Backwashable slow-sand filtration using anthracite coal as a filter medium for domestic use in isolated rural communities

Filtração lenta retrolavável utilizando carvão antracito como meio filtrante para uso doméstico em comunidades rurais isoladas

ABSTRACT

Optimizing decentralized water treatment systems aims to ensure access to potable water for isolated rural communities, which often face a challenging scenario of scarcity and contamination of this resource. The aim of this study was to evaluate the efficiency of a backwashable slow-sand filtration (BSSF) system using anthracite coal as the filter medium as a treatment alternative for application in rural communities. The BSSF system was assessed over a period of 88 days, during which data were collected on hydraulic performance, water quality, and filter medium performance. The results showed that 95% of the total head loss in the filter medium occurred in the upper layer (0–0.1 m). The average removal rates for turbidity, apparent color, and true color were 74.8, 39.2, and 55.9%, respectively. The system also achieved an average removal of humic substances of 52.2%. Also, the first 15 cm of the filter medium was primarily responsible for dissolved oxygen (DO) consumption. This layer accounted for approximately 81% of the total consumption on average. In the final filtration runs, the average consumption of DO in the lower filter medium layers (15 cm–40 cm) accounted for up to 63% of the total consumption among the studied layers. Furthermore, the presence of indicator microorganisms throughout the filter medium suggests intense microbiological activity. Compared to conventional slow-sand filters, the BSSF system demonstrated similar performance in water treatment. However, it offers significant operational advantages by reducing both the volume of water required for backwashing and the time needed to produce filtered water.

Keywords
decentralized treatment; backwashable slow-sand filter; filter medium; water quality