Effect Of Melanoidin On Methane Production By Anaerobic Digestion Of Thermally Hydrolyzed Sludge

The reduction,stabilization,harmless and resource treatment of sludge has become one of the key problems to be solved urgently in the field of urban sewage treatment.Thermal hydrolysis enhanced anaerobic digestion methanogenesis technology is considered as an economic and promising sludge treatment technology because of its low energy consumption and good energy recovery effect.However,in the process of thermal hydrolysis,the sludge will produce non-biodegradable melanoidin,thus inhibiting the subsequent anaerobic digestion reaction.Therefore,it is the key to realize the further application of sludge thermal hydrolysis enhanced anaerobic digestion technology to identify the formation and evolution of melanoidin in the process of sludge thermal hydrolysis and to find out the effect of melanoidin substance on sludge anaerobic methane production.In view of the influence of sludge melanoidin on the subsequent anaerobic digestion methane production,the paper studied the formation and evolution of melanoidin in the process of sludge thermal hydrolysis,analyzed the influence of melanoidin content on the anaerobic digestion methanogenesis process,and determined the influence of melanoidin on the characteristics of microbial community in the anaerobic digestion system.The main conclusions are as follows:Temperature,time and p H all have significant effects on the formation of melanoidin in the process of sludge thermal hydrolysis,and the order of influence is p H > temperature > time.When the p H value was 11.0,the time was 120 min and the temperature was 180 ℃,the concentration of melanoidin was the highest.Temperature,time and p H value have significant interaction effects on sludge biodegradability,and the order of influence is temperature p H value > time p H value > temperature time.In the early stage of thermal hydrolysis,the formation rate of melanoidin is low,and the main precursor protein is tryptophan,which leads to the polymerization of high molecular weight melanoid.In the later stage of thermal hydrolysis,the production rate of melanoidin was accelerated,the main precursor protein was tyrosine,and the proportion of high molecular weight melanoidin gradually increased.Under the conditions of thermal temperature=170 ℃,time=60 min and initial p H=7.0,the anaerobic reaction system of thermolysis sludge was established based on different concentration of melanoidin.Melanoidin could inhibits the hydrolysis process of anaerobic digestion of hydrolyzed sludge,and the higher the concentration of melanoidin is,the stronger the inhibition is,which is mainly due to the inhibition of hydrolysis of protein substances.However,high concentration of melanoidin can weaken the effect of ammonia nitrogen and VFAs on anaerobic methanogenesis,thus reducing the inhibition of anaerobic digestion of hydrolyzed sludge.Melanoidin inhibited the methanogenic process of anaerobic digestion of hydrolyzed sludge in varying degrees,but high concentration of melanoidin could weaken the effect of ammonia nitrogen and VFAs on anaerobic methanogenic production,thus reducing the inhibition of anaerobic digestion of hydrolyzed sludge.High throughput sequencing technology was used to study the microbial population characteristics of thermolysis sludge anaerobic digestion system with different melanoidin content.The results showed that Proteobacteria and Bacteroidetes were the dominant phylum in the anaerobic digestion system of hydrolyzed sludge with different melanoidin content at phylum level.At the family level,hydrolysates such as Flavobacterium,Trueperaceae and Porphyromonadaceae and acidogenic bacteria such as Comamonadaceae,Xanthomonasdaceae and Trueperaceae exist in the anaerobic digestion system of hydrolyzed sludge with different melanoidin content.However,there were significant differences in relative abundance among different families.For archaea,Methanothrix and Methanospirillum were the dominant archaea in hydrolyzed sludge anaerobic digestion system with different melanoidin content at genus level,which was related to their strong tolerance to melanoidin.Methanamassiliicoccus is the unique dominant genus in the anaerobic digestion system of high content of melanoidin sludge,which may be the main reason for the weakening of inhibition of methanogenic process in the anaerobic digestion system of high content of melanoidin sludge.