Study Of Light-Weight Aggregates-Based Constructed Wetlands For Wastewater Treatment And Development Of Sludge Media

Water shortage and the increasing water pollution are two serious problems faced to water environment in China. Especially for poor rural area, where economic strength is weak, and the infrastructure constructionis poor. A large number of untreated sewage was discharged directly into water, which pollutes environment seriously. It is extremely urgent to take effective measures to treat wastewater immediately. Constructed wetlands (CWs) have a broad application and have been widely used in the developing countries, because of their lower cost, less operation and maintenance requirements, and without energy inputs. As the skeleton of constructed wetland, substrate plays a vital in composition of wetland system. The particle size distribution, porosity, and chemical composition of substrate are important factors which affecting the purification effect and life of CW. As a result, it is of great significance to develop a new type of matrix and focus on the study of decontamination mechanism of substrate.This study evaluated the performance of horizontal flow constructed wetlands (HF CWs) for secondary domestic wastewater treatment, using lightweight aggregates (LWA) as upper substrate. The treat performance of HF CWs based on LWA was evaluated, and the accumulation of solids was investigated in this study. In addition, to analyse the differences of microbe quantities and community structure of different plant rhizospheres to assess the changes in infiltration capacity of LWA after operation for 19 months for both systems investigate. At the same time, the physical and chemical properties and adsorption characteristics of the sludge were investigated, and the feasibility of preparation of sludge ceramsite was discussed to provide theoretical basis for the development of new ceramsite and technical support. Additionally, the performance test of sludge ceramsite and phosphorus adsorption characteristics were alsoconducted to discusses the feasibility of choosing sludge ceramsite as substrate constructed wetland.The main research conclusions are as follows:(1) The use of LWA allowed average removal rates are 31～44%,55～75% and 42～59% for TP, COD, and TN respectively. No significant decline in removal efficiency was observed during the monitored period. After operation for 19 months, total 4.19～4.61 Kg/m2 of organic matter was accumulated and annual solids accumulation rates ranged from 5.3 to 6.0 kg DM /m2 year. High porosity and specific surface area of LWA favored to a slight reduction (6.8～13.6% of initial value) of hydraulic conductivity in both systems. Overall, results showed that LWA can be used as candidate materials in engineered wetlands and has a potential to delay the wetland clogging and prolong the lifetime of CW.(2) This study examined the maximum phosphorus-adsorption capacity of dewatered alum sludges derived from four different water treatments in Shandong province, China. Experiments have demonstrated that the Yu Qing alum sludges has the largest P adsorption capacity (6.06 mg P/g), followed by Xue Shan (3.95 mg P/g) and Que Hua (3.07 mg P/g), while San He sludge has the least (2.06 mg P/g). The reason is that the San He sludge had the largest initial P content (7.15 mg/g TP). The results indicated that all the sampled sludges have good great potentials in China for P-adsorption. Results indicated that the composition of waterworks sludge was similar to clay, and the main inorganic components of waterworks sludge were SiO2, AI2O3 and Fe2O3, which came from the water source and flocculating agent. Thus, the sludge has good potential to make ceramsite.(3) The raw material, temperature, holding time, composition of the sludge, curve of temperature is main factors influencing the preparation of sludge ceramsite. In this paper, the sludge collected from Yuqing waterworks was chosen as main raw materials of ceramsite. Clay is accessories with the content of 50%. The optimal dry conditions was 105℃,2 hours. Preheat condition was:400℃,20 minutes. Roasting condition was:1150 ℃,10 minutes. Physical and chemical analysis indicated that the average particle size of sludge ceramsite was 4～6 mm. The specific surface area and density was 4.55～4.85 m2/g and 1.28～1.37g/cm3 respectively. The heavy metal content was in a small amount, which did not exceed the values in national standard GB5085.3-2007 standard.(4) The sludge ceramsite had rough surface, and rich micropore structure. The pore of ceramsite was bigger (1-5 μm). In addition, strong physical adsorption capacity, and high mechanical strength, high specific surface area and porosity of ceramist were also good characteristics in favor of being used as substrate. The sludge ceramsite has very strong adsorption capacity for phosphorus. According to the Langmuir equation, the maximum phosphorus adsorption capacity was 319 mg/kg. Energy spectrum and component analysis indicated that the results of main metal elements in ceramsite were Al, Fe, Ca and Mg, which were the key factors influencing the adsorption capacity for phosphorus.(5) Using the sludge as main material to produce ceramsite was in favor of achievements the sludge harmless, utilization and industrialization. In addition, it is beneficial to protect land resources and water resources, reduce the construction investment, operation cost using sludge ceramsite as substrate in CW. It has high value in economic, social and environmental aspects. It is of great importance to achive the social, environmental and economic benefits.Constructed wetlands based on ceramsite have a broad application in small and medium-sized cities and rural areas.