Experimental Study On Biogas Production From Anaerobic Co-digestion Of Water Hyacinth And Sludge

Sludge is rich in organic matter,and water hyacinth contains more cellulose,both of which can be used as substrates for anaerobic digestion.The anaerobic co-digestion of sludge and water hyacinth can overcome the defects of their separate digestion,realize the stabilization of sludge,dilute the potential toxic compounds,increase the load of biodegradable organic matter,improve the efficiency of digestion and gas production,and reduce the harm of water hyacinth to the ecosystem,as well as the realization of the resource utilization of sludge and water hyacinth.In this study,dewatered sludge and water hyacinth were used as experimental materials,the effects of solid content,different forms of water hyacinth,organic loading rate and thermal treatment on anaerobic digestion were investigated by batch experiment and semi continuous anaerobic digestion reactor tests.A batch test was used to study the effect of different solids content on anaerobic digestion of sludge.The result showed that TS methane production rate with solid content of 6%and 8%were the highest,which were 92.02 m L/g TS and 94.33 mL/g TS,respectively.Under the condition of solid content of 6%and 8%,different forms of water hyacinth and sludge were mixed and combined for anaerobic digestion experiments.The cumulative methane production,the peak of daily methane production,the TS methane yield and the degradation rate of TS and VS were the highest with the co-digestion of sludge and water hyacinth residue.When the solid content of the system is 8%,the cumulative methane production amount of the water hyacinth residue is 3892 m L,and the TS methane yield of the solid content of 8%is obviously higher than that of the solid content of 6%.Then,a semi continuous anaerobic digestion reactor was used to study the gas production performance and system stability of the anaerobic co-digestion of sludge and water hyacinth residue under different organic loading conditions.The results showed that with the increase of organic load,the daily methane production and the daily methane production are on the rise.When the organic load is 2.12 g VS/?L�d?,the methane yield is the highest,the system is relatively stable,and the anaerobic digestion has the best methane production performance.Under different thermal treatment temperatures and time,the effect of thermal treatment on the characteristics of the sludge was studied.The results show that when the thermal treatment temperature is 70?,the dissolution rate of SCOD is the most significant.When the treatment temperature exceeds 70?,the SCOD concentration slows down.Finally,the sludge was treated at 70�C,60 min,and 90�C for 60 min to investigate the effect of sludge thermal treatment on semi-continuous anaerobic digestion of sludge and water hyacinth residue in gas production,system stability,and microbial community.The results showed that the VFA and ammonia nitrogen in the two reactors were at a low level,and no accumulation of VFA and ammonia nitrogen was formed.The thermal treatment can improve the digestibility of the system.The average daily biogas production and the average daily methane production of the R2 reactor?thermal treatment at 90�C?are 11.57%and 16.92%higher than those of the R1reactor?thermal treatment at 70�C?,respectively.The results of 16 rRNA analysis showed that the microbial diversity of the initial material was rich.Along with the anaerobic digestion,the abundance of the bacteria decreased.Methanosaeta is the dominant genus in the digestion process,accounting for an increase from 42.42%?raw material?to 76.10%?70�C?and 74.36%?90�C?.The relative abundance of acetic acid-based methanogens is much higher than that of hydrogen-type methanogens.Therefore,the main pathway for CH₄ production in reactors is the decomposition of acetic acid.