Additive Usage at Wastewater Treatment Facilities - PUB2653

This factsheet is intended to guide wastewater treatment permittees who are considering the application of chemical or biological additives to improve their current operations. The use of additives at wastewater treatment plants is common and can serve a variety of purposes. The addition of acids and bases, such as hydrochloric acid and sodium hydroxide, are commonly used to adjust pH. Chlorine gas and sodium hypochlorite are often used to kill pathogens and disinfect wastewater and sodium sulfite or sodium bisulfite are often used in tandem to dechlorinate these effluents. There are many compounds that serve as coagulants, flocculants and filter aids, such as aluminum sulfate, ferric chloride and polymer based compounds. Quite a few facilities use herbicides to control algae or other nuisance aquatic plants. Some operations can be improved with the use of enzymes and surfactants that stimulate bacterial action by cleaving fat, oil and grease, and sugar and starch molecules into basic components so that they can be destroyed by bacterial action. Other operations can also benefit from the addition of nutrient solutions or bacteria that also can serve augment biological action. Foam control agents might be useful for systems that have foam drift of overflow problems. And some wastewater treatment systems require the addition of alkalinity and carbon sources such as methanol to function properly.

Operating permits do not prohibit the use of these additives unless their use is expected to result in a change or impact to effluent quality. The department does not review or approve the usage of specific additives or applications.  Existing permits (Standard Conditions Part I, Section B) require permitees to “give notice to the department as soon as reasonably possible of any planned physical alterations or additions to the permitted facility.” In general this refers to how these alterations or additions may affect their discharge. When considering the addition of a new additive the permittee must determine if it will adversely affect the quality of their effluent or change the characteristics of their biosolids. In many cases chemical or biological additives are expected to improve effluent quality and therefore do not require a modification to the operating permit. An example might be the addition of a flocculent to a final clarifier to improve settling performance without negatively affecting effluent quality.

Permittes must be careful to consider the unintended consequences of chemical addition and they need to question whether the chemical may cause toxicity to aquatic organisms or affect narrative water quality criteria. such as causing scums, color or turbidity, or odors. Operating permits include conditions that prohibit permittees from causing these conditions. It may be difficult to know if a particular additive has the potential to cause toxicity, and product vendors can sometimes help with this determination. To determine toxicity, the department relies on Whole Effluent Toxicity (WET) testing. WET testing methods can be found in 40 CFR 136.3 and in the U.S. Environmental Protection Agency's guidance on WET testing. Many operating permits include requirements to conduct WET testing, and sampling should be done during periods in which additives are being used so that their contribution to toxicity is considered. In the event that a permittee expects that an additive application will result in an adverse impact to their effluent, they will need to contact the department to have their operating permit modified and the activity may have to undergo Antidegradation review. An example of this would be the installation of a chlorination or dechlorination system for disinfection because the addition of these chemicals is expected to affect the quality of the discharge. For this reason the installation of a chlorination or dechlorination system requires a modification to their operating permit. And because this project would involve the installation of equipment that is subject to design standards a construction permit would also be required.

When applying for an operating permit modification permittees must specify the conditions that require the additive, explain the dosages, and describe how this is expected to affect effluent quality. It is incumbent on the permittee to evaluate the effectiveness of such a product and make sure that they are adhering to their permit conditions. If the department suspects that a particular chemical or biological additive may be affecting effluent quality, the department may reopen the operating permit and include conditions to address the concern.