The Removal Efficiency Of Multi-stage Coupled CWs And Its Application In The Ecological Water Purification

River ecosystem possesses tempo-spatial difference, so the flow, water temperature, and nutrients show a trend of variance, which influence the exertion of river ecosystem function.River ecosystem degradation is serious as river losses its self-purification capacity in recent years. Constructed wetlands (CWs) have been proved to be effective measures for pollution reduction, river water purification, and restoration, especially for the reduction of endogenous nitrogen.Different types of CW with different pollutants removal efficiencies, since influenced by design parameters and environmental factors. In this paper, according to the laboratory model mechanism and applied basic research, lab scale R&D and operation parameter study, pilot scale test, and demonstration project to verify the effects of multi-stage coupled CWs purification efficiency and its application in river ecological purification, in order to propose optimization parameters, finally promote the application in the Huai River or river with similar background.In multi-stage coupled CW system, water purification process is divided into several steps. In addition to the different flow patterns, we screened aquatic plants, gradated different matrixes, matrix internal electrolysis, and test pollutants removal efficiencies under different hydraulic retention time. The operation parameters were used in the river ecological water purification demonstration project in the upstream of the Jialu River, the most appropriate coupled multi-stage CWs mode for different pollutants removal efficiency be identified, thus the research has very important practical application value for the heavy pollution river control and management.The results of our research show that:(1) The average removal efficiencies for COD and NH4+-N were respectively 62.10% and 79.50% for calamus (Acorus calamus Linn),59.20% and 70.22% for Scirpus (Scirpus tabernaemontani),52.50% and 60.89% for the control which without plants. Studies have shown that if organic pollutant concentrations of the wastewater are elevated, the oxygen concentration will decrease substantially in CWs without plants, but remain within the aerobic zone in wetlands with plants. Vertical flow constructed wetlands (VFCWs) with higher oxygen transfer capacity and good organic matter removal efficiencies. In horizontal flow constructed wetlands (HFCWs), most of organic carbon source was difficult to biological degradation, and due to the lack of carbon source, thus resulting in the effluent COD a little high.(2) The four matrixes gravel, zeolite, ceramsite, and slag matrix combination performed effective phosphorus removal capability. When HRT=4h, group A (ceramic, zeolite, and gravel) achieved the highest COD removal efficiency of 70.28±10.24%, the highest TN removal efficiency 9.38±6.98% appeared in group C (ceramic, gravel, and slag), and TP removal efficiency in group B (ceramic, zeolite, and slag) of 80.25±18.75%.(3) Experiments were carried out in laboratory for the study of the catalyzed iron inner electrolysis in wastewater treatment, and explore specific operating parameters. The reaction kinetics of Fe/Cu method was electrochemical reaction, and different ratio has a significant influence on the removal of TP in wastewater. The results show that the initial phosphorus removal averaged 62% when Fe:Cu=1:1, and reached 87% when Fe:Cu=10:1, indicating that the contact area between Cu and Fe, and the pollutants with the matrix increased in the internal electrolysis reactor, leading to the reaction activity increased. The electro-iron system has been proven to be more efficient for nitrate reduction. At first with the increase of pH value, nitrate reduction rate increased due to the iron corrosion reaction. During the experiment period the nitrate almost completely conversed, and decreased rapidly in the later stage.(4) The connection modes included series (Ser), parallel (Par), series-parallel (Ser-Par) and parallel-series (Par-Ser), while HRTs of 1,2,3,4 and 5h were studied. The results showed that the Ser-Par mode had the highest TN removal efficiency (45.16%) at HRT of 3h and the highest TP removal efficiency (74.55%) at HRT of 5h. In terms of COD, the Par system had the highest removal efficiency (75.90%) at HRT of 4h. The highest removal efficiency for NH4+-N (68.39%) was observed in the Ser system at HRT of 4h. HRTs have effects on pollutants removal efficiencies. Shorting HRT represents improve wastewater contact time by increasing the flow rate, first to prevent excessive hypoxia conditions in matrix; second, a shorter HRT means a greater pollutant loading in the wetlands.(5) We chose the Jialu River basin, one of the most polluted tributaries of the Huai River, implement our water ecological purification demonstration project based on the background value. We monitored the temporal and spatial variation of nitrogen along the whole river, to assess the validity of measures. The most obvious change is NH4+-N reduced by an average of 63.76±31.63%, NO3--N by 42.10±5.88%, and the TN concentration decreased from an average of 16.17 mg/L to 3.50 mg/L. The spatial variation of nitrogen concentration in rivers can be potentially applied to predict the trend of effluent concentration. We propose the application framework of water ecological purification optimization design in the river basin, which requires a comprehensive monitoring to determine the overall effectiveness of the engineering measures applied in other watersheds. The plant restoration can achieve good denitrification effect. Most notably, NH4+-N was reduced by 63.76±31.63%, NO3--N were reduced by 42.10±5.88%, and TN was reduced by 78.17±14.68%. All sites showed similar seasonal percentage nitrate-N removal performance, but there were significant variations between years (p<0.05), as a result of seasonal influence on plant activities. The ammonium nitrogen concentration was lower in summer, due to the dilution of rainfall, so the rainfall and vegetation are considered some of the many variables that determine the performance of water treatment.Single horizontal flow CWs can not guarantee effective nitrification because of the restriction of oxygen transfer capacity, and vertical flow CWs can not guarantee efficient denitrification. So single wetland system often fails to meet the desired effect. Therefore, hybrid systems of various types of CWs combined have been introduced to achieve higher treatment efficiency. The coupled wetland systems included series, parallel, series-parallel and parallel-series systems. In addition to the system itself and its combination process, the design parameters including hydraulic loading rate (HLR), hydraulic retention time (HRT), environmental conditions including temperature, pH, system elements including plants, matrix, and so on, influence the wetland purification ability.In the premise of understanding the mechanism of coupled CWs purification capability and removal passway, we focus on the use of CW for ecological river and enhanced purification technology, multi-stage coupled CWs technology, so that improves the application of river ecological purification engineering measures, in order to provide a reference for the Huaihe River basin and other polluted rivers.