Experimental Study On The Reutilization Of Wenruitang River Sediment:an Approach To Fabricate Bricks

With the rapid development of the city, urban river pollution becomes increasingly serious. Pollution of river sediment draws an increasingly attention to the public, and the disposal of dredged river sediment has become an urgent problem to solve after large-scale dredging project. The reutilization of river sediment can achieve both the reduction of the polluted sediment and the beneficial products. This thesis can be divided into four parts: the fabrication of the brick by using river sediment; characterization of the brick specimens; biological toxicity analysis of the leaching solution from the brick specimens; application of the brick as a water-purifying material in water treatment and the efficiency analysis.Frist of all, the main chemical contents, particle size distribution, mineral composition and heavy metals contents in the river sediments from Wenruitang River were determined. Results showed that sediment samples were similar to clay minerals with respect to chemical composition, which indicated the possibility of reutilization of river sediment as an alternative to clay. Heavy metal content in the sediment was relatively high but not so high to be treated as hazard waste. Therefore, it is necessary to analyze the conversion of heavy metals during the sintering process in case of secondary pollution.Secondly, river sediment was used as the major raw material, plant straw, glass powder and water glass were used as the auxiliary materials. The proportion of each raw material in the brick was determined through orthogonal experiment. The optimum formula was85wt%for sediment,5wt%for binder,10wt%for the glass powder,0.1wt%for bagasse. The order of the four factors that affect the compressive strength of the brick specimens was:glass powder> binder>sediment> bagasse. Under the experimental conditions the compressive strength of the brick specimen was18.92MPa, the compressive strength level reached MU15.Thirdly, basic properties of the brick such as water absorption and bulk density were measured. Mineral composition was analyzed via X-ray diffraction. Scanning electron microscopy was used to analyze the surface morphology and microstructure of the brick. Heavy metal concentration of the leaching solution of the brick was measured. Leaching concentration of Cu, Cd, Cr and Pb from the fired brick specimens was lower than that from the original river sediment, which proved that the mobility of the heavy metals in the fired brick specimens were greatly decreased. Under normal rainfall environment, the leaching concentration of Cu, Cd, Cr and Pb from the brick is far less than the requirements of Integrated Wastewater Discharge Standard GB8977-1996.Fourthly, designing biological toxicity test and choosing Luminescent bacteria and of Xenopus tropicalis embryos to find the bio-toxic effects of the leaching water from sediment bricks, the results showed that the potential toxicity of bricks was greatly reduced than the raw river sediment. The sediment brick is almost harmless to the environment.Finally, the research used the sediment brick as a water-purifying material. Results of the purification test showed that the removal efficiency of total nitrogen reached27.2%; removal efficiency of NH4+-N was98.2%; removal efficiency of total phosphorus was57.3%; removal efficiency of CODcr reached50.0%. The benefit analysis indicated that the reutilization of river sediment by using it to fabricate brick have certain economic benefits and significant environmental benefits.