CROSS-REFERENCE TO RELATED APPLICATIONS

This is the United States national phase of International Patent Application No. PCT/CN2018/110409, filed on Oct. 16, 2018, which claims priority to Chinese Patent Application No. 201811059860.7, filed on Sep. 12, 2018, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present application relates to a method and a device for treating ammonia-nitrogen wastewater using a microbial electrolytic cell assisted SANI system, belonging to the field of environmental technology and water treatment.

BACKGROUND

Nowadays, the massive discharge of nitrogen-containing wastewater greatly affects the balance of the ecosystem, especially in the water system, a representative example of which is the red tide caused by eutrophication of water bodies. The traditional biological nitrification and denitrification process is widely used in ammonia treatment. Although some novel technologies, such as the A/O technology, appear constantly, the traditional process has been used because of its advantages of low energy consumption and high efficiency. However, the traditional nitrification and denitrification technology needs addition of additional alkalinity and electron donors, which increases the overall cost consumption. In addition, the traditional nitrification and denitrification process is carried out by heterotrophic denitrifying bacteria consuming organic substrates, so a large amount of sludge will be produced.

In view of these two points, the SANI process has successfully solved the above problems. An SANI process is a process combining sulfate reduction, sulfide autotrophic denitrification and nitrification. The SANI process has successfully treated municipal wastewater in Hong Kong. However, for some industrial wastewater, such as petroleum wastewater, metallurgical wastewater, food industrial wastewater, pharmaceutical wastewater, etc., the N concentration (ammonia concentration and nitrate concentration) is much higher than that of municipal wastewater. For this wastewater, if only SANI process is used for denitrification, the oxidation of high ammonia nitrogen will cause the pH of nitrification chamber to be too low, which will affect the denitrification efficiency of the whole system. Secondly, due to the S/N requirement of the SANI system, it is necessary to have a high S concentration. However, increasing the S concentration in influent water in the SANI process has the following three shortcomings: first, a high concentration of sulfide is harmful to microorganisms; second, a higher S concentration will lead to more H2S gas being produced in the sulfate reduction process, so more H2S gas will escape in the whole process; third, a higher S concentration requires more operating costs. Therefore, certain improvements have to be made to use the current SANI process to treat industrial wastewater with high ammonia nitrogen.

As a new technology, the application of a microbial electrolytic cell (MEC) in water treatment has been widely studied in the past ten years. Hydrogen autotrophic denitrifying bacteria can denitrify on the cathode surface of the MEC by using hydrogen produced by the cathode, so the cathode chamber of the MEC can act as a secondary denitrification chamber, thus indirectly reducing the S concentration requirement in the influent of the SANI process. In addition, the MEC cathode produces hydrogen and produces a large amount of alkalinity, while the nitrification process in the nitrification chamber produces a large number of protons. Under suitable conditions, the two can adjust each other to achieve a long-term stability of the pH of the system. Therefore, the e-SANI process, which couples MEC and SANI processes, is expected to become a promising technology for treating high ammonia-nitrogen wastewater.

SUMMARY

According to the present invention, by coupling the MEC and SANI processes, the SANI process is strengthened so as to adapt to the treatment of wastewater with high ammonia-nitrogen. By using the extra electrons and alkalinity provided by the MEC, the denitrification process is additionally carried out and the pH of the nitrification chamber is adjusted, thus achieving the capability of the system to treat wastewater with high ammonia nitrogen.

A device for treating ammonia-nitrogen wastewater using a microbial electrolysis cell assisted SANI system according to the present invention includes an SANI system, a 4#chamber, a 5#chamber and a power supply, the 4#chamber is a cathode chamber of a MEC, the 5#chamber is an anode chamber of the MEC, and the 4#chamber and the 5#chamber are separated by a separator; the cathode chamber and the anode chamber of the MEC are respectively connected to a negative electrode and a positive electrode of the power supply, and a cathode electrode in the cathode chamber is enriched with hydrogen autotrophic denitrifying bacteria; and an outlet of a sulfide autotrophic denitrification chamber of the SANI system is connected to an inlet of the cathode chamber of the MEC; and an outlet of the cathode chamber of the MEC is connected to an inlet of a nitrification chamber of the SANI system.

Preferably, an outlet of the nitrification chamber of the SANI system is connected to the anode chamber of the MEC.

Preferably, the separator is used for isolating the anode and cathode chambers, and can be a proton exchange membrane, a cation exchange membrane or the like.

Further, the 4# chamber is filled with a graphite filler which is led out by a graphite rod to be connected to the power supply, and the 5# chamber uses a DSA electrode.

Further, the 4# chamber is in an anoxic condition, with a dissolved oxygen DO<0.5 mg/L; the 5# chamber is in an aerobic condition, with a dissolved oxygen DO>0.5 mg/L; and the SANI system, the 4# chamber and the 5# chamber are all fully stirred.

The present invention further discloses a method for treating ammonia-nitrogen wastewater by the device, the method including: entering a wastewater through a bottom of a sulfate reduction chamber of the SANI system, and reducing sulfate in the wastewater to sulfide by sulfate reducing bacteria under a condition of complete mixing, during which electrons are sourced from organic matters in the wastewater;

after an effluent from the sulfate reduction chamber reaching the sulfide autotrophic denitrification chamber of the SANI system, fully mixing the effluent with the wastewater flowing back from the nitrification chamber at a bottom of the sulfide autotrophic denitrification chamber; converting NH4+in the wastewater into NO3−by nitrifying bacteria in the nitrification chamber so that a large number of NO3−exist in the sulfide autotrophic denitrification chamber, and converting NO3−into N2under anaerobic conditions by sulfide autotrophic denitrification microorganisms growing in the chamber, wherein electrons are sourced from sulfide coming from the sulfate reduction chamber; entering an effluent from the sulfide autotrophic denitrification chamber into the cathode chamber of the MEC, and isolating the anode chamber from the cathode chamber by a separator in order to avoid mutual interference between ion migration in the cathode chamber and that in the anode chamber; in the cathode chamber, performing deep denitrification for further denitrification by hydrogen autotrophic denitrifying bacteria, and then flowing an effluent from the cathode chamber through an upper outlet to the nitrification chamber to convert NH4+in the water into NO3−; effectively neutralizing a large number of protons produced during nitrification process in the nitrification chamber by a large number of hydroxyl radicals produced in the cathode chamber along with a hydrogen generating reaction; and finally, directly discharging or pumping an effluent from the nitrification chamber into the anode chamber of the MEC for oxidation treatment to remove sulfide in the water to be directly discharged.

Further, a flow ratio of a water discharging amount of the nitrification chamber to an amount of water flowing back to the sulfide autotrophic denitrification chamber is 1:0.5-1:5.

Further, temperatures of the SANI system, the 4# chamber and the 5# chamber are controlled at 25±5° C., and a hydraulic retention time of each chamber is 18-36 h.

Furthermore, a cathode potential ranges from −0.4 V to −1.2 V.

Furthermore, an anode potential ranges from 0.5 V to 2.3 V.

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

1) it can be applied to treatment of wastewater with a high ammonia-nitrogen content (≥200 mg NH4+—N/L);

2) pH self-adjustment can be achieved without additionally adding alkalinity or acidity;

3) the denitrification efficiency is higher; and

4) the sulfide in the effluent is further oxidized and removed using the anode chamber of the microbial electrolytic cell.

