Summer brings higher temperatures, increased microbial activity, and frequent rainfall, all of which can significantly affect wastewater treatment system performance. Operators often encounter challenges such as floating sludge, sludge bulking, low dissolved oxygen, excessive foam, odor generation, and nutrient removal failures.
This article outlines eight common wastewater treatment problems during hot weather and practical solutions to maintain stable plant operation.
1. Floating Sludge and Rising Sludge in Secondary Clarifiers
Causes
High temperatures accelerate sludge metabolism and promote anaerobic and denitrification reactions within the secondary clarifier. Poor sludge settling characteristics and delayed sludge removal can further contribute to sludge flotation.
Solutions
- Maintain adequate dissolved oxygen (DO) levels in the aeration tank.
- Prevent anoxic conditions in the secondary clarifier.
- Control MLSS at 3,000–4,000 mg/L.
- Remove accumulated sludge regularly.
- Inspect and maintain sludge scrapers and collection systems.
2. Sludge Bulking and High SVI
Causes
Warm temperatures favor filamentous bacteria growth. Combined with low DO, low organic loading, or nutrient imbalance, sludge bulking can occur, leading to elevated Sludge Volume Index (SVI).
Solutions
- Increase dissolved oxygen levels.
- Optimize sludge wasting rates.
- Supplement carbon sources when influent COD is insufficient.
- Conduct jar tests before dosing PAC or sodium hypochlorite to suppress filamentous bacteria.
3. Low Dissolved Oxygen in Aeration Tanks
Causes
As water temperature rises, oxygen solubility decreases while microbial oxygen demand increases, resulting in lower DO concentrations.
Solutions
- Monitor temperature fluctuations closely.
- Improve aeration efficiency.
- Cool high-temperature industrial wastewater when necessary.
- Adjust blower operation according to oxygen demand.
4. Excessive Foam and Viscous Scum
Causes
Higher microbial activity and the accumulation of oils, grease, and surfactants can generate thick foam on the biological treatment surface.
Solutions
- Increase sludge wasting to prevent sludge aging.
- Use water spray systems for foam suppression.
- Control influent oil and surfactant concentrations.
- Apply antifoaming agents when required.
5. Influent Quality Fluctuations and Shock Loads
Causes
Frequent rainfall, industrial discharge variations, and accelerated organic decomposition can cause significant fluctuations in influent flow and pollutant concentration.
Solutions
- Utilize equalization tanks for flow and load balancing.
- Reduce sludge concentration before the rainy season.
- Strengthen influent monitoring.
- Increase aeration and reduce system loading during shock events.
6. Odor Problems and Elevated Hydrogen Sulfide (H₂S)
Causes
High temperatures accelerate anaerobic decomposition of wastewater and sludge, producing hydrogen sulfide and other odorous gases.
Solutions
- Remove screenings and grit promptly.
- Clean sediment accumulation regularly.
- Cover sludge storage tanks.
- Apply deodorizing agents when necessary.
- Enhance pre-aeration to reduce anaerobic conditions.
7. Excessive Total Phosphorus in Effluent
Causes
High temperatures may alter phosphorus removal performance. Inadequate sludge age and insufficient phosphorus release in anaerobic zones can result in elevated effluent phosphorus levels.
Solutions
- Optimize biological phosphorus removal processes.
- Maintain proper sludge retention time (SRT).
- Supplement chemical phosphorus removal using PAC, ferric chloride, or specialized phosphorus removal chemicals.
8. Reduced Ammonia Removal Efficiency
Causes
Although nitrifying bacteria remain active in warm conditions, oxygen transfer efficiency decreases significantly at higher temperatures. Combined with hydraulic and organic load fluctuations, nitrification performance may decline.
Solutions
- Maintain aerobic zone DO ≥ 2.5 mg/L.
- Reduce excessive MLSS levels to minimize oxygen competition.
- Stabilize influent loading conditions.
- Extend nitrification retention time when possible.
- Continuously monitor ammonia nitrogen concentrations.
Conclusion
Summer conditions can place significant stress on wastewater treatment plants through higher temperatures, lower oxygen transfer efficiency, increased microbial activity, and influent fluctuations. By proactively monitoring process parameters and implementing appropriate operational adjustments, treatment facilities can maintain stable performance and ensure compliance with discharge standards throughout the hot season.
