Optimization of tapioca wastewater treatment in sequencing batch reactor (SBR) using alkaline pre-chlorination.

This study was conducted to determine alkaline pre-chlorination effects on chemical oxygen demand (COD) removal and poly-β-hydroxybutyrate (PHB) production in tapioca wastewater treatment. The alkaline pre-chlorination effect was evaluated by applying various chlorine (Cl₂) dosages (0, 2, 4, 6, and 8 mg/L) to the wastewater with a pH of 8 before being treated in a sequencing batch reactor (SBR). The cycle time of the SBR consisted of 1 h of filling and 8 h of aeration. COD and mixed liquor suspended solids (MLSS) of the effluent were measured at 2 h intervals during the aeration period. Both parameters were to estimate the optimum Cl₂ dosage corresponding to the organic removal kinetics, the maximum specific growth rate, and the relationship between substrate utilization and microorganism's growth rate. The effluent of tapioca wastewater pre-chlorination under optimum Cl₂ dosage was treated using the SBR with the cycle period: filling (1 h), aeration (8 h), and settling (8 h). PHB, COD, and MLSS of effluent were measured at 2 h intervals of aeration and settling period for estimating PHB formation kinetics parameter values. For the Cl₂ dosage of 6 mg/L, SBR shows the best performance in terms of COD removal rate constant (k) and maximum specific growth rate (μ_max) with values of 0.327 and 2.681 h^-1, respectively. First-order kinetics, Contois equation, substrate utilization rate based on Monod equation considers cell death, and non-growth associated product formation was being appropriate models to describe organic removal rate, specific growth rate, kinetic of COD conversion to PHB, and PHB production rate, respectively. Another result showed excessive aeration time and settling time application decreased the level of microbial conversion of COD to PHB and PHB production rate per cell mass formed. Maximum yield coefficient of COD to PHB (Y_P/S) of 0.01 mg PHB/mg COD and non-growth associated PHB yield coefficient (β) of 9.07 × 10^-4 mg PHB/mg MLSS/h was achieved when the aeration time was about 6 h. These results suggest that the alkaline pre-chlorination can effectively enhance the performance of the SBR system, especially treating the tapioca wastewater. The optimum process of this treatment is when SBR operated with a cycle consisted of 1 h of filling, 6 h of aeration, and 0.5 h of settling with a Cl₂ dosage of 6 mg/L (pH 8) as wastewater pretreatment. [ABSTRACT FROM AUTHOR]