Eco-Friendly Enhancement of Secondary Effluent Characteristics with Air and Oxygen Nanobubbles Generated by Ceramic Membrane Filters

Nanobubbles (NBs) have potential properties, are environmentally friendly, and are sustainable to be used in a variety of applications: industries, agriculture, medical technology, and engineering applications such as water/wastewater treatment. This paper focuses on improving the characteristics of municipal secondary effluent (SE) utilizing oxygen bubbles (OBs), conventional coarse air bubbles (ABs), oxygen nanobubbles (ONBs), and air nanobubbles (ANBs). NBs were generated by injecting pressured gases through a tubular ceramic membrane with nanopores. Several tests have been used to determine the quality of tested SE before and after different injection times, including dissolved oxygen concentration (DO), pH, chemical oxygen demand (COD), biochemical oxygen demand (BOD 5 ), total dissolved solids (TDS), total suspended solids (TSS), sulfide, orthophosphate, organic nitrogen, ammonia, oil and grease, and Escherichia coli ( E. coli ). The results show the priority of ONBs in the enhancement of SE quality. For example, after injecting ONBs, OBs, ANBs, and ABs in SE, the TSS was reduced by 57%, 42%, 28% and 14%, the COD by 62%, 41%, 26% and 12%, the BOD 5 by 73%, 56%, 43% and 21%, and the organic nitrogen decreased by 19%, 11% and increased by 14% and 9%, respectively. These findings are intended to grasp the gaps in our understanding of how NBs affect the advanced treatment of SE. Highlights The use of nanobubbles to enhance secondary effluent was investigated. Oxygen nanobubbles result in an eightfold increase in the level of dissolved oxygen. Oil and grease content is decreased by 33% with oxygen nanobubbles. Escherichia coli is decreased by 94% due to free radicals of nanobubbles collapse.