Technology And Mechanism Of Microorganism Reduction For Septic Tank Nightsoil Sludge

With the development of urbanization, the environmental pressure of septic tank nightsoil sludge pollution becomes increasingly pronounced. Artificial clearing will take lots of time and vigor, and also, landfill treatment of nightsoil sludge will bring secondary pollution. Therefore, the study of septic tank nightsoil sludge reduction in situ has important practical significance. In virtue of anaerobic theory and enhanced biological sludge reduction technology, the feasibility of using compound microorganisms (EM, HBH-Ⅱand MCMP) to strength nightsoil sludge anaerobic digestion reduction was investigated firstly in this paper; the proper dosage of EM,HBH-Ⅱand MCMP to aggrandize nightsoil sludge anaerobic digestion reduction was studied secondly; the effect of initial pH and temperatures on nightsoil sludge anaerobic digestion reduction aggrandized by EM,HBH-Ⅱand MCMP were discussed, the best technology condition of HBH-Ⅱto reduce nightsoil sludge was also brought forward. Moreover, the combined effect reduction mechanism of alkaline pretreatment and HBH-II bioaugmentation was discussed by using Polymerase Chain Reaction-Denature Gradient Gel Electrophoresis (PCR-DGGE) technology. The effect and the benefit of HBH-Ⅱon the reduction of septic tank nightsoil in practical applications was discussed lastly. The results of this research can offer a certain theoretical basis and useful technical support to reduce septic tank nightsoil sludge in situ and improve the security capability of septic tank. The main results were given as follows:①Study the feasibility of using EM, HBH-Ⅱand MCMP for septic tank nightsoil sludge anaerobic digestion reduction. After 21 days of anaerobic digestion, the removal rates of Total solid(TS), Volatile solid (VS) and COD as well as the digestion efficiencies of nightsoil sludge of the 3 experimental groups are followed by T1 (adding 0.005% compound microorganism in the original nightsoil sludge system)> T2 (adding 0.005% compound microorganism after the nightsoil sludge was sterilized by pasteurism)> CK (without compound microorganism). There are significantly positive (p<0.01) relations between T1 and CK as well as T1 and T2 in the removal rate of TS, VS and COD. The configuration of nightsoil sludge isn't destroyed by pasteurism; the difference of TS, VS and COD reduction effect among the treatments is mostly caused by the different quantity and species of the microorganism of the treatments. The corporate effect of EM, HBH-Ⅱand MCMP and the original microorganism of the nightsoil sludge system is more propitious to reduce septic tank nightsoil sludge; it is feasible for adding EM, HBH-Ⅱand MCMP to septic tank directly to reduce nightsoil sludge production.②Study the effect of EM, HBH-Ⅱand MCMP adding dose on anaerobic digestion reduction of nightsoil sludge. After 20 days of anaerobic digestion, the maximum removal rates of TS and VS of the 3 experimental groups appear in E2, H3 and M2 treatment under 0.01%, 0.05% and 0.01% dosing quantity of EM, HBH-II and MCMP, respectively. The removal rates of TS and VS of E2 are 32.51% and 42.34%, respectively; that of H3 are 36.43% and 49.11%, respectively; and that of M2 are 33.74% and 46.05%, respectively. In this experiment, adding 0.01% EM, 0.05% HBH-II and 0.01% MCMP have the best reduction effect of nightsoil sludge.After 20 days of anaerobic digestion, the cumulative biogas yield of E1~E6, H1~H6 and M1~M6 are 60.74%~214.70%, 93.91%~218.83% and 50.78%~254.82% higher than that of the control (CK). EM, HBH-II and MCMP can improve the anaerobic digestion reduction efficiencies of nightsoil sludge as well as increase the gas production. The gas production of the treatments which adding HBH-II is slightly lower than that of the treatments which adding EM and MCMP correspondingly, thus the chance of biogas poisoning and blasting of the treatments adding HBH-II is least. The strengthen effect of EM, HBH-II and MCMP on anaerobic digestion reduction of nightsoil sludge displays mainly in the former 8 days. So, it is necessary to add compound micro-organisms once a week to improve the reduction effect in practical applications.③Study the effect of initial pH on anaerobic digestion reduction of nightsoil sludge which were biologic enhanced by EM, HBH-II and MCMP. The bioaugmentation effect of EM, HBH-Ⅱa nd MCMP on the removal rate of TS and VS can be very significant improved when adjust the initial pH to 9.0~10.0, whereas the strengthen effect on the removal rate of TS and VS can be very significant suppressed when adjust the initial pH to 5.0.The maximum removal rates of TS and VS of the 3 experimental groups appear in E-pH10, H-pH10 and M-pH9, respectively. After 20 days anaerobic digestion, the removal rates of TS and VS of E-pH10,H-pH10 and M-pH9 reach to 36.69% and 47.14%, 43.03% and 54.67%, 40.70% and 51.13%, respectively. Adjusting the initial pH to 9.0~10.0 is propitious to the anaerobic digestion reduction of nightsoil sludge biologic enhanced by EM, HBH-II and MCMP. This conclusion can offer a technical support to anaerobic digestion reduction of nightsoil sludge aggrandized by bioaugmentation and alkaline pretreatment jointly.E-pH9, E-pH10, H-pH9 and H-pH10 have the best reduction of TS, VS and COD; meanwhile the gas production of these 4 treatments is relatively less. M-pH9 has the best reduction of TS, VS and COD; while the gas production of these 2 treatments is obviously increased; so it is necessary to prevent hidden safety dangers such as biogas poisoning and blasting in the real application of using MCMP to reduce septic tank nightsoil sludge in practical application.④Study the effect of temperature on anaerobic digestion reduction of nightsoil sludge which were biologic enhanced by EM, HBH-II and MCMP. When the temperature is 35℃, the removal rates of TS, VS and COD of the 3 experimental groups, ie. adding 0.01%EM, adding 0.05%HBH-II and adding 0.01% MCMP, is the highest , secondly at 45℃, and thirdly at 25℃. Under the same temperature, the enhancement on TS and VS reduction are followed by: HBH-II>MCMP>EM; the cumulative biogas yield of the 3 experimental groups under 35℃are followed by: MCMP> EM> HBH-II.⑤Through orthogonally experiment, TS, VS and COD removal rates were taken as the index for investigation, the optimum conditions for anaerobic digestion nightsoil sludge reduction biologic enhanced by HBH-Ⅱare as follows: temperature is 35℃, initial pH is 10 and the dose of HBH-Ⅱis 0.075%. Under this condition, after 20 days anaerobic digestion, TS, VS and COD removal rates of nightsoil sludge reach to 50.26%, 65.45% and 58.51%; respectively.⑥The microbial communities in 6 nightsoil sludge samples taken from the beginning and the 8th days of the 3 anaerobic digestion reactors, ie. the original nightsoil sludge (A), adding 0.0075% HBH-II (B) and adding 0.075% HBH-II under initial pH 10(C), were studied using PCR-DGGE technique. At the beginning of reaction, the microbial communities of the 3 reactors are not changed greatly and the Dice coefficient (Cs) of microbial populations of different nightsoil sludge samples are 0.762~ 0.889. On 8th day, Cs of microbial populations of A and C reactors as well as that of B and C reactors are relatively low (0.727~0.750), it show that alkaline pretreatment can change the microbe community structure of nightsoil sludge system clearly. The 21 kinds of dominant bacterium in the 6 nightsoil sludge samples have near genetic relationship with Clostridium, Bacteroidetes, Acinetobacter, Firmicutes, Staphylococcus and Eubacterium .They are only 4 of them keeping good coherence between homology analysis and phylogenetic tree, and they are same generic microbe with Acinetobacter, Clostridium and Bacteroidetes; it can not find the contiguous kind in the phylogenetic tree of the rest 17 kinds of dominant bacterium. The combined augmentation effect of alkaline pretreatment and HBH-II can let Clostridium and Bacteroides propagate largely and then become the dominant population in the nightsoil sludge system, and this conclusion explain the reason why the combined effect of alkaline pretreatment and HBH-II can reduce the nightsoil sludge production as well as the marsh gas production of anaerobic digestion nightsoil sludge.⑦HBH-II is choosed to apply in septic tank nightsoil reduction of a certain district in Nanping, Chongqing. The depth of harden layer of the septic tank can decrease more than 70% after adding 0.05% HBH-II a month later. At the same time, adding HBH-II in the septic tank onsite can decrease biogas output. Comparing to cleaning and landfill treatment of nightsoil sludge, the onsite nightsoil soil reduction by adding HBH-II can reduce 69.44% of the treating cost. And also, the onsite nightsoil soil reduction by adding HBH-II has good environmental and social benefit.