What indicates an increase in BOD levels in wastewater?

The correct answer highlights that an increase in microbial activity due to organic pollution directly correlates with an increase in Biological Oxygen Demand (BOD) levels in wastewater. BOD measures the amount of dissolved oxygen that microorganisms will consume while decomposing organic matter in the water. When organic pollutants are present, they provide a food source for these microorganisms, resulting in higher microbial activity. As the microorganisms break down this organic material, they demand more oxygen, thus leading to elevated BOD levels.

This understanding is crucial for wastewater treatment processes, as high BOD can indicate poor water quality and potential impacts on aquatic life. Promoting the removal of organic pollutants is essential in maintaining optimal BOD levels during wastewater treatment.

The other options relate to factors that either contribute to reducing BOD or do not directly correlate with increased microbial activity in the presence of organic matter. For instance, a decrease in organic matter would typically lead to lower BOD levels, while a reduction in nutrient levels could hamper microbial growth, consequent to a decrease in BOD. Similarly, while an increase in total suspended solids can affect water quality, it is not directly indicative of increased BOD, as the solids themselves may not be organic in nature.