Integration Of Constructed Wetland With Microbial Fuel Cell For Power Production And Removal Of Antibiotics

Antibiotics are badly overused in China, and not only can it’s excretion cause serious chemical pollution and ecotoxicity, but also leading to a selective pressure on the environmental bacteria and forming antibiotic resistant bacteria(ARB) and antibiotic resistance genes(ARGs). Tetracycline(TC) and sulfonamides(SMZ), two of the most widely used antibiotics, were selected as the typical medicine for study. Constructed wetland(CW), possessing the favorable structure condition for constructing microbial fuel cell(MFC) and the potential decontamination ability for removing refractory organics, was equipped with MFC for the degradation of antibiotics. The figure and operating conditions of CW-MFC system were optimized based on a number of contrast experinments. The mechanism of antibiotic removal was revealed by analyzing the distribution of antibiotics, ARB and ARGs along the system. The main contents and results were as follows:1) CW and CW-MFC system were successfully formatted, and maintained stable for over half a year. The final COD removal of each system can reach over 95%, and the open-circuit voltage(OCV) of CW-MFC(M) and CW-MFC(2M) reached up to 630mV, of CW-MFC(1/2M) was about 580mV. The OCV of CW-MFC(L) and CW-MFC(H) wavered, but still came up to 615mV and 550mV in average. The feasibility of simultaneous bioelectricity generation and wastewater treatment in CW-MFC was well established.2) The figure and operation condition for higher power production were optimized. Dissolved Oxygen(DO) along the system was tested, and the result showed that the lowest DO appeared at 20cm from the bottom(set as anode), and the highest at the top(set as cathode). The power generation was compared between CW-MFC with immersed and lifted cathode, and CW-MFC with lifted cathode was proved to have higher maximum power density and lower internal resistance. It can be illustrated that, OCV of CW-MFC raised with higher concentration of biodegradable co-substrates and lower concentration of antibiotics in effluents, however, the internal resistance came up simultaneously. Taken together, CW-MFC(M) had the best power produce capacity for it came out the highest maximum power density(0.0572W/m2) with relatively high OCV and comparetively low internal resistance.3) The operation condition for better removal of antibiotics were optimized. It was found that the concentration of antibiotics and co-substrates in influents significantly affected the removal efficiency of antibiotics. With increasing of the initial concentration of antibiotics, the amount of adsorption increased as well as the amount of ARB, the order of removal efficiency was CW(H)> CW(M)> CW(L), and CW-MFC(H)> CW-MFC(M)> CW-MFC(L). Addition of co-substrates decreased the adsorption of antibiotics mainly by competing adsorption sites, with the order followed as CW-MFC(1/2M)> CW-MFC(M)> CW-MFC(2M), while increase of co-substrates lead to larger amount of ARB, which accelerated the biodegration in CW-MFC(2M). In additon, CW-MFC(1/2M) also showed a strong biodegradation ability, for antibiotics might be used directly as a secondary carbon source.4) Compared to CW, CW-MFC was proved to have better purification effect for antibiotics. The construction and materials of two electrodes contributed to a better adsorption and degradation property, and the electrochemical interaction at anode not only lead to a further electrochemical decomposition of degradation products of antibiotics, but also caused changes of the cell membrane structure and the enzyme activity of becteria, promoting the decomposition and utilization of organic matters including antibiotics.5) Preliminary analysis on antibiotics, ARB and ARGs distribution along the system demonstrated that physical adsorption appeared to be the most important pathway for tetracycline removal, which attributed to the polar functional groups on TC, while biodegradation made limited contribution after operating a period of time. With high water solubility and low chelating ability, sulfonamides were easily excreted out of the system during the early operation, however, it was more susceptible to biodegradation with shorter degradation half-time.