Vertical and Hybrid Constructed Wetlands as a Sustainable Technique to Improve Domestic Wastewater Quality

Abstract

Developing safer and environmentally friendly methods for wastewater management is a crucial issue worldwide. Pollutants stemming from pure elemental, organic or inorganic compounds, or microbial sources, are an increasing problem in domestic wastewater. Constructed wetlands (CWs) have been used as an effective and low-cost method of treating different types of polluted water. This review paper focuses on the effectiveness of pollutant-removal from domestic wastewater using vertical flow constructed wetlands (VFCWs) and hybrid constructed wetlands (HCWs). Meta-analysis and ANOVA tests were conducted to analyse the potentiality of VFCW and HCW as a remedy for domestic wastewater and the effect of using different substrates and plant species. Meta-analysis shows a high significance (p = 0.001) between the interactions (method, plant, and substrate) on the pollutant’s removal efficiency. In both analysis methods, there were no significant differences between VFCW and HCW for the same pollutant (p > 0.05); the average removal percentages when using VFCW and HCW (according to ANOVA analysis) were 80% vs. 90% for BOD, 78% vs. 77% for COD, 75% vs. 83% for ammonium-N, 48% vs. 56% for TN, and 60% for TP, respectively. Moreover, this review article presents a comprehensive overview of the removal mechanisms for organics, inorganics, and metals from domestic wastewater using VFCW, and the effects of environmental parameters including substrate type, plant species, and dissolved oxygen which have direct and indirect impacts on physical, chemical, and biological removal mechanisms. In conclusion, VFCWs and HCWs seem to be an excellent approach, offering economical and environmentally friendly techniques for domestic wastewater treatment, but VFCW is considered simpler and more applicable for setting up on-site near houses, as there is no significant difference (p > 0.05) between applying VFCW or HCW on removal percentages for most pollutants, according to ANOVA testing. More work is needed to study the effect of non-planted VFCWs and HCWs on removal efficiency.