What could cause an abnormal increase in BOD levels in wastewater?

An abnormal increase in Biochemical Oxygen Demand (BOD) levels in wastewater typically indicates a higher concentration of biodegradable organic material present. Excessive industrial discharges can introduce a significant amount of organic pollutants into the wastewater system, which directly contributes to elevated BOD levels. Industries often discharge waste that contains high levels of organic compounds, which require more oxygen to decompose, thereby increasing the BOD measurement.

In contrast, low organic matter would likely lead to lower BOD levels, as there would be less biodegradable material for microorganisms to act upon. High dilution rates would generally reduce BOD levels because the organic matter is spread out over a larger volume of water, leading to a lower concentration of pollutants. Improved treatment efficiency would typically result in lower BOD levels, as better treatment processes are more effective at removing organic matter. Thus, the correct answer highlights the impact of excessive industrial discharges on increasing BOD in wastewater.