Test Of Constructed Wetlands Based On The Matrix Of Water Plant Sludge Removed Phosphorus

With the social and economic development, protection of resources and environment with protection of the safety in production and life had been the needs of society. In order to achieve the goal for sustainable development of waste, many countries have made great efforts. water plant sludge was inevitable by-product in water purification by using flocculants. Since the problem of imperfect disposal and a wide number of water plant sludge, caused the potential harm for the ecological environment and human health. So exploring the water sludge utilization had become one of the problems to be solved at present water plants.In this papers, as a research object to water supply sludge, conducting static adsorption properties for the phosphorus according to their physical and chemical properties, investigating the effects of initial concentration, particle size, pH, dosage and other factors on adsorption. Through basic experimental studies, the water supply sludge had been made into a composite filling wetlands, carrying on the wetland based on the filling of water supply sludge dealing with rural sewage. The results showed that:1. Water sludge characterization experimentsUsing SEM / XRD and EDS characterization methods, analyzing the surface morphology and structural characteristics of the water sludge characterization. The results show that the substrate surface roughness, constituted by a number of platelet morphology and structures broken loose. The main elements of O, Si, C, Al, about 90% of the mass fraction of the matrix composition, and secondly, Fe, Ca content was also high. The main ingredient was SiO2 crystals, a small amount of AlPO4 crystals existed, the main component of SiO2, Al2SiO5(OH)2, Fe3FeSiO4(OH)5, indicating that the substrate in the iron, aluminum and other elements mainly amorphous form.2. Water supply sludge adsorption testsThe water plant sludge was used to investigate the adsorption of phosphorus in simulated phosphorus containing wastewater as the absorbent. Based on the single factor experiment, the effects of particle size, adsorbent dosage, pH, contact time on adsorption were studied. Parameters for alum sludge of adsorption phosphorous were optimized by orthogonal experimental method. Compared with the orthogonal experiment and single factor experiment, the best scheme was found: pH of 3, particle size of 1.98 mm, adsorbent dosage of 8.0g/L, contact time of 24 h. Based on the single factor and orthogonal experiment, using Box-Behnken design matrix in response surface methodology, dosage, pH and particle size were perfectly employed to study interactive effects of different factors and optimization of phosphorus removal. A predictive model of polynomial quadratic equation was founded as well as optimum level values was successfully. The optimum conditions of phosphorus removal were determined to be 3.88 g/L dosage pH=3.00, 1.00 mm particle size, the removal rate of phosphorus was up to 95.13% under the optimal conditions. Thus the response surface methodology could be viable to optimize the process of removing phosphorus.3. Thermodynamics kinetics experimentsSecondly, the phosphorous adsorption characteristics of water plant sludge substrate were studied by isotherm adsorption, adsorption kinetics and thermodynamics experiment. Although Langmuir, Freundlich and Dubinin-Radushkevich(D—R) isotherms models were used to greatly describe the kinetic parameters, the Freundlich equation was the best model that describes the adsorption behavior according to correlation coefficient. When temperature is 298 K, 308 K, 318 K respectively, the saturated extents of adsorption of phosphorous were 3.47mg/g, 3.84mg/g, 4.39mg/g separately. The adsorption free energy value(E=10.77-10.83 kJ/mol) derived from the D-R equation indicates that the adsorption was controlled by ion exchange adsorption. The pseudo-second order kinetic equation was the best model that accounts the adsorption characteristic of phosphorus onto water plant sludge substrate. The Intra-particle diffusion equation demonstrated that the adsorption were governed by liquid film diffusion and intra-partial diffusion. The calculation values of thermodynamic present that the adsorption was spontaneous and endothermic reaction.4. Production testTaking advantage of the results of orthogonal experiment and response surface prepared the water plant sludge composite fillings, Subsurface Constructed Wetland was used to deal with rural sewage based on water plant sludge composite fillings. During the wetland running, when the influent concentration of TP between 12.41~15.34mg/L, the effluent concentration between 0.21~0.76mg/L, TP removal rate can be maintained for more than 90%; when the influent concentration of NH4+-N between 122~143mg/L, the effluent concentration between 13~29mg/L, NH4+-N removal rate can be maintained in between 79~90%; when the influent concentration of CODCr between 153~192mg/L, the effluent concentration between 31~54mg/L, CODCr- removal rate can be maintained for more than 70%.