Rethinking DEWATS: a cost-effectiveness analysis of the system for ease of adoption in developing countries

ABSTRACT

Decentralized wastewater treatment systems (DEWATS) offer a low-cost, low-maintenance sanitation solution for communities lacking centralized infrastructure. This study evaluates the treatment performance, pollutant load reduction, regulatory compliance, and economic efficiency of a DEWATS, comprising a settler, anaerobic baffled reactor (ABR), planted gravel filter (PGF), and polishing pond, installed in a settlement in Khulna, Bangladesh. Wastewater samples were collected across seven paired sampling events and analyzed for BOD5, chemical oxygen demand, TSS, TDS, nitrate, and phosphate. Statistical analysis used the Wilcoxon signed-rank test with false discovery rate correction and rank-biserial correlation. Three treatment scenarios were evaluated using lifecycle cost (LCC) and cost-effectiveness ratio frameworks. The settler–ABR sequence accounted for the dominant share of pollutant removal, achieving 55 and 50% BOD5 reduction, respectively, while the PGF tripled the total LCC for only 12 additional percentage points of overall removal. ABR outlet concentrations for TSS, TDS, and nitrate already met Environmental Conservation Rules (ECR) discharge standards. Where effluent is discharged to municipal drainage, the settler–ABR alone provides sufficient treatment. The findings recommend formal recognition of the optimized settler–ABR configuration in the Bangladesh National Building Code and a tiered ECR compliance framework for decentralized systems.