Nanobubbles reduce surfactants by 50 percent at water resource recovery facility

By By Andrew Dugan, PE   

Features COVID-19 Moleaer nanobubbles surfactants wastewater treatment water resource recovery

Goleta Sanitation District's Water Resource Recovery Facility.

Goleta Sanitation District’s (GSD) Water Resource Recovery Facility (WRRF) serves 95,000 residents near Santa Barbara, CA. The WRRF’s capacity is 9.5 MGD dry weather flow, treating 4.2 MGD on average. Since the 1940s, GSD has evolved to meet regulations, population, and economic growth.

Like most WRRFs, GSD navigates the operational upsets that soaps, detergents, and disinfectants create for biological wastewater treatment. When COVID-19 arrived, the district faced the perfect storm of reduced influent flow and higher concentrations of surfactants, like quaternary ammonia compounds (QAC), from pandemic-conscious households. While the district’s industrial program addressed surfactants, it needed an onsite solution to address this indirect source.

Not Our First Rodeo

The global pandemic wasn’t GSD’s first encounter with surfactants harming their treatment process. “Our issue with surfactants started in 2016, at the peak of the last major drought,” says John Crisman, then GSD’s operations manager. Slugs of surfactants from local industry led to costly operational expenses and risked permit violations. Fortunately, offering Best Management Practices to these dischargers addressed the WRRF’s problems. The plant returned to typical operations.

Scrubbing Surfactants

Surfactants inhibit biological treatment through a combination of decreased oxygen transfer and toxicity to microorganisms. During the pandemic, detergent and soap use skyrocketed, while the community tried to conserve water in drought-stricken California. Unfortunately, no “bolt-on” treatment methods addressed surfactants directly. With impending changes to their discharge permit, GSD began considering a multi-million dollar plant upgrade to manage the issue.

As neighbouring communities made the news for treatment violations caused by pandemic surfactant levels, Crisman fortunately read a TPO article about how Moleaer’s nanobubbles-as-a-service solved Fallbrook Public Utility District’s (PUD) surfactant problem.

Specialized Solution

High surfactant levels made operating Fallbrook PUD’s 2 MGD treatment plant ineffective and expensive. After installing Moleaer’s nanobubble (NB) generator, operations staff noted that QAC concentrations dropped 78 percent and chemical oxygen demand (COD) dropped 61 percent below previous primary clarifier effluent levels.

Nanobubbles, which are 2,500 times smaller than a grain of salt, allow the scarce resource of water to do more with less. They supersaturate water with oxygen, form natural oxidants for disinfection, improve plant health, and increase water’s ability to permeate soil and rock.

Moleaer’s patented nanobubble technology provides the highest oxygen transfer rate in the aeration and gas infusion industry, with an efficiency of more than 85 percent per foot of water. Its nanobubble generators are a cost-effective, chemical-free solution proven to increase sustainable food production, reduce chemical usage, restore aquatic ecosystems, and improve natural resource recovery.

“Reading about the specific actions that Moleaer took to remove surfactants from wastewater, and that it was chemical-free, met all the objectives Goleta would strive for regarding energy and chemical use reduction,” says Crisman.

Due to their size, NBs have unique characteristics that produce hydroxyl radicals, a strong oxidant. Hydroxyl radicals dissolve FOG and surfactants, improving wastewater quality without chemical addition. NBs slowly deliver dissolved oxygen to their environment, eliminating anaerobic conditions that cause process upsets, degrade treatment, and generate odor and corrosive compounds like hydrogen sulfide.

In May 2022, GSD installed a Moleaer six-inch, 2,700 GPM NB generator (NBG 6) between the WRRF’s fine screens and primary clarifiers. “We decided the biggest benefits would come from treating in the front of the plant, to see the effects throughout the process,” explains Crisman. GSD ran a three-month pilot to see the full effects on their process. The pilot required a rental pump, Moleaer’s NBG 6 system, and 30 minutes of maintenance monthly.

Real Results

Over the three-month trial, GSD’s wastewater quality parameters improved. The NBs broke up raw wastewater emulsions, providing a better compacting sludge blanket and clearer supernatant. Lab results confirmed observations: there was a 10 percent increase in primary clarifier TSS removal. GSD’s staff observed that foam—a sign of surfactants— subsided in the equalization basins and the primary clarifiers. “Following that, we saw a reduction in demand for blower air,” says Crisman.

Downstream at the aeration basins, this new-found wastewater quality continued to deliver. The oxygen uptake and transfer rates improved as lower surfactant levels led to stronger bacteria. Efficient oxygen dissolution and happier “bugs” led to a 43 percent reduction in aeration demand and US$32,000 in annual savings.

Before the NB pilot, GSD implemented a bioaugmentation program to maintain the plant’s biology while facing high surfactant levels. After adding Moleaer’s NBG, the district dropped the program, saving US$44,000.

Downstream Dividends

The reduction of surfactants and organics brought a 44 percent reduction in chlorine demand during disinfection, saving GSD $15,000 in annual chemical costs. “Greater removal from the primary clarifiers precipitated savings. Chemical and energy use fell as a direct result of restoring oxygen transfer efficiency, reducing loading, and removing surfactant-induced environmental stress,” boasts Crisman.

Moleaer’s pilot resulted in a 40 percent removal of total QACs, 54 percent of total nonionic surfactants, and 51 percent of total anionic surfactants from GSD’s raw influent. After witnessing the NBG 6’s effects on treatment, GSD decided to enroll in Moleaer’s nanobubbles-as-a-service program, leaving generator maintenance and upgrades to the manufacturer. GSD’s total predicted savings are US$87,000 per year, considering permanent installation costs[BG1] .

What’s Next

GSD can now access innovations that surfactants made impossible. “GSD is saving money, but that’s only one aspect of how nanobubbles changed things. The plant’s stabler and increased its organic capacity, offsetting capital expenses,” Crisman explains. “GSD can entertain technologies like ammonia-based aeration control, for further energy savings. They wouldn’t consider upgrades like this operating in less stable conditions.”

New technologies continue to reshape wastewater treatment. Pretreatment with NBs enabled GSD WRRF to change the direction of their capital and operational expenses to a previously unthinkable degree. Direct surfactant removal intensified the facility and balanced wastewater quality while reducing chemical addition. “I love that we’re not bringing chemicals onsite, and nothing is hauled away,” Crisman adds. Academics and industry are still exploring NB generator applications at treatment plants, meaning this is only the beginning for the technology.

This article was contributed by Hawthorne, CA-based Moleaer. Andrew Dugan, PE, is the founder of WaterWrites and technical staff writer at Creative Raven, a marketing and content production firm specializing in serving the communication needs of the wastewater/water infrastructure, treatment, and related civil infrastructure industry segments.

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