A Subsurface Upflow Wetland System for Removal of Nutrients and Pathogens in On-Site Sewage Treatment and Disposal Systems

Abstract

On-site sewage treatment and disposal systems, commonly referred to as a septic systems, consist basically of a septic tank and soil adsorption field or drainfield. It may represent a large fraction of nutrient loads and pathogen impacts in vadose zone and groundwater systems. It includes not only nitrogen (N) and phosphorus (P), but also pathogen indicators such as fecal coliform and Escherichia coli, which indicate the presence of other disease-causing bacteria flowing into the aquatic system and potentially adversely affecting public health. Constructed wetlands, an effective small-scale wastewater treatment system with low energy and maintenance requirements and operational costs, will cover current needs for nutrient and pathogen removal. In our study, a next-generation subsurface upflow wetland system that is filled with green sorption media (e.g., mixes of recycled and natural materials) along with selected plant species was tested as a substitute for the conventional drainfield in septic tank systems. Four parallel subsurface upflow wetlands (i.e., three planted versus one unplanted) were built to handle 454 L/day (120 gallons/day) of septic wastewater flow. It proved effective in removing both nutrients and pathogens. During the test run in 2009, the planted wetlands achieved a removal efficiency of 84.2%, 97.3%, 98.93%, and 99.92% in total nitrogen, total phosphorus, fecal coli, and E. coli, respectively. A stress test conducted in winter 2010 successfully verified the reliability of this treatment process. Denitrification and precipitation were shown to be the dominant pathways for removing N and P, as evidenced by mass balance and real-time polymerase chain reaction analyses.

Modeling integrated urban water systems in developing countries: case study of Port Vila, Vanuatu

“…Enabling plant-based nutrient uptake (Chang et al 2011), it is a cheap, low technology, low energy approach to wastewater management and in warm tropical climates; it promotes rapid plant growth and nutrient removal, while enabling local urban agriculture and can be used as a source of local fresh produce.…”

A tracer study for assessing the interactions between hydraulic retention time and transport processes in a wetland system for nutrient removal

“…Four parallel 1.52 m wide 9 3.05 m long 9 0.91 m deep cells were constructed in the test bed, three with different plant species and one with no species to serve as the control case ( Fig. 1) [19]. For the purpose of groundwater protection, each cell was encased from surrounding soil by a wooden frame containing an impermeable liner at bottom, a gravel substrate (30.48 cm thick), fabric Fig.…”

“…For the purpose of groundwater protection, each cell was encased from surrounding soil by a wooden frame containing an impermeable liner at bottom, a gravel substrate (30.48 cm thick), fabric Fig. 1 Profile view of wetlands [19] interlayer (DuPont TM Weed Control Fabrics), a 15.24 cm sand layer, a 30.48-cm thick pollution control media (50% Citrus grove sand, 15% tire crumbs, 15% sawdust and 20% lime stone; PC media hereafter) layer, growth media (75% expanded clay, 10% vermiculite and 15% peat moss; G media hereafter), and selected plants (Fig. 1).…”

“…1). The tracer experiment was conducted in one of the four wetland cells with Canna planted for the enhancement of nutrient removal because Canna outperformed the other two cells planted with blue flag and bulrush [19]. All three planted cells exhibited better removal efficiencies than the control cell with no plant species [19].…”

“…The tracer experiment was conducted in one of the four wetland cells with Canna planted for the enhancement of nutrient removal because Canna outperformed the other two cells planted with blue flag and bulrush [19]. All three planted cells exhibited better removal efficiencies than the control cell with no plant species [19]. The upstream septic effluent was the inflow for final treatment at the selected wetland cell, and the nutrient removal efficiencies were measured based solely on the inflow and outflow at the wetland cell.…”