| The decentralized domestic wastewater refers to the wastewater produced by individual houses or single-family buildings in remote and rural areas.Unlike centralized wastewater,the decentralized domestic wastewater cannot be collected and treated uniformly through municipal pipeline network but needs to be collected and treated in situ.At present,the commonly used single biological treatment or ecological treatment methods cannot meet the increasingly stringent wastewater treatment discharge standards.Therefore,it is of great practical significance to develop an efficient bio ecological combination technology to strengthen the reduction of main pollutants in dispersed domestic sewage.In this study,a bio-ecological combined treatment process based on catalytic Fe-C micro-electrolysis-based baffled septic tank pretreatment-A/O biochemical secondary treatment-vertical flow constructed wetland advanced treatment is established to treat decentralized domestic wastewater.Catalytic Fe-C micro-electrolysis carrier is also used in the restoration of receiving water bodies of decentralized domestic wastewater,and the development of ecological floating island and sediment covering agent based on catalytic Fe-C micro-electrolysis to simultaneously remediate the external and internal sources of receiving water bodies pollution of decentralized domestic wastewater.The results indicated that:（1）Catalytic Fe-C micro-electrolysis coupled with baffled septic tanks pretreat and decentralized domestic wastewater,which can simultaneously realize anaerobic digestion,aerobic nitrification,and anoxic denitrification processes.Studies have shown that when the HRT is controlled for 24 h and the influent C/N ratio is 7.0±0.8,the removal efficiencies of TN,NH4+-N,TP and COD in black water can reach 69.6%,60.7%,94.1%and 82.1%respectively.Among them,the amount of N removed by autotrophic denitrification accounted for 37.0%of the total amount of N removal.It shows that after coupled catalytic Fe-C micro-electrolysis,the system can improve the biodegradability of black water.Compared with the traditional three-format septic tank,it has a more efficient COD removal rate and has the function of simultaneous N and P removal.Analyzing the microbial population structure of activated sludge and biofilm in septic tanks,it is found that Romboutsia,Nitrosomonas,and Hydrogenopha are the main functional bacteria of anaerobic digestion,aerobic nitrification,and anoxic denitrification in the system,respectively.The addition of Fe-C micro-electrolysis realizes the function of efficient denitrification and organics removal in the pretreatment and decentralized domestic wastewater in the baffled septic tank.（2）Catalytic Fe-C micro-electrolysis coupled with A/O secondary biochemical treatment system treats septic tank effluent and washing wastewater（gray water）.Studies have shown that control DO is 3.5 mg/L,reflux ratio is 4.5:1,and HRT is 12 h,the average removal efficiencies of TN,NH4+-N and COD were 86.9%,97.6%and85.3%,respectively.The denitrification capacity of autotrophic denitrification accounts for 50.8%of the total denitrification capacity.It shows that the catalytic Fe-C micro-electrolysis carrier provides sufficient Fe2+and reduced state[H]for the denitrification process and achieves the efficient removal of TN and COD through chemical catalysis and biological processes of simultaneous heterotrophic and autotrophic denitrification,which provides a new method for the treatment of wastewater with low C/N ratio.Analysis of the microbial population structure of the biofilm in the A/O secondary biochemical treatment system found that the dominant bacteria in the anaerobic are Thiobacillus and Denitratisoma,both of which are common denitrifying bacteria.Thiobacillus ahs been proved to use Fe2+as electrons to realizes autotrophic denitrification.Flavobacterium and Nitrospir are the dominant bacteria in the aerobic reactor and also the functional bacteria in the nitrification process.In addition,the Nitrosomonadaceae,Nitrospira,Ferritrophicum and Acidovorax found in the system play an important role in the system’s nitrogen cycle（nitrification and denitrification）and iron cycle（iron oxidation and iron reduction）.（3）Catalytic Fe-C micro-electrolysis coupled with vertical flow constructed wetland for advanced treatment of the secondary effluent of decentralized domestic wastewater.Studies have shown that when the HRT is 48 h and the influent C/N ratio is2.5,the removal efficiencies of TN and TP in the secondary effluent from the constructed wetland reaches 88.6%and 92.2%,respectively.When operating under low temperature conditions,the effluent quality is slightly lower than that at room temperature,but the removal efficiencies of TN and TP is still as high as 72.7%and89.2%.The catalytic Fe-C micro-electrolysis carrier is used as the substrate of the constructed wetland can provide inorganic electrons for denitrification through Fe2+and reduced state[H]generated by the micro-electrolysis reaction to make up for the problem of insufficient carbon source,and meanwhile realize the function of co-precipitation for phosphorus removal.In addition,Fe-C micro-electrolysis achieves efficient and stable operation of constructed wetlands under low temperature conditions through chemical reduction for nitrogen removal and chemical precipitation of phosphorus removal.Compared with the advanced treatment of traditional constructed wetlands,this system has higher nitrogen and phosphorus removal functions and low temperature resistance.Analysis of the microbial population structure on the surface of the constructed wetland carrier revealed that Denitratisoma,Micrococcales,and other functional bacteria related to the denitrification process are widely present in the biofilm of the catalytic Fe-C micro-electrolysis substrate surface.（4）Comprehensive evaluation of the environmental benefits of the decentralized domestic wastewater bio-ecological treatment technology based on catalytic Fe-C micro-electrolysis,the autotrophic denitrification process of catalytic Fe-C micro-electrolysis does not require an additional organic carbon source,which reduces the emission of CO2.In addition,the treatment system does not discharge activated sludge,so it will not cause eco-toxicity risks to fresh water and soil.The economic benefits of the bio-ecological combined treatment process based on catalytic Fe-C micro-electrolysis was evaluated.Although the initial investment in the construction of the process structure and the purchase of the catalytic Fe-C micro-electrolysis carrier is relatively high,the long-term operating cost is relatively low,and the cost of wastewater treatment per ton is only 0.94 yuan.（5）The effluent of the advanced treatment of decentralized domestic wastewater into the receiving water body is a commonly used method of wastewater regeneration and reuse.To solve the external pollution of the water body caused by the decentralized domestic wastewater receiving water body,a catalytic Fe-C micro-electrolysis-based ecological floating island technology has been developed.Firstly,it was investigated that the catalytic Fe-C micro-electrolysis carrier has the effect of simultaneous algae killing,nitrogen and phosphorus removal on the water body.The floating island technology effectively slows down the eutrophication of the water body.Additionally,a sediment covering technology based on catalytic Fe-C micro-electrolysis was developed to inhibit the internal transmission of pollutants.Long-term operating were effectively removed,and the P pollutants were converted into inert phosphorus compounds are fixed in the sediments,and the release rates of N and P pollutants in the sediments to the overlying water are reduced by 29.9%and 70.2%,respectively.Studying the conversion of Fe in the sediments in long-term operation found that the Fe2+released by the micro-electrolysis reaction is mainly converted into the less reactive PRS-Fe and mag-Fe in the sediments,which will not cause secondary pollution and side effects to the water body.The research results show that the catalytic Fe-C micro-electrolysis carrier has high environmental and economic benefits and has great application prospects for the remediation of exogenous and endogenous pollution of eutrophication receiving water bodies.The thesis reveals the efficiency and mechanism of catalytic Fe-C micro-electrolysis for denitrification and phosphorus removal in different treatment processes of decentralized domestic wastewater and establishes a new decentralized advanced wastewater treatment technology with a complete theoretical system and practical application value.This study groundbreakingly combines chemical,biological and ecological treatment processes,provides a new idea for domestic wastewater collection and advanced treatment in the vast rural areas of China,supplements the deficiencies of advanced denitrification process of domestic wastewater and remediation of water and sediment,solves the problem of increasingly serious water shortage and reuse,and provides scientific theoretical basis and technical support. |
