The Importance of the Arrhenius Law in Biological Wastewater Treatment in Canadian Climate

The Arrhenius Law, introduced by Swedish scientist Svante Arrhenius in 1889, is fundamental in understanding how temperature influence’s reaction rates in chemical reaction kinetics. This principle extends beyond chemistry and can play a crucial role in biological systems, particularly those involving microbial activity.

One significant application is in biological wastewater treatment.  Here, Arrhenius Law can be used to insightfully show how temperature variation can influence the metabolic rates of microorganisms, which ultimately drives the efficiency of the treatment process. Understanding this relationship is essential for optimizing biological systems, especially in regions like Canada, where climate conditions can significantly impact these processes.

Understanding the Arrhenius Law

Arrhenius Law describes how the rate of a chemical or biological reaction depends on temperature.  It is represented by the equation:

Where:

• K is the rate constant of the reaction.
• A is the pre-exponential factor or frequency factor, which indicates the frequency of collisions with the correct orientation for a reaction to occur.
• e is the base of the natural logarithm.
• E_a is the activation energy, the minimum energy required for the reaction to take place.
• R is the universal gas constant (8.314 J/(mol·K)).
• T is the absolute temperature in Kelvin.

If the minimum requirements for activation energy have been met, this equation shows that as temperature increases, the corresponding reaction rate will increase in an exponential fashion. Reactions with low activation energy mean they can proceed more easily at lower temperatures, while those with higher activation energy require a higher temperature to achieve the same reaction rate. This highlights the crucial role temperature plays in determining the speed at which both chemical and biological reactions unfold.

Application in Biological Wastewater Treatment

In biological wastewater treatment, Arrhenius Law is essential for predicting and managing the rates of biochemical reactions carried out by microorganisms such as bacteria and archaea. These microbes are responsible for degrading organic pollutants and transforming nitrogen compounds and are highly sensitive to temperature change.  As a result, their metabolic rates, which determine the efficiency of wastewater treatment, are governed by the principles outlined in the Arrhenius equation.

Impact of Canadian Climate on Wastewater Treatment Efficiency

Canada’s diverse climate poses unique challenges for wastewater treatment facilities. In the colder regions, winter temperatures can plunge well below freezing.   During these months, the subsequent reduction in water temperature will have a negative impact on the rate constant K in the Arrhenius equation, which in turn will slow down microbial activity and reduce the rate at which organic matter and nitrogen compounds are consumed.  To counteract this, wastewater treatment facilities must implement several strategies.

• Increase system retention time: This will give microorganisms more time to break down pollutants, thereby compensating for their decreased activity.
• Enhancing mixing: This will help maintain uniform temperature distribution and prevent localized cooling, which can be detrimental to microbial efficiency.
• Supplemental Heating: In extreme cold conditions, external heating systems might be necessary to ensure wastewater temperatures stay within an optimal range for microbial activity. For most mesophilic bacteria, the approximate range is 20°C to 40°C.
• Insulation: Insulating tanks and covering reactors are practical measures to retain heat and minimize the impact of cold air infiltration. This is crucial during prolonged cold spells, where maintaining a stable internal temperature is vital for consistent treatment performance.
• Seasonal adjustments – Increasing the concentration of active biomass or adding supplemental nutrients, can further support microbial activity during these challenging periods.

Challenges During Canadian Summers

While Canadian winters pose significant challenges, the summer months can also create complications for wastewater treatment. In some regions, high ambient temperatures can increase water temperatures significantly, which can lead to an acceleration of microbial activity beyond optimal levels, promote process imbalances (difficulty maintaining DO) and in some cases unwanted cellular attrition (die-off).

To mitigate the challenges tied to excessively high water temperatures, treatment plants may implement a number of the following measures.

• Provide adequate shelter or shading to prevent overheating of exposed tanks and reactors.
• Increase aeration to ensure dissolved oxygen levels are high enough to support microbiological activity or demand.
• In some cases, supplemental cooling systems might be employed to maintain temperatures within a manageable range, preventing the risk of microbial die-off due to overheating.

How Can Aquasan Help?

Aquasan can provide your team with technical assistance and the insight they need to help predict how changes in temperature can impact your wastewater treatment system.  With regular site visits and comprehensive monitoring, our team can assess current environmental and operating conditions and fine-tune applied chemistries to ensure optimal performance. If you’ve been facing seasonal challenges, reach out to our experts. We can help you navigate these difficulties with our expertise and tailored support, smoothing out your operational issues and optimizing your treatment process year-round.