Vertical-horizontal subsurface flow hybrid constructed wetlands for municipal wastewater treatment in developing countries: A review

Abstract

The use of low-cost on-site wastewater treatment technologies, including constructed wetlands (CWs), is wide spread. Despite the purported high performance of vertical-horizontal subsurface flow (V-H SSF) hybrid CWs, data on implementation and performance in developing countries is scarce. Here, the design, operation and performance of V-H SSF hybrid CWs for treatment of municipal sewage in an effort to encourage and direct future research and assist technology choice were reviewed. Literature reveals that successful performance of V-H SSF hybrid CWs depends mainly on system design and is independent of mode of feeding. Moreover, performance and final effluent quality is high for biological oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) which are all reduced by over 80%. Despite high removal of ammonium-nitrogen (NH 4 + -N), concentration in the final effluent remains above desired levels, which is attributed to the design of V-H SSF hybrid CWs based on BOD as a parameter of choice, rather than nitrogen. It was argued that further research on performance of V-H SSF hybrid CWs based on designs that consider both nitrogen in the form of NH 4 + -N and BOD and assessment under different climatic conditions, is essential prior to mass implementation of this technology in developing countries.

Long-Term Performance of a Hybrid-Flow Constructed Wetlands System for Urban Wastewater Treatment in Caldera de Tirajana (Santa Lucía, Gran Canaria, Spain)

“…Another more recent review [ 49 ] has reported removal efficiencies of 84–96% for BOD 5 , 74–95% for COD, 85–99% for TSS, 26–78% for total N, and 19–91% for NH 4 . In this case, all of the values that were obtained in the present study are within these ranges.…”

“…Nonetheless, low nutrient removal efficiencies have again been observed, especially for nitrogen compounds. This may be due to the fact that the system design was based on the use of BOD 5 as the parameter of choice and not nitrogen [ 49 ]. The low performance may be correctable by maintaining high levels of oxygenation in the VFCWs [ 33 ] and/or ensuring that the water that is to be treated in the HFCW has sufficient organic matter in order to enable heterotrophic bacteria to carry out the denitrification reaction [ 25 ].…”

Discard Coal as Filter Bed Material in Horizontal Subsurface Flow Constructed Wetlands: a Preliminary Study

“…Constructed wetlands are engineered systems that use natural functions of vegetation, soil and microorganisms to treat wastewater (Vymazal, 2008;Parde et al, 2021;Tebitendwa & Cowan 2021). Although used as a sanitation technology, CW is not specifically designed for pathogen removal.…”

“…Similar to natural wetlands, a CW acts as a biofilter and either reduces or removes pollutants including suspended solids, organic matter, nutrients (nitrogen and phosphorus) and heavy metals (Gorgoglione & Torretta, 2018). There are essentially two main types of CW: subsurface flow and surface flow CW (Tebitendwa & Cowan 2021) capable of treating a range of different waste streams (Vymazal et al, 2021). The planted vegetation or macrophyte plays an important role in contaminant removal and is potentially a source of renewable energy (Avellána & Gremillion, 2019) while the filter bed, consisting usually of sand and/or gravel, has an equally important role to play (Tebitendwa & Cowan, 2021).…”

“…There are essentially two main types of CW: subsurface flow and surface flow CW (Tebitendwa & Cowan 2021) capable of treating a range of different waste streams (Vymazal et al, 2021). The planted vegetation or macrophyte plays an important role in contaminant removal and is potentially a source of renewable energy (Avellána & Gremillion, 2019) while the filter bed, consisting usually of sand and/or gravel, has an equally important role to play (Tebitendwa & Cowan, 2021). Here, we describe the outcome of a study conceived and carried out to determine the potential of South African waste bituminous coal (i.e., discard) for use as filter bed material in CW.…”