Preventing Biological Treatment Upsets

What is so upsetting about biological treatment system upsets? To the owners and operators of these systems, these upsets lead to halts or decreases in production with costly ramifications. ATI is often called upon to investigate issues of this nature.

Regardless of the type of industry (pulp and paper, dairy, beverage, chemical, etc.) and the type of biological treatment system used (anaerobic, aerobic, high-load, low-load, fixed film, suspended microorganism, etc.), commonalities exist between the upsets experienced by our clients. We routinely receive calls concerning upset systems ranging from a perceived deterioration in performance to a confirmed extinction of biological activity. These problems often require swift remedial action.

When comparing the problems brought to our attention in 2007 to those of previous years, several causative factors stand out. The number one cause of biological treatment system upsets is organic overloading – too much food (BOD or COD basis) for the resident population of microorganisms. Organic loading can be a transient problem, generated by a surge or spike discharge of waste that is not normal compared to an “average” day. The reasons for the discharge can typically be identified with a thorough investigation of the incident, which then leads to the development and implementation of a plan to avoid repeat incidents. Production personnel is then responsible for ensuring that this incident is not repeated.

Organic overloading can also creep into the picture as production plant wasteloads increase with time and no provision is made to handle the change, such as an increase in the capacity of the biological treatment system or the addition of pretreatment capacity upstream. This is a more difficult problem to resolve, as it typically requires careful evaluation of the treatment plant, a review of alternatives to provide additional treatment capacity, and the expenditure of capital funds to implement the expansion. Nonetheless, keep in mind that wastewater treatment should be treated like any other plant utility (e.g., electrical power, potable water, etc.) requiring expansion with production increases.

The second major cause of biological treatment upsets is the discharge of “nasties” – material that is not readily biodegradable within the design parameters of the treatment system. Examples of this range from something as seemingly innocuous as butterfat (dairy plant FOG), to something as deadly as sanitation chemicals. In the former case, although animal-based FOG are often readily biodegradable, their presence in significant quantities (perhaps greater than 100 mg/L) can interfere with aeration and settling processes and seriously degrade the effluent quality of the treatment plant. In the case of sanitizing chemicals, the uncontrolled discharge of spikes of quaternary ammonium (quats) or chlorine-based cleaners may kill most, if not all microorganisms in a biological system.

We recommend following these general rules to avoid biological treatment system upsets:

1. Communicate frequently and clearly with production personnel regarding any extraordinary waste discharges that might happen or happened recently.
2. Sample and test waste streams and treatment process influent and effluent regularly to determine baseline wasteloads and “normal” performance levels and to allow identification of those production periods that are causing problems.
3. Track wasteloads and production levels versus treatment system performance and anticipate the need to expand the treatment plant.
4. Be sure to have sufficient equalization capacity, and calamity storage capacity if required, to handle spikes in discharge loads and accidents.