| The protections of water and environment,especially in rural areas,have gained momentum in rural areas of China and the world at large.Formally,most of the water and wastewater treatment were carried out in conventional treatment plants,but in current years,some technologies such as Horizontal subsurface flow,Vertical subsurface flow,Free water surface flow,and hybrid constructed wetlands have been successfully employed for the treatment of water and wastewater in the rural areas.The results are of great significance to explore a technology that has low energy consumption,with high efficiency and utilization and above all is very simple in operation and maintenance.The primary objective of this research project is to carry out a study on a small-scale horizontal subsurface flow constructed wetland?HSSF-CW?for Rural Domestic Wastewater Treatment to ensure the water quality and purification before discharge to the water bodies to meet the Chinese discharge standard.Influences of Hydraulic retention time?HRT?,Hydraulic loading rate?HLR?,the pH and temperature on the treatment efficiency of the constructed wetlands during the treatment processes of this research project were assessed.This research project was conducted in two phases of experimental duration with different vegetative plants in both summer?Apium graveolens,Lactuca sativa and Capsicum annuum?while in winter?Apium graveolens,Spanacia oleracea and Cilantro?respectively.The summer experiments?May-September 2018?and winter experiments?November–February 2019?was conducted with a constant Hydraulic retention time?HRT?of 1.25 days after thirty hours and hydraulic loading rate of 180 mili liter/minute respectively.The final results obtained in summer experiments revealed pH varied in the range of 6.98 to 7.19 with an average value of 7.09 and the temperature varied between 20.4oC to 34.9oC with an average temperature of 27oC respectively.The average removal efficiency of the three vegetative species of plants for total nitrogen?TN?,nitrate?NO3-N?,ammonium?NH4+N?and total phosphorus?TP?was 76.6%,70%,82.4%and 92.4%with the average effluent concentrations of 6.5 mg/L-1,1.37 mg/L-1,2.7mg/L-1 and 0.21 mg/L-1 respectively.The removal efficiency often increased with increase in temperature and by the interception of the media,the microbial transformation and the adsorption of the plant.In comparison with the three species of vegetative plants in removal efficiencies,Apium graveolens achieved high pollutant,followed by Lactuca sativa and finally capsicum annuum for total nitrogen?TN?,NO3-N,NH4+N and total phosphorus?TP?respectively.While the main results obtained in the second round of experimental duration?winter?revealed pH values varied in the range of 6.72-6.98 with the average value of 6.85 and the temperature varied between 9oC-15oC with the average of 12oC.The average removal efficiency of the three vegetative species of plants for total nitrogen?TN?,nitrate?NO3-N?,ammonium?NH4+N?and total phosphorus?TP?reached 66%,63.8%,73.3%and 86.4%with the average effluent concentrations of 5.1 mg/L-1,0.86 mg/L-1,2.66 mg/L-1 and 0.17 mg/L-1 respectively.The removal efficiency decreased with a decrease in temperature and decreased in the microbial activity due to low temperature.In comparison with the three different species of vegetative plants in removal efficiencies,Apium graveolens achieved high pollutant,followed by spanancia oleracea and finally cilantro for total nitrogen?TN?,NO3--N,NH4+-N and total phosphorus?TP?respectively.Furthermore,the efficiency of horizontal subsurface flow constructed wetland?HSSF-CW?also revealed signifant results during the whole experimental periods.TN,NO3-N,NH4+N and TP influent fluctuates differently and the average removal efficiencies?RE?reached 77%,71.1%,82.5%and 91.1%with the average effluent concentrations of 6.5 mg/L-1,1.3 mg/L-1,2.7 mg/L-1and 0.23 mg/L-1 respectively?Summer?and 66%,63.7%,73%and 86.4%with effluent concentrations of 5.1 mg/L-1,0.87 mg/L-1,2.7 mg/L-1 and 0.17 mg/L-1 respectively?Winter?.The results of the system showed that horizontal subsurface flow constructed wetland?HSSF-CW?was efficient,feasible and suitable for rural domestic wastewater treatment.The Total nitrogen?TN?is removed by the influence of temperature and hydraulic retention time?HRT?that determines the relationship to the activities of nitrifying bacteria and denitrification potential in the treatment of wetlands.NH4+N removal is by the matrix surrounding plants'roots and nitrification microorganisms transform them into nitrate.NH4+-N is also removed by direct ingestion and evaporation that occurs best in warmest periods related to better oxic condition due to higher oxygen released by plants root that promotes nitrification process.In total phosphorus?TP?removal,the bed media is a significant sink for removal efficiency in a constructed wetland?CW?.The removal involves both biotic?uptake by vegetation,periphyton and microbial,and burial,adsorption and precipitation,exchanges between soil and overlying water column process?.Overall,the effluent discharged from the system met the Chinese discharge standards?Standard‘'1''for TN,NO3-N,NH4+N,and TP discharge standard?as regulated by the Chinese standard for wastewater treatment?GB 18918-2002?. |
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