Free Ammonia-based Pretreatment Promotes Short-chain Fatty Acid Production From Waste Activated Sludge

With the wide application of biological denitrification technology,searching for an effective technology for low-carbon source wastewater treatment becomes a problem in the field of environmental engineering.At the same time,with the rapid increasing amount of sludge,organic biomass in sludge are degraded to valuable biochemical such as volatile short-chain fatty acids,which is an effective way to realize the recycle of resource,reduce of sludge and harmless treatment.In this paper,the pretreatment method based on free ammonia(FA)is used for enhancing SCFA production from anaerobic fermentation of waste activated sludge,more details are as follows:First,the optimal pretreatment time and the optimal pretreatment concentration of free ammonia are determined in the study.The results showed that the optimal free ammonia pretreatment time was 3 days.The maximum SCFA yield of 267.3 mg COD/g VSS was achieved at 8 d in the 176.5 mg FA/L reactor.At the same time,acetic acid was the predominant SCFA via analyzing the composition of individual SCFA at 8 d in reactors under the optimal fermentation conditions,which is beneficial to improving the biological nitrogen removal.Then,the effects of free ammonia as pretreatment method on the solubilization,hydrolysis,acidogenesis,acetogenesis,homoacetogenesis,and methanogenesis process in anaerobic fermentation of WAS were analyzed.Experiments results showed that the release of LDH reached 119%in the fermentation liquid for 2 h at 176.5 mg FA/L reactor.Compared with the blank,FA not only caused increased fluorescence intensity wavelength but also red-shifts of emission at 24 h.Meanwhile,the proportion of viable bacteria in the fermentation liquid was 66.7%,lower than 90.8%of the blank.It can be therefore concluded that FA accelerated the disruption of EPS and cell envelop of sludge cells,benefited the damage of cell membrane,and facilitated the organics released from WAS,which thereby provided more substrates for subsequent SCFA production.However,free ammonia also inhibited hydrolysis,acidogenesis,homoacetogenesis,and methanogenesis process in anaerobic fermentation.The experimental results showed that the degree of inhibition of free ammonia on methanogenic stage is greater than that of hydrolysis,acidification and homoacetate.Therefore,mechanism is revealed that FA enhanced SCFA production from anaerobic fermentation of WAS.Finally,it was explored that the production of SCFA from sludge fermentation by FA treatment method can be used as not only preferred carbon sources for nutrient removal enhancement but also raw substrates for biodegradable plastic productions.In this paper,we proposed a new wastewater treatment process for WWTPs treating wastewaters with low C/N ratios,the traditional wastewater treatment process was added by the FA-based strategy.The results shows that the FA-supported strategy would save?$1.7 million per year in a WWTP(Q = 105 m3/day),as compared with the conventional operation paradigm.Therefore,the findings reported in this paper not only advanced the scientific understanding of the effect of FA on sludge anaerobic fermentation significantly but also support the operation of WWTPs in sustainable paradigms with low energy input in the future.