This article is in response to the many questions I get regarding information on the biodegradation of quaternary ammonium (quat) biocides (ADBAC and DDAC) and the relationship to potential impact on the functioning of wastewater treatment systems.
There are three primary considerations when examining the impact of the quats on treatment systems: 1) biodegradation of the quat; 2) toxicity of the quat to the microorganisms; and 3) the overall removal of the quat from the system.
- Both ADBAC and DDAC have been shown to be readily biodegradable (>90% degradation in 28 days) in stringent laboratory studies in which no organic material is
- In simplified terms, the toxicity of quats to the microorganisms of a treatment facility is based on the bioavailable concentration of the quat, the concentration of the microorganisms, and the acclimation of the organisms to the quat (acclimated organisms more efficiently degrade quats than microorganisms that have never been in exposed to the chemicals). When entering the waste treatment system, the quat is substantially diluted from its use concentration (e.g. 400 ppm) by wash and waste water as well as the system volume. Generally, this dilution is adequate to reduce the concentration of the quat to non- antimicrobial
- In addition, quats bind rapidly to organic matter and as such the vast majority of the quat is not in solution or bioavailable to harm the working organisms of the treatment facility. These bound quats are then degraded as the organic matter to which they are bound is
A number of reviews of the behavior and treatment of quats have been produced. For example, Boethling (Environmental Fate and Toxicity in Wastewater Treatment of Quaternary Ammonium Surfactants.
Water Res. 18:1061-1076, 1986) reviewed the sewage treatment of quaternary ammonium compounds (QAC) and concluded:
“A considerable mass of evidence suggests that QAC concentrations in the soluble phase should be reduced by at least 90% in POTWs under normal circumstances. Both sorption and biodegradation contribute to QAC removal, but sorption is more rapid, so that biodegradation is expected to occur mainly on sludge solids. Many QACs will in fact undergo ultimate biodegradation in aerobic biological treatment. … Whereas toxicity of QACs would obviously be mitigated by any opportunity for acclimation and by the relatively low concentrations in sewage, anionic surfactants will also play a role in reducing toxicity.”
Based on this type of information, the U.S. Environmental Protection Agency in its recent Reregistration Eligibility Decision (RED) Preliminary Risk Assessment, concluded:
“Breakdown in the environment and via sewage treatment is rapid and well documented in the literature.”
In conclusion, the evidence clearly indicates that the incorporation of ADBAC and DDAC into properly functioning waste treatment facilities poses no concern for the proper function of the facility and results in rapid and virtually complete removal of the quats.