Influence Mechanism Of Temperature On Methane-producing From Treatment Of Sugarcane Vinasse Wastewater In Fixed Bed Reactor

Organic wastewater from the processing of agricultural products possesses very high chemical requirements and total organic carbon,which can cause serious pollution to natural water.Among them,sugarcane vinasse wastewater is the most type of organic wastewater.Large quantities of vinasse wastewater are discharged with rich organic matter,which can be used as a resource for energy utilization through anaerobic fermentation.The anaerobic fixed-bed reactor can effectively treat sugarcane molasses wastewater and produce methane.Temperature is one of the key factors that affect the anaerobic fermentation process.However,the mechanism of the effect of temperature on the methane production in the treatment of molasses wastewater by fixed-bed reactors is not yet clear.In practical projects,there is no high efficient technology of anaerobic fermentation using vinasse wastewater at different temperatures.In view of the above problems,using vinasse wastewater as raw material,enriched acclimating of methane-generating and non-traditional anaerobic sludge for reactor start-up was done at high temperature(55℃),moderate temperature(35℃),low temperature(15℃).The effects of moderate and low temperature anaerobic sludge storage and high temperature start-up process on the subsequent moderate temperature anaerobic fermentation in fixed-bed reactors were studied.The influence of organic load promotion of vinasse wastewater at the low and moderate temperature on the methane production efficiency and microbial succession was investigated.The co-fermentation efficiency and microbial community characteristics of organic wastewater and dry straw at moderate and high temperature were studied.The effects of different aerobic exposed time for straw silage on methane production potential at moderate temperature.(1)In order to start the reactor efficiently,the original sludge of non-anaerobic sludge from different sources was selected as the source of microorganisms.Molasses wastewater was used as raw material and acclimated at three temperatures of 15℃,35℃,and 55 ℃.Along with acclimation carried out,the methanogenic capacity of the active sludge and pond sludge was changed higher,and their production capacity even higher than the anaerobic sludge,so the domestication of active sludge and pond sludge is completely used as biogas project started seed anaerobic sludge.Acclimation to the high temperature to some extent increased the efficiency of acclimation of sludge,but acclimation of the sludge at high temperatures did not show the ability to produce methane at low temperatures.Sludge acclimated at a higher temperature for the lower temperature methanogenic fermentation can significantly increase the methane production efficiency of the sludge.During the operation of biogas project,re-acclimation of the sludge by alternately increasing the operating temperature of 15-20℃ may increase the efficiency of the reactor operation.(2)The seed sludge stored at low and moderate temperatures was used to activate the fixed-bed reactor;the moderate temperature anaerobic fermentation was started at high temperature.Lack of balance in the microbial composition of cryopreserved sludge resulted in rancidity in the started medium-temperature reactor,and low temperature was not suitable for the storage of the anaerobic sludge in the start-up reactor.The pre-55℃ short-time high temperature start-up increased the diversity of microorganisms in the system and increased the efficiency of late-stage anaerobic fermentation.The pre-high-temperature start-up process also determined the composition and abundance of the microorganisms in the post-moderate fermentation.Streptococcaceae led to the accumulation of lactic acid,which contributed to the increase of methane yield.Thermotogaceae could survive in mesophilic fermentation system and symbiotic relationship with methanogenic bacteria,which played an important role in promoting the methanogenic process of the system.(3)The methane-producing potential of the anaerobic fixed-bed reactor at sub-optimal moderate temperature(15℃、20℃、25℃、35℃):under sub-optimal moderate temperature,organic load and temperature had significant interaction on methane production by anaerobic fermentation,and the effect of temperature on biogas production increased with the increase of organic load Increase.Temperature and bacterial abundance showed a significant positive linear relationship,but the impact on microbial metabolism is stronger than the impact on microbial abundance and diversity.There is a positive correlation between methane production and archaeal diversity.Together,temperature and organic load shape the microbial community niche.Methanosaetaceae is the major methanogen.The reactor volume was determined by a simplified mathematical simulation,the main influencing factors to determine the reactor volume,which is in reference for the design of the reactor.(4)We found the complementary effects of co-fermentation of two kinds of raw materials(dry straw,organic wastewater)in improving the fermentation efficiency and the stability of anaerobic fermentation system by setting dry straw,organic wastewater single fermentation and co-fermentation under the moderate and high temperature.Co-fermentation of molasses wastewater and rice straw with the same proportion significantly improve the methane production potential of both,especially at high temperature,the addition of cellulosic material to organic wastewater increases the diversity of microorganisms in the fermentation system,enhances the methane production capacity,and improve the fermentation system to withstand the impact of load capacity.Methane production from straw with molasses wastewater as fermentation medium prolongs the operation period of straw reactor during the process of increasing straw load,so as to form a fermentation process with low straw content and high methane output.The superposition effect of straw,wastewater and temperature determines the type,quantity and function of microorganisms in the system,which directly affects the operation efficiency and stability of the fermentation system.(5)Effects of aerobic exposure time of silage stored straw on potential methane production.straw silage aerobic exposure caused the consumption of soluble substances,the longer the exposure time,the more the methane production capacity decreased,so that in the temperature(37℃)fermentation system,the growth of fermentative bacteria was slow,the methanogen abundance was low and the methanogenic capacity of the fermentation system was decreased.The aerobic exposure caused the succession of Clostridia to Bacteroidia and Anaerolineae in the fermentation system of silage straw.The reduction of soluble organic matter in straw has led to an increase in the hydrogenotrophic methanogenic process in biogas fermentation systems.Aerobic exposure of straw significantly reduced the hydrolysis activity of the reaction system,reducing the degradation rate of cellulose hemicellulose,is not conducive to the system methanogenic process.