Inoculation And Alkali Coeffect In Volatile Fatty Acids Production And Microbial Community Shift In The Anaerobic Fermentation Of Waste Activated Sludge

As consequence of the widespread use of activated sludge technology in wastewatertreatment in China, the management of waste activated sludge (WAS) has become a seriousissue. The most popular way for WAS reuse is methane fermentation expecially focus onpretreatment methods which could increase the WAS hydrolysis. According to previous studyan alternative strategy for the treatment of WAS is the fermentation of volatile fatty acids(VFAs). As VFAs generation through WAS anaerobic fermentation under alkaline conditioncould be regard as alkaline pretreatment combine with a biochemical process, it is necessaryto investigate the impact of microbial inoculum and microbial community shift during thefermentation process when different seed sludge are added, also the hydrolytic enzymesactivities is also necessary for clarifying the mechanism, in addition lowering alkali consumeand finding the optimum operation parameters.1. WAS of nucleotide acid factory anaerobic fermentation under alkaline condition withoutinoculums was conducted. Soluble chemical oxygen demand（SCOD） level can be taken asan indication of a change in WAS hydrolysis,4pH level(8,9,10,11) wrere chosen in thepresent study. Alkali consume of WAS anaerobic fermentation under alkaline condition waslinear relative to pH level, afer20h Alkali consume of different pH was linear to fermentationtime. SCOD concentration at pH10was higher than other condiontion. VFAs concentrationunder pH10peaked at day2.So optimum pH of non-inoculated WAS anaerobic fermentationunder alkaline condition was pH10.2. pH9and pH10was chose for inoculums experience. Two kinds of sludge were used in thiswork as seed which were paper mill anaerobic granular sludge (PAS) and printing and dyeingmill anaerobic sludge (DAS). Hydroloysis of inoculated WAS was increased at pH9yet notincreased at pH10. The inoculation increased the VFAs accumulation at pH9, with thehighest values obtained at day10with PAS-inoculated (52.4mg/gVS) samples followed byDAS-inoculated samples, while the non-inoculated samples produced the lowestaccumulation. The inoculation of WAS samples at pH10failed to increase VFAs productioncompared to the respective non-inoculated samples incubated at the same pH. 3. The trend of alkali addition was monitor. Inoculums at pH10did no change the trend,alkali consume was linear to fermentation time after50hours’ fermentation, but change thetotal amount of alkali. Inoculums at pH9did no affect the trend as well as the total amount ofalkali consume. Alkali consume linear to fermentation time happen only at the middle of thefermentation.4. All sludge sample of different fermentation condition was analysis by PCR-DGGE, in orderto analysis the microbial community. Results indicated that many bacterial involved in VFAsproduction was present in all the conditions of this study, no matter what kind of sludge seedwas inoculated. This evidence highlight the intrinsic ability of WAS to produce VFAswhatever alkaline condition or inoculation is used. Some of the bacterial species identified inthe starting materials, disappeared when fermented at pH10. DGGE bands representproteocatella sphenisci, Tepidibacter formicigenes and Clostridium cylindrosporum weredisappeared at pH10could be observed at pH9in non-inoculated and in DAS-inoculatedsamples, but they disappeared in PAS-inoculated pH9. It is deduce that inoculation of WASwith PAS increased the hydrolytic power of the alkaline environment and efficientlyhydrolyzed these species.A solubilization test in strong alkaline condition and hydrolytic enzymes activities assaywere performed at the present study to clarify the mechanism of Inoculation and alkalicoeffect in volatile fatty acids production. According to the results the inoculation loweredSCOD and soluble protein levels of sludge samples compared to those non-inoculated, mainlybecause of the relative low alkaline soluble material originally present in the inocula. Therelatively low value of soluble proteins obtained by the strong alkaline solubilization test wasprobably due to a partial decomposition of proteins into amino acids due to the high pH. Thusthe lower VFAs production obtained in inoculated samples could be a direct consequence oftheir relatively low concentration of alkaline SCOD and proteins, compared withnon-inoculated samples. Data of hydrolytic enzymes activities assay clearly indicate adramatic decrease of enzymatic activity in samples fermented at pH10which is consistentwith the lack of any additional biotic effect displayed by inoculated samples at this pH. The higher alkaline protease activity of PAS-inoculated samples might be related to the higherVFAs production exhibited by these samples.