—Henze, et al.
Temperature has a significant effect on the growth rate of microorganisms. Those operating at a higher temperature range have a higher maximum growth rate than those operating at a lower range. The optimal range of temperature for each group is relatively narrow. With an increasing temperature, a gradual increase in growth rate is observed until an abrupt drop is observed due to the denaturation of proteins at a higher temperature. The generally used terms to describe these microorganisms are psychrophile below about 15°C [59°F], mesophile for 15−40°C [59−104°F], thermophile at 40−70°C [104−158°F], and hyperthermophile which are active about 70°C up to around 110°C [230°F].
Source: Henze, Mogens, et al. Biological Wastewater Treatment: Principles, Modelling and Design. London: IWA Publishing, 2011. (See pages 18−19)
—Berne and Cordonnier
Four remaining causes of trouble in biological purification should be avoided: temperature, pH, shock effects, and sludge “leaching.”
Aerobic purification by mesophile bacteria can be carried out in a wide range of temperature from 10 to 35°C [50 to 95°F], but load and efficiency conditions are optimum between 18 and 32°C [64.4 and 89.6°F]. Also to be avoided are dramatic variations in temperature in a time frame of a few hours.
Source: Berne, Francois and Jean Cordonnier. Industrial Water Treatment: Refining, Petrochemicals, and Gas Processing Techniques. Houston: Gulf Publishing Company, 1995. (See pages 109−110)
—International Water Association
Biological processes are affected by temperature. Generally speaking, the higher the temperature, the higher the microbial activity until an optimum temperature is reached. Further increase of the temperature beyond its optimum value results in a precipitous decrease of microbial activity.
In addition to the denaturation of proteins at relatively high temperatures, cell lysis has been observed to increase sharply with increasing temperature, especially when substrate is exhausted (Allen 1950).
Source: International Water Association. Advanced Biological Treatment Processes for Industrial Wastewaters. London: IWA Publishing, 2006. (See pages 32−33)
—Rabinowitz, et al.
LaPara and Alleman (1999) divided the operating ranges of activated sludge into mesophilic (<35°C), transitional (35°<T<40°C) and thermophilic (>45°C) temperatures. There appears to be a “no man’s land” between 41°C and 44°C. In the mesophilic range, temperature seems to exert little effect on the removal by activated sludge of collectively measured pollutant parameters such as BOD5 and COD. This was clearly demonstrated by Parks et al. (2000), who found no significant change in the soluble COD removal efficiency in an activated sludge process treating a warm, high-strength pharmaceutical wastewater at temperatures between 24°C and 44°C.
However, when more specific reactions, such as the removal of individual organic compounds, are measured, distinct temperature effects can be seen. For example, the biological removal rate of polyvinyl alcohol (PVA) in the activated sludge process is very sensitive to temperature variations, becoming extremely low at temperatures below about 12°C (Schonberger et al., 1987).
The relative insensitivity of temperature on the removal of collectively-measured pollutant parameters such as BOD5 and COD is likely due to the fact that there are many groups of heterotrophic organisms in activated sludge, each with its own optimum temperature, that are capable of “BOD5” or “COD” removal. Thus, when biodegradation by one group of organisms slows down, there is another group ready to take over. For more specialized substrates there may be only one, or a very limited number, of microorganisms able to carry out the necessary biochemical reactions. In these cases, a more distinct temperature optimum will be observed.
Source: Rabinowitz, Barry, et al. “The Effect of High Temperatures on BNR Process Performance.” (See the attached paper.)
—Cruikshank and Gilles
Biological Treatment Systems are sensitive to temperature as is every other living entity. Conventional mesophilic bacteria has been shown to perform most optimally when the reactor wastewater temperature is maintained between 78° and 95°F (26° and 35°C). Nitrifying bacteria have an even tighter range of optimal reactor temperature between 85° and 92°F (29° and 33°C). Many industrial processes that generate wastewater from such unit operations as distillation bottoms, stripping, tank cleanouts, quenching can produce elevated temperatures that exceed the ideal environment for robust biological treatment. These warmer wastewaters can cause the biomass to operate at a much lower efficiency ultimately lowering the effluent discharge quality from the facility. Elevated temperatures also affect oxygen transfer in the reactor further affecting the performance of the wastewater treatment plant.
During development of process design parameters and preliminary engineering of mechanical systems for new or upgraded wastewater treatment facilities, an engineer should evaluate influent temperature variations, atmospheric conditions, and mechanical inputs that may affect the biological system. This evaluation should be completed using data from different seasons of the year taking into account local weather data, the storage volume of the tanks or basins, materials of construction for these systems, as well as the energy (heat) input to the overall process through aeration and/or mixing.
Source: Cruikshank, Christa L. and David G. Gilles. “Temperature Modeling and Control for Biological Wastewater Treatment Design.” (See the attached paper.)
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