Rapid temperature changes tend to cause more problems than gradual drift in WW. Even with slow increase in temperatures, you reach inflection points where system drifts above the growth range of most common mesophilic organisms. Most common genera in WW thrive up to 38oC. Once you go above 40 – 42 oC, you start to see impacts of high temperatures. High temperature issues are compounded by lower oxygen solubility.
Signs of heat stress in MLSS
- Higher turbidity and TSS
- Deflocculation and bulking as bacteria biofilms become less binding
- AOB & NOB activity drops – combination of lower DO and temperatures above normal growth range
- Microscopic exam shows less protozoa and metazoan diversity & increased free bacteria cells
When does high temperature become a problem
- 38 oC – normal listed max temp for many mesophilic WW organisms
- 42 oC – where normal signs of stress become visible with loss of flocculation
- 45 oC – normal maximum for mesophilic system and transition to more thermotolerant and thermophilic organisms starts
- 55 oC – move to thermophilic organism zone
Using bioaugmentation to rapidly increase thermotolerant organisms in the system.
When faced with flocculation problems related to high temperatures, adding thermotolerant microbes improves floc formation and stabilizes the system. By adding higher temperature organisms, you reduce the time required for MLSS stabilization.