Precious Nneka Amori

Suspended growth biological process (SGBP) with post-ozonation (O3) was investigated for treatment of simulated complex mixed industrial and domestic wastewater at specific conditions. The SGBP was operated under complete aeration, 30/30-min and 60/30-min on/off aeration cycles and effluent was exposed to ozone at 250 mgO3/h fixed dose and contact time 1 to 60-min. The SGBP performance was maximum under 60/30-min aeration conditions achieving 92.1, 90.6, 83.3 and 83.8% reduction in COD, BOD5, TN and PO4-P respectively. Nitrification (64.1%) was uninhibited even on transition to pulse aeration cycles. The concentrations of diesel oil and methylene blue dye were reduced by 83.6 and 93.5% respectively. Post-ozonation oxidized residual organics up to 19.9%, based on COD measurement, and increased effluent BOD5 up to 49.5%. The results including the crop growth outcomes indicate that SGBP-O3 process has great potential to improve the quality of mixed industrial and domestic wastewater considerably for various water reuse applications.

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.

Due to the increasing freshwater deterioration and demand for irrigation, there is pressing need to reclaim and reuse wastewater for agricultural operations. While this practice is gaining significant traction in developed world, it is quite rare in most developing countries with inadequate or no functional sewerage facilities and treatment systems at both municipal and industrial levels occasioned by high investment and operational costs. Consequently, wastewaters generated are in complex heterogenous mix of industrial, domestic, municipal and agricultural runoff wastewater. Biological technologies which utilize the expertise of microorganisms are considered robust, efficient and economically attractive for treatment of wide range of wastewaters and they have high suitability in developing countries. This work therefore assessed the potential of suspended growth bio- logical process (SGBP) for reclamation and reuse of mixed wastewater composed a mixture of domestic effluent, pharmaceutical, textile, petroleum discharges and agricultural runoff for irrigation of edible crops (lettuce and beets) with plants phenological parameters as measuring indicators. The germination and phenological characteristics of crops were studied in a hydroponic unit under four irrigation regimes: tap water as control, mixed wastewater, SGBP treated wastewater, and tap water mixed with nutrient solution as upper control, for a duration of 45-d. The results proved that the SGBP treated wastewater had no negative impact on germination responses of the seed crops. However, residual recalcitrant compounds caused early stunted growth in plant root systems with resultant limited access to nutrients. Consequently, plant vegetative growth and phenological development as well as chlorophyll production were reduced. In comparison to nutrients supplemented solution, nutrients deficiency and imbalance in treated wastewater contributed to the poor development in irrigated plants. The outcomes of seed germination and plant growth experiments show a positive indication for reuse of mixed wastewater in agriculture. However, there is need for further research to explore the long-term benefits and limitations of reusing such treated wastewater.

The unrestricted discharge of domestic and industrial wastewaters along with agricultural runoff water into the environment as mixed-wastewater pose serious threat to freshwater 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 the suspended growth process 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 semi-continuous bioreactors (R1 & R2) operated at constant operating conditions, namely 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 56.8% and 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.