| With the increasing number of wastewater treatment plants,more and more municipal sewage sludge is produced.Due to the absence of sound treatment method, most of the sewage sludge was piled in temporary places and becoming new potential pollution sources.There is an urgent need for a safe disposal option.In this thesis,heavy metals(HMs)and polycyclic aromatic hydrocarbons(PAHs) in sewage sludge from twelve different wastewater treatment plants(WWTPs)of Zhejiang province,China,were investigated.Concentrations of HMs in most of the sludge were all below the regulatory limits for the sludge to be used in agriculture in China except the concentrations of Zn in two sludges and the concentration of Cd in one sludge,indicating that HMs in tested sludge should not be the prominent problem for the sludge to be used in agriculture.However,Σ9 PAHs concentration values in all of the tested sludge had far exceeded the safety limits,which suggested that sludge from these WWTPs should not be recommended for agricultural application unless the PAHs concentrations in sludge could be reduced through proper treatment.Composting appeared to be an effective method for the removal of PAHs in sewage sludge.After 50 days of composting,a significant reduction of concentration of the total PAHs was detected as compared with that in the initial composting material.More than 79%of theΣ16 EPA-listed PAHs was removed andΣ9 PAHs declined from 53.4 mg kg-1to 11.5 mg kg-1(d.m).The decrease could be possibly resulted from the combination of biodegradation by thermophilic and mesophilic populations and volatilization.Among the three most dominant components, phenanthrene decreased about 92%and dibenz(a,h)anthracene reduced about 84%, while the loss of fluorene was less than 50%after 50 days composting.Fluorene became the most recalcitrant and became the primary residual PAH in the composted material.Further studies are needed to enhance the removal of fluorene in order to achieve a safe utilization of this sludge.Laboratory-scale experiments were carried out to investigate the effects of bio-charcoal on nitrogen conservation and mobility of Cu and Zn during the course of sludge composting.The result indicated that the incorporation of bio-charcoal into the sludge composting material could significantly reduce the nitrogen loss.With the amendment of 9%bio-charcoal,total nitrogen loss decreased 64.1%as compared with the no bio-charcoal amendment control at the end of comporting.Mobility of Cu and Zn in the sludge could also be lessened.DTPA-extractable Cu and Zn contents in composted sludge declined 44.4%and 19.3%,respectively,in comparison to that in original sludge composting material.At the same time,composting improved the retention capacity of bamboo charcoal particles for ammonium resulting from a significant increase of the amount of total surface acid groups,especially carboxylic groups,due to bio-oxidation during composting.In addition,the amendment of bio-charcoal can enhance PAHs removal rate.Terminal restriction fragment length polymorphism(T-RFLP)was used to analysis the temporal shift of bacterial community compositions in both treatments with and without bamboo charcoal.The result showed that bamboo charcoal could increase the microbial-diversity and microbial numbers in the sludge compost.A rational use of sludge compost aims to take advantage of its beneficial effect as nutrient source for plant production while avoiding potential deleterious effects on soil and plant.On one hand,land application of sludge compost can improve certain physical and chemical soil characteristics and plant growth.On the other hand,at high application rate it can increase the levels of heavy metals and soluble salts in the amended soil, increasing the potential for soil pollution.The risk is mainly dependent on specific soil and compost characteristics and application rate.The sludge compost amended with bio-charcoal resulted improvement not only in the plant growth but also less negative effect on plant and soil,even at high dosage.It is mainly because bio-charcoal amendment causes to slow release of nutrient in sludge composting and retains the nutrient to a high level at the budding and maturation stage,in which stage nutrient are more necessary for plant.At the same time,the bioavailabilities of heavy metal and PAHs in sludge composting were reduced by bio-charcoal,which resulted in the lower absorption and accumulation of plant to contaminants.In addition,ryegrass has better effect to accelerate the removal of PAHs.
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