Method for reducing toxicity of nano-zinc oxide in anaerobic digestion sludge based on polyferric sulfate (PFS)

Abstract

The invention relates to a method for reducing the toxicity of nano-zinc oxide in anaerobic sludge by using polyferric sulfate (PFS), which belongs to the technical field of novel pollutant environmental protection, and mainly comprises the following steps: the polyferric sulfate (PFS) is used as a coagulant commonly used for sewage treatment, is simple and easy to obtain, and is relatively low in cost; the PFS can reduce the toxic influence of nZnO on anaerobic digestion of the sludge by generating a low-toxicity soluble Zn complex, improve the methane production performance under the stress of nZnO, and provide technical support and guidance for toxicity control in the anaerobic digestion process of the sludge; the invention aims to promote anaerobic digestion of sludge to further become an efficient sludge treatment technology which synchronously realizes sludge stabilization and resource recovery, is low in treatment cost and is convenient for actual operation.

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 reducing the toxicity of nano zinc oxide (nZnO) to anaerobic digestion sludge by utilizing polyferric sulfate (PFS). (II) Background technology

[0002] Due to population growth and industrial development, China currently has more than 4,000 sewage treatment plants. Most sewage treatment plants treat domestic sewage through the activated sludge process, so that a large amount of particulate impurities, harmful substances and chemicals are removed from the water in the form of primary sedimentation and residual sludge. The treatment and disposal of activated sludge is becoming a severe challenge facing today's sewage treatment plants. The advantage of anaerobic digestion is that it can not only reduce the volume of sludge, reduce the production of harmful substances, and kill some pathogens, but also simultaneously produce high calorific value biogas and high fertility biogas residues, and even produce beneficial resources such as hydrogen and short-chain fatty acids by adjusting the reaction conditions.

[0003] Metal oxide nanoparticles such as zinc oxide nanoparticles have been widely used in antibacterial coatings, catalysts, biopharmaceuticals, skin creams and toothpastes due to their excellent magnetic, electrical and optical properties. Taking nano zinc oxide particles as an example, its annual production ranks third in the world in the production of metal nanoparticles. Through urban pipe networks, a large number of nanoparticles released without treatment may be collected in wastewater treatment plants operating with activated sludge technology. After being absorbed, aggregated and precipitated by activated sludge, nanoparticles are easily transferred and retained in waste activated sludge, which poses a severe challenge to the treatment of activated sludge in sewage treatment plants. Since nano zinc oxide can release Zn 2+ It has a toxic effect on the microbial community in the anaerobic sludge, inhibits the production of methane, and has an adverse effect on the anaerobic digestion process. Therefore, reducing the toxic effect of nano zinc oxide in the anaerobic consumption process is crucial to ensure the smooth progress of the anaerobic consumption process.

[0004] Polyferric sulfate, also known as polyferric, is prepared by partial neutralization of iron salts and is a cationic inorganic polymer coagulant. After PFS is dissolved in the aqueous phase, it will hydrolyze into a macromolecular iron polymer containing hydroxyl and sulfate groups, which can provide a variety of nuclear hydroxyl high-valent complex ions, thus having excellent coagulation properties. It is often used to remove suspended matter, treat dyes, and reduce heavy metal ions in water. In the sewage treatment process, PFS is often used in the pretreatment stage to enhance coagulation and chemical phosphorus removal processes or to condition sludge to obtain better dewatering performance. Therefore, the use of polyferric sulfate is expected to improve the toxic effect of nano zinc oxide on anaerobic sludge. (III) Summary of the invention

[0005] The purpose of the present invention is to utilize polyferric sulfate (PFS) to reduce the toxic effect of nZnO in sludge, to provide technical support and guidance for toxicity control in sludge anaerobic digestion process, in order to promote sludge anaerobic digestion to further become an efficient sludge disposal technology that simultaneously achieves sludge stabilization and resource recovery, has low processing cost, and is easy to operate in practice.

[0006] The technical solution of the present invention is: a method for reducing the toxicity of nano zinc oxide in anaerobic sludge based on polyferric sulfate (PFS) coagulant, 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 PFS 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] (5) Detoxification effect analysis method: In this study, the gas production inhibition rate was used as the evaluation index of sludge gas production performance, and the calculation formula is as follows:

[0012]

[0013] Among them, R I，i is the gas production inhibition rate (%), V0 is the cumulative methane production of the blank control group (mL), V i is the cumulative methane production (mL) of the treatment group.

[0014] The detoxification rate is used to quantify the antagonistic effect between coagulant and nZnO on sludge gas production in the sludge system. The calculation formula is as follows:

[0015] R D，i =R I，i1 +R I，i2 -R I，i3

[0016] Among them, R D，i is the detoxification rate (%), R I，i1 is the gas production inhibition rate of single nZnO group (%), R I，i2 is the gas production inhibition rate of the single coagulant group (%), R I，i3 is the gas production inhibition rate (%) of nZnO+coagulant group.

[0017] (IV) Beneficial effects

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) Adding a certain amount of PFS to the anaerobic reactor can reduce the toxic effect of nZnO on anaerobic digestion of sludge by producing low-toxic soluble Zn complexes. On the one hand, PFS produces a large amount of highly charged polymerized cations after dissolving in water, and the competitive adsorption between PFS and sludge and the floc protection reduce the Zn 2+ On the other hand, the addition of PFS can also increase the Fe 2+ and sulfate, promoting the stimulation of key enzyme activities and reducing Zn 2+ , improving the methanogenesis performance under nZnO stress.

[0020] (2) The polyferric sulfate (PFS) used in the present invention is a commonly used coagulant in sewage treatment, which is simple, easy to obtain, and has a low cost. It has a significant effect on the detoxification of nano zinc oxide in anaerobic digestion sludge. (V) Description of the drawings

[0021] Figure 1 It is the inhibition rate of different concentrations of PFS under nZnO stress of the present invention.

[0022] Figure 2 Detoxification rate of different concentrations of PFS under nZnO stress. (VI) Specific implementation methods

[0023] The present invention is further described below through specific implementation cases. The embodiments of the present invention are intended to enable those skilled in the art to better understand the present invention, and do not limit the present invention in any way.

[0024] The specific implementation modes of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] (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.

[0026] (2) The reaction was carried out in a closed brown glass bottle. PFS with concentrations of 5, 10, 20 and 30 mg / g TS and the corresponding substrate were added to the sludge containing nano zinc oxide and mixed evenly. The interpretation effect was achieved using a fully automatic methane potential test reactor.

[0027] (3) The detoxification effect was achieved by using the fully automatic methane potential test system reactor. Before operation, nitrogen was introduced into the reaction bottle for 4 minutes to drive out oxygen, and the operating temperature of the sludge anaerobic digestion reactor was maintained at 35±2℃.

[0028] (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.

[0029] (5) The detoxification effect of PFS on sludge stressed by nano-zinc oxide and the inhibitory effect on nano-zinc oxide were calculated based on the measured gas production and the corresponding formula.

[0030] Figure 1 The inhibition rate of different concentrations of PFS under nZnO stress can be seen. The inhibition rate of nZnO on gas production is 39.5-46.6%. As the reaction time increases, the inhibition rate shows a downward trend, indicating that the toxic effect of nZnO on gas production by anaerobic digestion of sludge weakens with time. After adding PFS at different time points, the inhibition rate of the nZnO+PFS group was significantly lower than that of the nZnO group, indicating that the addition of PFS produced a detoxification effect. This was particularly evident at 6h, when 40 and 80 mg / g TS of PFS promoted gas production by 7.3 and 51.0% (p>0.05), respectively, further indicating the antagonistic effect between PFS and nZnO on gas production by anaerobic digestion of sludge. Analyzing the same time point, the gas production inhibition rate decreased with the increase of PFS dosage, indicating that this antagonistic effect increased with the increase of PFS dosage within the experimental concentration.

[0031] Figure 2 The detoxification rate of different concentrations of PAC under nZnO stress shows that the detoxification rate increases with the increase of PFS dosage, while the same dosage of PFS decreases with the extension of time. Among them, the detoxification ability of 80mg / g TS PFS is the most obvious, reaching 69.8% at 6h, and the detoxification rate is above 27% within 24h.

[0032] In summary, the coagulant PFS has a certain detoxification effect on the stress of short-term high concentration of nZnO, and the detoxification effect gradually increases with the increase of PFS concentration.

Claims

1. A method for reducing the toxicity of nano zinc oxide in anaerobic sludge based on polyferric sulfate (PFS), characterized in that The following steps are involved: 1) Construction of equipment for anaerobic digestion of sludge; The anaerobic digestion experiment of sludge 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, the sludge containing nZnO and coagulant is simulated to enter the anaerobic digestion tank of the sludge treatment plant for anaerobic digestion of sludge. 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) Detoxification effect analysis method: In this study, the gas production inhibition rate was used as the evaluation index of sludge gas production performance, and the calculation formula is as follows: in, R I，i is the gas production inhibition rate (%), V0 is the cumulative methane production of the blank control group (mL), V i is the cumulative methane production (mL) of the treatment group. The detoxification rate is used to quantify the antagonistic effect between coagulant and nZnO on sludge gas production in the sludge system. The calculation formula is as follows: R D，i =R I，i1 +R I，i2 -R I，i3 Among them, R D，i is the detoxification rate (%), R I，i1 is the gas production inhibition rate of single nZnO group (%), R I，i2 is the gas production inhibition rate of the single coagulant group (%), R I，i3 is the gas production inhibition rate (%) of nZnO+coagulant group.

Images