Anaerobic Digestion Of Water Hyacinth With Waste Activated Sludge And Zero-valent Iron

Anaerobic digestion(AD)of water hyacinth to achieve its energy utilization is a hot topic in recent years.In the practical engineering application of AD,adopting a higher organic load(OLR)can increase the utilization rate of equipment and save the cost.However,as OLR exceeds a threshold value,organic acids may accumulate,causing the inhibition of the methanogenic process.Therefore,effectively alleviating the accumulation of organic acids under high OLR is of great significance to promote AD of water hyacinth.In this paper,the effects of adding waste activated sludge alone(Series 1),zero-valent iron(ZVI)alone(Series 2)and both(Series 3)on AD of water hyacinth were studied.In series 1,five kinds of waste activated sludge and water hyacinth ratio of 4: 0: 3: 1: 2: 2: 1:3 and 0: 4 were set up.The effects of different mixing ratios on AD of water hyacinth were discussed.The changes of microbial flora in AD system of water hyacinth were analyzed by high throughput sequencing.In series 2,four groups of different ZVI dosages(0,0.12,0.36 and 0.6 g/g-VSS)were set up.The effects of adding ZVI on hydrolysis,acidification and methane production were discussed.The effect of ZVI on microorganism in AD system of water hyacinth was analyzed.Based on the optimal excess sludge ratio obtained from series 1,four groups of different ZVI dosages(0,0.12,0.36 and 0.6 g/g-VSS)were set up,and the effects of ZVI on AD of water hyacinth and waste activated sludge were studied.The changes of microbes in the AD system were analyzed by pyrophosphate high-throughput sequencing.The main results were as follows:(1)The results of series 1 experiment showed that when the mixture ratio of waste activated sludge and water hyacinth was 1:3,the methane accumulation yield was the highest,which increased 67.7% compared with water hyacinth alone.The synergistic effect was the most obvious under 3:1 mixing condition,and the actual value of methane yield increased by 23.4% than the theoretical value.Microbial analysis showed that the addition of waste activated sludge could increase the diversity of microbial colonies and change the dominant microbial flora in the digestive system,the sytrophonomous and methanoculleus formed mutual metabolism.Thus,the digestibility of water hyacinth is improved.(2)The results of series 2 experiments showed that the optimum dosage of zero valent iron was 0.36 g/g-VSS.The addition of ZVI promoted the hydrolysis and acidification process,the cumulative methane production increased 36.8%,the TSS removal rate increased from 22.18% to 25%,the VSS removal rate increased from 27.34% to 31.65%,respectively,and the partial pressure of hydrogen in the AD system decreased.The relative abundance of acidogenic bacteria,sphaerochaeta and methanosaeta were increased.(3)The results of series 3 experiments show that the addition of ZVI has no obvious effect on hydrolysis and acidification,but can promote methanogenesis.Under the optimum dosage of 0.12 g/g-VSS,the cumulative methane production increased 19.667%,the removal rate of TSS increased from 15.35% to 17.34%,the removal rate of VSS increased from 23.83% to 25.49%,respectively,and the relative abundance of sphaerochaeta and methansarcina were increased with the addition of ZVI.In conclusion,the mixed AD of excess sludge and water hyacinth can promote hydrolysis and acidification by balancing raw material nutrition,enriching microbial diversity and mitigating system acidification.At the same time reducing the redox potential and hydrogen partial pressure of the system can promote the propionic acid decomposition.Adding waste activated sludge and adding metal ZVI is an effective way to promote anaerobic digestion of water hyacinth.