Aquaculture wastewater treatment by ozonation: Effect of process parameters and degradation kinetic studies

The aquaculture industry is overgrowing to meet the demand of the rising population. This growth promotes fish farming production, which occurs intensively with high cultivation densities. At present, most aquaculture practices in Malaysia do not adopt proper wastewater treatment due to lack of awareness of the environment and the high cost of water treatment. The discharge of untreated aquaculture wastewater contributes to water pollution and affect water sources. This study aims to investigate the efficacy of the ozonation technique to degrade different types of pollutants and also to assess its use as a potential treatment in aquaculture wastewater. The ozonation process was carried out in stirred tank reactor where the gaseous ozone was continuously fed at a constant flowrate to the reactor. The performances of the ozonation process were conducted at different parameters which were concentration of ozone (1.0 - 2.0 mg/L) and pH value (2 - 12). The implementation of ozonation in aquaculture wastewater was to observe the performance of ozone in removal efficiency towards pollutants. The efficiency of ozonation treatment was firstly determined in terms of the degradation of humic acid, ammonia, and E. coli. From this study, it was found that the highest removal for HA was 98% and the removal for E.coli was 99% at pH 7 with 2.0 mg/L of ozone concentration. The highest removal for ammonia was 42% at pH 10 and 2.0 mg/L of ozone concentration. The ozonation treatment was then further applied in aquaculture wastewater to observe the quality of wastewater and the degradation efficiency of ammonia, chemical oxygen demand (COD), and bacterial inhibition before and after treatment. The results exhibited the advantages of ozonation as a treatment which improved the quality of wastewater and enhanced the biodegradability of the bacterial activity up to 99 % and COD removal efficiency of 98 % at pH 7, and 2.0 mg/L of ozone concentration. To get a systematic understanding of the degradation process affected by ozonation treatment, a kinetic study of the targeted pollutants was investigated by applying first-order and second-order reaction models. Furthermore, the kinetic and mass transfer equation was implemented to develop a dynamic model in a semi-batch system of aquaculture wastewater treatment. The mass-transfer coefficient and kinetic parameters that represent the behaviour of the process were estimated and the dynamic model was successfully validated using the experimental data. The highest rate reaction in degradation of COD was at 2.0 mg/L of ozone concentration with the value of kcod is 0.0074 min'. Meanwhile, the highest rate reaction in microbial degradation was at 1.0 mg/L of ozone concentration with the value of kmic is 0.0218 min These findings suggest that the ozonation process can be effectively used in wastewater treatment to improve the biodegradability of recalcitrant organic compounds. The information gathered can be used in future studies to integrate this ozonation method with other treatments to improve water recovery and reuse the system of aquaculture wastewater treatment.