Explain how changes in influent wastewater temperature affect the performance of biological treatment processes and what operational adjustments are necessary.

Influent wastewater temperature significantly impacts the performance of biological treatment processes because it affects the metabolic activity of the microorganisms responsible for pollutant removal. Biological treatment relies on bacteria and other microorganisms to break down organic matter, ammonia, and other pollutants. Temperature influences the rate of these biological reactions; generally, higher temperatures increase reaction rates up to an optimum point, while lower temperatures decrease reaction rates. In activated sludge systems, decreased temperatures reduce the microbial growth rate. This can lead to a slower rate of organic matter removal (BOD and COD) and nitrification (ammonia removal). The settling characteristics of the sludge can also be affected, potentially leading to poorer solids separation in the secondary clarifier. Conversely, increased temperatures can accelerate biological reactions, but excessively high temperatures can inhibit or even kill certain microorganisms, disrupting the balance of the microbial community. In trickling filters, low temperatures can reduce the activity of the biofilm, decreasing the removal efficiency. High temperatures can promote excessive biofilm growth, leading to clogging and reduced aeration. Operational adjustments to compensate for temperature changes include adjusting the sludge age (solids retention time, SRT). At lower temperatures, increasing the SRT allows for a longer retention time of the microorganisms in the system, compensating for their slower growth rate and maintaining a sufficient biomass concentration. This may involve reducing sludge wasting. At higher temperatures (within the optimum range), decreasing the SRT can prevent overpopulation of the microorganisms. Adjusting the dissolved oxygen (DO) levels is also necessary. Lower temperatures increase the solubility of oxygen in water, so DO levels may need to be reduced to avoid excessive energy consumption. Conversely, at higher temperatures, DO levels may need to be increased to ensure that the microorganisms have sufficient oxygen for respiration. Optimizing the nutrient balance (C:N:P ratio) can also help to maintain optimal microbial activity at different temperatures. Monitoring the effluent quality closely is essential. Regular monitoring of BOD, COD, ammonia, and other parameters allows operators to detect problems early and make necessary adjustments to the treatment process. For example, in cold climates, insulating or covering treatment units can help to maintain higher wastewater temperatures and improve treatment efficiency. Therefore, managing temperature fluctuations requires a combination of SRT adjustment, DO control, nutrient balancing, and close monitoring to ensure stable and efficient biological treatment.