Efficiency And Mechanism Research Of Stabilizing Sludge Ecologically In Reed Beds

At present, the treatment and disposal of surplus sludge has become an urgent issue to be solved. In order to solve it efficiently, the efficiency and mechanism research of reed beds for sludge stabilization was carried out in the thesis, focusing on revealing the migration and transformation rules of pollutants during the process of sludge stabilization. The experiments were setup in three sludge drying beds; Bed I was a conventional sludge drying bed, unplanted and functioned as a control bed; Bed ? and ?were reed beds and planted with reeds. Bed I and II were connected to the atmosphere through overlying porous tubes. The experiments lasted for three years, the first two years was sludge loading period, the third year was a natural stabilization period. During the first two years,8.4 m of raw sludge was loaded and an average sludge loading rate of 41.3 kg (TSS)·m-2·a-1 was obtained.Results show that in comparison with traditional drying bed, the removal efficiency of sludge percolate COD by reed beds is much higher. Denitrification process occurred in all the three beds, among which, Bed III bears the highest efficiency, reaching 30.38%. The removal rate of organic matter, nitrogen and phosphorus in surplus sludge by reed beds is higher than unplanted drying bed. Ventilation is helpful to the organic matter degradation and nitrogen removal. PAH contents tend to decrease in stabilized sludge with time going. The total PAH contents in the surface, middle and bottom sludge layers in the sludge drying bed were 4.161, 3.543 and 3.118 mg-kg-1, respectively, the corresponding removal rate is 6.91%,37.77% and 45.23%; The total PAH contents in those of reed bed are 2.722,1.648 and 1.218 mg-kg-1 respectively, the corresponding removal rate is 52.18%,71.05% and 78.60%, respectively. In comparison with the traditional drying bed, the average removal rate of PAH by reed bed is 29.86% higher. Among the PAHs, bi-or tri-cyclic aromatic hydrocarbon dominates.At the same time, in the stabilized sludge, PAHs were enriched obviously by reed beds. In September, October and November of the second experimental year, the PAHs contents in the roots, stems and leaves of tested reeds showed increasing tendency month by month. In November of the third experimental year, the total PAH contents in the roots, stems and leaves are 7.642,7.713 and 7.946 mg-kg-1(DW) on the average, respectively, which are 8.5,3.52 and 3.08 times of those in native ones, and lower molecular weight PAHs are dominant. PAHs contents in reeds are observed to be significant positive correlation with their coarse fat contents.In sludge drying reed bed, the main organic matter removal ways are classified as follows:insoluble organic matter can be removed by filtration, sedimentation, and plant interception, etc; the trapped insoluble organic matter can be utilized by microorganisms. Soluble organic matter can be removed by means of substrata adsorption, plant uptake and microorganism metabolism. If there is not enough organic matter to provide the required energy for microbial activity, microbial metabolic activities will be carried out inside the microorganism and reduce the organic content of sludge as a result.Reeds plays an important role in PAH cycle during the sludge stabilization. PAHs can be absorbed by the root of reed from the soil, and then transfer from the root to the stem and leaf. During the process, fat-soluble PAHs are more likely to be released, i.e., the availability of PAHs is improved, thus providing the conditions for the degradation of PAHs.The phosphorus removal mechanisms of sludge drying reed bed include filtration, substrata adsorption, plant uptake, precipitation, physic-chemical reactions and microbial translation, and the main removal mechanisms are adsorption and precipitation. The removal of nitrogen in reed beds includes evaporation, ammonification, nitrification, denitrification, plant uptake and substrate adsorption, etc.The research results in the thesis prove the efficacy of sludge stabilization by means of reed bed technology, which provides a scientific foundation for the extended application of reed bed technology.