other components. The substrate includes trace elements, glucose, nutrient broth and yeast extract; the other components, including PAC and nano zinc oxide, are in solid form. The interpretation effect is achieved by using a fully automatic methane potential test reactor. Before operation, nitrogen was introduced into the reaction bottle for 4 minutes to drive away oxygen, and the operating temperature of the sludge anaerobic digestion reactor was maintained at 35±2℃. The other components, including PAC and nano zinc oxide, are in solid form. 3) Gas production measurement: Set the stirring motor to 65rpm to ensure good nutritional conditions. The CO2 fixed unit is equipped with 3M NaOH solution (containing 0.5% phenolphthalein) to absorb acidic gases such as CO2 and H2S produced during anaerobic digestion, thereby ensuring that the gas entering the host measurement volume is CH4. A pulse meter is installed in the measuring device. When CH4 enters the measuring device, it is divided into bubbles of certain size. By recording and calculating the number of bubbles, the real-time sludge anaerobic digestion methane production curve and rate curve are obtained. 4) Based on the measured gas production and the corresponding formula, a graph of methane production of sludge under nano-zinc oxide stress under different concentrations of PAC was drawn.

Images