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.

Keywords:

• Dual stage peat bed
• Wastewater treatment
• Small community wastewater
• Saprist peat
• E. coli
• Cost

Acknowledgements

This study was conducted at the Institute of Water Research and the Department of Civil Engineering (University of Granada), with the invaluable support of the Provincial Government of Granada.