Enhanced Short-chain Fatty Acids Production From Waste Activated Sludge By Combining Calcium Peroxide With Free Ammonia Pretreatment

Nowadays,the number of urban sewage treatment plants in China is increasing rapidly,with the production of a large amount of waste activated sludge(WAS),which not only pollutes the environment but also endangers human health.The anaerobic fermentation of sludge for short-chain volatile fatty acids(SCFA)is an effective method of sludge reclamation,innocuity and reduction.However,there is not any treatment in sludge anaerobic fermentation,the SCFA accumulation could at low levels.Hence,reutilization of WAS to produce short-chain fatty acid(SCFA)via anaerobic fermentation has recently attracted increasing interests.Using calcium peroxide(CaO2)as an additive to pretreat waste activated sludge(WAS)has recently attracted increasing attention due to its effective in removing endocrine disrupting compounds,enhancing WAS dewaterability and disintegration,and promoting short-chain fatty acids(SCFA)production from WAS.However,the dosages of Ca02 was 0.2 g/g VSS,which largely diminish its value in full-scale application.It was found in this work that the pertinent addition of free ammonia(FA)in the stage of WAS pretreatment not only enhanced SCFA yield but also reduced Ca02 dosage.This was demonstrated by comparing the SCFA yields from WAS pretreated by different levels of Ca02 and FA.Experimental results showed that the optimal SCFA yield of 338.6 mg COD/g VSS was achieved when WAS was pretreated with 0.05 g/g VSS of CaO2 + 180 mg/L of FA for 3 d,which was 2.5-fold of that from Ca02 pretreatment and 1.5-fold of that from FA pretreatment.The mechanism investigations exhibited that calcium peroxide combined with free ammonia can accelerate the fragmentation of sludge cells.Although calcium peroxide has strong oxidation,it is not sufficient to mineralized some organic compounds,which leads to lower dissolved COD(SCOD)under combined conditions than free ammonia pretreatment because the release of Ca2+ can make the cracking sludge cells re flocculated,so that more SCOD could not be released.At the same time,the study found that Ca02 combined with FA can produce more biodegradable organic compounds,providing more available organic compounds for the production of subsequent SCFA.Calcium peroxide combined with free ammonia pretreatment had inhibitory effects on hydrolysis,acidification and methanation,and the inhibition rates were 23.65%,35.04%and 72.40%respectively.The data showed that the inhibition degree of methanation was far greater than the inhibition degree of hydrolysis and acidification.Economic analysis based on experimental and bibliographic data shows that the new model of Ca02 combined with FA pretreatment sludge produce SCFA is economical.It is preliminarily demonstrated that the technology is economically feasible.Considering that FA could be in situ produced in the anaerobic WAS fermentation process,the findings achieved here advanced the application of CaO2-based pretreatment in real-world situations.