Study On Sludge Process Reduction Activated Sludge(Spras) Wastewater Treatment Technology

Sludge process reduction activated sludge(SPRAS)wastewater treatment process is an originally-innovated technology,and can simultaneously achieve wastewater treatment and complete reduction of sludge except for mineral materials,indicating promising application prospect.Nevertheless,the SPRAS technology are still facing to many problems,such as lower nitrogen and phosphorus removal efficiency,uncertain sludge reduction mechanism,etc.Aiming at these key problems,the long-term stable operation characteristics of the SPRAS technology were analyzed by the pilot-scale test in the Bailonggang wastewater treatment plant(WWTP),and performances of organic degradation,nitrification,denitrification and phosphorus removal were systematically studied and improved.Furthermore,the sludge reduction mechanism was preliminarily investigated.The SPRAS technology achieves effective removal of COD and BODS,with their effluent concentrations meet requirements of Grade 1A of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants(GB18918-2002).The in-process organic pollutants concentrations illustrates that the front aeration tank in sludge process reduction(SPR)module could achieves 50%COD removal and 75%BOD5 removal,respectively.The front setting tank in the SPR module can also removes a certain level of organic matters.Under the same operating conditions,the SPRAS process yields higher removal efficiencies of organic matters and more stable effluent quality than the anoxic/anaerobic/aerobic(RAAO)process.Because of the theoretically infinite sludge retention time(SRT),the nitrification efficiency of the SPRAS process was relatively high and much less affected by temperature.Under low temperature below 12?,the average effluent NH3-N concentration of the SPRAS system was 7.25±5.25mg/L with 100%qualified to the requirement of Grade 1B of the GB 18918-2002,significantly lower than the average effluent NH3-N concentration(16.34 ±8.78mg/L)of the RAAO system.The test results also showed that such toxic substances as sulfide and landfill leachate have significant inhibitory effects on activity of nitrifying biomass in the Bailonggang WWTP.It was determined that the maximum specific growth rate of nitrifying biomass in the SPRA,S process was 1.18d-1 at 20?,significantly higher than the value 0.50 d-1 in the RAAO process of the Bailonggang WWTP and the value 0.78 d-1 in the AAO process of the Quyang WWTP.It was also higher than the recommended value 0.80d-1 in the Activated Sludge Models(ASM).The phenomenon is probably attributed to that the front aeration tank in the SPR module could effectively remove toxic substances in the wastewater,and thus enhances the activity of nitrifying bacteria in the subsequent nitrification module.Under the same SRT,ammonia oxidation rate(AUR)of the SPRAS process was 3 times of the RAAO process.The front aeration tank of the SPRAS system can degrade more than 50%influent COD,resulting in inadequate carbon source supply for the subsequent denitrification process.Therefore,the step-feed module was employed in the pilot-scale test to enhance denitrification efficiency.With 50%influent directly fed into the subsequent nitrogen removal module,effluent total nitrogen of the SPRAS system can sharply decrease from 24.25±5.17mg/L to 14.87±3.41mg/L,and the qualified rate of Grade 1A increases from 16.7%to 66.6%.The in-process concentrations of nitrogen pollutants illustrates an obvious simultaneous nitrification and denitrification(SND)phenomenon under ambient temperature,and the SND efficiency achieves optimal with influent C/N ratio close to 10 and DO concentration of the front aeration tank in the SPR module controlled at 0.4mg/L.The SPRAS system was operated without sludge discharge in a long period;therefore,the system has no biological phosphorus removal performances.A chemical phosphorus removal module is designed for the secondary clarifier effluent.Chemical phosphorus removal effects of polyaluminium chloride(PAC)and polyferric sulfate were compared by jar test,and the PAC was chosen for chemical phosphorus removal with optimal dosage of 60mg/L.The effect of initial phosphorus concentration on optimal dosage was analyzed,and the result showed that the best Al/TP ratio decreases with initial phosphorus concentration increasing.The addition of PAC to secondary clarifier effluent in the pilot test can yields effluent TP and P04-P lower than 1.0mg/L and approaching 0.0mg/L,respectively.The ratio between volatile suspended solids to suspended solids in the activated sludge mixed liquor declined from 0.75 at the start-up of pilot-scale test to 0.33 after 307 days operation,and the sludge volume,while the Sludge Volumetric Index(SVI)decreased from 244.4mL/g at start-up to 82.3mL/g after 228 days operation.The SRT of SPRAS technology by the pilot-scale test in the Bailonggang WWTP was 276 days,within 307days the system's sludge reduction was 90.9%,the results showed the SPRAS process had a very significant reduction effects.The pH and ORP at the bottom of front settling tank in SPR module both fell down.The pH value declined from 7.89 at startupto 5.88 after 90 days operation,and then fluctuated in the range from 4.98 to 5.97;the ORP decreased from 54mV at start-up to-198mV after 228 days operation.After 150 days operation,ORP was lower than-1 00mV,demonstrating a significant anaerobic condition.The mechanism of SPRAS technology has been preliminary studied.Through three indicators of sludge reduction percentage,sludge decay rate and sludge decay coefficient,compared SPRAS system and the traditional system of sludge digestion,Analysis of sludge reduction mechanism by ORP,carbohydrates,protein,UV254 and other parameters.Ultimately sludge reduction process module mass balance model has been used to calculate the reduction effect.Compared to the traditional sludge digestion,SPRAS system has some advantages,Within 48h the system's sludge reduction was 34.3%,sludge reduction rates and sludge decay coefficient were 4890 mg/(L-d)and 17.2 mg/(mg-d).Through the comparative study,it found that effluent flow in the system can speed up SPRAS sludge reduction,High sludge concentration,low ORP contributed to the effective excess sludge reduction in SPRAS system,and the cell lysis effect is one of main factors of SPRAS system to reduce sludge production.Through analyze the reduction of sludge process dynamics,it found that sludge reduction process in line with a dynamic equation:SS = 15.896 e-0.675t(R2 = 0.9886)The sludge process reduction rate constant is 0.1675 d-1,which is significantly higher than the recommended range of sludge decay rate constant(0.04-0.075 d-1)in Code for Design of Outdoor Wastewater Engineering(GB50014-2006).