What is a common consequence of high levels of BOD in treated effluent?

High levels of Biochemical Oxygen Demand (BOD) in treated effluent indicate that there is a significant amount of organic material present that requires oxygen for microbial decomposition. When BOD levels are elevated, it can lead to a reduction in treatment efficiency. This is because the treatment processes, particularly biological ones, may become overwhelmed as microorganisms consume the available oxygen to break down the organic matter. If the oxygen demand exceeds what is available in the treatment system, it can hinder the ability of the system to effectively treat the wastewater, potentially leading to inadequate removal of pollutants and resulting in poorer effluent quality. A decrease in treatment efficiency not only affects the immediate output quality but can also contribute to environmental issues if the effluent is discharged into receiving waters.