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The unrestricted discharge of domestic and industrial wastewaters along with agricultural runoff water into the environment as mixed-wastewater pose serious threat to freshwater 2 resources in many countries. Mixed-wastewater pollution is a common phenomenon in the developing countries as the technologies to treat the individual waste streams at source are lacking due to high operational and maintenance costs. Therefore, the need to explore the potential of suspended growth process (SGP) which is a well-established process technology for biological wastewater treatment, is the focus of this paper. Different wastewater constituents: representing domestic, pharmaceutical, textile, petroleum, and agricultural runoff were synthesized as a representative of mixed-wastewater and treated in two semicontinuous bioreactors (R1 & R2) operated at constant operating conditions vis., MLSS (mg/L): 4640-R1, 4440-R2, SRT: 21-d, HRT: 48 -72-h, and uncontrolled pH. The system attained stable condition in day 97, with average COD, BOD and TSS reduction as 84.5, 86.2, and 72.2% for R1; and 85.1, 87.9, and 75.1% for R2 respectively. Phosphate removal on average was by 74.3% in R1 and 76.6% in R2, while average nitrification achieved in systems 1 and 2 were 56.8and 54.7% respectively. The biological treatment system has shown potential for improving the quality of mixed-wastewater to the state where reuse may be considered and tertiary treatment can be employed to polish the effluent quality.

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Pollution and increasing water demand, especially for agriculture, put severe stress on freshwater sources, and as a result, there is progressive deficit in the global water supply and severe water scarcity is projected in the coming decades. Discharges from domestic, industrial and agricultural activities are potential sources of water pollution, impacting human and environmental health. In the face of growing water scarcity and droughts, coupled with the increasing water demand for irrigation, integration of high water-volume and nutrient-rich industrial effluents, into the existing water management plans for agriculture, could play an important role in tackling the problem of water scarcity. However, there is a gap in knowledge about integration of industrial effluents to sewage treatments and the reuse potential of biologically treated mixed industrial and domestic wastewater in agriculture. This study, therefore, provides a critical review on biological treatment of industrial effluents, including petroleum, textile and pharmaceutical wastewater to better understand the capability of bioprocesses and conditions for efficient degradation of pollutants. The effectiveness of activated sludge-based processes, for the treatment of mixed industrial and domestic wastewater, was critically examined, and biomass acclimation plays a vital role in enhanced biodegradation performance. Finally, the reuse potential of mixed industrial and domestic wastewaters for crop irrigation was assessed by studying the reuse outcomes in different cases where industrial effluents were utilized for crop production. Management practices, such as cultivation of salt-and metal-tolerant crops, blending and dilution of industrial wastewater with freshwater and sewage, could make industrial effluents valuable for irrigation.