| In this paper,according to the requirements of upgrading and reconstruction of a waste water treatment plant in Lanzhou,the corresponding reaction device was designed.Through the analysis of the correlation among the multi-parameter characteristics of the mixed liquid in the membrane bioreactor(MBR)process under different hydraulic retention time(HRT),the engineering feasibility of the combination of suitable HRT regulation and various methods and strategies of adding powdered activated carbon(PAC)to cope with membrane fouling in MBR was sought.The main conclusions are as follows:1)The experiment on the influence of membrane filtration on effluent water quality and operation cycle was carried out.Membrane flux has no significant effect on effluent quality.Through the distribution analysis of membrane pressure difference and membrane resistance,it was found that the irreversible resistance accounted for the highest proportion,accounting for 60-80% of the total resistance.2)The influence of mixed liquid characteristics in MBR process under different HRTs was explored.The results showed that the elongation of HRT shortened the operation cycle of membrane module,the ratio of SMP content and high molecular weight increased,the decrease of polysaccharide content and sludge particle size in EPS had a great effect on membrane resistance,which led to the rapid increase of TMP and accelerated the process of membrane fouling.At the same time,the increase of sludge Zeta potential and the decrease of sludge viscosity lead to the weakening of sludge cohesion and mass transfer capacity,resulting in the reduction of treatment capacity and the deterioration of effluent water quality.3)The field experiment of PAC enhanced MBR for the treatment of biochemical tail water was carried out.The effects of PAC addition on the properties of sludge mixture,effluent water quality and microorganism were analyzed.The results showed that the contents of SMP and EPS showed a decreasing trend with the increase of PAC dosage,which was mainly reflected in the continuous decrease of polysaccharide content,protein content basically remained unchanged,and the increase of sludge particle size in the mixture.The decrease of SMP and the increase of sludge particle size were beneficial to the slow growth of TMP and alleviate membrane fouling.The increase of PAC dosage led to the increase of sludge concentration in the mixed liquid,which further affected the increase of the mixture viscosity.Meanwhile,the molecular weight measurement showed that the molecular weight distribution range in SMP was wider.Compared with SMP and sludge particle size,these factors had less influence on membrane resistance.Adding PAC also improved the sludge settling and water removal.Biochemical tail water nutrient concentration is low,leading to a lower microbial activity,through the genus level species classification analysis,that the main microbes in the MBR for proteobacteria and bacteroidetes,when PAC is added to the mixture,the proportion of proteobacteria increases,which promotes the treatment efficiency of organic matter and nitrogen.Adding PAC can steadily improve the removal efficiency of COD and TN,and reduce the ratio of bacteroidetes and bitrospirae.The lower ratio of bacteroidetes is conducive to alleviating membrane pollution and prolonging the operation cycle of MBR.The research results provide a technical guidance method for MBR to be effectively applied in the advanced treatment of domestic sewage treatment tail water,and to enhance the operational reliability and control means. |
