A Study On Sediments Contamination And In-situ Stabilization Of Urban River

Nowadays,most of urban rivers in China had been seriously polluted during the urbanization process.There are a large number of oxygen-consuming substances, nitrogen and phosphorus pollutants,organic pollutants and heavy metals pollutants in sediments,to radically improve the water quality,we should not only cut off external sources of pollution,but also address the internal pollution sources of sediments.In this paper,Suzhou creek was studied as an example.For resolving the two prominent problems of low dissolved oxygen and high nutrient content,the pollution characteristic of Suzhou creek sediments was investigated,the degree of pollution was assessed consulting some relevant sediment quality standards.Aiming at Suzhou Creek sediment characteristics,the release rule of pollutants from sediments and sediment oxygen-consuming mechanism were studied.To actively seek a solution,an in-situ stabilization experiment of Suzhou Creek contaminated sediments was conducted based on the previous experimental findings.The vertical distributions of ammonia nitrogen,Kjeldahl nitrogen,total organic carbon and acid volatile sulfide in Suzhou Creek sediments are basicly hump-shaped, the concentrations of pollutants in surface sediments are relatively low,the concentrations in Silt layer are the highest,the concentrations in original soil layer are the lowest.Pollutants contained in Silt layer are gradually increased from the upstream section to the downstream section along Suzhou Creek,the change trend of pollutants in other layer has little difference.According to the relevant sediment quality standards, organic pollution and ammonia nitrogen pollution in surface layer and silt layer all reach a serious pollution level,the total Kjeldahl nitrogen pollution degree is lower,the heavy metal toxicity do not exist.Temperature,disturbance and dissolved oxygen content of water body are important environmental factors,which effects the pollutants releasing from sediments. The pollutants in water and sediments will be more stable under low temperature condition,the higher temperature is,the releasing and transforming velocity of pollutants is faster.Disturbance can cause the rapid release of particulate pollutants and dissolved pollutants from sediments in a short time.Under anaerobic conditions,the iron/manganese-bound phosphorus will release in the form of orthophosphate,the nitrogen pollutants will release in the form of ammonia.The product of organic anaerobic mineralization will cause the increase of COD_Cr and TOC content in water body.Improving dissolved oxygen in water can effectively inhibit the the release of nitrogen,phosphorus and organic pollutants from sediments.The oxygen-consuming material in Suzhou Creek mainly consist of sulfide, ammonia,organic matter and low valence metal ion,the release capacity of ferrous ion and sulfide to overlying water is the strongest,the oxygen consumption rate is the fastest,ammonia follows by,organic carbon is the slowest worst.The oxygen equivalent of pollutants in Suzhou Creek silt layer sediment is maximum,in which oxygen consumption equivalent caused by organic carbon is the highest,but it can only consume less oxygen because of the slow release and mineralization.The oxygen consumption by sulfide and ammonia has the greatest contribution to sediments oxygen demanding,the oxygen consuming rate of sulfide is faster.The simulated Experiment results show that the SOD value of Suzhou Creek gradually increases from upstream to downstream,the SOD value in silt layer is the highest,the value in surface layer follows by,the value in original soil layer is the lowest.Temperature can remarkably influence the SOD value,the SOD values of Suzhou Creek are all less than 1gO₂/m²Â·d in winter, but will obviously increase in summer.Potassium permanganate,calcium peroxide and calcium nitrate could increase the ORP in sediments,calcium peroxide and potassium permanganate would significantly increase the alkalinity of sediments.calcium nitrate could effectively reduced the organic pollutants content in sediment,the removal rate of TOC reached up to 18.72%. Calcium peroxide and calcium nitrate could effectively inhibit phosphorus release from sediments,the PO₄^3- content in interstitial water respectively reduced 0.003 and 0.094mg/L,and the inhibitory effect was quietly stable.Four kinds of stabilizer could not significantly improve dissolved oxygen content in water body,the stabilization effect of the four stabilizer on nitrogen pollutants in sediments was not ideal,in the early stage they would promote ammonia release from sediments at different degree, calcium nitrate could result in the nitrate infiltration upward to overlying water.Four kinds of stabilizer would reduce the content of acid-volatile sulfide in sediment, increase theΣSEM/AVS ratio,and enhance the biological toxicity of heavy metals.