Bio-conversion Of Cyanobacteria Waste By Black Soldier Fly(Hermetia Illucens)

Cyanobacterial blooms can severely impair the water quality of lakes and rivers,causing significant damage to aquatic ecosystems and posing a threat to human and animal health.The most common emergency response to cyanobacterial blooms is interception and salvage treatment.After the salvaged cyanobacteria slurry is dewatered through cyanobacteria-water separation stations,its moisture content decreases from 99% to 85-90%.However,if the resulting cyanobacteria waste is not properly disposed of,it can cause secondary pollution to the surrounding environment.Cyanobacteria waste is rich in organic matter,and its efficient utilization is a critical issue in the management of cyanobacterial blooms.One potential solution for utilizing cyanobacteria waste is to feed it to black soldier fly(Hermetia illucens)larvae(BSFL),which can convert organic waste into biomass rich in protein and lipids.BSFL can be used as animal feed or as a raw material for biodiesel production,while the separated residue is nutrient-rich and can serve as an ideal raw material for organic fertilizer production.In this study,a scheme for utilizing cyanobacteria waste by feeding BSFL with a substrate containing cyanobacteria waste was proposed.The effect of changes in the dry weight content of cyanobacteria waste in the feeding substrate on the growth and development of BSFL and the humification process of residues was investigated.The substrate containing cyanobacteria waste was pretreated using microbial agents and the effect of pretreatment agent type and duration on the feeding substrate and BSFL treatment was analyzed.Aerobic composting of wheat straw and residues was conducted to analyze the effect of wheat straw addition on the composting process.Overall,this study provides a novel solution for the resource utilization of cyanobacteria waste.The research contents and the main conclusions are as follows:(1)Feasibility study on bio-conversion of cyanobacteria waste by black soldier fly larvaeIn this chapter,The feasibility of bio-converting cyanobacteria waste into insect biomass using BSFL was investigated.The dry weight content of cyanobacteria waste(0-50%)was varied in the BSFL feeding substrate and larval growth and development,process efficiency,changes in organic matter in the substrate,and intestinal bacterial communities were analyzed.The results showed that increasing the content of cyanobacteria waste in the feeding substrate prolonged larval development time.For example,larvae fed with a substrate containing 50% cyanobacteria waste were 14 days behind in development compared to control group larvae.The content of cyanobacteria waste in the feeding substrate within 0-20% had no significant effect on larval length and weight.However,as the content of cyanobacteria waste increased further(20-50%),bio-conversion rate,larval length and weight,and crude protein content of larvae decreased significantly.At the same time,the presence of cyanobacteria waste in the feeding substrate reduced its degradation efficiency.Analysis of dissolved organic matter showed that increasing the content of cyanobacteria waste was not conducive to larval degradation of substrate into simple organic matter and further degradation into humic-like substances.In addition,the presence of cyanobacteria waste in the feeding substrate significantly affected the intestinal microbial communities of larvae.Compared to control,when the content of cyanobacteria waste in the substrate was 20%,the relative abundance of Firmicutes decreased from 92.43% to 81.24%,while the relative abundance of Proteobacteria increased from 4.10% to 8.75% and that of Bacteroidetes increased from 2.93% to 7.51%.In summary,our results suggest that BSFL can bio-convert cyanobacteria waste into insect biomass.However,to optimize larval growth and development as well as degradation of cyanobacteria waste,the content of cyanobacteria waste in the feeding substrate should be controlled at less than or equal to 30%.(2)Effect of microbial agents on biological conversion of cyanobacteria waste by black soldier fly larvaeIn this chapter,the effect of pretreating substrates containing cyanobacteria waste with microbial agents(Bacillus,Trichoderma reesei,and mixed agents)for 0,7,and 14 days on the biological conversion of cyanobacteria waste by BSFL was investigated.Changes in total solids(TS)and volatile solids(VS)contents before and after pretreatment were analyzed and BSFL were fed with pretreated substrates to evaluate their effects on larval growth and development,material degradation,and the humification process.The results showed that as pretreatment time increased,the VS content of substrates containing cyanobacteria waste decreased,and the VS content of BSFL fed with pretreated substrates also decreased.BSFL fed with substrates pretreated for 7 and 14 days had a development time of 8 days,which was 2 days earlier than those fed with substrates pretreated for 0 days.However,their final larval weight was lower than that of larvae fed with substrates pretreated for 0 days or control.Larvae fed with substrates pretreated for 0 days had slower weight gain in the early and middle stages but faster weight gain in the later stages of feeding and achieved a higher final weight.The crude lipids content of substrate pretreated for 14 days was the lowest,and the crude lipids content of its larvae was also lower than that of other treatment groups.In the early and middle stages of pretreatment,degradation of complex organic matter into simpler organic matter was the main process.In the later stages of pretreatment,simple organic matter was synthesized into humic-like substances.BSFL treatment after pretreatment significantly promoted degradation of organic matter and the humification process.The BSFL treatment group using substrate pretreated for 0 days with Trichoderma reesei had a higher material reduction rate and biological conversion rate compared to other treatment groups,achieving the best treatment effect in terms of material reduction and larval biomass conversion.(3)Effect of wheat straw content on aerobic composting of cyanobacteria waste residuesIn this chapter,the effect of wheat straw content on the aerobic composting of cyanobacteria waste residues for harmless and resource utilization was investigated.The ratio of cyanobacteria waste residues to wheat straw was adjusted and changes in p H,temperature,conductivity,carbon,and nitrogen during composting were analyzed.Spectroscopy was used to analyze changes in organic matter before and after composting to evaluate the maturity of compost products.At the end of composting,the total organic carbon(TOC)degradation amplitude of each treatment was 18.70-29.52%.The total Kjeldahl nitrogen(TKN)of compost products from treatments with added wheat straw increased by 12.42-34.09% compared to initial materials for composting,indicating that the addition of wheat straw can promote degradation of organic matter and reduce nitrogen loss.Spectroscopic analysis showed that under suitable conditions,aerobic composting can promote degradation of organic matter in cyanobacteria waste residues and wheat straw as well as generation of humic-like substances.The compost product from treatment T4 reached maturity standard and can be used as an organic fertilizer or soil amendment agent for application.This indicates that cyanobacteria waste residues need to be composted with sufficient conditioning agent to obtain an ideal compost product.