The Operation Parameters Control And Phosphorus Removal Pathway In Near-zero Sludge Discharge UCT-MBR Process

The excessive discharge of phosphorus leads to serious environmental problems as eutrophication and caused especially concern. Biological phosphorus removal is achieved by wasting P-rich sludge, however the discharge of numerous sludge and its release of P take into a new pollution. The MBR process treated wastewater and sludge at same time under complete sludge retention time condition in the practical engineering. The MBR treatment system could achieve Discharge Standard of phosphorus, however it was unkown that the removal pathway and mechanism of phosphorus. This study combined UCT with MBR process and compared the performance including removal efficiencies, sludge properties, fouling of two membrane module of disk-plate and hollow fiber ultrafilter with near zero sludge discharge. In particular focuses on the removal pathway of phosphorus by analyzed the distribution of phosphorus forms in liquid and solid phase, phosphorus mass balance calculation. It investigated the influence of different cations on P-release, P-uptake and the sludge change of phosphorus form. Moreover, it explored the impact of different cations on membrane fouling and biologically induced phosphorus precipitation.In the performance and operation parameters control of two membrane systems with near zero sludge discharge, the average concentration of COD, NH3-N, TN were well below the class A of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (WWTP)(GB18918-2002) in China. The MBR systems could achieve near zero sludge discharge when the aerobic MLSS concentration was12g/1and the concentration of TP could basically achieved the class A of Discharge Standard. And it proposed the optimum design and operation parameters to achieve near zero sludge discharge of UCT-MBR process. The design parameters such as membrane module type, HRT, recycle ratio, F/M, MLSS and the operation parameters of ORP, DO, SV30, SVI, the observed sludge yield, SRT, and discharge sludge weight.It indicated that the disk-plate UCT-MBR process had better removal performance of COD、NH3-N、TN、TP than hollow fiber system. In addition, the two membranes showed various degree rejections for COD, NH3-N, TN, TP and had better rejection for COD and TP. The membrane fouling investigation of two membrane module found that the disk-plate was three stages falloff, while hollow fiber was two stages. It showed that the phosphorus concentrations of systems and sludge accumulated obviously at initial and mid stage. Along with operation the concentration of TP increased obviously at anaerobic stage and the capacity of uptake P improved and achived maximum. And the concentrations of phosphorus and mixed liquor suspended solid increased and accumulated until it reched a peak. In the condition the sludge decay and phosphorus loss appeared and subsequently sludge growth and removal of phosphorus tending towards stability. In addition, the accumulation of TP and mixed liquor suspended solid no longer appeared.In particular focuses on analysis of distribution of phosphorus in liquid and solid phase, and phosphorus mass balance investigation. It concluded that the particle phosphorus was easiest removal, and the dissolved orthophosphate was easier removal than dissolved organic phosphorus. And the systems have PAOs microorganism for P removal. In addition, the removal of P has correlation with metal ions and coordination of EPS. It concluded that five phosphorus removal pathways and ratios of inorganic metal bound phosphorus precipitation, EPS induced P removal, PAOs excessively uptake P, phosphine transformation, discharges with effluent.It has shown that potassium and magnesium were all involved in phosphorus release and uptake reactions. Howerver, Calcium does not appear to be required. The phosphorus removal efficiency would inceared when the molar ratio of K/P, Mg/P, Ca/P were1.99,0.8,0.75and mixed liquor was neutral or alkalescent. Three cations of potassium, magnesium and calcium presented multiple linear relationships with total phosphorus. And the correlations of calcium and magnesium were nagetive and positive, respectively. The correlations of potassium depended on the molar ratio of K/P. The phosphorus contents of sludge were increased by poly-P synthetized of PAO, precipitation of inorganic metal bound phosphorus compounds, adsorption of EPS.The interaction of magnesium as well as impact of three cations in the feed wastewater on membrane fouling was investigated. Based on the orthogonal analysis of this study, the optimum concentration of three cations with respect to fouling rate and phosphorus removal were proposed. The concentrations of Na, Mg and Fe has different impact on fouling rate in the order of Fe>Na>Mg, and the Na/Mg ratio higher than2or concentration of Fe more than30mg/1induced to seriously fouling. It indicated that the concentrations of Na, Mg, and Fe have different influence on properties of mix liquor such as EPS and its components, SMP, SVI, floc size and showed different fouling rate. EPS and its components, SMP, SVI had positive relationships with the membrane fouling resistance (Rf). The total EPS, protein EPS, and SVI proved to be significant correlation between fouling resistance. However, SMP was weak than EPS correlation. The EPS and SVI presented multiple linear relationships with the ratio of permeate flux to transmembrane pressure (SF). The SVI and EPS showed negative correlation with SF and the effect of SVI was weak than EPS.