Concentrations of hydrogen sulfide at the headworks of the Rancocas Road Treatment Facility in Mount Holly, N.J., reached 100 parts per million by volume (ppmv) or higher. The staff treated the enclosed building as a confined space.

The headworks, installed in the early 1980s, had no odor control. Aeration of the uncovered grit chamber drove gases into the atmosphere and out a vent 60 feet from the main road into town. During humid weather or on still days, the odor was especially offensive for drivers.

With the aging plant pushing its 5 mgd design capacity and new developments projected to deliver an additional 1 mgd, William Dunn, executive director of the Mount Holly Municipal Utilities Authority, worked with his staff to plan an upgrade to the facility, build a new 3 mgd Maple Avenue plant, and divert some flow to it.

“One priority was making our presence undetectable to our neighbors,” says Joel Hervey, deputy director for plant operations. “We had tried dual scrubber odor control systems and a packed-tower scrubber system at the Rancocas Road facility. Neither was very effective, and both were labor intensive. We needed a better mousetrap.”

BioAir Solutions won a bid for odor control work with EcoFilter biotrickling reactors. The installation, the largest of its kind in the state, eliminated the odor problem.

 

First things first

The Rancocas Road facility takes flows from six towns, the farthest 6.5 miles away. Long detention times in the force mains, and flows insufficient to flush them, generate sulfides.

During design, Dunn hired Robert Bowker, P.E., of Bowker and Associates, a consulting firm in Portland, Maine, that specializes in odor control. He sampled points in the collection system and throughout the plant to determine loadings for the new plant in Lumberton. Moving beyond the grit chamber, Bowker identified other odor sources: two sludge storage tanks and a leachate storage tank, both covered.

Based on Bowker’s study, BioAir proposed two EcoFilter EF 124 units for the Rancocas Road facility and three EF 62 units for the Maple Avenue plant.

“One EF 124 reactor with 4,800 cfm blower is installed between the headworks and a sludge storage tank and rotary drum thickener, which is a new piece of equipment,” says Hervey. “The other reactor with a 4,000 cfm blower is between the leachate storage tank and second sludge storage tank on the opposite end of the plant. The microbes in the second unit also treat some ammonia.”

The Maple Avenue facility has two reactors with 1,030 cfm blowers at the headworks and one reactor with a 515 cfm blower at an internal drain pump station. The turnkey units include control panels, piping, blowers, spray nozzles, structured synthetic media, integral airflow channels, and an exhaust stack.

To prepare for their arrival at the Rancocas Road facility, Allen A. Myers, a construction company in Worcester, Pa., installed fiberglass covers on the grit channels, sealed them airtight, and installed piping off the covers. The firm also piped the storage tanks, poured concrete pads for the reactors, and ran water and electrical lines.

 

Into action

After Myers set and plumbed the reactors, workers inoculated the media with bacteria from the aeration basin. Plant operators supplemented the microbes with nitrogen and phosphorous to accelerate population expansion.

Myers also installed a temporary pump on each unit to return sloughing biomass in the drain water to the spray nozzle. “Recirculating the water for the first month reduced the inoculation time,” says Hervey.

The blowers pull air through manhole covers outside the building, across the odor sources, and into the bottoms of the reactors. As air flows up through the engineered channels, water trickling down captures odorous compounds, and microorganisms on the media oxidize them. Clean air leaves through the exhaust stack.

At regular intervals, a programmable logic controller opens the motorized ball valve in the EcoPanel, sending effluent at 65 psi to the spray nozzles. “Irrigation keeps the media and microbes moist,” says Hervey. “After the water percolates down and flows to the drain, we pipe it into the influent line. The reactor is self-cleaning because sloughing bacteria go out with the water.”

 

Give it time

It took one month for the microbes to acclimate to the pollutants at the Rancocas Road facility. “Anything they did was an improvement,” says Hervey. Carbon canisters on the headworks at the Maple Avenue facility controlled odors until those reactors were at full capacity.

To comply with the state Department of Environmental Protection air permits for the Rancocas Road facility, operators monitor hydrogen sulfide concentrations at the inlets and exhausts weekly. Once a month, they run a one-hour test on the levels. They also monitor airflow levels, ambient temperature, and drain water pH weekly and check the valves and system for leaks daily.

“Because we split our flows, hydrogen sulfide at the Rancocas Road headworks peaks around 20 to 30 ppmv at the inlet and almost zero at the exhaust,” says Hervey. “At Maple Avenue, the peak headworks numbers average 5.35 ppmv and almost zero at the exhaust.” Third-party testing confirmed that the technology removes 99 percent hydrogen sulfide and ammonia and 95 percent of overall odors.

“It’s much more pleasant walking around the Rancocas Road facility now,” says Hervey. “We still monitor the headworks building for employee safety, but we haven’t recorded hydrogen sulfide in that space since we inoculated the reactors. We couldn’t be more pleased and neither could our neighbors.”