The Research On Enhanced High-rate Filtration Technology For Wastewater Reuse Using Metal-oxides-coated Sand Filter Media

In order to remove turbidity, COD and phosphate from municipal secondary effluent for wastewater reuse, high-rate filtration technology (filtration rate≥30m/h) using granular media (natural quartz sand and anthracite) is put forward and investigated. Several new types of modified filter media—metal-oxides-coated sands were prepared for enhancing filtration.Treatment efficiency of reclaimed wastewater with or without preoxidation (KMnO4) enhanced microflocculation high-rate filtration was investigated. The results show that effluent quality by high-rate filtration can meet (GB/T 18920-2002). Moreover, hydraulic flow pattern of high-rate filtration were investigated. Meanwhile, backwash method and main operation parameters of high-rate filtration were determined.By experiments in 11 cycles of different operation conditions (gradation and bed depth of double-layer media), the results indicate that, the particle size of sand ranges from 0.6~1.2mm, bed depth=50cm, effective particle size=0.7mm, L/d100=714; the particle size of anthracite ranges from 1.2~1.6mm, bed depth=60cm, effective particle size=1.2mm, L/d10=500,ΣL/d10=1214. The initial filtration rate of high-rate filtration should be controlled at naturally largest filtration rate. Hydraulic flow pattern of high-rate filtration was calculated by two different Reynolds number formulas, and hydraulic flow pattern was thought to be turbulent flow.Reclaimed iron oxide was used to prepare iron-oxide-coated sand (RIOCS) in order to solve waste sludge deriving from micro-electrolysis process. The experimental results also can provide a beneficial idea which waste solutions containing high concentrations of metal (iron, aluminum or manganese) ions can be used for coating sand filter media in view of solving waste disposal problem. The effects of different MOCS (RIOCS, IAOCS, IOCS) and natural quartz sand (QS) on the removal of pollutants were researched for wastewater reuse.Two new types of iron-oxide-coated sand filter media IOCS-1 and IOCS-2 (prepared at low coating temperature and high coating temperature, respectively) were investigated for phosphate removal. SEM, XRD, FTIR and EDAX analysis were conducted for the characterization of IOCS-1 and IOCS-2. In batch experiments, the effects of initial solution pH, contact time and dose of IOCS on phosphate removal were investigated. The adsorption isotherms of phosphate by IOCS were fitted using Langmuir, Freundlich and Temkin equations at various temperatures (15℃,25℃, 35℃). The phosphate adsorption kinetics and thermodynamics of IOCS-1 and IOCS-2 were researched. The results indicate that the removal efficiency of PO43- by IOCS-1 was greater than IOCS-2. The sequence of anions studied competing with phosphate on IOCS-1 was HCO3->SO42->Cl-, but the effect of competitive adsorption was not great.The results of column filtration incate that phosphate removal depends on initial pH, flow rate and bed depth. Moreover, Phosphorus adsorbed IOCS-1 can be effectively regenerated by 0.1 M NaOH solution and column kept almost constant phosphate removal consecutively during three cycles.Results of this study showed that IOCS can be used as a new type of filter media through reforming filtration unit for removal of low concentration phosphate in water and wastewater treatment.