Preparation Of Modified Micro-electrolytic Filler And Study On Denitrification And Dephosphorization For Low C/N Wastewater

The traditional biological treatment for denitrification and dephosphorization of low C/N wastewater are unable to meet increasingly stringent emission standards,leading to a large amount of nitrogen and phosphorus emmisions which causes a great threat to the ecological security.Thus,how to effectively achieve the denitrification and dephosphorization of low C/N wastewater has become an urgent problem.Microelectrolysis can not only improve the biodegradability,but also provide electron donors for microorganisms and make up for the lack of organic carbon source in wastewater.Therefore,in this paper,microelectrolysis and activated sludge processes are used to treat municipal domestic wastewater and waste leachate,which are representative of low C/N wastewater,forming a new integrated process for nitrogen and phosphorus removal of low C/N wastewater.The modified micro-electrolytic filler was applied to the experiment and mechanism study of nitrogen and phosphorus removal in simulated urban domestic wastewater.The optimal preparation conditions of the modified micro-electrolytic filler were obtained from single-factor experiments:roasting temperature of 800°C,Fe/C of 4:1,clay content of20%and additive content of 5%.Under these conditions,the removal efficiencies of TP and NH₃-N were 97%and 62.88%,respectively.The compressive strength of the filler was 3.5 Mpa and the specific surface area was 154.2 m²/g,which reached the standard of artificial ceramic filter media for water treatment according to"Lightweight Aggregates and Its Test Methods"（China,GB/T17431.1-2010）and"Artificial Ceramisite Filter Material for Water Treatment"（China,CJ/T 299-2008）.The mechanism of the nitrogen and phosphorus removal experiments was investigated by scanning electron microscopy-energy dispersive spectrometer（SEM-EDS）,X-ray photoelectron spectroscopy（XPS）and X-ray diffraction（XRD）.Results showed that the removal of nitrogen and phosphorus from water bodies was the combination of surface adsorption and chemical precipitation,and the main products were MgNH₄PO₄·6H₂O,MgHPO₄,Mg₃（PO₄）₂ and Fe PO₄.The modified micro-electrolysis filler was applied to the nitrogen and phosphorus removal of landfill leachate to investigate its treatment effect of actual wastewater.Single factor experiment was carried out to investigate the influence of various factors on the effect of Fe/C-MgCO₃filler,among which reaction time,initial p H and ventilation rate had great influence.After that,the optimal reaction conditions were achieved by response surface optimization experiments with TP removal rate as the response value:the reaction time was 360 min;the initial p H was 3.35,the ventilation rate was 0.32 m³/h,and the TP removal rate predicted by the model was 80.64%（95%Confidence interval:76.92%to 84.36%）.The verification experimental results showed that the TP removal efficiency was 83.19%,within the 95%confidence interval.Finally,long-term performance test and Excitation-Emission-Matrix Spectra analysis were conducted,which proved the good anti-platelet performance of the filler.Based on the action of microelectrolysis,the large molecules of organic matter which were difficult to be biodegraded in waste leachate were removed efficiently,improving the biochemical performance of landfill leachate.For the actual wastewater,although the single micro-electrolysis system has high efficiency of phosphorus removal,the nitrogen removal efficiency was only 22.5%,which is poor for nitrogen substances.Therefore,micro-electrolysis process was combined with activated sludge process in the subsequent experiments to achieve better nitrogen and phosphorus removal effect.The integrated microelectrolysis/activated sludge process adopted the material loading method of A+Fe-C/O+Fe-C.The optimal reaction conditions for each factor were obtained through single-factor experiments as follows:HRT was 48 h,the initial p H range of wastewater was 7.5～8.5,the ratio of biological iron to carbon was 2:1,DO content was 6～8 mg/L.In the stable operation stage,the removal efficiencies of COD,TP,NH₃-N and TN in landfill leachate by micro-electrolysis/activated sludge coupling process were 68.5%,83.22%,71%and 66.65%,respectively.Compared with A+Fe-C/O process,A/O+Fe-C process,single iron carbon process and single A/O process,the TP removal efficiency of the integrated process remains at a higher level,and the NH₃-N removal efficiency increased about 48.5%.Therefore,the integrated process had higher pollutant removal efficiency and system stability.It also facilitates the decomposition of refractory organic matters such as fulvic acid and humus-like substances.This study shows that the integrated process is a complex system integrating micro-electrolysis reaction and biological action,which has important application value in landfill leachate treatment.