Research On Short-Flow Wastewater Treatment Technology Based On Rapid Adsorption Regeneration Of Ammonia Nitrogen

In recent years,the discharge standard of pollutants for municipal wastewater treatment plants?WWTPs?becoming more stringent to prevent the discharge of substantial nutrient into water bodies.In China,the national Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant?GB 18918-2002?mandated a reduction of total nitrogen?TN?and total phosphorus?TP?to 15 and 0.5 mg/L,respectively.Many local standards domestic and foreign with more stringent nutrient discharge limit were issued.In WWTPs,TP can be effectively controlled by enhanced biological phosphorus removal process coupled with tertiary treatment by chemical precipitation.However,nitrification and denitrification were both commonly become bottlenecks of WWTPs because they are easily inhibited by environmental conditions,shortage of carbon source,toxic substances,etc.The conventional nitrogen removal in WWTPs have been encountering enormous challenges facing to rising discharge standards.Therefore,the short-flow wastewater treatment process based on an ammonium nitrogen?NH₄⁺-N?adsorption and regeneration?AAR?was constructed to address the above problems.In this research,AAR was constructed by a zeolite-packed column and a NaClO-NaCl regeneration unit,and coupled with an anoxic/aerobic?AO?system?AO-AAR?to achieve efficient and simultaneous removal of carbon,nitrogen and phosphorus under short hydraulic retention time?HRT?and sludge retention time?SRT?.Compared to anaerobic/anoxic/aerobic?AAO?process,the proposed AO-AAR process achieved more stable and efficient nitrogen removal with greatly shorter SRT?8 d?and HRT?5.6 h?at 10.4 ?,with TN and NH₄⁺-N in the effluent below 8.0 and 1.5 mg/L,respectively.The AO-AAR obtained efficient phosphorus removal?< 0.5 mg/L?by dosing aluminum in aerobic tank.Short SRT and high load deteriorated sludge settleability and dewaterability,but enhanced specific methane production?SMP?by improving sludge biodegradability.Dosing aluminum made the AO module operated more stable with improved dewaterability and settleability,and further enhanced SMP.Short SRT and HRT also resulted in the thriving of filamentous bacteria?Thiothrix?and heterotrophic nitrifiers?Rhodobacter,Pseudomonas and Acinetobacter?in the AO module.They helped in enhancing denitrification potential and nitrification efficiency under low temperature.Long-term operation showed that exchange capacity and physicochemical properties of zeolite were unchanged under NaClO-NaCl regeneration.Techno-economic analysis showed that the AO-AAR process will significantly greatly reduce land occupancy,improve nitrogen removal,achieve efficient reduction of CO₂ emission from aerobic tank and generate easily degradable sludge with high SMP.Although AO-AAR has a good effect in removing water pollutants,the TN concentration in the effluent is still a little high.Therefore,in order to achieve more effective TN removal and shorter HRT,the chemical enhanced primary treatment?CEPT?,AAR and biological aerated filter?BAF?were coupled,and showed rapid and efficient pollutants removal with total HRT below 5.0 h.With retention time of empty column?ECRT?of 37.5 min for zeolite-packed column and 3 h for BAF,the pilot-scale CEPT-AAR-BAF system obtained effluent with COD of 17.9 ± 6.0 mg/L,NH₄⁺-N of 0.5 ± 0.3 mg/L,TN of 2.4 ± 1.0 mg/L and TP of 0.08 ± 0.05 mg/L.The AAR module achieved outstanding NH₄⁺-N adsorption performance with NaClO-NaCl regeneration.The BAF treated wastewater mainly containing soluble organic substances enriched faster-growing heterotrophic bacteria?Pseudomonas,Comamonas?,while relative abundances of hydrolytic bacteria and AOB were relatively low.Techno-economic analysis showed that the CEPT-AAR-BAF system obtained low and stable TN to meet more stringent discharge standard with at least 60% savings of occupation and project investment,and the treatment cost?$ 0.149/m₃?should be further reduced by investigations on the regeneration of loaded zeolite.Since the core of AO-AAR and CEPT-AAR-BAF are both AAR,this study used different modification methods to modify the zeolite to obtain higher NH₄⁺-N adsorption capacity and exchangeability.The adsorption steps of natural zeolite on ammonia nitrogen were divided into two steps: membrane diffusion and internal diffusion,which conform to pseudo second-order kinetic model and the Langmuir isothermal adsorption model.The adsorption phenomenon mainly originated from ion exchange and physical adsorption.The experimental results showed that when the temperature was 25 ?,the concentration was 25 mg/L and the volume was 200 m L of ammonia nitrogen wastewater,the optimal zeolite adsorption amount was 8 g.The results of the adsorption kinetics test displayed that the optimal adsorption time was 40 minutes,and the ammonia nitrogen removal rate reached 95.4%.Zeolites modified by KCl,MgCl₂,NaCl,CaCl₂,CH₃ COONa and NaOH can improve the adsorption capacity and exchange capacity of natural zeolite in AAR system to a certain extent.The R2 of the Freundlich adsorption isotherm model of modified zeolite is higher than 0.94,which is significantly higher than the R2 of Langmuir and Temkin adsorption isotherm model,indicating that Freundlich adsorption isotherm model is more suitable for describing the adsorption equilibrium process of modified zeolite to remove ammonia nitrogen.If the modified zeolite is used in AO-AAR and CEPT-AAR systems,the NH₄⁺-N and TN concentrations in the effluent will be lower.