Microbial Pretreatment On Dewatered Sludge And Optimization Of Anaerobic Digestion Process Performance

With the rapid development of the construction of sewage treatment facilities, sludge is increasing its amount, as an inevitable byproduct. In order to achieve easy transportation and centralized processing, most sewage treatment plants apply flocculants to dewater the sludge, reducing its moisture content. But this method only reduces water from sludge rather than achieve stabilization of sludge. It leads to a serious phenomenon of "paying attention to water but looking down on sludge". Polyacrylamide is a commonly used flocculant. It is a high-molecular polymer, which has a very strong biological resistance, preventing sludge from microorganism. Therefore, the disposal of sludge is imperative. First of all, this study screened the microorganism which could degrade PAM. Then, the optimum technology parameters for anaerobic digestion of sludge were studied through experiments at different organic loadings. On the basis of former researches, experiments were carried out to optimize the digestive process under different kinds of microorganisms, pretreatment methods, amounts of microorganism additive and organic loading. The main results of the research are as following:Three kinds of microorganism were found for degrading PAM, including micrococcus luteus, fungus paecilomyces variotii and self-screening functional microbe. It could be found that the mesophilic anaerobic digestion experiment of dewatered sludge had short biogas production cycle and small amount of biogas product. Feed concentration of3%and4%were better than2%and5%in producing biogas. Therefore, feed concentration of3%and4%were chosen for the subsequent pretreatment researches.There are two microbial pretreatment methods:direct adding before digestion (abbreviation:DA) and2days pretreatment adding before digestion (abbreviation:2d PA). Using the micrococcus luteus pretreatment, when the total number of microorganism was7.6x1010, the biogas production of DA treatments (micrococcus luteus cultivation for one day, two days and three days) was increased by12.27%、15.09%and21.24%respectively compared with the sludge without microbial pretreatment. As the total number of microorganism increased to7.6×1011, both2d PA and DA had positive effects on biogas production. Using the paecilomyces varioti pretreatment, when the total number of microorganism was8.3×109, the biogas productions of2d PA and DA were increased by19.87%and22.91%compared with the sludge. When the total number of microorganism was7.6×1010, the effects of microbial pretreatment were better obvious, and the biogas productions of2d PA and DA (paecilomyces varioti cultivation for four day) increased by19.87%and22.91%respectively compared with the sludge. When the total number of microorganism was7.6×1011, the biogas productions of2d PA and DA (paecilomyces varioti cultivation for five day) increased by30.91%�'�79.39%respectively compared with the sludge. Using self-screening functional microbe pretreatment, when the total number of microorganism was8.7×109and7.6×1010, the biogas productions of2d PA and DA increased by18.16%,12.50%and67.61%,44.55%respectively compared with the sludge. These experiments proved that microbial pretreatments of dewatered sludge would optimize of anaerobic digestion process and promote biogas production. When the feed concentration rising to4%and dewatered sludge feed amount was unchanged, the effect of microbial pretreatments was not obvious because of the low inoculation proportion. It could be suggested that the inoculation of methanogens was very important for anaerobic digestion of microbial pretreatments dewatered sludge. When feed concentration was increasing, the amount of inoculation of methanogens must be enhanced. After analysis it was found that DA was better for micrococcus luteus and paecilomyces varioti. And effect of fungus paecilomyces varioti was best among the three kinds of microorganism.Using the methane production dynamic model to simulate the anaerobic digestion process for different microbial pretreatments, it could be concluded that this model could simulate the digestion process with a high accuracy, and each R2was more than0.98. Using CSTR digestion tank with effective volume of17L, continuous anaerobic digestion experiments of different microbial pretreatments were conducted. It was showed that the efficiency of biogas production, methane concentration and organic matter degradation was promoted after microbial pretreatment, which would provide the theoretical basis of biogas engineering operation for solving dewatered sludge resourceful treatment.