Effect Of The Urban Sewage Sludge Composts On Greenhouse Gas Emissions In Soil

In recent years,the urban wastewater treatment capacity in China has increased rapidly,and sludge production has increased rapidly.The annual sludge production has exceeded 43 miooion tons.The pressure of sludge treatment and disposal has been increasing,and its resource utilization has also become a research hotspot.The new environmental protection law and water pollution prevention and control action plan both emphasize the importance of sludge treatment and disposal.Sludge compost and land application is a sludge resource treatment and disposal method,but the secondary pollution problem has limited its wide application.Sludge compost will increase the heavy metal content when it is applied to soil.And emissions of the greenhouse gas can not be ignored.At present,more studies have been conducted on the problem of heavy metal pollution caused by land use of sludge,and studies on greenhouse gas emissions have been lacking.So,the effect of application of sewage sludge compost on the emission of greenhouse gas from soil was investigated by analyzing the dynamic characteristics and emission factor of CO₂,CH₄ and N₂O in soil after spiking two different composts?compost with biochar and compost without biochar?with varying fertilizing amount into soil.Screening treatments that are suitable for crop growth and that have relatively low soil carbon emissions.Based on this,the effects of different types of fertilizers?compost with biochar,compost without biochar,urea,NPK compound fertilizer,and no fertilizer?on soil greenhouse gas emissions were further studied,estimate the net greenhouse gas emissions of soil and analyze the influencing factors of soil greenhouse gas emissions.It is expected to provide basic datas for the further study of urban sludge land use carbon emissions and propose corresponding carbon emission reduction measures.The main findings are as follows:?1?The results of different sewage sludge composting application on soil greenhouse gas emissions indicated that emissions of CO₂ and CH₄ mainly occurred in the plant growth period with low fertilizer amount of biochar charcoal compost reducing CO₂ emissions,and high application content increasing CO₂ emissions.CH₄emission fluxes showed negative,indicating that the soil could adsorb CH₄,and adsorbing amount for control was significantly higher than that for other treatments?p<0.01?.The absorbing amount in treatment compost with biochar increased with the fertilizing amount?p<0.05?.N₂O emissions mainly occurred at the germination and seedling stages,and emission fluxes increased with the fertilizing amount?p<0.01?.N₂O was considered as the main generated greenhouse gas during agricultural process with sludge compost,and its emission factor from sludge compost soil was1.02%-1.90%?compost with biochar?and 1.28%-2.93%?compost without biochar?,respectively.Biochar could significantly reduce the carbon emission,as the total greenhouse gas released from soil with biochar compost was less 19.49%to 35.56%than that in soil without biochar,which was more obvious for N₂O emission reduction?compared with CH₄ mitigation?.The carbon sequestration of crops with sludge composting is relatively high,and the net CO₂ emission increases with the increase of fertilizer application.Comparing the treatments,it was found that the application of200 kg·hm^-2 of compost with biochar resulted in relatively good growth of crops and relatively low greenhouse gas emissions.?2?The results of different types of fertilizers on soil greenhouse gas emissions shows that accumulated emissions of CH₄ ranged from-33.194-14.244 mg·kg^-1,and the total amount of soil used for sludge composting was CH₄ emissions.The application of inorganic fertilizer and unfertilized soil showed the absorption of CH₄,and the unfertilized treatment of CH₄ absorption was greater than the application of inorganic fertilizer.The cumulative CO₂ emissions ranged from 875.907-1824.546mg·kg^-1.The overall performance was that the CO₂ emission rate increased with crop growth.The emission of CO₂ from unfertilized soil was about 70.6%of the fertilization treatment,indicating that fertilization is an important factor in promoting soil CO₂emissions.Biochar charcoal has a certain emission reduction effect on soil CO₂emissions,but the emission reduction effect is not significant?p>0.05?.Compared with other fertilization treatments,the application of soil containing biochar sludge compost can reduce CO₂ emissions by 7.0%-14.5%.And the CO₂ of emission is affected by seasons,and the summer emission intensity is higher than other seasons.The accumulated emissions of N₂O ranged from 366.780-537.558 mg·kg^-1.More than 81%of N₂O emissions during radish cultivation were concentrated in the first 30 days,and more than 60%of N₂O emissions of cabbage were concentrated in the first 24 days.The N₂O emission from the application of ordinary sludge composting is equivalent to the application of urea and NPK compound fertilizers,compost with biochar can reduce 13.5%-22.5%of N₂O.Compared with inorganic fertilizers,application of ordinary sludge compost does not have N₂O emission reduction effect,and compost with biochar has significant N₂O emission reduction effect?P<0.05?.During the entire test period,CO₂ emission equivalents were between108.989-159.916 g·kg^-1.Compost with biochar has the least equivalent CO₂ emission,and can reduce the CO₂ emission equivalent by 13.1%-22.2%.Comparing with other three kinds of fertilizers,the net emission reduction of CO₂ in soils containing compost with biochar was 10.4%-23.3%,and biochar charcoal has an inhibitory effect on soil carbon emissions.Biochar should be considered when applying sludge compost.?3?Application of sludge compost and inorganic fertilizer had no significant effect on vegetable yield,but fertilization increased soil organic carbon content,and different types of fertilizer had different effects.Sludge composting can significantly promote soil organic carbon accumulation,while urea and NPK compound fertilizers have no significant effect on soil organic carbon?p>0.05?.Sludge compost and inorganic fertilizer can increase soil total nitrogen content,but the short-term effect is not obvious?p>0.05?.The emissions of CH₄,CO₂,and N₂O are affected by soil temperature,moisture content,conductivity,and temperature,but there are differences in the effects of different treatments at different stages.