Microbial Pretreatment Enhanced The Transformation Of Cyanobacteria By Black Soldier Fly(Hermetia Illucens L.)

With the rapid development of social economy,a large number of pollutants are discharged into the natural environment,resulting in a series of environmental pollution problems such as water eutrophication.Survey data show that more than 75% of the lakes in China have been eutrophicated.Eutrophication in rivers and lakes can easily lead to the outbreak of cyanobacteria blooms,and it is difficult to effectively control them at present,so offshore treatment of cyanobacteria after salvage and dehydration is still the mainstream treatment method at present.Cyanobacteria sludge has the characteristics of high moisture content,rich organic matter content and poor biological stability,so it is urgent to find an effective way of resource utilization.Insect biotransformation represented by Hermetia illucens is a promising organic waste treatment technology,which can obtain insect protein and insect manure organic fertilizer while achieving reduction,but there are few reports on the treatment of cyanobacteria.In view of this,the black soldier fly was used to treat cyanobacteria mud in this paper.Firstly,the effect of rice husk as filler was investigated,and then microbial enhancement and biological pretreatment techniques were used to improve the growth performance and substrate transformation efficiency of black soldier fly.On this basis,the feeding residues were treated with aerobic composting in order to obtain high-quality organic fertilizer,so as to achieve full resource utilization.The main results of this paper are as follows:(1)When the pure algae was used as the substrate of the black soldier fly,the survival rate of the larva was only 29.70%,and the average wet weight of the worm was only 62.12 mg.The dry matter degradation rate and larval yield of algal mud were 25.72% and 72.92 mg/g(in terms of dry weight),respectively.Rice husk as a filler can reduce the moisture content of the substrate and increase the oxygen content,and significantly promote the growth,development and transformation efficiency of larvae by optimizing the addition ratio of rice husk and algae mud.When the addition ratio of algae mud to rice husk(dry weight)was 1: 1,the survival rate of larvae reached 78.12%,and the average wet weight and body length were 35.01 mg and 11.35 mm,respectively.The dry matter degradation rate and larval yield of algae mud were increased to 35.58% and 132.1 mg/g,respectively,and the reduction rates of crude protein and lignocellulose were 50.85% and 35.51%,respectively.In addition,compared with the control group(pure algae mud as substrate),the activities of β-glycosidase,protease and acid phosphatase in the mixed substrate group of algae mud and rice husk(the addition ratio was1:1)were significantly higher than those in the control group.The results showed that the higher growth activity of larvae could also enhance the biochemical activity in the substrate and promote the transformation of organic matter.(2)The intestinal protease activity and cellulase activity of black soldier fly larvae were significantly enhanced in the pretreatment group of Arthrobacter glassy + Bacillus subtilis.The average wet weight and body length of harvested larvae were 52.45 mg and 15.01 mm,respectively.The dry matter degradation rate of algae mud reached 44.58%,and the reduction rates of crude protein and lignocellulose reached 56.32% and 44.31%,respectively.Microbial pretreatment also significantly promoted the biochemical activity of substrate,and the activities of matrix β-glycosidase,protease and acid phosphatase in the whole biotransformation process were significantly higher than those in the control group.The structure of microflora in the intestinal tract of larvae in the microbial pretreatment group changed significantly,among which the most significant population belonged to Bacillus.Thus it can be seen that microbial pretreatment changed the intestinal population structure of black soldier fly larvae,strengthened the intestinal metabolic function,and effectively promoted the growth and substrate transformation of larvae.(3)The enzyme-assisted pretreatment process further enhanced the biotransformation efficiency of the black soldier fly,and the final 150 g dry matter of algae mud could reach 50.92%degradation rate after 15 days of biotransformation,and 19.52 g dry matter of larva could be harvested.The proportion of nutritional structure of black soldier fly larvae is balanced,the transfer amount of microcystins in larva is only 0.23%,the degree of enrichment is low,and has good feeding value and safety.The resource utilization of culture residue can be realized by aerobic composting process.Under the condition that the initial C/N ratio is 25,the nitrate nitrogen content,humus content,humic acid content and seed germination index can reach370.83 mg/kg,72.46 g/kg,48.08 g/kg and 90.55% respectively,and all the indexes of composting products meet the Chinese national agricultural organic fertilizer standard(NY525-2012).The whole process lasted about 30 days,while harvesting high value-added larval biomass and organic fertilizer,the reduction,harmless and resource utilization of algae mud were effectively realized.