Study Of Anaerobic Co-digestion Of Sludge Straw

In China,about 700 million tons of waste straw and 30 million tons of sludge are produced each year.Most of the straw is directly discarded or incinerated,which causes great environmental pollution.A large amount of sludge can not be effectively treated and become serious environmental issues.Anaerobic digestion is an effective method for sludge treatment,which can also generate energy at the same time.Therefore,it is of great significance to study sludge anaerobic digestion.Ultrasonic lye pretreated straw and municipal sludge as substrate for anaerobic digestion of biogas production.First,the batch test was designed by response surface methodology to determine three parameters,TS concentration,pretreatment alkali concentration and sludge stalk ratio.The advantages of pretreatment and co-digestion as well as existing problems were investigated at 30% and 50% inoculation rates.When the inoculation rate is 30%,the pretreated straw can easily lead to acidification and stop the gas production.Using sodium bicarbonate solution to adjust the pH can recover the gas production to a certain extent,but the gas production effect can not be optimized.When the inoculation rate was 50%,the pretreatment mixed substrate unit VS methane output reached 143.38ml/gVS,which increased 372.73% compared with the single sludge substrate and increased 172.02 compared with the non-pretreated mixed substrate %.Sodium ions above 2000 mg/L and lower pH will both lead to the accumulation of propionic acid,whereas n-butyric acid will only accumulate due to lower pH,with little effect on sodium ions.According to the batch test to determine the parameters of feed ingredients,semi-continuous flow domestication and operation of the volume of 5L single-phase anaerobic reactor.After the reactor was stable,SRT was 20 days,16.7 days,12.5 days,10 days,8.3 days,7.1 days,6.25 days,5 days each running a cycle.The influence of SRT on the semi-continuous anaerobic reactor was studied by monitoring gas production,gas composition,SCOD,ammonia nitrogen,alkalinity,pH,redox potential and other indicators.The experimental results show that the semi-continuous flow reactor works best when SRT is about 8 days,with high gas production efficiency and lowest SCOD.As the SRT decreased,the load increased,the alkalinity and ammonia nitrogen decreased,the redox potential increased,and the VFA content remained almost unchanged.In order to understand the effect of added enzymes on the anaerobic digestionprocess using sludge as substrate,batch experiments were carried out in anaerobic digestion before adding cellulase,hemicellulase,neutral protease for anaerobic digestion.The results showed that cellulase and hemicellulase improved the digestion process,and the amount of methanogenic units per unit VS increased by 43.28% and17.05% respectively compared with the blank group without enzyme addition.Neutral protease was added to the reactor,due to dosage problems,microbial extracellular polymers were destroyed,resulting in gas production worse than the blank group.At the same time,another batch of experiments showed that during the process of anaerobic digestion under low load,the gas production was only proportional to the carbon source content in the substrate,and the change of nitrogen source would not affect the gas production.Therefore,the addition of neutral protease to enhance the anaerobic digestion gas production is not obvious.After anaerobic digestion,the increase of cellulose enzyme in anaerobic digestion was also not obvious.