Dual-stage peat beds in small community wastewater treatment

Abstract

In this study, the quality of water treated by two dual-stage peat bed systems was compared with a single-stage system, and a costs analysis was performed. The experiment was carried out on a pilot scale using pre-treated urban wastewater. The pilot setup consisted of a single-stage system with a hydraulic loading of 0.6 m3/m2d, and two dual-stage systems. The first of these worked with hydraulic loadings of 1.2 and 0.6 m3/m2d for the initial and second stages respectively. For the second dual-stage system hydraulic loadings were 1.8 and 0.9 m3/m2d. In comparison with the single-stage system, the dual-stage systems produced effluents with a substantial improvement in physicochemical quality (suspended solids, COD and BOD) and microbiological quality (faecal and total coliforms). Quality parameters were similar to a conventional system, meeting the legislative standards of European Union Directive 271/91 for wastewater treatment. Total costs of the peat-bed systems showed a reciprocal X-model regression depending on the average daily volume of urban wastewater to be treated, with a tendency towards convergence of costs between the single and dual-stage systems. The main problem with the dual-stage systems is the greater surface area required for their installation, which can be estimated by linear regression depending on the average volume of water to be treated per day.