Abstract
Constructed wetlands are one of the best technologies for wastewater treatment in small towns, small businesses or farms and/or livestock breeding. In this work, a wastewater depuration ecological system implemented in a hybrid constructed wetland to remove nutrients and organic matter from small urban agglomerations is studied. It comprises two processing stages: a primary treatment carried out in two hydrolytic up-flow sludge bed digesters working in parallel and a secondary one made up of two vertical flow constructed wetlands, which are alternatively used, followed by a horizontal flow constructed wetland. An internal recirculation system connects the output of the vertical flow constructed wetlands to the input of the hydrolytic up-flow sludge bed digesters with the aim of promoting the nitrification-denitrification process. High nutrients and organic matter removal efficiencies were observed when treating highly polluted wastewater from an animal farm. Therefore, this ecological depuration system, designed with an internal recirculation to enhance nitrogen reduction, may be considered an efficient alternative to treat wastewater from small urban agglomerations and diffuse contamination from agricultural industries and livestock farms polluting surface waters with nitrates, which may cause serious environmental problems, such as eutrophication.
Highlights
It is widely recognized that diffuse pollution is one of the major causes of poor water quality in surface waters [1,2]
Water policies have succeeded in protecting water resources, especially by introducing highly restrictive limits to water discharges from wastewater treatment plants (WWTP) of big urban agglomerations, in order to minimize the eutrophication of water bodies [6]
Four different points were selected to carry out the sampling process: the first was in the influent, before the pretreatment; the second was before the vertical flow constructed wetlands (VFCW); the third was before the HCFW; and the fourth point was in the effluent
Summary
It is widely recognized that diffuse pollution is one of the major causes of poor water quality in surface waters [1,2]. It has been recently shown that total nitrogen removal efficiency in CWs drops under conditions of excessive dissolved oxygen, because it might restrain the denitrification process [12,16] For this reason, in this work, a hybrid constructed wetland with an internal recirculation system connecting the output of the vertical flow constructed wetland to the input of the hydrolytic up-flow sludge bed digesters has been developed and studied as an alternative to the forced aeration system, with the aim of improving nitrogen removal. To remove suspended solids, perform hydrolysis and carry out the denitrification process, while in the second stage two VFCWs and one HFCW will treat the wastewater to nitrificate ammonia, and to improve the removal efficiency of total suspended solid, organic matter and phosphorous The combination of these two stages allows improving nitrogen removal efficiency without introducing a forced aeration system.
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