Challenge of Seasonal Wastewater Flows & Loadings

Facilities with seasonal flows such as wineries, vegetable processing, or vacation resorts often have period of low flows at light loadings followed by a rapid increase in both waste volume and concentration. This situation is rarely discussed in textbooks, but is surprisingly common. The challenge is combining equilization, buffering capacity, bioaugmentation, and polymer addition to meet treatment requirements. By fully considering the options before the season flow starts, operators can manage the event with fewer problems.

Here is how I evaluate the various options:

1. Equilization - a common strategy available then when there is lagoon space or in rare cases, tank space. You can use equilization to slowly ramp up the flows and allow the biomass to grow in response to the higher loadings. Often aeration/mixing of the EQ basin is required to prevent odors.
2. Existing buffering capacity - activated sludge systems have an adsorption capability where the MLSS acts like a sponge to hold excess organics. This increases sludge volumes going to the digester or dewatering, but it gives a buffer to increases in influent loadings. To best utilize this strategy, operators will increase MLSS/MLVSS before the seasonal loading. Limits to MLSS building are governed by system solids capacity (clarifier, aeration, etc) and the presence of influent organics to maintain a higher, active MLSS.
3. Bioaugmentation - when a system requires a rapid increase in active biomass, the quickest way to bring about the change is to add "exogenous cultures" or "bugs". The preserved cultures are highly concentrated and usually consist of k-rate strategists (fast growing microbes). This helps to prevent effluent permit issues by rapidly increasing the viable portion of the MLSS.
4. Polymer or other chemical addition - polymers to control biological solids and remove influent organics in primary treatment offers a very powerful control tool. Key issues to consider are correct polymer chemistry for the waste stream, dosing points for maximum effectiveness, and the impact on downstream solids handling.
   

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