Study On The Treatment Of Decentralized Domestic Sewage With Aged Refuse-substrate Hybrid Constructed Wetland

Decentralized rural domestic sewage possess the characteristics such as tiny emission,large diurnal variation coefficient and easily-biodegradable,due to residents spread dispersedly and weak economic foundation in rural region,the decentralized rural domestic sewage generally could not be incorporated into the urban sewage pipeline for collection and emission.To solve environmental pollution caused by random discharge of decentralized rural domestic sewage and enhance the rural environment,an aged refuse-substrate horizontal-vertical hybrid constructed wetland was developed;it has small land occupation and easily operation maintenance.The vertical stacking structure of horizontal wetland and vertical wetland could reduce the land occupation of hybrid constructed wetland,and the flood/drain operation mode of vertical wetland could prevent the clogging problem to a certain extent.This research studied the treatment efficiency of aged refuse-substrate hybrid constructed wetland to treat decentralized sewage under different operation parameters.The slow-release solid carbon source was added to the constructed wetland to improve the total nitrogen removal performance and the treatment effect was studied after adding carbon source.And the phosphorus adsorption characteristic of aged refuse and the phosphorus removal pathways of aged refuse in the biological filtration process were analyzed.The results can be listed as follows:When the influent hydraulic loading rate increased from 0.03m3/(m2·d)to 0.29m3/(m2,d),the hybrid constructed wetland had good aeration capacity for the sewage,the average DO concentration in the influent,middle tank and effluent were 0.63,3.79 and 6.37 mg/L respectively.In the constructed wetland system,the COD average removal efficiency was90.11%and the average effluent COD concentration was 18.07mg/L,the ammonia nitrogen average removal efficiency was 97.48%,the effluent NH4+-N concentration ranged from 0.34 to 7.21 mg/L,the total phosphors average removal efficiency was 96.41%and the effluent TP concentration ranged from 0.01 to 0.84mg/L.The effluent concentration of COD,NH4+-N and TP could meet the first class B discharge standard of pollutants for municipal wastewater treatment plant.But TN average removal efficiency was 29.56%and the effluent TN concentration has not reached the discharge standard.Adjusting flood/drain ratios(2:1,3:1,4:1)did not much affect the effluent concentration of DO,COD,NH4+-N,TN and TP,the sewage DO concentration in the middle tank increased with the increase of flood/drain ratio.The TN removal efficiency increased under high organic loading rate,the average removal efficiency could reach to 75.02%,and the effluent TN concentration ranged from 18.44 to 34.77mg/L.Compared to untreated and acid-treated rice straw,the alkali-treated rice straw possessed larger cumulative COD release amount and saturation release quantity,which is the most proper denitrification carbon source.The alkali-treated rice straw had long-term carbon source release ability and its denitrification capacity ranged from 35.16 to 41.56g/(m 3·d).The slow-release solid carbon source was added in the primary horizontal wetland and middle tank successively.After adding carbon source to the hybrid constructed wetland,the average effluent TN concentration could be reduced from 49.14 mg/L to 32.66 mg/L,and the removal efficiency increased from 39.76%to 52.77%,but the effluent TN concentration has not reached the discharge standard yet.Pseudo-second-order adsorption kinetics and Freundlich isotherm model could fit the phosphorus adsorption process on aged refuse better,the adsorption process was happened on uneven surface and between monolayer and multilayer adsorption.Adsorption enthalpy was over 40KJ/mol,adsorption entropy was over zero,Gibbs free energy was over zero under 25 ?,less than zero under 35 ? and 45 ?,indicated that phosphors adsorption on the aged refuse was chemical adsorption process,it is a spontaneous and endothermal chemical adsorption process under high temperature.In simulated biological filtration system,almost all phosphors removed by simulated biological filtration system was entrapped on the aged refuse surface.The inorganic phosphors accounted for over 90%,occluded phosphors,calcium phosphors and aluminum phosphors were majority part,iron phosphors and exchangeable phosphors were minority part,indicating that chemical adsorption played the greatest role in phosphorus removal in the simulated biological filtration system.The inorganic phosphors reacted with Ca2+,Fe3+ and Al3+and its oxide and hydrate,formed insoluble compound adhered on the aged refuse surface,the growth of occluded phosphors was dominant mechanism of phosphors removal.The microbial phosphorus removal accounted for less than 10%,which is rare to phosphors removal.The research results showed that the aged refuse hybrid constructed wetland could treat decentralized domestic sewage well,the COD,NH4+-N,and TP effluent concentration except TN concentration could meet the first class B discharge standard of pollutants for municipal wastewater treatment plant.The aged refuse had good adsorption capacity to phosphorus;it is a kind of outstanding adsorption material.The research could provide theoretical basis for the application of aged refuse hybrid constructed wetland.The constructed wetland has the characteristic of small land occupation,simple operation maintenance,and has broad application prospects in treating rural domestic sewage,reclaimed water and initial rainwater.