Development Of A Novel Tidal Flow Construction Solid Waste(CSW)based Constructed Wetland And Its Application On Decentralized Campus Domestic Wastewater Treatment

Constructed wetlands,as a convenient and effective wastewater treatment technology,had a wide appliance foreground.However,there were still problems,for example,the improvement of pollutants removal,especially to enhance the dissolved oxygen supply and the ability of nitrogen and phosphorus removal.On the other hand,as an inescapable by-product of the construction process,construction solid waste has been brought to public attention because of its enormous quantities generated.Therefore,seeking suitable methods of CSW disposal was of great significance.Fly ash brick was one main component of CSW.Batch adsorption were conducted to study the adsorption characteristics of fly ash brick powder to phosphate,and the effects of various parameters on phosphate adsorption were also evaluated.Then a novel constructed wetland was developed for campus domestic wastewater treatment,whose substrates were fly ash brick and pisolite recovered from CSW.Because of the poor P removal capacity in traditional constructed wetlands,fly ash brick was applied to provide a significant P removal efficiency.The constructed wetlands,which employed a tidal flow and step-feeding strategies,also improved the dissolved oxygen supply and N removal efficiency.The adsorption characteristics of phosphate onto fly ash bricks powder were evaluated.Batch adsorption tests were conducted to study the effects of various parameters such as initial concentration,adsorbent dosage and solution pH on adsorption.Adsorption kinetics data were tested using pseudo-first-order,pseudo-second-order and intraparticle diffusion models.It showed that the adsorption process followed a pseudo-second-order reaction.The mechanism of the adsorption process was determined from the intraparticle diffusion model,external diffusion model,Bangham's equation and Boyd model.The mechanism studies revealed that the process was complex and followed both surface adsorption and particle diffusion.Langmuir,Freundlich and Temkin isotherms were used to analyze the equilibrium data,and the Langmuir isotherm fitted the experimental data significantly better.The phosphorous theoretical saturated adsorption capacity was 44.62 mg/g.Enhanced sedimentation pretreatment and multi-stage vertical subsurface flow constructed wetlands?MVSF-CW?,which employed tidal flow strategy and used construction solid waste as main substrate,was used to investigate the characteristics of typical pollutants of decentralized campus domestic wastewater from campus in Xi'an.The one piont feeding strategy(feeding the raw wastewater in the 1^st stage)was used for operational period 1,which was operated under 6 h,8 h and 12 h for each cycle?operated for 120 days?.When the influent COD,NH₄⁺-N and PO₄^3--P were92.13±23.94 mg/L,25.70±7.41 mg/L and 2.73±0.75 mg/L,the effluent concentrations were 53.07±12.68 mg/L,4.36±3.62 mg/L and 0.02±0.02 mg/L,respectively.The average removal efficiencies of COD,NH₄⁺-N and PO₄^3--P were 41.15%,84.52%and 99.35%,respectively.According to the first level A criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant?GB18918-2002?,26.83%,60.98%and 100%of the effluent COD,NH₄⁺-N and PO₄^3--P were met the discharge standard,respectively.Step-feeding strategy(feeding the raw wastewater in the 1^st,2^nd and 3^rd stage respectively under the feeding ratio of 1:1:1)was used for operational period 2?operated for 480 days?.When the influent COD,NH₄⁺-N,TN and PO₄^3--P were177.88±75.66 mg/L,56.85±12.86 mg/L,64.49±14.32 mg/L and 3.95±1.29 mg/L,the effluent concentrations were 43.66±17.23 mg/L,0.80±0.90 mg/L,19.46±11.28 mg/L and 1.48±0.33 mg/L,respectively.The average removal efficiencies of COD,NH₄⁺-N,TN and PO₄^3--P were 75.46%,98.64%,69.82%and 58.96%,respectively.According to the first level A criteria specified in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant?GB18918-2002?,72.93%,99.25%,43.94%and 0%of the effluent COD,NH₄⁺-N and PO₄^3--P were met the discharge standard,respectively.Fly ash brick based constructed wetland shown an excellent P removal performance.At the second stage constructed wetland?fly ash brick as main substrate?for different feeding strategies,the cumulative P removed against cumulative P loaded were 41.74mg-P/g-CSW and 187.58 mg-P/g-CSW,respectively.The lifetime of the fly ash brick in constructed wetland was reasonably longer than that determined from the adsorption batch test.By employing tidal flow and step-feeding strategies,the effluent quality improved significantly.The concentration of DO was greatly improved by the tidal flow strategy,then it would not be a limiting factor for nitration.Under two operational phases,the oxygen supply capacity of constructed wetland were 4.02 g/m²·d and 8.62 g/m²·d,respectively.Step-feeding provided sufficient carbon source to improve the denitrification process.Take the second stage constructed wetland?operated by step-feeding?for example,the average removal efficiency of TN rose from 36.25%to65.59%.These results suggest that step-feeding could achieve high nitrogen removal.