Odors from wastewater facilities can be a nuisance, not just to neighbors but to the operators who need to identify the causes and devise remedies.

There's no surer way for a clean-water agency to lose friends than to generate odors that bring complaints. The problems can be elusive and the solutions are not always obvious. The Mount Holly (N.J.) Municipal Utilities Authority is taking a big-picture approach to odor control with help from BioAir Solutions, a supplier of biotrickling filters.

Mount Holly has deployed the biotrickling filters in its two wastewater treatment plants and at strategic locations in its collection system, which includes 175 miles of gravity sewers and force mains and 42 pumping stations, all serving six towns. So far, the systems are complying with state Department of Environmental Protection (DEP) limits on odor discharges and have eliminated odor complaints from pump station and treatment plant neighbors.

They have done it under a concept BioAir calls Total Odor Solutions. Mount Holly Executive Director William G. Dunn Sr., Deputy Director of Operations Joel Hervey, and BioAir President Louis D. le Roux spoke about the concept in an interview with Treatment Plant Operator.

: What exactly is meant by Total Odor Solutions?

le Roux: It means taking a holistic approach to solving odor problems. Many times we see that plant teams are reactive and only deal with symptoms. The concept of Total Odor Solutions is that you can use biological odor control to treat all the various odor sources at the treatment plant as well as in the collection system to provide a comprehensive solution. Biological odor control can be used in the vapor phase for all these applications to provide a reliable, environmentally friendly solution. Mount Holly has used quite a lot of liquid-phase treatment, in which you add chemicals to the sewage to help prevent odor release at pump stations and drop structures.

: What's wrong with simply reacting to problems as they arise in the community?

le Roux: Typically, agencies look at where the complaints are coming from and say, "Let's see how we can solve the problem there." It's a very narrow approach, based on the assumption that the cause of the problem is located where the symptom is manifested. Often that is not the case. Sometimes the actual cause is upstream.

We say that if you have a problem in one area of the collection system, for example, let's look at the drawings of the sewer lines and see how can we get more bang for the buck. What we often do is look at the hydraulics of the sewer line, and at the pump stations, siphons and other structures. If you put one odor-control system in a strategic location, it can help with odor problems at multiple locations. That's part of what we have done with Mount Holly.

: Can you give an example to illustrate this concept?

Dunn: We have two main pump stations called Edwards Street and Kelly Drive, both of which, in turn, are fed by several other pump stations upstream. We have lines that have a 10- to 17-hour retention from the time the material leaves a given pump station until it gets to the next one.

The odors generally come in the morning after material in the line has been standing overnight. When the pumps start up, they eject material that has become odorous. We installed biotrickling filters at the two main pump stations that create a vacuum and draw on the lines coming into those stations. The odor is pulled in and treated, rather than waiting for the flow to reach the pump station and taking care of what's in the wet well.

le Roux: If we were taking a symptom approach, we probably would have installed two or three smaller odor-control systems in different locations, and they may not have been as effective. Instead, we installed a single unit at the pump station and created a vacuum into the various branches of gravity sewers.

: How does the biotrickling filter technology work?

le Roux: Whereas a biofilter typically uses organic media such as wood chips, a biotrickling filter uses structured plastic media to which bacteria adhere. The smelly air comes in the bottom of the reactor and flows upward through the media in countercurrent to water flow in the system.

The system contains zones of autotroph and heterotroph bacteria. As the air passes through the autotrophic zone, hydrogen sulfide is oxidized to sulfuric acid, which is flushed out of the system by the irrigation water. Farther up, in the heterotrophic zone, we oxidize organic compounds, such as methyl mercaptan, dimethyl sulfide and dimethyl disulfide. Then the clean air exits the top.

The system requires some water. At pump stations, we use potable water and add a little nitrogen and phosphorus and some micronutrients to make sure we feed the bacterial growth. At a wastewater treatment plant, we use secondary effluent as the water source.

: What about the wastewater treatment plants? What odor problems existed there?

Dunn: We have two treatment plants, one older plant on Rancocas Road and a newer plant at Maple Avenue. We were looking to kill the odors in the old plant that we'd been fighting for years, and in the new plant we didn't want any to begin with.

Hervey: At Rancocas Road, we commissioned a study by Robert Bowker, a leading authority on odor control. He identified and quantified the constituents that were causing the odors. One was an ammonia-based odor from our leachate storage tank. The other was hydrogen sulfide at our headworks and sludge storage tanks.

Dunn: We have two odor-control units at Rancocas Road. A 4,000 cfm unit draws from some of the sludge tanks and from the channel system at the headworks. A 4,800 cfm unit draws from a 350,000-gallon leachate tank and from the remaining sludge tanks.

: What equipment was installed at Maple Avenue?

Dunn: The Maple Avenue plant is two years old now. One of the mandates we had for that location was zero odor. Right next door to Maple Avenue is a rehab center for the hospital, which is only a couple of blocks away. It was a political battle to get a treatment plant approved for that location. We have an odor-control unit that covers flows coming into the plant from a pump station that serves the area, and another unit that covers our two trains of headworks.

: What results have you seen at the treatment plants? How do you measure success?

Dunn: We measure, first of all, by the fact that we're not getting any odor complaints. For years at Rancocas Road, we had a bad reputation. The systems there are permitted processes. The DEP came in, looked at the processes, and dictated the parameters they wanted us to monitor, and how frequently. For example, they limited our H2S discharge to 0.5 ppm by volume when the inlet concentration is less than 50 ppm, and to 0.01 times the inlet concentration if that level is greater than 50 ppm.

Hervey: For two years, we've been in total compliance with all the parameters DEP set for us, including discharge concentrations for H2S and ammonia. There has been almost no odor whatsoever.

: How successful have the units been at the pump stations?

Hervey: There, the effectiveness is determined by our neighbors and our operations personnel. There are no permits for the pump stations, but I can tell you firsthand that they have made a tremendous difference. When you drive up, you don't detect the H2S that you typically did before we installed the units.

The neighbors can tell. We record and respond to every odor complaint we get. We have not received a complaint at the Kelly Drive pump station since the startup of that unit about 18 months ago. At the Edwards Street station we installed the odor-control system during a major upgrade two years ago. That station sits in a wooded area surrounded by homes and within 300 yards of the center of the town, so odors there are not an option. Based on my own observation and those of everyone who has had contact at that pump station, any odors that existed before have virtually disappeared.

We do some periodic checks on the filter discharge stacks at both pump stations and we have yet to measure any detectable H2S concentrations.

: What has it been like to operate, maintain and service these systems?

Hervey: They have been virtually trouble-free since we installed them. From a maintenance standpoint, they are a dream to work with. They operate well, and the controls and systems are well-thought-out and well-designed. Our operators spend minimal time dealing with them.

: What are the next steps in the odor-control program? Are there plans to add more biotrickling filters in the collection system?

Hervey: The thought is there. We have another pump station in one of our outlying towns that has been troublesome in the past. It takes in wastewater from some pretty distant locations and has some long detention times in its force mains.

le Roux: Part of the uniqueness of the Mount Holly situation is that they have very diverse odor sources. In the sludge tanks, you have ammonia and organic odor issues. At the headworks, you have a lot more H2S and less organic odor. At the pump stations, again the odors are very different. If you know the source characteristics, you can effectively apply biotrickling filter technology. Mount Holly is taking a systematic approach toward that.