Quaternary Ammonia Compounds: Why are they so common, and why is nobody talking about them?

Abstract
Quaternary Ammonia Compounds (QACs) have long been recognized as niche contaminants in specialized industries outside of municipal wastewater treatment. They are known to affect biological processes, for example anaerobic digestion in agriculture settings. They are not regulated and are widely ignored as a factor for municipal wastewater treatment. Their use in everyday life skyrocketed following two pivotal moments: the ban on triclosan and triclocarban in soap products and the pandemic that resulted in widespread use of disinfection sprays across our society. Here, we report on two completely different wastewater treatment plants that had to deal with QACs causing upset to their biological processes (nitrification at one plant and anaerobic digestion at another plant). We employed contract labs to quantify QACs in influent wastewater along with toxicity testing. In one case, a new food preparation facility in Texas was utilizing cleaning products for daily routine cleaning and periodic deep-cleaning of specific equipment, unaware that the products contained QACs that could potentially cause an upset at the local wastewater treatment facility. One of their cleaning products they used was a detergent commonly used in households for dishwashing. Working closely with the local wastewater treatment, the facility significantly reduced their use of these products to enable them to safely discharge their effluent. At the other facility, QACs were attributed to upset startup with anaerobic digestion. We will present results on QACs and biological process function along with the models we employed to identify and remediate QAC issues.

Background
Quaternary ammonia compounds (QACs) are a class of compounds widely used for their disinfecting ability in the food industry for cleaning process lines as well as in the agricultural industry. QACs are the main active ingredient in disinfecting cleaner sprays (for example, Lysol) and liquid soap. QACs are widely used everyday, and they are widely detected in WRRFs (Mahoney et al., 2023).

QACs are used because they are intended to have negative consequences on microbial activity. Yet, WWRFs rely on microbial communities to carry out important processes, including nitrification and anaerobic digestion. While it is recognized that QACs can inhibit biological processes at WRRFs (Lu et al., 2024), they are rarely suspected to be the culprits for process upsets in everyday life. QACs are not regulated so they are not monitored. QACs are a broad class of compounds with several subgroups of chemicals. The variety of chemical types leads to a variety in inhibition.

This presentation will discuss completed results from two separate case studies on WRRFs that dealt with QAC problems. One was a small WRRF that knew where a primary source of QACs were originating from (Figure 1). We reveal how analytical chemistry work and modeling (Figures 1-3) allowed us to find another unsuspected source of QACs in the community. The second case study involved issues with QACs on the aeration basin that were caused by alterations in the sludge stabilization processes from supernatant recycle.

Methods and Results

Case Study 1
A small (<5 MGD) WRRF received discharge from a food processing facility, and was dealing with upsets to their mainstream biological treatment process. The facility worked closely with the WRRF to investigate their potential impact, substituting and reducing QAC-containing cleaning products and using a combination of toxicity testing of their discharged effluent with QAC analysis of wastewater to develop a management strategy. A dynamic model of the collection system upstream of the plant was developed to investigate ways of mitigating potential spikes in QAC concentrations that could cause problems for the WRRF. The model was developed using the GPS-X 8.1 simulator with an industrial pollutant library (Figure 2).

The investigation for the food preparation facility included two major tasks: (1) estimation of QAC concentrations and (2) toxicity testing. For the former, a process simulator was used to assess the dynamic impact of the discharge through a series of lift stations and altering their operation (depth used and flows) was modeled to show that they could lower the potential QAC spikes (Figure 3).

Toxicity testing revealed that the facility effluent did not decrease the measured SOUR, indicating it was not toxic to aerobic activity (including nitrification).

Case Study 2
A large (>50 MGD) WRRF employed a new process to improve anaerobic digestion. The process employed a pretreatment process that improved anaerobic digestion. However, the WRRF routinely monitored for QACs and noticed high concentrations in supernatant. The supernatant was recycled back to the head of the plant and coincided with decreased performance in the aeration basin. In this case, proactive monitoring of QACs allowed for easier assessment of the problem. QACs are not regulated so many WRRFs do not measure QACs. This case study will highlight lessons learned on how QACs can be released to the soluble phase and alter processes during startup.

A large utility monitored QAC in their aeration basins, raw influent and sludge processing units for 6 years. The data show a significant increase in QAC concentrations in the aeration basins. The increase correlates with the installation of a new anaerobic digester, likely caused by the recycle streams.