A novel horizontal-flow biofilter with polyurethane foam for decentralised post-treatment of UASB reactor effluent treating municipal wastewater

Abstract

Anaerobic sewage treatment with upflow anaerobic sludge blanket (UASB) reactors is widely implemented in tropical regions, yet the effluents often fail to comply with discharge standards, particularly for organic matter, solids, and surfactants. This study evaluated a novel horizontal-flow biofilter (HFBF) using polyurethane foam as a support medium for polishing UASB effluents. A pilot-scale unit was operated for over 100 days, and its performance was assessed through water quality monitoring, microbial characterisation, and upscaling analysis. Under stable operation, the UASB + HFBF system consistently met discharge standards for BOD, COD, TSS, and methylene blue active substances (MBAS). Average removals exceeded 90% for BOD and TSS and 80% for COD, while MBAS removal reached up to 90%, demonstrating the system's ability to eliminate surfactants, organic pollutants seldom addressed in conventional post-treatment units. Internal gradients of dissolved oxygen, organic matter, and nitrogen transformations are supported by changes in the structure of the microbial community, which is dominated by members of the phyla Pseudomonadota, Campylobacterota, and Bacteroidota. Upscaling analysis confirmed the compactness and economic feasibility of the HFBF, with a footprint of 0.08–0.15 m² inhab⁻¹ and an estimated construction cost of US$ 50 per inhabitant. The results highlight the HFBF as a robust, low-energy, and cost-effective polishing technology, especially suited for decentralised wastewater treatment in developing countries, where compactness and operational simplicity are essential for achieving compliance of discharge standards.