Purification performance of coconut fibers, palm kernel fibers, and shredded plastic bottles in biofilter septic tanks: efficiency and limitations

ABSTRACT This biofiltration system tests three substrates: plastic fragments (COD: -55%, turbidity: -95%, nitrates: -60%), palm kernel fibers (COD: -69%, turbidity: -95%, nitrates: -70%), and coconut fibers. The latter show optimal performances with a maximum reduction in COD (-75%), turbidity (-96%), nitrates (-78.15%), nitrites (-66.67%), phosphates (-43.4%), and sulfates (-67.19%). This study conducted over 56 days evaluates the purifying efficiency of three organic and synthetic substrates: coconut fibers, palm kernel fibers, and plastic bottle fragments within a biofiltration wastewater treatment system. The experimental device consists of three bi-compartmentalized units (effective capacity of 259 L; hydraulic retention time of 40 h), incorporating filter beds composed of gravel, charcoal, and the materials under test. Analysis of physicochemical parameters reveals a marked superiority of coconut fibers for pollutant removal: COD (−75%), turbidity (−96%), nitrates (−78.15%), nitrites (−66.67%), phosphates (−43.4%), and sulfates (−67.19%). Palm kernel fibers show intermediate performance with respective reductions of 69% (COD), 95% (turbidity), 70% (nitrates), 66.67% (nitrites), 23% (phosphates), and 59.38% (sulfates). Shredded plastic bottles display the lowest yields: COD (−55%), turbidity (−95%), nitrates (−60%), nitrites (−50%), phosphates (−11%), and sulfates (−53.13%). Although pH neutralization is observed, an increase in BOD5 was recorded, particularly for organic substrates, suggesting a specific biological dynamic within the biofilters.