Efficiency of two constructed wetland systems for wastewater treatment: removal of bacterial indicators and enteric viruses

Abstract

BACKGROUND: Pathogenic microorganisms at the effluents of treatment plants entail a potential risk to public health. Enteric viruses such as adenoviruses (AdVs) and enteroviruses (EVs) are responsible for many waterborne diseases. Wastewater treatment methods eliminate successfully the load of indicators but other pathogens such as viruses have been detected in high concentrations at the effluents of wastewater plants. In this perspective, two constructed wetlands (CWs) systems (S1 and S2) were employed and fed with primary wastewater. S1 consists of a free water surface (FWS) wetland and a horizontal subsurface flow (HSSF) wetland working in series, while S2 consists only of the HSSF. Also, both systems included a sand filter (SF) after the HSSF.RESULTS: Results showed that these low-cost systems are capable of eliminating effectively the bacterial indictors (total coliforms, Escherichia coli, Enterococci) achieving removal rates of almost 99% for S1 (3.2-4 Log units) and 89-98% for S2 (1.9-2.7 Log units). Regarding viruses, AdVs, EVs and phages were detected at all sampling points and during all seasons, and they were only partly removed in S1 and/or S2. For example, the virus load was decreased by 2.5 Log units for AdVs and 3.4 Log units for EVs in the case of S1, while the respective values were 4.3 and 1.9 Log units for S2. CONCLUSIONS: Generally, CWs eliminated successfully the bacterial load, while the remaining virus load was significant, thus strengthening the argument that viruses could be a reliable indicator for fecal contamination.

Occurrence of various viruses and recent evidence of SARS-CoV-2 in wastewater systems

“…AdVs are among the most common viruses in untreated sewage, and their concentrations can be ten times greater than those of EVs. AdVs have been widely found in wastewater in France ( Kaas et al, 2019 ), Uruguay ( Lizasoain et al, 2018 ), Tunisia ( Ibrahim et al, 2018 ), the USA ( Gerba et al, 2018 , Jahne et al, 2020 ), Brazil ( Assis et al, 2018 ), Canada ( Qiu et al, 2018 ), Greece ( Kaliakatsos et al, 2019 ), and Japan ( Tandukar et al, 2020 ).…”

“…At least 100 human EV types have been identified. These viruses have been found in wastewater in Iran ( Moazeni et al, 2017 ), the USA ( Brinkman et al, 2017 , Gerba et al, 2018 ), Italy ( Pennino et al, 2018 ), Canada ( Qiu et al, 2018 ) ( Simhon et al, 2019 ), Greece ( Kaliakatsos et al, 2019 ), and Japan ( Tandukar et al, 2020 ). Most EVs are transmitted through the faecal-oral route, and these viruses are most frequently detected in wastewater-contaminated water.…”

Wetlands for environmental protection

“…About 99% removal of TC, E. coli and enterococci were observed in combined wetland systems in which a free water surface wetland was connected in series with HSSF‐CW. Furthermore, the removal of enteric viruses such as adenoviruses (AdVs) and enteroviruses (EVs) was also reported in the same study where virus load was decreased by 2.5 Log units for AdVs and 3.4 Log units for EVs (Kaliakatsos, Kalogerakis, Manios, & Venieri, 2019). However, the highest identity ranged from 83% to 99% of the molecular diversity of cyanopodoviruses was obtained in sediments of two coastal wetlands in northern china (Li, Sun, Sun, Liu, Yao, & Wang, 2019).…”

Efficiency of pollutant removal in a hybrid constructed wetland with Hedychiumcoronarium J. König: a sustainable alternative for poor communities

“…Besides the water quality improvement, CWs also provide a multitude of other functions, such as biodiversity, habitational, climatic, hydrological, and public use functions (WU et al, 2018). Furthermore, playing an important role in the environmental plan to achieve both federal, state regulatory compliance for effluent discharges (XU et al, 2019), and have been used effectively for the inactivation of bacterial indicators (KALIAKATSOS et al, 2019).…”

“…CWs are categorized according to its hydrology to the free water surface (FWS) CWs and the subsurface flow (SSF) CWs. FWS systems are like natural wetlands, with shallow flow of wastewater over-saturated substrate (KALIAKATSOS et al, 2019). For the construction of such systems, it would be economically feasible to use naturally available materials and local vegetation as filler agents.…”