Experimental criteria of sequential continuous ozonation and semi-continuous biodegradation for the decomposition of 4-chlorophenol

This study presents experimental criteria for developing a sequential treatment that couples continuous ozonation with aerobic biodegradation to degrade 4-chlorophenol (4-CP). The ozonation of 4-CP (60, 120, and 240 mg L−1) was carried out in semi-continuous and continuous modes to select suitable experimental conditions in terms of the decomposition efficiency (DE) of 4-CP and its toxic ozonation products (for continuous mode). Complete degradation of 4-CP (98–100% DE) was achieved within 10–30 min of ozonation in the semi-continuous mode and with hydraulic retention times (HRT) of 30, 45, and 60 min in the continuous system. Continuous ozonation resulted in 46.7% and 36.8% reduction of total organic carbon (TOC) for 4-CP initial concentrations of 120 and 240 mg L−1 at 60 min of HRT, respectively. Based on these results, the combination of ozonation and biological treatment was evaluated. Biodegradation experiments were conducted in batch, fed-batch, and continuous operation modes using a microbial consortium adapted to the pre-ozonized 4-CP. In this step, the TOC of pre-ozonized solutions was reduced by 93%. The global efficiency of ozonation followed by biodegradation system reached up to 96% of mineralization. Suitable experimental conditions were obtained through mathematical modeling of continuous ozonation and biodegradation data. The mineralization achieved was the target result of the proposed treatment scheme, with the maximum mineralization of ozonation products in the bioprocess serving as a critical criterion for its efficacy. Based on a proposed mathematical model, the experimental results were used to conduct kinetic studies of ozonation and biodegradation in continuous mode.