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A Study on the Removal of Chromium from Sewege Sludge and Aerobic Composting

Author: LiangShuang
Tutor: JinWenBiao
School: Harbin Institute of Technology
Course: Environmental Science and Engineering
Keywords: Reclaimation of sludge Heavy metal Chromium Ion exchange Aerobic composting
CLC: X703
Type: Master's thesis
Year: 2008
Downloads: 31
Quote: 0
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Abstract


The wasted biochemical sludge produced from the EHYBFAS process employed in the Buji sewage treatment plant in Shenzhen City was chosen as the subject of this research. A lab-scale test has been developed for almost ten months. First, a leaching experiment was conducted to remove the heavy metal Chromium. Then an ion exchange experiment was carried on to reclaim the leachate such that the Chromium in the leachate can be recycled. Finally, for the purpose of the agricultural use of the sludge, an aerobic composting test was conducted to search the optimal composting condition of three materials.Analysis of the ingredients and chemical properties revealed that the sludge contains high organic, nitrogen, phosphorus and low potassium, which can completely meet the nutrient requirements for the agricultural use. Only Chromium can not meet the standard GB4284-84. As a result, it must be pretreated to remove Chromium before composting.Results of lab tests indicated that the optimal operating conditions for Chromium removal are: 0.36 mol/L citric acid, leaching at a velocity of 0.5ml/min and at the dosage of 1000 mL/kg, then the Chromium removal percentage can achieve 57.43%, which means Chromium remaind in the sludge is 1278×(1-57.43%)=544.04 mg/kg, and Chromium in the residual state accounts for 29.52%,which completely meet the national standards GB18918-2002 and GB4284-84. Using an ion-exchange resin to remove Chromium from the leachate, upfolw at a velocity of 5mL/min, a removal perecentage of over 95% can be obtained and the citric acid can be recycled, 8% NaOH is used to regenerate the resin, and the optimal condition is that volume ratio of NaOH:resin=2:1, such that the washout percentage can reach to 85%. Al is chosen to replace Chromium from the leachate, and when the replacement time reaches 3 days, the replacement percentage can come up to 63.3%, the liquid after replacement can be used to produce PAC.An aerobic composting test was developed for the leached sludge with three different working conditions. Variations of pH value, temperature, water content, Germination Index were monitored during the composting so that the composting maturity can be judged. Results of lab tests indicated that the proportion of the materials under working conditionⅡis most suitable with a ratio of sludge : sawdust : mashroom residue = 35:5:7. Under this condition the temperature of composting can rise over 55℃and last 3~4 days and the GI can reach to 68.3% in the 12th day. The hygiene indicators meet the US standard A of EPA sludge products, as well as Chinese national standard GB18877-2002.A feasibility analysis in technology and economics has also been developed and results reveal that the method is totally feasible, which provides the theoretical support and guidance for the further applications of this process.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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