Geomembrane covers solve difficult odor issue in Texas wastewater plants
By Tonya Chandler and Sharon Paterson
Off-site odors and complaints in the vicinity of a wastewater treatment plant are common across the United States. Hydrogen sulfide (H2S) odors can be a problem in any sewer collection system and treatment plant. This noxious gas wreaks havoc on pipes, buildings and anything else that it comes in contact with, including human beings. The Human Detection Level (HDL) of H2S is 0.5 parts per billion (ppb). Levels that reach over 100 ppm become a safety issue for those in proximity to the source. So, what happens when high-end housing is built next to the primary treatment plant in the city? How do you control odors in the open channels that lead to a primary bar screen without breaking the bank? This was a problem that the Laguna Madre Water District, in Port Isabel, Texas, faced in 2018.
“We had all this new construction getting closer and closer to the plant (Laguna Vista) — newer and more expensive homes — and we were concerned about keeping the nuisance (odors) within our buffer zone,” said Charles Ortiz, district engineer for Laguna Madre Water District.
Off-site odors at one plant were averaging above 88 parts per million (ppm) just above the channel surface, with peak spikes registering above 860 ppm. Laguna Madre explored a variety of options to ensure that the technology it selected would be effective, environmentally friendly, and provide the least amount of disruption to plant operations.
Chemical treatment and scrubbers were explored, but the costs and labor associated with these treatments were high, as were the safety and environmental impacts. Laguna Madre reached out to Anue Water Technologies to explore its non-chemical odor control options.
Anue Water’s flexible geomembrane system offers a unique “breathable” design. Pockets in the geomembrane material contain replaceable carbon-infused filters that allow water and air to pass through but “trap” the odor-causing compounds. The system is custom-designed to each application to ensure successful odor control. The company’s breathable geomembrane solutions would allow Laguna Madre to benefit from effective odor treatment without changing the footprint or operations of the plants — and it was a fraction of the cost associated with the chemical and scrubber systems.
“We had considered a $45,000 air scrubber for the Laguna Vista location, [but] the total cost to put the geomembrane system in at all three of our plants was less than the cost of the one scrubber,” Ortiz said.
The project went forward in three parts, with the first installation at Laguna Vista acting as the pilot installation, in March 2019. No special equipment was needed for the installation. Workers removed the grating above the channel, secured the membranes to the underside of the grating, and replaced the grating. The excess membrane was trimmed, and some neoprene and silicone were added to ensure a proper fit with the uneven structure. Behind the bar screens, a separation underneath the grates was installed. A crossbar attached to the wall on both sides of the influent channel holds a flap made of the membrane material. The bottom edge of the flap has a floating “boom” incorporated, allowing the flap to follow the liquid level changes while keeping the air on both sides separated.
Prior to installation of the membrane system, a portion of the bar screens needed to be removed to a level approximately 2 inches below the channel edge, allowing for continuous treatment of the headspace regardless of what is happening in the tank. Installation took less than two days.
“You know odor can be relative — some people are more sensitive than others. One resident we used to hear from said it’s a lot better than it was before, and the next-door neighbor has no issues whatsoever. We showed them what we did to make improvements and they appreciated having an advocate from the Water District listen to them and make things better,” Ortiz said of the community response after installation.
The typical performance of the filter is 9-12 months without replacement; however, due to the high-level nature of the H2S spikes at the Laguna Vista plant, the carbon-infused filters needed to be replaced in roughly six months. Although atypical of average performance, it was still acceptable to Laguna Madre.
Laguna Madre is scheduled to complete its additional installations at the Andy Bowie plant and Isla Blanca plant in fall 2019. Additional applications of lift stations, manhole inserts, tanks and a 3D structure for the bar screen are under consideration for the future.
“We still have a little tweaking to do here and there — nothing is perfect,” Ortiz said. “But as odor controls go, I would say that the geomembrane system has done its job.” WW