Bio-Ecological Wastewater Treatment For Rural Domestic Wastewater

Limited water resources and ensuring access to clean water confront the world with critical environmental challenges.In highly industrialized countries,such as china,the rate of water pollution is high,leading to a shortage of fresh water needed for human consumption.In that respect,large scale centralized wastewater treartment systems are considered a characteristic of highly industrialized countries,and for long have been regarded as an extremely successful approach in the wastewater treatment.Despite the availability of this approach in China,the country has continued to experience freshwater shortage and deterioration.In general,rural domestic wastewater has become a significant source for the pollution of freshwater bodies.The conventional treatment processes are expensive to build especially for areas of low socioeconomic status.Therefore,cost-effective and environmentally sound methods of treating wastewaters are needed.Bio-ecological wastewater treatment methods have gained popularity from the last several years and have been used as an alternative to conventional wastewater treatment methods because of their easy maintenance and operation,low energy consumption,and water recyclability.A modified bio-ecological A20-wetland system for rural wastewater treatment consisting of a biological unit(anaerobic baffled reactor,anoxic tank and oxic unit,A20)and an ecological unit(horizontal flow constructed wetland)was developed,and key performance indicators were identified.The performance and the characteristics of ABR(anaerobic baffled reactor)were investigated during different seasons.ABR successfully achieved COD removal efficiencies 74%during summer,68%during Autumn/spring and 62%during winter.Compartment ?,? and ? showed high removal rate of COD during whole study period.At lower OLR(organic loading rate),COD removal rate was high.The analysis of biogas production during all seasons showed downward trend with increase of HRTs(hydraulic retention time).Compartment ? showed high VFA(volatile fatty acid)synthesis compared to others compartments.The ABR has the potential to provide a greater efficiency and be applicable for all type of seasons and temperature conditions.The performance and the characteristics of anoxic digestion during A20-CW processes were investigated for denitrification and deoderization.Key parameters such as;reflex ratio,dissolve oxygen(DO)and nitrogen load were studied to optimize chemical oxygen demand(COD),total nitrogen(TN),ammonia(NH4-N),threshold odor number(TON)and sulfide removal in anoxic tank.The reflex ratios of 100%,150%and 200%were optimal for summer,winter and winter,respectively.Optimum TON removal efficiency was 92%in summer,90%in winter and 93%in winter.The TON value increased linearly with the concentration of sulfide.By increasing of influent DO the removal efficiency of TON and sulfide increased whereas dnitrification process decrease.The system characteristic is high anoxic digestion for denitrification and deoderization.During overall performance,the bio-ecological treatment system showed high removal efficiency for pollutants,successfully achieving 91%,85%,78%,and 92%removal efficiencies for chemical oxygen demand(COD),ammonium(NH4-N),total nitrogen(TN),and total phosphorus(TP),respectively.The concentrations of pollutants in the effluent from the system were lower than the Class 1 A regulated values of the Chinese National Standard GB18918-2002.The system offered high removal efficiency,simple operation,and low energy consumption.The A20-wetland is a good alternative for rural wastewater treatment systems.Constructed wetlands are used to treat wastewater and their applications,performance and usage can be improved by selecting suitable substrate.The different plants may differ in their capacity to assimilate nutrients in constructed wetland system.In this research,Michaelis-Menten kinetic provides a useful tool for the identification of plant nutrient uptake efficiency and selection of plants.Six economical plant species(P.heteroclada,M.hispida,Ipomoea aquatica,B.juncea,C.esculenta,A.tuberosum)were selected to investigate the uptake kinetics Michaelis-Menten constant(Km)and maximum uptake rate(Imax)for nutrients.I.aquatic showed higher maximum uptake capacity for all three nutrients(PO4-P,NO3-N and NH4-N),then second highest uptake capacity for PO4-P,NO3-N and NH4-N was found for.tuberosum,B.juncea and M.hispida.I.aquatica has the highest Imax and lowest Km values for all three nutrients and it has good capabilities to adjust in high PO4-P,NO3-N and NH4-N nutrient condition.Imax and Km of P.heteroclada were relatively small and suitable for low nutrients concentration environment,whereas the Imax and Km of A.tuberosum,M.hispida and B.juncea were relatively large,which is suitable for treating wastewater with high nutrient concentration.The use of constructed wetland for wastewater treatment by growing economic vegetables can play a role to overcome water and food scarcity.A.tuberosum.,P.heteroclada,I.aquatica Forsk.And C.esculenta plants were selected to grow in hybrid constructed wetland under natural conditions.The impact of ratio of nitrate to ammonium nitrogen on ammonium and nitrate N removal and total nitrogen were studied.I.aquatica Forsk.and P.heteroclada showed higher removal efficiency for ammonium N under higher ammonium concentration whereas A.tuberosum,showed higher nitrate N removal when NO3-N concentration was high in wastewater.C.esculenta showed little efficiency for both N source compared to other vegetables.Removal of nutrients from wastewater is essential to protect receiving water bodies from deterioration.Pilot-scale hybrid constructed wetland(CW)system was the combination of Constructed Floating Treatment Wetlands(CFW)and horizontal flow constructed wetlands(HFCW)and operated for whole years covered all seasons.The research was conducted to investigate the performance of CW system,regarding spatially,water depth and seasonally removal of nutrients.Different species of economical plants were selected and divided into four groups to grown in four CW systems(CW-? to CW-?)seasonally.Removal efficiencies increased along the bed and most of the TP removal occurred in second bed,whereas TN and NH4 removal were associated with plant root system and biomass.Optimum removal of nutrients with respect to water depth was at 35 cm.TN and NH4 removal pattern was almost similar in different CWs.TN and NH4 removal were higher during summer compared to winter,only CW-? showed vice versa.