A different angle on algae and Euglena in wastewater - a story from the last few months.
In one of the plants Maji work with, starting in early July, the operator began seeing unusual algae accumulation in the secondary clarifiers. We are talking about a relatively small municipal plant in an agriculture/dairy-intensive area. Also, during the summer, temperatures are high, reaching more than 35°C / 95°F, with long days.
Secondary Clarifier
At the same time, algae and Euglena were clearly visible under the microscope in the aeration basins as well. Week by week, the abundance increased, secondary effluent turbidity started to rise, and the high algal load also began creating issues in the membranes. There was also a clear daily pattern. Conditions were worse in the morning and improved toward the night, and at one point daytime turbidity reached around 15 NTU.
In the beginning, the directions were to close one of the clarifiers to reduce contact time, or adjust RAS rates. Every option had its own pros and cons. But at the last minute, a different strategy was chosen, and we decided to tackle the root cause: where were the algae actually coming from??
This question was the starting point for an upstream investigation. The team started sampling and testing the reservoirs feeding the plant. One of the reservoirs showed a very high abundance of algae and Euglena, matching exactly what we had been seeing inside the process. We decided to go into a small experiment: the inflow from that reservoir was stopped.
The response was very fast. Within a few days, Euglena was no longer detected, influent turbidity decreased significantly, and much less algae was observed in the secondary clarifiers and across the process. A few weeks later, no algae was detected. This strategy has a con: the MLSS increased. However, in this specific case, it is an issue that is much easier to handle.
The outside-the-box thinking, a big part of which came from one of the operators, was very interesting and enabled the utility to avoid many of the costs this algae issue was creating - membranes, fines, chemicals, and more.