Study On The Aerobic Composting Characteristics Of Cyanobacteria/Cyanobacteria Biochar With Pig Manure

Aerobic composting is an effective means to achieve large-scale resource utilization of organic solid waste.Cyanobacteria have high water content and also have seasonal outbreaks,so direct composting has great limitations in terms of production and product quality.In addition,cyanobacteria are often used to make biochar in the process of resource utilization,but at present,the application of cyanobacterial biochar is mainly focused on water treatment and soil remediation,and there are few reports on the application in optimizing aerobic composting technology for livestock and poultry manure.Therefore,in this study,two composting systems were constructed,one using cyanobacteria and pig manure co-composting,and the other using cyanobacterial biochar as a conditioning agent and pig manure co-composting,and firstly,the effects of cyanobacteria/cyanobacteria biochar and pig manure co-composting on the basic physical and chemical properties,gas emission,organic matter degradation,nutrient conversion and humus composition of the compost were investigated.Secondly,the feasibility of co-composting and cyanobacterial biochar composting was scientifically evaluated with the help of mathematical models and the final compost product parameters and gas emissions.Finally,the microbiological mechanisms of biochar composting were revealed using high-throughput sequencing technology.This study can provide reference ideas for the resource utilization of cyanobacteria and its industrial chain extension.The main results of the study are as follows:（1）Co-composting of cyanobacteria with pig manure increased the global warming potential（GWP）and promoted the emission of methane（CH₄）during composting,but reduced ammonia（NH₃）emission by 1.79%to 14.14%and nitrous oxide（N₂O）emission by 5.97%to17.83%.In addition,co-composting increased the total Kjeldahl nitrogen（TKN）content of the composted product.5%and 10%cyanobacteria composting promoted the degradation of organic matter（OM）and fulvic acid（FA）,and when the cyanobacteria mixture was too large（20%）,it significantly inhibited the degradation of OM and FA during composting,and reduced the total nutrient content of the composted product.At the end of the composting process,the ratio of humic acid to fulvic acid（HA/FA）was 10%（1.75）>5%（1.70）>0%（1.68）>20%（1.34）for each treatment group,which indicated that the appropriate amount of cyanobacteria could improve compost maturation.Grey correlation analysis showed that only20%of the cyanobacteria and pig manure aerobic composting products were not decomposed,and the rest of the groups were basically decomposed.10%of the cyanobacteria and pig manure composting is feasible,but in terms of greenhouse gas emissions,the cyanobacteria and pig manure aerobic composting method need to be further optimized.（2）Addition of cyanobacteria biochar to pig manure compost reduced GWP by reducing N₂O（29.38%-39.78%）,CH₄（52.76%-69.15%）,and NH₃（12.03%-31.81%）emissions.The addition of biochar contributed to the rapid initiation of the composting reaction and promoted the degradation of OM and DOC by extending the days of high temperature period,with OM degradation rates in descending order of 2.5%>5%>10%>0%.Biochar promoted the degradation of OM and also promoted the emission of CO₂（9.6%～28.8%）.Compared to the control group,biochar promoted the conversion of NH₄⁺-N to NO₃^--N,which increased the NO₃^--N content in the compost product by 89.28%～185.71%.The addition of biochar facilitated nutrient retention,which increased the total nutrient content by 1.86%～8.85%.In addition,biochar treatment facilitated the production of huminic acid（HA）.At the end of composting,10%biochar had the highest HA/FA of 2.44,while the rest were 5%（2.18）,2.5%（2.01）,and 0%（1.79）in that order.0%and 2.5%of the treatment groups were well decomposed,and 5%and 10%were fully decomposed.Biochar,as an additive to pig manure composting,has a balanced role in regulating greenhouse gas emission reduction,improving nutrient retention and promoting pile decay,and 10%biochar addition is the best.（3）The addition of biochar facilitates the enrichment of dominant microorganisms at the phylum（Proteobacteria,Bacteroidetes,Ascomycota,Basidiomycota）and genus（Longispora,Coprinopsis）levels by optimizing the substrate conditions for rapid bacterial and fungal succession during the composting process,forming a microbial community structure that helps to promote decay and reduce emissions,and adjusting the C and N metabolic functions of the community,which is of great importance in improving the quality of compost.