Waste plastic bottle strips as biofilter media for a sustainable onsite sanitation system

This study explores the use of waste plastic bottle strips as biofilter media for improved urban on-site sanitation systems. Initially, Synthetic wastewater was treated in column reactors packed with plastic strips of varying sizes (3 mm, 5 mm, and 7 mm) as biofilter (BF) media. The biofilter system demonstrated a reduction in hydrolysed and acidified fractions, alongside elevated oxidation-reduction potential values (exceeding −250 mV) under both winter and summer conditions. The non-woven plastic matrices provided effective support for biofilm formation and biosolid retention, while simultaneously addressing plastic waste problems. Over a 150-day ambient laboratory-scale study, the striped BF achieved average chemical oxygen demand (COD) removal rates of 72%, 71%, and 70% for 3 mm, 5 mm, and 7 mm sizes, respectively, under an optimum hydraulic retention time (HRT) of 12 h. The UASB + BF onsite treatment system can produce a much-improved effluent quality compared to a conventional onsite sanitation system using a septic tank. These findings underscore the potential of waste plastic bottle strips as a cost-effective, sustainable biofilter medium for decentralised sanitation, offering dual benefits of wastewater treatment and plastic waste reuse.