Which factor most significantly affects the rate of biochemical oxygen demand (BOD) reduction?

Temperature is a critical factor affecting the rate of biochemical oxygen demand (BOD) reduction because it directly influences the metabolic rates of microorganisms that decompose organic matter in wastewater. Higher temperatures generally increase the kinetic energy of these microorganisms, leading to enhanced microbial activity. This results in a more efficient breakdown of organic pollutants, thus reducing BOD more rapidly compared to lower temperatures.

In wastewater treatment processes, maintaining optimum temperature ranges is essential for maximizing biological activity. When temperatures are too low, microbial processes slow down, leading to longer retention times and less effective BOD reduction. Conversely, excessively high temperatures can be detrimental, as they might inhibit certain microbial populations or lead to the denaturation of important enzymes.

While factors like pH level, solids concentration, and detention time also play roles in the BOD reduction process, their impact is often overshadowed by the influence of temperature on microbial activity. For instance, although pH levels can affect enzyme activity and microbial growth, most decomposing microorganisms have a tolerance range within which they can effectively perform, highlighting the primacy of temperature as a driving force in the biochemical processes of BOD reduction.