The heavy use of Quaternary Ammonium Compounds (QACs) and other surfactants cause operational issues in Water Reclamation and Recovery Facilities (WRRFs) causing passthrough of Fats Oils and Grease (FOG), other colloidal materials, and Total Organic Carbon (TOC) to Advanced Water Treatment Facilities (AWTFs). Issues include accelerated micro/ultra-filtration and reverse osmosis (RO) membrane fouling, requiring more energy for backwashes and chemicals for clean-in-place (CIP) procedures.
Since QACs and surfactants coat the surface of water, bubbles, colloids, and biomass, they disrupt wastewater treatment by emulsifying wastewater, impeding oxygen transfer, and inhibiting nitrification.
QACs are used by the food and beverage industry, hotels, hospitals, and the military for their disinfecting properties. Their increased use due to recent pandemics has put immense strain on WRRFs and AWTFs alike.
What are surfactants?
The U.S. Environmental Protection Agency (EPA) define surfactants as “substances that lower the surface tension of a liquid, the interaction at the surface between two liquids (called interfacial tension, or that between a liquid and a solid. Surfactants may act as detergents, soaps, wetting agents, degreasers, emulsifiers, foaming agents and dispersants.” They also state that “many surfactants used in conventional products biodegrade slowly or biodegrade into more toxic, persistent, and bioaccumulative chemicals, threatening aquatic life.”
It's important for end users and WRRFs to lessen the detrimental effects of surfactants for more sustainable and environmentally friendly effluent wastewater. John Crisman with Moleaer discusses ways end users can help in this article about the Simple way to lighten the load on our water treatment plants in Pacific Coast Business Times. This blog covers how WRRFs can mitigate the negative effects of QACs and surfactants with nanobubble technology.
How can nanobubbles degrade and remove surfactants?
Nanobubbles, ~100 nanometers in diameter, degrade contaminants in wastewater to improve treatment efficiency and increase process performance. FOG and surfactants are attracted to and accumulate at the hydrophobic surface of nanobubbles. Nanobubbles generate hydroxyl radicals and release energy upon collapse that breaks apart carbon chains converting slowly biodegradable chemical oxygen demand (sbCOD) to readily biodegradable COD (rbCOD).
The following definitions are from a presentation by Alloway at Ohio WEA:
- “Readily biodegradable (rbCOD, SS): Consists of small molecules that are directly available for biodegradation by heterotrophic microorganisms (volatile fatty acids, alcohols, amino-acids, simple sugars)
- Slowly biodegradable (sbCOD, XS): Consists of larger molecules requiring extracellular breakdown (hydrolysis) before being biodegraded by the heterotrophic microorganisms (proteins, FOG, complex carbohydrates)”
Case Study: Nanobubbles Remove Surfactants and Improve Plant Efficiency, Reduce Costs
During a recent trial at Goleta Sanitation District (GSD) WRRF, Moleaer’s nanobubble technology was used to treat 4.2 million gallons per day (MGD) of municipal wastewater to remove inhibitory compounds like QACs. The GSD WRRF recycles 30% of their tertiary effluent as Title 22 water for irrigation.
By pretreating wastewater with air nanobubbles, the GSD WRRF increased primary clarifier solids removal by 10%, increased secondary treatment capacity by 40%, reduced aeration power draw by 43%, decreased chlorine usage by 44%, eliminated odors and foam, and eliminated the need for bioaugmentation. These improvements lead to an overall lower carbon footprint in the WRRF processes to free up resources for AWT, including the possibility of microfilter water due to a reduction in TOC that would have contributed to biofouling and increased chemical consumption and energy use during AWT.
Two additional pilots aimed at quantifying the effects of using nanobubbles to remove TOC ahead of microfiltration are in progress in California.
The GSD data shows that by removing the environmental pressures of sbCOD from surfactants and FOG in wastewater, the secondary process maintains a biomass that responds with increased agility to changes in nutrient loading and process controls. This results in a significant increase in secondary treatment capacity and a significant decrease in aeration power draw, lowering the overall carbon footprint of the water cycle.
The data also shows that by converting sbCOD to rbCOD, the biological process more efficiently converts BOD to TSS to further improve effluent water quality at WRRFs and decrease chlorine demand. The end result is a higher quality effluent (lower TOC and nutrients) that reduces the amount of chemical treatment and energy required for AWT.