New system eliminates odors
When neighbors complained about odor problems at the South Monmouth Regional Sewerage Authority (SMRSA), an innovative odor abatement system, that saved an estimated $1.5 million in construction costs, $130,000 in fines and helped the plant regain its good neighbor status was implemented.
South Monmouth’s water treatment plant – a 9.1-mgd facility in Belmar, N.J. – is the first in the United States to use a specially-designed system for induced-air ventilation of rock-media trickling filters to capture odors and provide efficient control of wastewater aeration.
Within the past several years, the area around the facility was developed with new, upscale residential housing, and residents began complaining about the plant’s odor. Following action by the New Jersey Department of Environmental Protection and Energy, SMRSA agreed under an administrative consent order to install an odor-control system.
According to SMRSA Executive Director Boyd Miller, the standard method of abating odors from trickling filters is to build costly enclosures, which can hinder the efficiency of the wastewater treatment process.
“Even if we had installed enclosures over the filters, special air handling equipment would have been needed to maintain air pressure and move the gases to odor control equipment,” says Miller. “Of greater concern than the cost is the fact that the enclosures may actually reduce the natural flow of air needed for the filters to work properly, adversely affecting the wastewater treatment process and contributing to greater odor production.”
Taking a more innovative approach to the problem, SMRSA contracted Jacobs Environmental, Piscataway, N.J., to develop a system that would effectively and quietly control odors. (Not only was odor pollution a concern, but, because the facility is so close to a residential development, noise was a factor as well.)
A forced ventilation system featuring Ceilcote air pollution control fiberglass-reinforced plastic (FRP) fans and odor abatement equipment was designed. Eight fans with non-overloading backward curved blades and FRP construction make up the system. They deliver efficiencies ranging to more than 75 percent and provide quiet operation with less than 85 dBA noise levels.
Each one of the two trickling filters is 186 feet in diameter and contains approximately 7 feet of rock media. Wastewater is applied uniformly over the rock surface by a rotating distributor arm, and a filter block underdrain system supports the rock and collects the filter effluent.
Microorganisms live and grow on the rocks and consume biodegradable substances in the wastewater as part of the treatment process. A fresh supply of oxygen is critical to maintaining the microorganisms, regardless of atmospheric conditions that effect natural draft ventilation rates.
The filter’s center channels have manholes at each end for access and ventilation. The effluent flows out of the filter though the center channels to the effluent pump station. Four-inch-diameter vent pipes, spaced every 6 feet around the perimeter of the filter, connect the underdrain to outside air.
Different sizes and configurations of fans enable the system to be flexible, allowing system optimization, even in changing weather conditions.
The scrubber system for each trickling filter consists of two 12-foot-diameter scrubbers connected in parallel to a single 52-foot-high exhaust stack.
The odorous gases from each trickling filter are captured by creating a slight vacuum within the filter underdrains to induce the air flow downward through the trickling filter media. Four fans per trickling filter are used for this purpose.
Two of the fans are connected to the effluent manhole. Two additional fans are connected to the upstream manhole and 20 of the trickling filter vent pipes. The other vent pipes have been capped.
The air-handling system can be controlled by the plant operator to treat the appropriate amount of air to meet the weather and atmospheric conditions. The whole system operates throughout the late spring and summer, but during the winter months it is only necessary to run half of the system.
To prevent excessive cooling of the wastewater during cold weather, each scrubber train can be operated to withdraw 10,000 cfm. In warm weather, each train can withdraw 40,000 cfm. When both series of scrubbers are used, the total exhaust rate can reach 80,000 cfm. At full load, the fans run quietly enough that they can’t be heard in the adjoining neighborhood.
Typically, aerobic microbial growth occurs on the top 2 to 3 feet of the rock media, but Miller anticipates that with this system providing a constant supply of oxygen to the microorganisms, regardless of the ambient air temperature, the microbial growth will extend deeper and the treatment capacity of the filters will increase correspondingly.
“In the future, we may be able to increase our treatment capacity without constructing additional filters for even greater efficiencies,” Miller says.