Regulate Sulfur Conversion By Built-in Electrode And Analysis The Mechanism Of Sulfur Conversion In Sewer

Hydrogen sulfide?H₂S?gas generated in the municipal sewer is not only toxic to human,but also causes aging and corrosion of sewer.The sulfide for a certain length of sewer can be controlled under traditional methods,but the addition of chemicals or nitrate?NO₃^-?and other electron acceptors tend to flow with the sewage,it is difficult to control the node of sewer with high concentration of sulfide.At present,there is a lack of applicable control technology for the"point source"with strong continuous sulfide production in sewer.In this work,the idea of sulfur transformation(SO4^2-?S^2-?S⁰)with electrode-mediated is proposed to control the production of H₂S gas in sewer.The joints of pipelines with high sulfide concentration in sewer are taken as research objects.The domestication effect of bio-anode and pipeline biofilm is discussed.The effects of water quality parameters(sulfate(SO4^2-)and organic matter)and different operating conditions?conductivity,cathode area and anode potential?on sulfur transformation with electrode-mediated in sewer are investigated;the pathways of sulfur transformation in sewer are analyzed under the action of electrode-mediated.The main conclusions are as follows:?1?Sulfide oxidizing bacteria?such as Rhodobacter and Arobacter?and sulfur oxidizing bacteria?such as Thiobacillus?are continuously enriched on the surface of the anode during the process of microbial domestication.From the sixth cycle,the maximum concentration of elemental sulfur?S⁰?in the system is maintained at 72 mg L^-1.At this time,the active electricity production bacteria and sulfur-oxidizing functional bacteria are successfully enriched on the anode surface.After long-term domestication,the corresponding functional colonies in pipeline biofilm are also obtained.The enrichment of these functional bacteria provides a guarantee for the microbial electrode system to regulate sulfur conversion and control H₂S gas production.?2?The change of concentration of SO4^2-has no effect on the conversion of anode sulfur when the SO4^2-concentration is range from 50 to 200 mg L^-1.When the organic matter concentration is between 100 to 300 mg L^-1,the higher proportion of S⁰ in the effluent and better control effect of H₂S are obtained with higher concentration of organic matter under the action of bio-anode.When the concentration of organic matter reaches 300 mg L^-1,the proportion of sulfide(H₂S and S^2-)in effluent remains at 14%,and the control effect of H₂S does not change.?3?It was found that when the conductivity was 9.75 mS cm^-1,the proportion of sulfide(H₂S,S^2-)in the effluent is lowest?8%?and the proportion of S⁰ is highest?71%?under the action of bio-anode,the microbial electrochemical system shows best result of sulfur transformation.When the diameter of the cathode is larger than 8 cm,the proportion of sulfide(H₂S,S^2-)in the effluent remains at 8.2%and the proportion of S⁰ remains at 70%.The control effect of H₂S is no longer affected by the area of the cathode,so the optimum diameter of the cathode is 8 cm.When the anode potential is 100 mV,94%of sulfides are oxidized to S⁰ under the action of microbial anode.The proportion of H₂S in the effluent is almost 0%and the anode potential is most suitable at 100 mV.?4?Under the action of the electrode system,the sulfur transformation path in sewer is mainly as follows:on the surface of the anode,S^2-is oxidized to S⁰ under the action of sulfide oxidizing functional bacteria firstly.44%of S⁰ is washed away by water flow or falls into the bottom of the pipe while the other part of S⁰ covered on the surface of the anode is further oxidized to SO₄^2-by sulfur oxidizing bacteria.Therefore,S⁰ deposition can be effectively alleviated.The S^2-oxidation rate is 4.4 times higher than S⁰ on the surface of the anode.The rate difference between them provides the possibility for the directional regulation of S^2-conversion to S⁰ and the control of H₂S production.At the bottom of the pipeline,SO₄^2-in sewer produces S^2-under the action of sulfate-reducing bacteria,and the generated S^2-produces S⁰ on the surface of the anode.S⁰ falling into the bottom of the pipe is reduced to S^2-under the action of elemental sulfur reducing bacteria.The reduction reaction of SO₄^2-and S⁰ at the bottom of the pipe occurs simultaneously.The symbiotic microorganisms in the system play a key role in these processes.