Study On The Transformation Of Heavy Metals Speciation Distribution In Biological And Chemical Remediation For Contaminated River Sediment

Remediation of contaminated sediment is an important part of the comprehensive improvement of river. In situ remediation is a mature governance technology, which is an effective solution to the sediment problem of blackish-odor, and less secondary pollution. Calcium nitrate and calcium peroxide are dosing agents with more applications. However, in the application of pharmaceutical dosage to repair sediment, which might produce sediment disturbance, and led to sediment contaminants(such as ammonia, heavy metals) or external agents(such as nitrate) abnormal release to the overlying water. Existing studies have investigated abnormal release of ammonia and nitrate, but changes of heavy metals is still lack of systematic understanding. Therefore, this paper studied mobility behavior of heavy metals and its potential environmental impacts during in situ remediation, and to provide a theoretical reference and data for the improvements of sediment remediation technology and the control of subsequent environmental impact.In this study, use bioremediation technologies with dosing calcium nitrate and chemical oxidation technologies with dosing calcium peroxide to repair contaminated sediment, and investigate their effect in terms of sediment black-odor, ORP, and TOC, studied the changes of heavy metals’ distribution in sediments. Through cloning and sequencing techniques to explore the microbial activity and make a thorough inquiry reason of microbial in heavy metal speciation changes; through small scale experimental to study peroxide affects in morphological changes of heavy metals in sediments. Using AVS/SEM and bioaccessibility to evaluation ecological risk of heavy metals in sediments.The results show that adding Ca(NO3)2 and Ca O2 can improve anaerobic conditions in sediment, removing black-odor phenomenon of sediment and also remove some organic matter. Repair process will result in some heavy metals in sediment(Cu, Ni) transformed from a more stable form to the unstable form. The reason of transformed of heavy metals in sediments vary of these two additional agents, adding calcium nitrate is due to the promotion of the sediment microbial activity, Thiobacillus denitrificans play the major role in transformed of heavy metals; and dosing calcium oxide is because of its strong oxidation, under the influence of chemical oxidation, cause morphogenetic transformation of heavy metals. Sediment after remediation of 35 days, AVS/SEM values decreased, the potential migration of heavy metals increased; Bioaccessibility of heavy metals have different degrees of benthic potentially harmful increases.