Response Characteristics Of Septic Tank Under The Background Of Food Waste Increment

With the implementation of the waste classification regulations,more and more residents choose food waste disposers（FWDs）to crush food waste（FW）and discharge it into the sewage system,which changes the quality of domestic sewage and the concentration of suspended solids.Most of the urban drainage systems in China are equipped with septic tanks.The deposition and transformation of FW in septic tanks will inevitably affect the operation of septic tanks.In this paper,by setting up a septic tank reactor in the laboratory,simulating FW into the septic tank,the long-term detection of water quality and gas,and the detection of septic tank sediment by high-throughput technology,the generation of harmful gases,the change of water quality,the physicochemical properties of sediment and the response characteristics of microbial community under the effect of FW increment were studied.The results show that:（1）Investigation and analysis show that FW is mainly composed of food,vegetables,bone and meat,accounting for 35%,45%,10%and 10%respectively;the main elements are carbon,hydrogen,oxygen and nitrogen,while phosphorus and sulfur account for a relatively low proportion.When the penetration rate of fwds was 25%and75%,the FW increment was 0.5g/l and 1.5g/l,and the soluble chemical oxygen demand（SCOD）increased by 47.6mg/L and 151.3mg/L respectively,while the concentration of TN and TP changed little.（2）FW increased the production of hydrogen sulfide（H₂S）and methane（CH₄）in the septic tank.The results showed that the concentration of H₂S（g）in the septic tank increased from less than 1.0 ppm to 4.0～5.0 ppm after FW increased compared with the blank control experiment.When FW concentration increased from 0.5g/L to 1.5g/L,CH₄release cycle shortened from 20d to 10d,and the maximum CH₄ release concentration increased to 105～110LEL indicating that CH₄ release cycle shortened and CH₄ release concentration increased with FW increment.The above results show that FW entering into the drainage system will further induce the septic tank to become a potential hot spot of harmful gas emission.（3）In terms of water quality changes,when FW increment is 0.5g/L,1.5g/L and2g/L,the concentration of sulfide(S^2-（l）)in septic tank effluent increases by 242.1%,386.7%and 532.5%,SCOD increases by 6.9%,23.0%and 32.4%,C/N increases by 5.2%,26.3%and 35.23%,and C/P increases by 3.59%,15.77%and 27.72%,respectively.It indicated that the increase of FW resulted in the increase of S^2-（l）,SCOD,C/N and C/P.（4）Analysis of microbial community composition in septic tank sediments showed that the increase of FW significantly increased the species abundance of bacteroidea and negativitites.Among them,SRB abundance increased by 57%,while sob decreased by20.9%,which was the main reason for the increase of H₂S（g）and S^2-（l）concentration in septic tank;increasing FW could promote the proliferation of Methanosaeta and Methanobacterium,change the community composition of methanogens（MA）in sediment,and lead to the change of CH₄ production and release characteristics in septic tank.