Study Of Sludge Disposal Technology Based On Plant Bed In Small Towns

As the gradual increase in urban sewage treatment rate, the production of sludge is also increasing rapidly. Sludge resource utilization has become one of the focus topics all over the world. Sludge ecological stabilization system is one way of sludge land application, which can achieve the reduction, stabilization, harmless and resource treatment of sludge. It is very suitable for the disposal of sludge in of sewage treatment systems in rural areas and small towns, consistent with the situation of our country. Compared to conventional sludge drying beds, Sludge ecological stabilization system increased the plant, which is a very practical teachnology set of solar drying, composting, plant processing systems, organic fertilizer production and so on. In addition to the direct effects of the plant, the significant effect of plants in sludge ecological stabilization system is the roots secrete oxygen to form a diversified microbial environment in sludge layer, which can greatly increased the role of microbial communities.In this paper, in order to compare the effect the plant bed composed of elephant grass, reeds, cattail, one lab-scale plant bed and four pilot-scale plant beds have been constructed to analyzes the leachate, sludge TS and VS, total amount of heavy metals and its’speciations.Experiments show that season and plants growth conditions affect dewatering and stabilization of sludge in plant bed. In summer, the sludge TS in elephant grass bed and cattail bed can respectively increase from2.6%～9.3%to22.2%～25.9%and24.4%-27.2%. In winter cattail bed sludge TS dropped17.5%t～19.9%, reed bed sludge TS18.8%-20.9%. Comprehensive comparison dehydration effect:Summer> Winter; reed> cattail> elephant grass. This experiment also found that elephant grass can not adapt to the high load of sludge environment shows it can not be used in plant bed.The major mechamism of sludge dewatering is percolation. the contribution of plant uptake and transpiration on sludge dewatering is influenced by plants growth conditions and season. as dewatering amount of plants which grow vigorously in summer is almost equal to that of percolation.The plant bed mainly rely on the absorption by filter layer packing has obvious removal on TP. as the average concentration of TP in leachate only1.41-5.55mg/L. and the removal rate of TP is up to83.6%～95.8%,compared with sludge filtrate. Nitrification-denitrification is the major process of TN removed in leachate. Plants growth conditions affect roots secrete oxygen capacity, and further influence the bed’s aerobic&anaerobic environment. The concentration of COD in leachate is40.4-83.5mg/L, which goes through a greater fructation in summer than in winter.The content of heavy metals in all sludge reached the Class B sludge requirements in《Disposal of sludge from municipal wastewater treatment plant-Control standard for agricultural use CJ/T309-2009》, it can be used for a particular crop directly. All heavy metal content of sludge in plant bed systems were decreased after4months. The fraction of heavy metal also changed。The steady-state of Zn, Cr, Ni, As has increased to some extent; all fraction of Cu, Pb relatively stable. while steady-state of Cd reduced significantly, and large increase in Fe-Mn oxides, enhanced the biohazardous of Cd. Sweet grass removal of heavy metals and stabilization are weaker than cattails; while the performance of reeds were instability due to growth conditions.