Treatment Efficiency of Diffuse Agricultural Pollution in a Constructed Wetland Impacted by Groundwater Seepage

Abstract

Diffuse agricultural pollution degrades water quality and is one of the main causes of eutrophication; therefore, it is important to reduce it. Constructed wetlands (CW) can be used as an effective measure for water quality improvement. There are two possible ways to establish surface flow CWs, in-stream and off-stream. We studied treatment efficiency of the in-stream free surface flow (FSW) Vända CW in southern Estonia from March 2017 until July 2018. The CW consists of two shallow-water parts planted with cattail (Typha latifolia). According to our analyses, the CW reduced total phosphorus (TP) and phosphate (PO4-P) by 20.5% and 16.3%, respectively, however, in summer, phosphorus removal was twice as high. We saw significant logarithmic correlation between flow rates and log TP and log PO4-P removal efficiency (rs = 0.53, rs = 0.63, p < 0.01 respectively). Yearly reduction of total organic carbon was 12.4% while total inorganic carbon increased by 9.7% due to groundwater seepage. Groundwater inflow also increased the concentration of total nitrogen in the outlet by 27.7% and nitrate concentration by 31.6%. In-stream FWS CWs are a promising measure to reduce diffuse pollution from agriculture; however, our experience and literature data prove that there are several factors that can influence CWs’ treatment efficiency.

Enhancing Nitrate Removal from Waters with Low Organic Carbon Concentration Using a Bioelectrochemical System—A Pilot-Scale Study

“…Assessments of groundwater aquifers made in Portugal, Iran, Saudi Arabia, France, and other countries have shown that in many cases, nitrate (NO 3 − ) concentrations are exceeding the safe drinking water threshold of 50 mg NO 3 − L −1 , which is specified by the World Health Organization [3][4][5][6][7][8]. High NO 3 − concentrations in surface water and groundwater are causing environmental problems, such as eutrophication [9], and since NO 3 − becomes toxic to humans at concentrations of 50 mg NO 3 − L −1 and above, this relates to health issues like methemoglobinemia and cancer [2,8].…”

Hybrid Constructed Wetland to Improve Organic Matter and Nutrient Removal

“…The VFCWs are planted with Phragmites Australis, with a density of 3 plants per m 2 . They have been included because of their great contribution to the removal and absorption of nutrients [23].…”

“…It is widely recognized that diffuse pollution is one of the major causes of poor water quality in surface waters [1,2]. An excess of nutrients in surface waters (mainly nitrogen and phosphorus) causes major environmental problems as eutrophication [3].…”

In Situ Nutrient Removal from Rural Runoff by A New Type Aerobic/Anaerobic/Aerobic Water Spinach Wetlands

“…As an environmentally friendly natural treatment system, the CW has shown advantages over conventional techniques due to its low cost, good performance, and simple operation [7,9]. Recently, CW technology has also been used widely to treat rural runoff due to the easy maintenances and low energy demand [10][11][12]. These results show that CW has potential effects on nitrogen and phosphorus removal.…”

“…There are many mechanisms that are involved in nitrogen and phosphorus removal in CW including adsorption, precipitation, plants adsorption, and bacteria transformation during the rural rain runoff treatment processes in CW [9,10]. Biological nitrification and denitrification are regarded as the important removal mechanisms for nitrogen removal in CW, while the other mechanisms, including plant and substrate adsorption, are also important [11].…”