Exploring shredded waste PET bottles as a biofilter media for improved on-site sanitation

Abstract This study explores an improved alternative on-site treatment for unsewered urban Bhutan. The system combines up-flow anaerobic sludge blanket for black water treatment and anaerobic biofilter for a mixture of up-flow anaerobic sludge blanket effluent and grey water. Shredded waste plastic bottles are used as novel biofilter media that provides a large surface area for attached growth while addressing waste plastic problems. A bench-scale up-flow anaerobic sludge blanket (operated at hydraulic retention time or HRT of 1 to 10 days) and anaerobic biofilter (HRT of 0.25 to 3 days) study were conducted for 188 days. At two-day HRT, up-flow anaerobic sludge blanket removed 70-80% of chemical oxygen demand (COD) while anaerobic biofilter achieved 90-98% COD removal at eight-hour HRT. Combined up-flow anaerobic sludge blanket and anaerobic biofilter achieved final effluent with COD less than 50 mg/L and turbidity of less than 3 NTU that meets the discharge standard of Bhutan. The study shows that shredded waste plastic bottles can be an effective biofilter support medium for low-cost on-site treatment while helping address waste plastic problems.