Preparation Of Modified Calcium Silicate(MCS) And Application In Phosphate Removal From Livestock Wastewater During Anaerobic Treatment Process

Nitrogen and phosphorus in livestock wastewater could not be effectively removed by traditional methods, resulting in a large amount of wastewater containing nitrogen and phosphorus being discharged into rivers and lakes, and bringing serious eutrophication problems. Moreover, impact of phosphorus on the algae blooming was much larger than nitrogen, and the removal of phosphorus in wastewater had become crucial problems in dealing with livestock wastewater. At present, there were many traditional ways to removal phosphorus in livestock wastewater, while single chemical or biological phosphorus removal processes were not desirable. In this study, combined chemical and biological anaerobic processes were adopted to achieve the efficient phosphorus removal from livestock wastewater by adding chemical adsorbent to anaerobic reactor.First of all, four factors including dispersion doses, temperature, calcium-silicate ratio and agitation intensity were selected for the investigation based on precipitation methods. Response surface analysis(RSM) methodology was used to investigate key factor impacting on phosphorus adsorption for determining optimum preparation conditions to achieve the best phosphorus adsorption efficiency. It indicated that agitation intensity had the maximum effect on phosphorus adsorption capacity of MCS in term of single factors, followed by dispersion doses and temperature, while the effect of calcium-silicate ratio was relatively small. The optimum preparation conditions of MCS were as followed: temperature 50 ℃, agitation intensity 170 r·min-1, calcium-silicate ratio 1.53, dispersion doses 3.54%.Secondly, characterization and analysis of MCS were determined by FT-IR, XRD and SEM. The partical size of MCS obtained by chemical precipitation method was around 200 nm appeared in the surfacestructure as honeycomb. The MCS possessed high purity with no impurities rest, and it was semi crystalline with low order degree. It showed that MCS belonged to calcium silicate hydrate. Compared with conventional calcium silicate, MCS with honeycomb structure could be more faor of phosphorus removal. Besides, phosphorus adsorption and reaction processes of MCS were fitted with the curves of adsorption kinetics and adsorption isothermal. It indicated that Langmiur model and quasi two-level kinetic model were able to account for the phosphorus removal usingMCS. In addition, the principle of precipitation-dissolution was adopted to explore the ion-exchange mechanism between MCS and phosphorus. The priority of anions reacting with MCS was PO43->F->CO32->C2O42->SO42->CrO42-. It seemed that phosphates could combine with MCS tightly. In other words, the adsorption and precipitation reactions between MCS and phosphates were not subject to interference from other ions, hence phosphorus removal efficiency of MCS could be maximized, and MCS had an extraordinary phosphorus adsorption(ion exchange) capability.Finally, the average value of COD and TP reduced from 702.4 mg·L-1 and 22.7 mg·L-1 to 585.7 mg·L-1 and 0.4 mg·L-1 respectively for effluent, and the average removal rate of COD and TP increased from 91.1% and 75.3% to 92.6% and 99.6% respectively by adding MCS to the anaerobic reactor. It showed that the addition of MCS could improve the carbon and phosphorus removal efficiency of UASB. Meanwhile, after the addition of MCS, the average particle size of granular sludge and the cumulative size of D80 increased by 27.18% and 32.16% respectively compared to the control. In this study, EPS, methane production, and dehydrogenase activity of sludge were also analyzed, and the change of sludge characteristic was studied by using the Zeta potential method. It was found that Zeta potential of sludge in U-2 varied greatly within 20 days, which dropped from 19.8 mV to 10.8 mV and was nearly 3.5 mV lower than that infrom U-1; In contrast to the sludge in U-1 at the same period, EPS, methane production and dehydrogenase activity of sludge increased by 11%, 23% and 3.5% in U-2, respectively. It seemed that the addition of MCS not only enhanced the activity of sludge and methane production, but also possessed positive-valued Zeta potential on its surface, so as to neutralize the negative Zeta potential on the surface of sludge, which promoted the formation and growth of anaerobic granular sludge.