City of Escalon

Situation

The municipal treatment plant at the City of Escalon treats 1.2 million gallons per day of high-strength wastewater (over 5,000 mg/L BOD) from two large food processors. Four treatment ponds with aeration treat influent wastewater. Influent enters treatment flow in parallel into two of the ponds (Ponds 2 and 3) before flowing in series through the next two ponds (Pond 1, then Pond 4).

Ponds 2 and 3 have robust aeration for digesting BOD; Ponds 1 and 4 provide retention time for further BOD reduction, but these ponds provide less aeration to allow for solids settling. The plant experienced odor issues that they wanted to improve.

Our Approach

The City of Escalon reached out for a solution to reduce BOD and TSS in their ponds. The recommendation was to dose microbes to digest soluble BOD and decrease the solids content of their wastewater. The microbes consist of a dry product containing 10 billion colony forming units of a Bacillus bacteria blend, freeze-dried on a wheat bran. Bacillus bacteria are best suited for aerobically digesting heavy organic loads and soluble BOD that cannot be removed mechanically.

In 2017, the plant saw influent loading rates of 700 mg/L BOD and 2000 mg/L TSS. No microbes were added, and effluent levels were around 100 mg/L BOD and 280 mg/L TSS. During this time, Escalon’s wastewater treatment plant had occasional odor issues. A trial of the bacteria blend was designed to ramp up throughout the industrial season in August and September.

2018 Ponds During Bacterial Dosing

In 2018, the plant saw influent loading rates of 500 mg/L BOD and 1700 mg/L TSS. The City purchased four pails of the ten billion CFU (colony forming unit) bacteria blend to add to the ponds as a trial. They added 20 pounds of dry microbes per day in each pond, Pond 1 and Pond 2. They did this for two weeks and measured BOD and TSS in Ponds 1, 2, and 3. During this period, the BOD and TSS in Pond 1 were reduced by at least 78%. In addition, Pond 2 had a greater TSS reduction by 29% compared to Pond 3.

2019 Ponds During Bacterial Dosing

In 2019, the plant saw influent loading rates of 900 mg/L BOD and 1700 mg/L TSS. To adjust for the increase in BOD levels, the City dosed bacteria through the industrial season, from August to September. In the start of the season, the City kickstarted the bacteria population in Ponds 2 and 3 by adding about 40 pounds per pond the first two days, then 25 pounds per day per pond twice a week. They bloomed the dry microbes in rain barrels before adding the solution to the influent point of the ponds. To maintain the bacteria population through the season, they added 20 and 10 pounds per day per pond on an alternating basis through September.

While the bacteria was being dosed, Ponds 2 and 3 had a reduction of 65% and 67% in TSS and 36% and 28% in BOD, respectively. Through an aggressive and well-timed approach to dosing the right bacteria, the City of Escalon greatly reduced TSS and BOD in three of the four ponds.

Overall, this is a huge win for the City of Escalon since they dramatically improved their treatment ponds with our recommended approach without a large capital expense or retrofit to the facility.