One of the biggest problems the world is currently experiencing is wastewater treatment. Numerous pollutants are released into water bodies by enormous amounts of effluents from varied sources. This paper provides a concise summary of the state of the art in AOPs, biological treatment, and their efficient application for the degradation of the numerous recalcitrant organic contaminants found in wastewater. The employment of a photoreactor is necessary for the efficient execution of the majority of photocatalytic processes. This review examines the effectiveness of several reactor configurations with varying geometries. Integrating different AOPs and AOPs with biological approaches for degrading pollutants in wastewater was also discussed. It is important to emphasize that an integrated AOP/biological system produces by-products that are not hazardous, uses little energy, and completely degrades pollutants. The review also outlines the challenges and issues of wastewater treatment for an environmentally and economically feasible process.

This study is focused on the investigation of seven treatment strategies and the percentage reduction on COD and colour was evaluated and total time required for different treatment strategies were calculated. The results revealed that the COD and colour removal of 97% and 92%, respectively, was attained at 180 min of treatment for the coupled SPF-biological process, 97% and 90% of COD and colour removal was attained at 195 min of treatment for the coupled SPC-biological process whereas 98% and 95% of COD and colour removal at 95 min of treatment for the coupling of combined SPF-PC-biological process confirming the efficiency of the coupled process with a relatively shorter reaction time compared with the other processes. The values of the first order kinetics for the combined SPF-PC-biological process were 0.03 min-1 which is eight times greater than the biological process and 1.4 and 1.87 times faster than the coupled SPF-biological and SPC-biological process, respectively. The economic analysis of various AOPs and the relative cost of AOP-biological processes were discussed and the coupling of combined SPF-PC-biological process was found to be a technically and economically effective in treatment of pulp and paper mill wastewater to meet the effluent discharge standard.

a b s t r a c tThe efficiency of solar photocatalytic plug flow baffle reactor by using Fenton's reagent augmented with TiO 2 (solar/Fe 2+ /TiO 2 /H 2 O 2 ) process for the degradation and decolourisation of pulp and paper wastewater has been studied. For this study, a reactor has been designed with pyrexglass in the form of a pond divided with baffle plates. The experiment was performed by varying three significant independent variables such as flow rate in the range of 0-300 mL/min, liquid depth in the range of 2-6 cm and residence time in the range of 0-120 min. The standard response surface methodology (RSM) and central composite design were followed. The maximum COD and colour removal of 98% and 97% respectively was obtained at optimum conditions of flow rate = 75 mL/min, liquid depth = 5 cm and residence time = 75 min. Also, the effect of aeration and without aeration, addition of iron dosage and the kinetics was studied. It was observed that the sequential addition of iron is efficient than single addition and the kinetics followed the pseudo first order reaction with high correlation coefficients. The reaction rate constant for aeration was 2.33 times greater than the reaction without aeration.