Study On Degradation Of Straw Waste By Yellow Mealworm And Sorption Of Heavy Metal By Biochar Made From Worm Frass

Straw is rich in organic carbon,which is an important biomass energy.However,it is not biodegradable and difficult to be utilized.Yellow mealworm is a resource insect with extremely high economic value,and can degrade organic waste.In this regard,this paper proposes a straw recycling method of "the mealworms decompose straws-insect feces to prepare biochar for heavy metals’ sorption ".The main research contents and results are as follows:(1)Wheat bran(WB)and rice straw(RS),corn straw(CS),wheat straw(WS),rice husk(RH)and rice bran(RB)were selected and fed to yellow mealworm according to different nutritional formulas.The results showed that yellow mealworm showed a strong feeding preference to RS,CS and RB,and the total food intake reached 7.80～10.66 g(non-nutrition group)and 20.69～23.77 g(nutrition group)within 48 days.At the end of the experiment,the weight loss of the two groups was 17.82～28.62% and 8.47～22.13%,respectively;the survival rate of worms feeding on RS,RB and CS in the non-nutritive group was 56.67～69.72%,and the nutrition group increased 21.92～57.83%.This shows that mealworms can survive under the condition of straw as the main food,and the addition of appropriate nutrients is beneficial to improve the biological activity of larvae.(2)Characterization of straw and insect feces showed that compared with the raw materials,the C/H of insect feces decreased,the functional groups such as hydroxyl group and methyl group increased,and the content of benzene ring groups decreased,proving that the complex structure of straw was decomposed into small molecular substances.The degradation rates of yellow mealworm on lignocellulose in RS,CS,WS and RB reached 23.10～51.42%(hemicellulose),39.88～55%(cellulose),40.04～53.27%(lignin)respectively.In addition,comparing the sequencing results of the intestinal flora of yellow mealworm in this experiment with the published lignocellulose-degrading strains,it is believed that there are probably a large number of lignocellulose-degrading bacteria in the intestinal tract of the mealworm.(3)The straw and insect feces were decomposed into biochar for the adsorption of heavy metals.The results show that the adsorption capacity of insect feces-biochar is better than straw-biochar,of which FRSBC(biochar from yellow mealworm feces fed on rice straw)has the best effect,and the removal capacity of Pb2+,Cu2+,Cd2+,Cr6+,Zn2+ reaches 188.20±4.71,49.56±1.49,58.94±2.95,18.60±0.93 and 41.98±2.01 mg/g.Compared with RSBC(biochar from rice straw),the adsorption performance is improved by 24.34～67.65%.In addition,experiments have shown that the adsorption mechanism of biochar to heavy metal ions mainly includes electrostatic interaction,ion exchange,hydrogen bonding,electrostatic outer layer complexation and co-precipitation/inner layer complexation.(4)Taking FRSBC as the research object,the life cycle assessment method was used to analyze the environmental impact of the biochar preparation process in this experiment.The results showed that the two unit processes of insect feces collection and pyrolysis carbonization were the main environmental impact steps.The main reason for this phenomenon is the high power consumption of artificial incubators and tube furnaces;the order of the system’s environmental impact is eutrophication > photochemical ozone synthesis > acidification > greenhouse effect > non-renewable resource consumption>biological toxicity;Suggestions for improvement are put forward,such as replacing the artificial incubator with a hot steam humidifier,changing the heating rate,shortening the carbonization time,and choosing cleaner electrical energy.