Development And Application Of Novel Suspended Carrier

The moving bed biofilm reactor (MBBR) is an efficient and economical wastewater treatment process, which has been widely used at home and abroad. Suspended carrier is the central part of MBBR, and selecting the appropriate suspended carrier is the critical step for successfully operation of MBBR. In this paper, experience of predecessors on modified suspended carrier was summed up. The new formula of suspended carrier was researched and developed to enhance biological performance and physical properties. On this basis, combined with the machine-shaping characteristics of polyethylene plastic, mass production of novel suspended carrier was achieved by determining the process parameters of new suspended carrier.A series of pilot and full scale test were completed to test the performance of novel suspended carrier, which was successfully applied to the Upgrading and Modifying Project of Cheng Yang wastewater treatment plant. The comprehensive evaluation method of novel suspended carrier had been established, and its standardized future was discussed.Novel suspended carrier was developed by adding additives, hybrid modification and optimization of the machining technics, aimed at existing shortcomings in the application. The main raw materials of novel suspended carrier were high-density polyethylene, with a certain amount of microbial activity regulator, anti-aging, antioxidant and UV absorber added.The technology parameters of novel suspended carrier: temperatures of six-way heaters on extruding machine extruder are 160℃,170℃,180℃,185℃,180℃and 170℃in order. Vacuum degree of vacuum calibrating units is 3-6×104 Pa; Screw speed 22-29 r/min; pulling speed of caterpillar-tractor 300-400 r/min. Density of novel suspension carrier is 0.96-0.98 g/cm3; effective surface area of 500m2/m3, the service life 10 years.A series of experimental investigation were carried out to test the performance of novel suspended carrier, including pilot-scale experiment of low-temperature municipal wastewater, full scale experiment treatment of aquaculture waste in situ, pilot-scale experiment of chemical wastewater and the Upgrading and Modifying Project of Cheng Yang wastewater treatment plant, and achieved good results.The mean COD of pilot reactor effluent treating municipal sewage at low temperature (10-12℃) is 47.3 mg/L, NH3-N less than 0.3 mg/L, TP about 15 mg/L.After 60 days, COD and NH3-N in full scale reactor effluent treating aquaculture wastewater in situ were reduced to the 20 mg/L and 0.6 mg/L respectively. DO in water of fishpond reaches 6.1 mg/L. It costs about 0.027 RMB to treat a of such wastewater.Novel suspended carrier, using a new type of modified formulations, has an advantage over traditional suspended carrier in teams of the reactor startup rate COD removal and other aspects, dealing with chemical wastewater in a pilot. The average COD removal rate of I, II and III suspended carriers were 82.2%,81.8% and 70.6% respectively.In upgrading and modifying project of Cheng Yang wastewater treatment plant, after adding novel suspended carrier, the mean COD concentration in effluent of SBBR process is 29.5 mg/L, NH3-N 1.2 mg/L, TN 14.5 mg/LBased on the investigation and research, comprehensive evaluation of suspended carrier performance was established on the basis of Delphi, AHP method and Fuzzy decision-making theory. Hierarchic analysis structure for comprehensive evaluation of suspended carrier performance was constructed, taking technical and economic facts into account. The hierarchical structure was divides into two criterion rule levels including technical and economic, and into nine plan levels including specific investment and working expense, the effective surface area, biofilm activity, biofilm formation period, service life, technology maturity, mechanical strength and capacity of resistance to hydraulic loading impact.K=(0.2616,0.0540,0.0281,0.1311,0.1046,0.1016, 0.1421,0.0830,0.0939)。On these basis, suspended carrier ofⅠ,ⅡandⅢtypes were evaluated, combined with data in a chemical wastewater pilot test and products parameters provided by the manufacturers. The evaluation results show that: suspended carrier ofⅡtype is with best performance, suspended carrier of I type with better performance, andⅢtype with worst performance.Finally, the standardization of CESC was discussed from the reactor structures, test methods and evaluation results presentation and other aspects.