Mechanism Of Additives On Aerobic Composting Process Of Pig Manure

Traditional composting technology presents some drawbacks such as low quality of final product,nitrogen loss,greenhouse gases emission and the low efficiency of organic matter humification.The addition of mineral and chemical additives could effectively improve the aerobic composting technology and reduce the secondary environmental pollution.However,adding the single additive still has some limitations of composting promotion;it is necessary to further study whether the compound additives could efficiently improve the composting process and reduce the potential environmental pollution.Additionally,considering the economic benefits and operability,searching more mineral additives and investigating their effect and mechanism on composting process are beneficial to the development of composting technology.Hence,in this study,the pig manure,sawdust and wheat straw were used as the raw materials,while the Ca-bentonite,medical stone,biochar,zeolite,wood vinegar and their mixtures were used as additives and subsequently conducted to(1)Comparison of biochar,zeolite and their mixture amendment for aiding organic matter transformation and nitrogen conservation during pig manure composting;(2)Combining biochar,zeolite and wood vinegar for composting of pig manure:the effect on greenhouse gas emission and nitrogen conservation;(3)Investigate the influences of Ca-bentonite on pig manure composting;(4)Study the effects of calcium bentonite on Zn and Cu mobility and their accumulation in vegetables growth in soil amended with compost during consecutive planting;(5)Study the mechanism of medical stone on organic matter transformation and nitrogen conservation during pig manure composting.The main results and conclusions are listed as below:(1)Compared to the control treatment,adding biochar(B),zeolite(Z)and their mixture(B+Z)could obviously improve the organic matter degradation and reduce the nitrogen loss.Meanwhile,compared to the B and Z treatments,the addition of B+Z could futher improve the organic matter humification and decrease the mobility of Cu and Zn.Additionally,adding the B,Z and B+Z could obviously decrease the NH3 and N2O emissions.And the higest mitigation of NH3(63.40%)and N2O(78.13%)was observed in B+Z added treatment.Comparison of organic matter transformation,nitrogen conservation and heavy metal(Cu and Zn)mobility indicated that the combined use of biochar and zeolite could be more useful for pig manure composting.(2)The addition of biochar(B),biochar+zeolite(B+Z)and biochar+zeolite+different amounts(0.5%,1.0%and 2.0%)of wood vinegar(B+Z+WV)could shorten(2-4 d)the thermophilic phase and improve the maturity of compost.Compared to the control,WV mixed with B and Z could reduce ammonia loss by 64.45~74.32%and decrease CO2,CH4,and N2O emissions by 33.90%~46.98%,50.39%~61.15%,and 79.51%~81.10%,respectively.Compared to the B and B+Z,the addition of WV could react with the NH3,improve the adsorbed capacity of B and Z,as well as inhibit the activity of nitrobacteria,and consequently decreased greenhouse gases and ammonia emissions in B+Z+WV added treatment.Meanwhile,the B+Z+2.0%WV presented the best performance of reducing the greenhouse gase emission and nitrogen loss.Based on the maturity indexes used,nitrogen conservation,and efficiency of GHG emissions reduction,the B+Z+2%WV is suggested for efficient PM composting.(3)After composting,the organic matter and dissolved organic carbon degradation rate of control was 8.69%and 49.11%,while the degradation rate of Ca-bentonite added treatments was 5.96%~11.52%and 55.32%~62.93%.Results indicated that the addition of Ca-bentonite could promote the dissolved organic carbon and organic matter degradation,and the 10%Ca-bentonite presented the highest degradation.Meanwhile,the addition of Ca-bentonite could reduce the content of NO3~--N and NH4~+-N,and decrease the mobility of Cu and Zn through physical adsorbtion and complextion.With increasing the Ca-bentonite dosage,the DTPA-Cu and Zn were reduced by 4.43%~5.80%and 12.42%~16.89%.(4)The results showed that the addition of Ca-bentonite blended composts(CBC)increased the biomass and chlorophyll content of pakchoi,and the maximum overall yield was found in 7.5%CBC treatment(12.89 g).Additionally,the Ca-bentonite amendments showed a positive effect on restraining the DTPA-Zn mobilization in pakchoi and Chinese cabbage.Furthermore,DTPA extraction results showed significantly higher Cu and Zn contents in compost–soil mixture,but its availability for the grown plant was not confirmed during the consecutive planting,because of the consecutive decrease heavy metals contents in crops.(5)The results showed that medical stone amendment obviously promoted the organic waste degradation and accelerated the temperature increase as well as enhanced the compost maturity.Compared to the control,the degradation rate of organic matter in medical stone added treatments increased by 21.82%-43.70%.In addition,the humic acid in medical stone amended treatments increased by 5.58%~9.75%as compared to control,which could be due to the addition of medical stone could improve the lignocellulose,protein-like materials,lipid as well as polysaccharides decomposition.Adding the medical stone could reduce 27.9%-48.8%NH3 emission by decreasing the pH of compost and adsopbing the NH3,and the lowest ammonia emission was observed in 10%medical stone added treatment.The addition of medical stone could decrease 46.6%-85.3%N2O emission and improve the transformation from the NO2~--N to NO3~--N.The mobility of Cu and Zn in compost could be decreased by the physical adsorption and cation exchange of medicals.Meanwhile,the higher content of humic acid in medical stone could also promote the passivation of Cu and Zn in compost.The application of medical stone blended compost could obviously increase the biomass and chlorophyll content of pakchoi,and the 10%medical stone blended compost presented the highest biomass(8.16 g/pot)and chlorophyll content(36.88 SPAD-unit).