Environmental Valuation & Cost-Benefit News

Abstract: The capital and operating costs associated with a small package plant MBR for small-scale domestic duty has been appraised based on a medium-strength municipal wastewater. The three main membrane configurations were considered, these being multi-tube, hollow fibre and flat sheet, with the most appropriate plant design chosen for each configuration. The analysis proceeded via a consideration of the estimated amortised capital costs of the plant individual components and their installation, coupled with operating costs based largely on energy demand and residuals management. Energy demand was calculated from aeration and pumping costs, with aeration based on a combination of empirical relationships for membrane aeration and mass balance, and the modified Activated Sludge Model version 2 used for estimating tank size and sludge generation.

Results indicate that it is possible to produce a single household MBR at a capital cost similar to the current market cost for package treatment plants. Desludging and maintenance of these plants is similar but power requirements for an MBR are around 4 times that associated with more conventional package plants. Economies of scale exist from 6–20 p.e. plants but above 20 p.e. there is little cost difference per head, due to the design assumptions made. CAPEX and OPEX are to some extent interchangeable; reductions in CAPEX are associated with an increase in OPEX and vice versa. Whilst costs are high, the market for package MBRs is significantly influenced by the recycling potential of the effluent produced.

Keywords: Membrane bioreactor; Package plant; Capital cost; Operating cost; Sewage

by H. Fletcher, T. Mackley and S. Judd; Centre for Water Science, Cranfield University, Cranfield MK43 0AL, UK; Telephone: +44 1234 754842.

Water Research via Elsevier Science Direct www.ScienceDirect.com
Volume 41, Issue 12; June, 2007 Pages 2627-2635
http://dx.doi.org/10.1016/j.watres.2007.02.038