Modelling of a wastewater-treatment plant for process reliability and effluent reuse

Evaluation of wastewater-treatment plant (WWTP) performance is important to determine whether the plant produces an acceptable treated effluent satisfying the water quality standards for reuse. Modelling of WWTPs is required for optimising plant performance and choosing the optimum operation strategy. This study simulated the Kabd WWTP in Kuwait using the BioWin software. The plant receives 180 000 m 3 /day of domestic wastewater and comprises primary, secondary (activated sludge) and tertiary treatment stages. Daily data obtained from the WWTP during 2013–2018 were used for modelling plant performance under steady-state operation. The model could describe plant operation and accurately predict the effluent characteristics for the conditions examined. A high correlation (R 2 = 0.95–0.99) was obtained between the predicted and actual values of chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total suspended solids as main parameters characterising wastewater. The tertiary-treated effluent consistently satisfied the water quality criteria for reuse in irrigation. Using the model could aid in securing compliance of effluent quality with the local environmental standards. Factorial analysis revealed that COD and BOD are the most important parameters describing plant performance. Reliability analysis showed that the coefficient of variability was low (0.328) at a level of reliability of 95%, leading to a high coefficient reliability of 0.631, which indicates a highly stable plant performance. It is recommended to include reliability analysis in evaluating plant performance to demonstrate consistency in the ability of the plant to produce effluents satisfying requirements set by environmental authorities.