CN107244734B - A method for evaluating the ability to reduce selenate and nitrate using methane-based MBfR - Google Patents

Abstract

The invention relates to the technical field of bioremediation of oxidation state pollutants, and aims to provide an evaluation method for the capacity of reducing selenate and nitrate by using a methane matrix MBfR. The method comprises the following steps: adding a solute into deionized water, preparing simulated wastewater, and introducing argon for aeration; inoculating methane anaerobic oxidation coupling perchlorate reducing flora as an inoculation source in a methane plasma membrane bioreactor; adopting a continuous flow mode to feed water, and taking simulated wastewater as inlet water; seo in simulated wastewater₄ ^2‑Concentration remains stable, NO₃ ^‑The concentration is controlled in three stages, and the reactor enters the next stage after running to reach a steady state. The invention proves that the microorganism can take CH for the first time₄Driving SeO as sole Electron Donor₄ ^2‑Reduction of (2). The invention can repair the SeO₄ ^2‑The polluted water body can also realize the nano Se⁰And recycling and reusing the resources.

Description

A method for evaluating the ability to reduce selenate and nitrate using methane-based MBfR

technical field

The invention belongs to the technical field of bioremediation of oxidized pollutants, and in particular relates to a method for reducing selenate (SeO ₄ ^2- ) and nitrate (NO ₃ ^- ) by utilizing a methane (CH ₄ ) matrix membrane bioreactor (MBfR). assessment method.

Background technique

Selenium salts are widely found in industrial (such as electronics industry, glass products, dyes, metallurgical additives, photocells, pesticides, etc.) wastewater, ore smelting drainage, farmland irrigation drainage, etc., and have strong physiological toxicity. Accumulation in plants, animals and humans through the food chain can cause symptoms such as hair loss, nail breakage or fall off, skin lesions, and neurological disorders.

In the prior art, the treatment of water selenate pollution is usually adopted: physical removal methods include reverse osmosis, nanofiltration, and the like. The technology consumes a lot of energy, and is expensive to operate and maintain. At the same time, the resulting concentrated wastewater will increase the difficulty of post-treatment. Chemical treatment methods mainly involve the adsorption and precipitation of selenium, etc., which are expensive to deal with, and are prone to form high-concentration chemical sludge that is difficult to follow-up treatment.

Under anaerobic or aerobic conditions, microorganisms can use selenium salts as electron acceptors for dissimilatory respiration. Compared with physical and chemical methods, microbial treatment of SeO ₄ ^2- is more environmentally friendly, harmless, and cost-effective, so it is more and more popular.

In the process of dissimilatory respiration with selenium salts as electron acceptors, microorganisms need to use electron donors and carbon sources, and CH ₄ is a gas with strong greenhouse effect and a potential electron donor. As an electron donor, CH ₄ was first used in denitrification biological nitrogen removal of wastewater. Subsequent studies have shown that _CH4 can drive the bioreduction of pollutants in multiple oxidation states. Based on the high redox potentials of SeO ₄ ^2- /SeO ₃ ^2- and SeO ₃ ^2- /Se ⁰ (+440 mV and +210 mV, respectively), it is therefore feasible to study CH ₄ as an electron donor to drive the reduction of SeO ₄ ^2- Sex is very important.

NO ₃ ^- widely exists in surface water and groundwater, and is an accompanying pollutant of SeO ₄ ^2- . Therefore, it is necessary to evaluate the interaction between SeO ₄ ^2- and NO ₃ ^- in methane-based MBfR.

The final product of microbial reduction of SeO ₄ ^2- is nano-state Se ⁰ , which has excellent optoelectronic and semiconductor properties, and can be applied to optoelectronic components and semiconductor materials; nano-Se ⁰ also has anti-oxidation effect and is often used as an anti-cancer agent. Therefore, the use of some characterization techniques to identify the physical and chemical characteristics of nano-Se ⁰ , fully resource recycling has far-reaching impact.

SUMMARY OF THE INVENTION

The technical content to be solved by the present invention is to overcome the deficiencies of the prior art and provide an evaluation method for the ability to reduce selenate and nitrate by using methane-based MBfR.

For solving the technical problem, the solution of the present invention is:

Provided is a method for reducing SeO ₄ ^2- and NO ₃ ^- by using CH ₄ substrate MBfR, comprising the following steps:

(1) Configure simulated wastewater

Solutes were added in deionized water to make the simulated wastewater include: 1 mg/L CaCl ₂ , 0.4 mg/L NaOH, 5 mg/L MgSO ₄ ·7H ₂ O, 300 mg/L NaHCO ₃ , 2.085 mg/L FeSO ₄ ·7H ₂ O, 200 mg/L NaH ₂ PO4, 400 mg/L Na ₂ HPO ₄ ·12H ₂ O, 0.5 mg/L MnCl ₂ ·4H ₂ O, 1.8 mg/L HCl, 0.068 mg/L L of ZnSO ₄ ·7H ₂ O, 0.12 mg/L of CoCl ₂ ·6H ₂ O, 0.32 mg/L of CuSO ₄ , 0.095 mg/L of NiCl ₂ ·6H ₂ O, 0.242 mg/L of Na ₂ MoO ₄ · 2H ₂ O, 0.067mg/L of SeO ₂ , 0.05mg/L of Na ₂ WO ₄ · 2H ₂ O, 0.014mg/L of H ₃ BO ₃ ; the addition amounts of Na ₂ SeO ₄ and NaNO ₃ were determined according to subsequent experiments Concentration control was specified; 99.99% pure argon (Ar) was passed through the prepared simulated wastewater and aerated for 20 minutes to remove oxygen.

(2) Preparation of experimental equipment

The methane matrix membrane bioreactor was inoculated with 4 mL of methane anaerobic oxidation coupled with perchlorate reduction bacteria as the inoculum source; in the methane anaerobic oxidation coupled with perchlorate reduction bacteria, the content was calculated according to the mass ratio. of the following strains: α-Proteobacteria 27.13%, β-Proteobacteria 26.84%, γ-Proteobacteria 25.87%, Acidobacteria 4.97%, Sphingobacteria 3.88%, Green bacteria 2.20%, Deinococcus 0.96%, and the remaining The amount is the miscellaneous bacteria of the non-enrichment object;

The reactor was filled with simulated wastewater containing 10mgSe/L SeO ₄ ^2- , and self-circulated for 48 hours; the reactor used hollow fiber membranes, the temperature was controlled at 30±1℃ during operation, and the water was fed in a continuous flow mode. is 0.5mL/min, and the hydraulic retention time is 130min; both ends of the membrane are supplied with CH ₄ , and the partial pressure is 15psi; the reactor is self-circulated by a peristaltic pump, and the flow rate is 100mL/min;

(3) Reaction stage

The continuous flow method was adopted to feed the water, and the simulated wastewater was used as the feed water, and the SeO ₄ ^2- concentration was kept at 1 mg Se/L;

To evaluate the effect of NO ₃ ^- on SeO ₄ ^2- reduction, the NO ₃ ^- concentration in the simulated wastewater was controlled in three stages:

In the first stage, the NO ₃ -concentration ⁱⁿ the simulated wastewater was controlled to be 0mg/L, and the reactor continued to operate for at least two weeks after the operation reached a steady state; in the second stage, the NO ₃ -concentration ⁱⁿ the simulated wastewater was controlled to be 2.2mgN/L In the third stage, the NO ₃ ^- concentration in the simulated wastewater was controlled to be 10 mgN/L, and the reactor continued to run for at least two weeks after reaching a steady state.

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

1. In the present invention, it is confirmed for the first time that microorganisms can use CH ₄ as the sole electron donor to drive the reduction of SeO ₄ ^2- .

2. The present invention also has very important practical significance: it can not only repair the water body polluted by SeO ₄ ^2- , but also realize the resource recovery and reuse of nano-state Se ⁰ . (The end product of methane-based biofilm reduction is Se ⁰ , which accumulates on the biofilm surface as spherical particles of 300 to 500 nm in diameter.)

Description of drawings

Fig. 1: In the present invention, MBfR inlet water SeO ₄ ^2- and NO ₃ ^- , effluent SeO ₄ ^2- , SeO ₃ ^2- , calculated Se ⁰ , and NO ₃ ^- concentration;

Figure 2: SeO ₄ ^2- to SeO ₃ ^2- , SeO ₄ ^2- to Se ⁰ , and NO ₃ ^- removal percentage in the present invention

Figure 3: XPS analysis of MBfR biofilms in the present invention;

Figure 4: Schematic diagram of the structure of the main bacteria in the inoculation source and MBfR biofilms at different stages in the present invention.

Detailed ways

The experimental device in the present invention adopts a methane matrix membrane bioreactor (Methane-based Membrane Biofilm Reactor, MBfR) device, which is consistent with the device used in Lai et al. Bio-reduction of Chromate in aMethane-Based Membrane Biofilm Reactor 2016. A hollow fiber membrane (outer diameter 280 μm, inner diameter 180 μm) was used in the device. During operation, both ends of the membrane were supplied with CH ₄ , and the partial pressure of CH ₄ was stabilized at 15 psi (2.02 atm) through a pressure reducing valve. The effective volume of the reactor was 65 mL, and the water was fed in a continuous flow mode, and the influent flow rate was 0.50 mL/min (the hydraulic retention time was 130 minutes). The reactor was self-circulated by a peristaltic pump with a flow rate of 100 mL/min. The reactor was operated in a constant temperature chamber at 30±1°C.

The inoculation source used in the present invention is methane anaerobic oxidation coupled with perchlorate-reducing bacteria group (Luo et al., 2015), and its specific source is: activated sludge collected from a sewage treatment plant (the applicant collected from Hangzhou Qige sewage treatment plant), using nitrate as electron acceptor and methane as electron donor for enrichment culture for about half a year, and then inoculated into the MBfR reactor of methane anaerobic oxidation coupled with perchlorate until the operation is stable, and the bacteria can be obtained. Stable flora.

In the methane anaerobic oxidation coupled perchlorate-reducing bacteria group, the following bacteria species are included by mass ratio: α-Proteobacteria 27.13%, β-Proteobacteria 26.84%, γ-Proteobacteria 25.87%, Acidobacter 27.13% 4.97%, Sphingobacter 3.88%, Chlorobacterium 2.20%, Deinococcus 0.96%, and the balance is non-enrichment target miscellaneous bacteria.

The applicant undertakes to release the flora to the public within 20 years from the date of the patent application, so as to realize and utilize the technical solution of the present invention.

Example:

(1) Preparation of simulated wastewater

In the experiment, simulated wastewater was used, solutes were added to deionized water, and Aladdin's top-grade pure reagents Na ₂ SeO ₄ and NaNO ₃ were used as selenate and nitrate, and their concentrations were prepared according to the experimental requirements.

The simulated wastewater also includes: 1 mg/L CaCl ₂ , 0.4 mg/L NaOH, 5 mg/L MgSO ₄ ·7H ₂ O, 300 mg/L NaHCO ₃ , 2.085 mg/L FeSO ₄ ·7H ₂ O, 200 mg/L NaH ₂ PO 4 , 400 mg/L Na ₂ HPO ₄ .12H ₂ O, 0.5 mg/L MnCl ₂ .4H ₂ O, 1.8 mg/L HCl, 0.068 mg/L ZnSO ₄ .7H ₂ O, 0.12 mg/L CoCl ₂ .6H ₂ O, 0.32 mg/L CuSO ₄ , 0.095 mg/L NiCl ₂ .6H ₂ O, 0.242 mg/L Na ₂ MoO ₄ .2H ₂ O, 0.067 mg /L of SeO ₂ , 0.05 mg/L of Na ₂ WO ₄ ·2H ₂ O, 0.014 mg/L of H ₃ BO ₃ . High-purity argon gas (Ar: 99.99%) was introduced into the prepared simulated wastewater, and aerated for 20 minutes to remove oxygen. The simulated wastewater after aeration treatment is packed in an airtight anaerobic bag for use.

(2) Preparation of experimental equipment

The methane matrix membrane bioreactor was inoculated with 4 mL of methane anaerobic oxidation coupled with perchlorate reduction bacteria as the inoculum source; the reactor was filled with simulated wastewater containing 10 mgSe/L SeO ₄ ^2- , self-circulating 48 The reactor adopts a hollow fiber membrane, the temperature is controlled at 30±1℃ during operation, the water is fed in a continuous flow mode, the water inflow rate is 0.5mL/min, and the hydraulic retention time is 130min; both ends of the membrane are supplied with CH ₄ , divided into The pressure is 15psi; the reactor is self-circulated by the peristaltic pump, and the flow rate is 100mL/min;

(3) Reaction stage

The continuous flow method was used to feed the water, and the simulated wastewater was used as the feed water, and the SeO ₄ ^2- concentration was kept at 1 mgSe/L;

To evaluate the effect of NO ₃ ^- on SeO ₄ ^2- reduction, the NO ₃ ^- concentration in the simulated wastewater was controlled in three stages:

In the first stage, the NO ₃ -concentration ⁱⁿ the simulated wastewater was controlled to be 0mg/L, and the reactor continued to operate for at least two weeks after the operation reached a steady state; in the second stage, the NO ₃ -concentration ⁱⁿ the simulated wastewater was controlled to be 2.2mgN/L In the third stage, the NO ₃ ^- concentration in the simulated wastewater was controlled to be 10 mgN/L, and the reactor continued to run for at least two weeks after reaching a steady state.

The results are analyzed as follows:

Figures 1, 2 and Table 1 show that in stage 1, SeO ₄ ^2- reduction begins on the fourth day. When the influent electron acceptor contained only 1 mgSe/L SeO ₄ ^2- (the surface loading was 1.6 mmolSe/m ² -d), SeO ₄ ^2- was reduced to SeO ₃ ^2- and Se ⁰ step by step. After 68 days, the removal rate of SeO ₄ ^2- reached 100%, and >94% of SeO ₄ ^2- was completely reduced to Se ⁰ , so that the effluent concentration of SeO ₃ ^2- was lower than 50ugSe/L. The results show that the CH ₄ matrix MBfR can completely reduce SeO ₄ ^2- to Se ⁰ .

Table 1 Average electron acceptor and electron donor fluxes at various stages in the present invention

In stage 2 (days 84-122), when the MBfR feed water also contained 2.2 mgN/L NO ₃ ^- (surface loading was 19.7 mmolN/m ² -d), the reduction of SeO ₄ ^2- was initially inhibited, but then The reduction rate recovered to 100% and reached a steady state. At this time, most of the SeO ₄ ^2- was reduced to Se ⁰ (>75%), accompanied by the production of a small amount of SeO ₃ ^2- (<0.003 mmol Se/L). Therefore, the presence of 2.2 mgN/L NO ₃ ^- in the influent will not affect the removal of SeO ₄ ^2- , but will reduce the conversion of SeO ₃ ^2- to Se ⁰ . At this stage ^, _NO3- is completely reduced.

In stage 3 (days 124-144), when the influent NO ₃ ^- concentration was further increased to 10 mgN/L (surface loading was 87.9 mmolN/m ² -d), SeO ₄ ^2- and NO ₃ ^- were still simultaneously reduced , but at steady state, the SeO ₄ ^2- removal rate dropped to 60%, of which 50% of SeO ₄ ^2- was converted to SeO ₃ ^2- and 10% of SeO ₄ ^2- was converted to Se ⁰ . The removal rate of NO ₃ ^- in this stage is 70%. Insufficient CH ₄ supply may be the main reason for the limited reduction of SeO ₄ ^2- and NO ₃ ^- , and the CH ₄ flux required for NO ₃ ^- and SeO ₄ ^2- reduction in stage 3 is close to the maximum CH ₄ flux.

It can be seen from Figure 2 that XPS analysis confirmed that the selenium element in the zero-valence state mainly exists in the nano-selenium particles.

It can be seen from Figure 3 that the community composition of the dominant microorganisms on the membrane, compared with the inoculum source, the abundance of α-proteobacteria decreased in stage 1, but in stages 2 and 3, when the influent contained NO ₃ ^- , α-proteobacteria decreased. The abundance of Proteobacteria increased. In sharp contrast, β-proteobacteria and γ-proteobacteria dominated in stage 1, but decreased in abundance in stages 2 and 3.

Claims (1)

1. an assessment method utilizing methane substrate MBfR to reduce selenate and nitrate ability, is characterized in that, comprises the following steps: (1) Preparation of simulated wastewater Add solutes in deionized water so that the simulated wastewater includes: 1mg/L CaCl ₂ , 0.4mg/L NaOH, 5mg/L MgSO ₄ 7H ₂ O, 300mg/L NaHCO ₃ , 2.085mg/L FeSO ₄ • 7H ₂ O, 200mg/L NaH ₂ PO4, 400mg/L Na ₂ HPO ₄ • 12H ₂ O, 0.5mg/L MnCl ₂ • 4H ₂ O, 1.8mg/L HCl, 0.068mg/ L of ZnSO ₄ • 7H ₂ O, 0.12 mg/L of CoCl ₂ • 6H ₂ O, 0.32 mg/L of CuSO ₄ , 0.095 mg/L of NiCl ₂ • 6H ₂ O, 0.242 mg/L of Na ₂ MoO ₄ • 2H ₂ O, 0.067mg/L of SeO ₂ , 0.05mg/L of Na ₂ WO ₄ • 2H ₂ O, 0.014mg/L of H ₃ BO ₃ ; the addition amounts of Na ₂ SeO ₄ and NaNO ₃ are based on subsequent experiments Designated concentration control; Pour 99.99% argon gas into the prepared simulated wastewater, and aerate for 20 minutes to remove oxygen; (2) Preparation of the experimental device The methane matrix membrane bioreactor was inoculated with 4 mL of methane anaerobic oxidation coupled with perchlorate reduction bacteria as the inoculum source; in the methane anaerobic oxidation coupled with perchlorate reduction bacteria, the content was calculated according to the mass ratio. of the following strains: α-Proteobacteria 27.13%, β-Proteobacteria 26.84%, γ-Proteobacteria 25.87%, Acidobacteria 4.97%, Sphingobacteria 3.88%, Green bacteria 2.20%, Deinococcus 0.96%, the remaining The amount is the miscellaneous bacteria of the non-enrichment object; The reactor was filled with simulated wastewater containing 10 mgSe/L SeO ₄ ²⁻ , and self-circulated for 48 hours; the reactor used hollow fiber membrane, the temperature was controlled at 30 ± 1 °C during operation, and the water was fed in a continuous flow mode. The rate was 0.5mL/min, and the hydraulic retention time was 130min; both ends of the membrane were supplied with CH ₄ , and the partial pressure was 15 psi; the reactor was self-circulated by a peristaltic pump, and the flow rate was 100 mL/min; (3) Reaction stage The continuous flow method was used to feed the water, and the simulated wastewater was used as the feed water, and the SeO ₄ ²⁻ concentration was kept at 1 mgSe /L; To evaluate the effect of NO ₃ ^- on the reduction of SeO ₄ ²⁻ , the NO ₃ ^- concentration in the simulated wastewater was controlled in three stages: In the first stage, the NO ₃ ^{-concentration} in the simulated wastewater was controlled to be 0 mg/L, and the reactor continued to operate for at least two weeks after the operation reached a steady state; in the second stage, the NO ₃ ^{-concentration} in the simulated wastewater was controlled to be 2.2 mg N In the third stage, the NO ₃ ^- concentration in the simulated wastewater was controlled to be 10 mgN/L, and the reactor continued to run for at least two weeks after the operation reached a steady state; (4) Analysis of results In the first stage, SeO ₄ ²⁻ began to be reduced on the fourth day; when the influent electron acceptor contained only 1 mgSe/L SeO ₄ ²⁻ , SeO ₄ ^{2 −} was reduced to SeO ₃ ²⁻ and Se ⁰ step by step; After 68 days, the removal rate of SeO ₄ ²⁻ reached 100%, and >94% of SeO ₄ ²⁻ was completely reduced to Se ⁰ , so that the effluent concentration of SeO ₃ ²⁻ was lower than 50ugSe/L; indicating that CH ₄ matrix MBfR Can completely restore SeO ₄ ^2- to Se ⁰ ; In the second stage, the reduction of SeO ₄ ²⁻ was initially inhibited, but then the reduction rate returned to 100% and reached a steady state; at this time, most of the SeO ₄ ²⁻ was reduced to Se ⁰ , Accompanied by the generation of a small amount of SeO ₃ ²⁻ ; the presence of NO ₃ ^- in the influent will not affect the removal of SeO ₄ ²⁻ , but will reduce the conversion rate of SeO ₃ ²⁻ to Se ⁰ ; at this stage, NO ₃ ^- is removed by fully restored; In the third stage, SeO ₄ ²⁻ and NO ₃ ^- are still simultaneously reduced, but when the steady state is reached, the SeO ₄ ²⁻ removal rate drops to 60%, in which 50% of SeO ₄ ²⁻ is converted to SeO ₃ ^{2 −} , 10% of SeO ₄ ²⁻ was converted to Se ⁰ ; the removal rate of NO ₃ ^- was 70% at this stage, and the CH ₄ flux required for the reduction of NO ₃ ^- and SeO ₄ ²⁻ was close to the maximum CH ₄ flux.

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