Kenaf addition has mixed effects on process performance of sequencing batch reactors treating municipal wastewater

Abstract

The effects on wastewater treatment due to addition to the mixed liquor of a fine lignocellulosic powder made of dried kenaf were assessed using lab-scale sequencing batch reactors (SBRs) operated for over 200 days. The treatment reactor augmented with kenaf showed similar COD and phosphorus removals as well as total suspended solids concentrations in the effluent as the control reactor. Larger and less numerous floc particles were formed with the addition of kenaf, resulting in around 30% improvement in sludge settling in the kenaf SBR (SVI = 130 ml g⁻¹) than in the control SBR (SVI = 190 ml g⁻¹). During periods of low aeration, significantly higher (p < 0.01) removal of total nitrogen was observed in the kenaf SBR (87.3% removal) than in the control SBR (83.9% removal). This was attributed to higher levels of nitrite oxidizing bacteria in the kenaf SBR, leading to higher specific nitrate production rate. However, the overall microbial communities, as assessed using 16S rRNA gene sequencing, were similar in control and treatment reactors. Significantly higher concentrations of copper (45.6% increase), lead (25.5% increase) and zinc (65.7% increase) (p < 0.05) were detected in dried sludge solids from the kenaf treated SBR than in the control SBR. Cadmium, chromium and nickel did not accumulate differently in the solids, while selenium and cobalt were significantly (p < 0.05) less concentrated in the kenaf enriched sludge solids. Overall, the addition of kenaf in activated sludge systems may enhance nitrification under low aeration conditions, and improve sludge settling, but has no effects on other performance parameters.