[Effect of Sewage Sludge Compost Products Application on Total Mercury and Methylmercury in Soil and Plants].

Two different sludge composting products (with and without biochar) were applied in field to study the variations of total mercury (THg) and methylmercury (MeHg) in soil and plants,as well as their migration in the soil-plant system and accumulation ability in plants during the sludge compost land use process.The results indicated that the concentrations THg and MeHg in soil increased after applying sewage sludge compost products,while the THg level was still lower than the secondary standard of national soil environmental quality.Biochar was speculated to probably promote the soil mercury methylation with lower MeHg/THg ratios in different soil treatments.THg concentrations in mature plants were significantly lower than those in seedling stage,but MeHg levels were higher than those in seedling stage.An obvious influence of composting on MeHg enrichment in plants was observed,and this similar effect was not found for THg enrichment.MeHg concentration in the soils applied with biochar compost was significantly higher than that without applying biochar compost soil,while MeHg in plant presented a contrary trend with higher level observed in no-biochar compost soil,suggesting that the addition of biochar could be in favour of soil MeHg formation and inhibit the MeHg accumulation in plants by influencing its migration.Since a strong MeHg accumulation ability with BCF of 1.24-14.63 was present in plant,the mercury ecological risk in soil environment caused by long-term fertilizing should be noticed.

[Effect of Application of Sewage Sludge Composts on Greenhouse Gas Emissions in Soil].

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 (A:compost with biochar, B:compost without biochar) with varying fertilizing amount into soil. The results indicated that emissions of CO2 and CH4 mainly occurred in the plant growth period with low fertilizer amount of biomass charcoal compost reducing CO2 emissions, and high application content increasing CO2 emissions. CH4 emission fluxes showed negative values, indicating that soil could adsorb CH4, and the adsorbing amount for control was significantly higher than those for other treatments (P<0.01). The absorbing amount in treatment A 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 was 1.02%-1.90% (A compost) and 1.28%-2.93% (B compost), respectively. Biochar could significantly reduce the carbon emission, as the total greenhouse gas released from soil with biochar compost was 19.49% to 35.56% less than that in soil without biochar, which was more obvious for N2O emission reduction (compared with CH4 mitigation).

[Emissions Characteristics of Greenhouse Gas from Sewage Sludge Composting Process in Winter].

Sludge composting is an efficient way to realize the reclamation of waste sludge, while the Green House Gas (GHG) accompanying with it has raised great concern worldwide. However, we do lack the primary data in this area and a great uncertainty of the effect and GHG emission characteristics of sludge composting process in low-temperature environment also exists. This study is aiming to investigate the emission characteristics of GHG from composting in low-temperature environment by applying two different bulking agents to dewatered urban sludge. The results showed that aerobic composting could go smoothly even in an environment with lower temperature, yet the maturity was low due to a sharp drop of pile temperature at the stage of maturing. Sawdust treatment could reduce the total nitrogen loss compared with cornstalk treatment, while its GHG emission equivalence was higher (169.45 and 133.13 kg·t-1 dry sludge, respectively). The accumulative CH4 emissions of sawdust and cornstalk were 0.648 and 0.689 kg·t-1 dry sludge, respectively, of which over 75% was from the first two weeks; total N2O emissions of sawdust and cornstalk were 0.486 and 0.365 kg·t-1 dry sludge, of which more than 90% came from the decomposting process. On the whole, because of the relatively short duration of high temperature as well as the low temperature during mature stage, the process had an especially low emission of CH4 but a relatively high discharge of N2O. For composting in low-temperature environment, necessary measures should be taken to control N2O emission in the late period in order to realize GHG reduction.