Economic assessment of aerated constructed treatment wetlands using whole life costing.

There is increasing pressure on water treatment practitioners to demonstrate and deliver best value and sustainability for the end user. The aim of this paper is to evaluate the sustainability and economics, using whole life costing, of wastewater treatment technologies used in small community wastewater treatment works (WwTW) of <2,000 population equivalent (PE). Three comparable wastewater treatment technologies - a saturated vertical flow (SVF) aerated wetland, a submerged aerated filter (SAF) and a rotating biological contactor (RBC) - were compared using whole life cost (WLC) assessment. The study demonstrates that the CAPEX of a technology or asset is only a small proportion of the WLC throughout its operational life. For example, the CAPEX of the SVF aerated wetland scenario presented here is up to 74% (mean = 66 ± 6%) less than the cumulative WLC throughout a 40-year operational time scale, which demonstrates that when comparing technology economics, the most cost-effective solution is one that considers both CAPEX and OPEX. The WLC assessment results indicate that over 40 years, the SVF aerated wetland and RBC technologies have comparable net present value (NPV) WLCs which are significantly below those identified for submerged aerated filter systems (SAF) for treatment of wastewater from communities of <1,000PE. For systems designed to treat wastewater from communities of >1,000PE, the SVF aerated wetland was more economical over 40 years, followed by the RBC and then the SAF. The aerated wetland technology can therefore potentially deliver long-term cost benefits and reduced payback periods compared to alternative treatment technologies for treating wastewater from small communities.