The Research On Nitrogen Forms And Conversion Efficiency Of Agricultural Organic Wastes By Black Soldier Fly

With the rapid development of planting and breeding industry,a large number of agricultural organic wastes have been produced,resulting in waste of resources and increasingly serious environmental pollution.The problem of nitrogen pollution is particularly prominent.Excessive nitrogen emissions can cause many harms to the environment,such as the reduction of biodiversity in the ecosystem,soil acidification,and lake eutrophication.At present,there are methods of utilization of waste as resource,but which still exist some problems such as low conversion efficiency,long cycle and so on,and in this process,organic nitrogen is converted into inorganic nitrogen,and a large number of nitrogen-containing gases are produced,which become a new source of air pollution.While black soldier fly larvae（BSFL）can efficiently transform agricultural waste,realize the transformation of nitrogen to insect protein,which is considered to have great development and application potential.However,how does BSFL transform organic nitrogen into protein?What are the differences in the transformation and utilization capacity of different nitrogen forms?Can the addition of small molecule active substances further promote the accumulation of insect protein and inhibit the emission of nitrogen-containing gases（such as NH₃）?The answers to these questions are beneficial to deepen the understanding of the internal mechanism of efficient transformation of agricultural waste by BSFL,and promote the continuous improvement of the development and application technology of BSFL.However,relevant studies are still lacking.This study tried to explore the practical system of BSFL transformation,the variation of nitrogen form in artificial feed system,and take lactic acid additives to decrease ammonia to reduce nitrogen pollution.It was analyzed and determined from three aspects:gas,insect and substrate.The main results are as follows:1.The effect of BSFL on the changes of nitrogen forms during the conversion of chicken manureThe results demonstrated that the addition of BSFL could promote the mineralization of organic nitrogen in chicken manure into ammonium nitrogen.Compared with the control group（without BSFL）,the decomposition rate of organic nitrogen in the substrate increased by 15.1%,and the content of ammonium nitrogen in the substrate was higher than that in the control group.In addition,in the control group of the nitrogen reduction（initial nitrogen content-nitrogen content in residue）,92.35±8.84%was converted to ammonia emission,while the proportion of ammonia emission in the BSFL treatment group was significantly reduced to 64.64±0.26%,and 23.37±0.04%nitrogen was converted to insect substance.Therefore,BSFL promote the mineralization of organic nitrogen in chicken manure,and transfer available nitrogen to the BSFL to inhibit ammonia emission.2.Study on the change of nitrogen forms during the transformation of different nitrogen sources（organic nitrogen and inorganic nitrogen）by BSFLThe results showed that different kinds of nitrogen sources had significant effects on the growth of BSFL.Except that sodium nitrite exactly inhibited the growth of BSFL（survival rate 11.88%）,there was no obvious difference in survival rate among the remaining treatment groups（P>0.05）.Control,Na NO₃,NH₄CL,Organic nitrogen X and soybean protein treatments,the fresh weights of single insects harvested were respectively 25.99±1.91 mg,41.25±3.03 mg,22.07±4.24 mg,62.04±3.09 mg,and 106.63±6.06 mg.The crude protein content and fat content of all treatmets were 18.10%-35.19%and 29.04%-59.29%respectively.The highest crude protein content and the highest fresh weight were obtained in the soybean protein treatment,followed by organic nitrogen X.The results showed that the BSFL could utilize multiple nitrogen sources.Organic nitrogen protein was the most favorable for the growth of BSFL,followed by unconventional organic nitrogen X.Although the proportion of BSFL-N in the inorganic nitrogen treatment group to the nitrogen reduction（initial nitrogen content-nitrogen content in the residue）was higher than that in the organic nitrogen treatments,the actual nitrogen content of BSFL was not significantly different from the control group.The actual nitrogen content of the organic nitrogen treatments were significantly higher than that of the control group,and it promoted the emission of ammonia.The ammonia release of the organic nitrogen X and soybean protein treatments accounted for 24.85±7.29%and 43.05±6.18%of the nitrogen reduction,respectively.In addition,the content of each inorganic nitrogen component in the inorganic nitrogen treatments was relatively stable,while the organic nitrogen of the substrate in the organic nitrogen treatments was easy to transform into inorganic nitrogen（especially ammonium nitrogen）.3.Study on adding lactic acid to ammonia reduction during BSFL transformationCompared with the control treatment,with the increase of lactic acid supplemental level,the cumulative NH₃ emissions of LA3（3 m L）,LA4（4 m L）and LA5（5 m L）treatments decrease by 56.15%,58.10%and 64.51%,respectively and the fresh weight of larvae increases by 40.88%,41.35%and 57.20%.In addition,the crude protein content of larvae in LA3,LA4 and LA5 groups increases by 16.50%,23.15%and 19.37%respectively by supplementing lactic acid and the amino acid composition of larvae does not change.Meanwhile,the crude fat content of larvae in LA3,LA4 and LA5 increases by 2.52%,1.80%and 8.63%,respectively.Our experiment shows that,in the process of BSFL translating into protein-rich materials,adding lactic acid can reduce the loss of N（especially the emissions of NH₃）and enhance the directed accumulation of N into larval protein.In conclusion,BSFL can utilize a variety of nitrogen,including non-protein nitrogen.Organic nitrogen protein is the most conducive to the synthesis of BSFL protein.Compared with inorganic nitrogen treatment,organic nitrogen in the substrate is easy to convert to inorganic nitrogen,especially ammonium nitrogen,which leads to the increase of ammonia emission.As an additive,lactic acid can significantly reduce ammonia emission and achieve clean recovery of nitrogen resources.The results of this research provide a theoretical basis for the continuous improvement of the development and application technology of BSFL.