PERFORMANCE EVALUATION OF 50 KLD SMALL SCALE PVA GEL BASED MBBR SEWAGE TREATMENT PLANT AT KIRTINAGAR

Abstract

Several small-wastewater treatment technologies (mainly fixed film or moving film activated sludge process) are installed in India and incomplete degradation of organic matter, nitrogen and formation of pin point flocs are major problems arising in these treatment plants which causes high suspended solids in effluent. Moreover, majority utilizes non-porous media of low specific surface area. Polyvinyl alcohol (PVA)-gel is highly porous biomass carriers with high specific area (∼2500 m2/m3) and can escape from those drawbacks due to the excellent structure, which can trap and intercept the biomass efficiently. In lab scale studies it was observed that PVA-gel is not only efficient in organic removal but also achieve high nitrification rates. Based on the above advantages and results from pilot-studies, a 50 KLD small-scale Biological nutrient removal sewage treatment plant (STP) was installed in a small township Kirtinagar at the bank of River Alaknanda. The present work deals with the evaluation of performance of the sewage treatment plant in comprehensive terms. Considerable attention has been given on its performance under variable seasonal conditions, shock loads, simultaneous nitrification and denitrification (SND), carbon and nitrogen balances. The STP have three biological reactors including PVA-gel aeration tank-anoxic tank-aeration tank configuration having effective 6 hours hydraulic retention time (HRT). The equalized flow is pumped to distribution box, where 80 % of flow is transferred to PVA Gel tank while the remaining 20 % to anoxic tank which serves as carbon source for denitrification. v During almost one-year study, the raw sewage temperature varies between 8°C – 30°C, pH values were between 7  0.5 and DO concentration fluctuates 3.3 to 7.5mg/L, 0.1 to 0.2 mg/L and 2.6 to 5.5 mg/L in PVA gel tank, anoxic tank and aeration tank respectively. It was observed that average BOD, COD, TSS and TN removal efficiencies were 91 %, 90 %, 93 % and 84 % respectively. BOD, ammonia and total nitrogen removal rate was not affected by seasonal temperature variation. While, in PVA-gel tank nitrification rate and COD removal rate decreases with decreases in temperature. Organic and ammonia removal rate in PVA-gel tank was dependent on organic and ammonia loading rate respectively. The maximum organic and ammonia removal rate was 16 KgSCOD/m3gel/d and 2.4 KgNH4+/m3gel/d respectively. Also, in PVA-gel tank significant nitrogen removal occur due to SND which is affected by temperature and COD/N. Denitrification rate in anoxic tank is affected by COD/N ratio and also affected by temperature in low temperature range. The aeration tank not only resilient in COD loading but also helps in reduced sludge production by lysis and autooxidation. Therefore, COD concentration of treated waste water was always less than 50 mg/L and yield very less sludge production. Finally, PVA-gel based moving bed biofilm reactor (MBBR) excellent performance in terms of removal efficiency. The average BOD, COD, TSS and TN concentration of final treated effluent were <10 mg/L, <50 mg/L, <10mg/L and <8mg/L respectively which satisfies New effluent standards and CPHEEO guidelines for wastewater reuse. Operation and maintenance cost analysis was performed and it was observed that the specify treatment cost of wastewater is much higher than other large or centralized STPs.