Polyethylene terephthalate cap-based bioreactors for combined domestic and dye wastewater treatment

Abstract

In the current study, a sequencing batch reactor (SBR), a sequencing batch biofilm reactor (SBBR) and a moving bed biofilm reactor (MBBR) were designed and used to treat actual samples of combined domestic and dye (Congo red) wastewaters over a 10-hour cycle. A new application of reusing plastic bottle caps in the SBBR and MBBR was examined. In the SBR, maximum chemical oxygen demand (COD) removal of up to 66% ± 3% was achieved after nine cycles of operation. In the SBBR, a rapid increase in COD removal efficiency was observed during the first cycle, with a noticeable improvement in performance in subsequent cycles, eventually reaching a maximum COD removal efficiency of 77% ± 3%. In the MBBR, maximum COD removal of up to 88% ± 3% was achieved after nine cycles of operation. The biodegradation occurred during two phases in the SBR and SBBR, as an anaerobic phase in the first 2 hours and then as an aerobic phase in the last 8 hours of operation; the MBBR operated in the fully saturated aerobic phase for 10 hours. Of the three reactors used, results for the MBBR in the fully aerobic condition by using polyethylene terephthalate caps as a biocarrier, demonstrated the optimum conditions under which to treat and biodegrade Congo red at all concentration in each cycle. The maximum removal efficiency, which equalled 99% ± 1%, was recorded at an optimal concentration of 50 mg/L. Additionally, five kinetic models were proposed to assess microbial growth activity, and the results demonstrated the elimination of toxic effects when using polyethylene terephthalate caps as biocarriers in the MBBR. The laboratory experiments were consistent with the Monod model.