Research On Nitrogen Retention And Emission Reduction Effects Of Composting-vermicomposting Co-composting Of Pig Manure

Given the challenges posed by the rapid development of intensive and large-scale livestock farming,it is important to effectively treat the manure generated by these operations.Traditional aerobic composting has its drawbacks,including high nitrogen loss and large greenhouse gas emissions during the composting process,which contribute significantly to global warming.In recent years,vermicomposting has emerged as a simple,economic,and environmentally efficient method for treating livestock and poultry manure.However,the prevalence of pathogenic microorganisms and roundworm eggs in common vermicomposting poses a significant challenge.To address this challenge,this study improved on previous research by developing a composting-vermicomposting co-composting method for pig manure treatment.The study aimed to investigate the effects of this method on nitrogen retention and emission reduction of compost.Three treatment groups were set up,namely,AC(Aerobic composting),V(Vermicomposting),and CV(Composting-vermicomposting co-composting),to evaluate the composting effect,nitrogen retention and emission reduction effect,and mechanism of composting-vermicomposting co-composting of swine manure.The results of the study are as follows:(1)The composting-vermicomposting co-composting is an effective method for safely treating compost.Both the AC and CV groups experienced high temperatures(>55℃)for more than 5 days,which meets the standards for sanitary treatment.After composting,the number of fecal coliforms in the V and CV group’s compost products were 34 and 3,respectively,and the mortality rates of Ascaris eggs were 86.58%and 98.18%,all of which meet the harmless organic fertilizer standards of NY/T 525-2021.Moreover,the CV group’s fecal coliform count was significantly lower than that of the V group(P<0.05),and the CV group’s Ascaris egg mortality rate was significantly higher than that of the V group(P<0.05).(2)The composting-vermicomposting co-composting is a useful technique for speeding up the compost maturation process and improving the quality of compost products.After 49days of composting,the germination index(GI)of seeds in the AC,V,and CV groups were116.88%,133.59%,and 168.10%,respectively,which all meet the maturation standards.The GI in the CV group was significantly higher than that in the other treatment groups(P<0.05).Additionally,the C/N ratio in the CV group(10.90)was significantly lower than that of the AC(14.98)and V groups(12.10)(P<0.05),while the humification index in the CV group(4.44%)was significantly higher than that in the AC(2.94%)and V groups(3.80%)(P<0.05).(3)The composting-vermicomposting co-composting method was found to increase the accumulation of total phosphorus(TP)in the compost.At the end of composting,the highest TP content was 19.02 g/kg in the CV group.(4)The composting-vermicomposting co-composting was found to be beneficial for nitrogen retention.At the end of composting,the accumulated NH3 emission was significantly lower than that of other treatment groups(P<0.05),which effectively reduced NH3 emission and N loss.The most significant effect on ammonium nitrogen(NH4~+-N)fixation and nitrate nitrogen(NO3~--N)accumulation(P<0.05),total nitrogen(TN)content was significantly higher than that of the AC and V groups(P<0.05),and the lowest absolute N loss rate was-25.87%.(5)The composting-vermicomposting co-composting was found to effectively promote the degradation of organic matter,reduce CO2 and CH4 emissions during composting,and slow down the increase of N2O emissions caused by vermicomposting.At the end of composting,the combined greenhouse effect CO2 equivalent of CV group was 66.799 g/kg,ranked as V>AC>CV.Compared with the single treatment group,the emission reduction was 15.06%and 24.18%,respectively.Therefore,the composting-vermicomposting co-composting treatment reduced the contribution to the greenhouse effect.(6)The composting-vermicomposting co-composting has the ability to mitigate the decline in microbial functional gene abundance caused by single vermicomposting,while increasing the abundance of microbial functional genes associated with carbon sequestration and nitrogen cycling.This method not only enhances the presence of composting nitrification genes(amo A,amo B)and denitrification genes(nir S,nir K,nor B,nos Z),but also significantly augments the levels of NH4~+-N and NO3~--N(P<0.05),effectively reducing N2O emissions.By promoting the expression of carbon sequestration genes(pcc A,acl B,acs A,and acs B),it is possible to reduce CO2 emissions.Furthermore,decreasing the abundance of mcr A genes and increasing the prevalence of pmo A genes result in a reduction in CH4emissions.In summary,the composting-vermicomposting co-composting treatment of swine manure can effectively achieve harmless composting,reduce greenhouse gas emissions,and enhance the quality and nitrogen retention of compost.This method also promotes organic matter degradation and increases the abundance of functional genes of microorganisms related to carbon sequestration and nitrogen cycling.Therefore,the composting-vermicomposting co-composting treatment has significant potential for broad application.