Study On Composting Of Green Waste And The Improvement Effect Of Products On Coastal Saline Soil

Green waste is generated in large quantities with the development of urban greening,and it has become the second largest municipal solid waste after domestic garbage.Because it is rich in organic components,it can be used as a soil remediation substrate.In recent years,due to acceleration of land reclamation,the ecological environment has deteriorated,most of the particles that make up the soil are silt and clay,salt accumulates in the soil,the soil nutrients have become poor,soil biological functions have lost,forming a severe saline-soil environment.In view of this,in order to solve the problem of the harsh ecological environment in the muddy coastal areas,the application effects of green waste compost products on improving the physical,chemical and biological properties of soil were explored.In this study,green waste(grass,branches)was used as the main material,through the changes in the physical and chemical properties of different raw material ratios of grass chips and wood chips during the composting process(single grass chips,grass-to-wood ratio 1:3,grass-to-wood ratio 1:1,and grass-to-wood ratio 3:1,single wood chips),the maturity and microbial diversity structure after composting were analyzed,and the products were comprehensively evaluated.On this basis,the compost products were applied to indoor soil column experiment and field experiment,suitable improvement methods were screened,the laws of soil water and salt transport,basic physical and chemical properties and soil enzyme activity changes were explored.The Illumina sequencing technology was used to study the influence of compost products on the bacterial and fungal community structure in the coastal saline soil environment,providing theoretical and practical basis for the efficient recycling of green waste and the construction of the silt coastal ecological environment.1.The changes of physical and chemical properties during the composting process of grass scraps and wood chips alone or in combination showed that the total carbon and fulvic acid content gradually decreased during the composting process,and the total nitrogen,humus and humic acid content gradually increased.With the increase of the proportion of wood chips,the faster the temperature of the pile decreased,the shorter the high temperature maintained.With the increase of the proportion of grass cuttings,the degradation rate of lignocellulose gradually increased,and it was positively correlated with the proportion of grass cuttings.The treatment with a volume ratio of grass to wood chips of 3:1 had the best aerobic composting effect,with the highest degradation rate of lignocellulose and the highest total nitrogen and humus contents in the pile.The treatment with the volume ratio of grass chips to wood chips of 3:1 had the best composting effect,and the degradation rate of cellulose,hemicellulose and lignin was the highest,respectively 45.32%,12.97%and 45.57%;the humus content in the pile reached 27.53%,an increase of 15.76%over the initial stage of composting.2.Studies on various physical and chemical factors,plant growth characteristics,microbial diversity and other indicators of different green waste compost products showed that:Proteobacteria,Chloroflexi,Bacteroidetes,Acidobacteria in the bacteria from the compost products of green waste belong to the dominant phylum;Agaricaceae,Microascaceae were the dominant family.The C/N ratio,p H,and EC values were the main factors affecting the abundance of bacterial and fungal populations.Humus,germination index(GI),humus index(HI),and C/N were selected as indicators,and comprehensive evaluation using gray cluster analysis showed that the G3W1(grass-wood ratio 3:1)group was highly rotted,the G4W0(single grass-crust)group and G2W2(grass-wood ratio 2:2)group were moderately rotted,G1W3(grass to wood ratio 1:3)and G0W4(single sawdust)were low rotted.3.Research on the indoor soil column experiment of the compost product of green waste shows that compost products have the effects of increasing the water infiltration rate,lowering the soil p H,salt content and sodium adsorption ratio.However,the addition of compost products will cause the loss of Ca²⁺and K⁺during the leaching process,and the addition of the inorganic modifier bentonite can effectively alleviate this problem.The mixed application ratio of 3%(wt./wt.)has the best effect.4.Field experiments on compost products of green wastes show that mixing compost products in the coastal saline soil subsurface pipe drainage can accelerate the leaching of soil salt,reduce salt content,and improve soil physical and chemical properties.The mixed application of compost products and bentonite has a more significant effect on improving soil nutrients,soil enzymes,and microbial biomass carbon and nitrogen.Soil organic matter content was 2.11 times that of CK;urease,invertase and dehydrogenase were 10.1 times,9.0 times and 4.5 times that of CK;soil microbial biomass carbon and nitrogen increased by 24.8%and 78.1%respectively compared with CK.5.The application of compost products to the soil increases the relative abundance of bacteria and fungi.The application of compost products alone or mixed bentonite can significantly increase the alpha diversity of bacterial communities.The treatment applied to green waste composting had higher Proteobacteria,Actinobacteria and Acidobacteria abundances.Among the fungi,Chaetomiaceae,Lasiosphaeriaceae and Agaricaceae had higher abundance.The mixed application of compost products and bentonite was different from that of single application.The relative abundance of sphingomonadaceae and Gemmatimonadaceae was higher than that in other treatment,and the relative abundance of Microascaceae and Nectriaceae in fungi was higher than that in other treatment.Combining the principal component analysis and the comprehensive evaluation results of soil improvement,the optimal application rate was to mix soil with 3%fermented green waste and3%bentonite.