The current research was focused mainly on the designing and construction of efficient laboratory scale hybrid constructed wetland (HCW) for the treatment of domestic wastewater. Parameters like COD, BOD5, PO4, SO4, NO3, NO2, and pathogenic indicator microbes were monitored after hydraulic retention time (HRT) of 4, 8, 12, 16, and 20 days. Treatment efficiency of HCW kept on increasing with the increase in hydraulic retention time. Maximum efficiency of HCW was observed with a 20-day HRT, that is, 97.55, 97.5, 89.35, 80.75, 96.04, 91.52, and 98.6% reduction from the zero time value for COD, BOD5, PO4, SO4, NO3, NO2, and fecal coliforms, respectively. After 20 days' time, the treated water was free of almost all nutrients and microbial pollutants. Hence, increasing hydraulic retention time was found to ameliorate the operational competence of HCW. Thus HCW can serve as a promising technology for wastewater treatment and can be scaled up for small communities in the developing countries. 1. Introduction Water is extremely essential for the survival of all living organisms. Like many other developing countries, Pakistan is also regarded as a water-stressed country, and it is likely to have a water scarcity in the near future [1, 2]. The quality and quantity of fresh water is deteriorated by the discharge of untreated municipal wastewater, and according to a recent report, only 12% of the urban wastewater is treated in municipal treatment plants [3]. The exploitation of raw wastewater is risky both from environmental and health perspectives, mainly because it contains biodegradable organic and inorganic matter, toxic substances, and disease-causing agents [4]. In the recent years, diverse technologies have been introduced for the treatment of municipal, domestic, industrial, and nuclear wastewater. The fundamental procedures being used in these innovative wastewater treatment technologies are of physical, chemical, and biological in nature [5]. In biological technologies, constructed wetlands (CWs) for wastewater treatment have the merits of minimum operational cost, ease in management, and environment friendly features [6], and they are the most recommended system for small communities [7]. CWs are artificially designed system composed of a medium such as soil or gravel planted with vegetation tolerant of saturated soil conditions [8] which is equally effective for pathogens, organic, and toxic metals [9]. The removal efficiency of CWs can be tuned by altering hydraulic retention time and temperature [10]. Most hybrid systems consist of vertical flow (VF)
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