The Seasonal Impact of Spring on Wastewater Treatment: Temperature Changes and Snowmelt Challenges

As winter gives way to spring, wastewater treatment plants (WWTPs) across Canada face a wave of seasonal challenges. Rising temperatures and snowmelt bring significant shifts in hydraulic load and biological processes, particularly in outdoor systems like lagoons, aerated ponds, and constructed wetlands, but they also impact other biological treatment systems.

While warmer temperatures increase microbial activity and improve treatment efficiency, the rapid influx of meltwater dilutes wastewater, shortens retention times, and disrupts biological stability. In outdoor treatment systems, thermal inversion in settling ponds can resuspend solids and release stored nutrients, affecting effluent quality. To maintain stable operations, operators must monitor conditions closely and adjust processes accordingly.

Springtime Effects on Biological Treatment

According to the Arrhenius Law (link here), biological processes speed up as temperatures rise. While this boosts microbial activity, the transition from winter dormancy to peak efficiency can be disruptive, requiring careful adjustments.

1. Increased Microbial Activity

During winter, cold temperatures slow microbial metabolism, reducing the breakdown of organic matter and nitrogen removal efficiency. As spring temperatures climb:

• Bacteria become more active, improving treatment performance.
• Oxygen demand rises, requiring aeration adjustments to maintain dissolved oxygen levels.
• Outdoor treatment systems experience temperature gradients, where surface layers warm faster than deeper ones, creating potential stability issues.

Although this increase in microbial activity is beneficial, sudden shifts in metabolism can throw treatment processes off balance if adjustments aren’t made in time.

2. Shock Load Effects on Treatment Systems

The abrupt shift from winter dormancy to peak microbial activity can overload biological treatment processes, leading to:

• Unstable microbial populations, where bacteria grow too quickly, consume available nutrients, and then enter a starvation cycle—causing fluctuations in treatment performance.
• Inconsistent organic matter and nutrient removal, requiring adjustments to nutrient dosing and retention times.
• Higher oxygen demand, which, if not carefully managed, can deplete oxygen levels or cause excessive turbulence in aerated systems.

To stabilize biological treatment, operators should adjust aeration rates, manage sludge retention times (SRTs), and optimize nutrient dosing gradually as microbial activity increases.

3. Ammonia and Nitrogen Removal Challenges

Nitrification, the biological process that converts ammonia into nitrates, relies on temperature-sensitive bacteria that recover slowly from cold winter conditions. In early spring:

• Nitrification rates remain low, potentially leading to higher ammonia concentrations in effluent.
• Nutrient discharge limits may be at risk, requiring adjustments to treatment processes.
• Extended retention times or temporary chemical dosing may be needed to maintain compliance until bacteria populations stabilize.

Optimizing aeration, pH levels, and microbial acclimatization is essential for ensuring effective nitrogen removal as temperatures rise.

Impact of Snowmelt on Hydraulic Loading in Outdoor Biological Systems

Beyond biological challenges, spring snowmelt brings an influx of water that can overwhelm treatment facilities, particularly those using outdoor biological systems.

1. Increased Hydraulic Load and Dilution Effects

As snow melts, excess water flows into wastewater systems, increasing hydraulic loading and diluting wastewater, leading to:

• Weakened biological treatment performance, as microbes struggle with lower concentrations of organic material.
• Reduced retention times, meaning wastewater moves too quickly through treatment stages, limiting pollutant breakdown.
• Bypass risks, where overloaded systems release partially treated water into receiving environments.

Operators can mitigate these challenges by using flow equalization strategies, optimizing retention times, and closely monitoring influent quality.

2. Thermal Inversion and Rising Solids in Settling Ponds

A less obvious but equally disruptive springtime challenge is thermal inversion in outdoor settling ponds and lagoons. This occurs when surface water warms faster than deeper layers, disrupting stratification and causing resuspended solids.

Consequences of thermal inversion:

• Increased suspended solids in effluent, reducing water clarity and potentially exceeding regulatory limits.
• Higher organic loads, placing extra strain on downstream treatment stages.
• Nutrient release from the sludge layer, which can contribute to algal blooms in receiving waters.

To reduce these risks, operators can:

• Use aeration strategically to prevent rapid stratification shifts.
• Implement baffles or flow control structures to minimize sludge disturbance.
• Increase solids removal efforts in late winter to limit resuspension.

Conclusion

Spring presents both opportunities and challenges for wastewater treatment plants. While rising temperatures boost microbial activity and improve treatment efficiency, the season also introduces risks, including shock loads, ammonia removal inefficiencies, hydraulic overload, and thermal inversion in outdoor systems.

By monitoring conditions closely, making gradual process adjustments, and managing hydraulic loads effectively, WWTPs can navigate seasonal disruptions while maintaining compliance and treatment efficiency.

Trust AQUASAN’s technical team. We have extensive technical expertise in all types of water treatment. With extensive training and technical know-how, and we bring creative solutions that ensure treated water quality is preserved.