There has been a long-standing challenge to find ways to capture or eliminate H2S, which resulted in the development of technologies using a range of emerging materials.
By Juan Gonzalez
Modern landfills are highly regulated, extensively engineered, and strictly permitted. They continue to play an essential role in how society reliably manages waste. However, landfills are not designed to break down waste materials, but to bury them resulting in landfill gas emissions that must be controlled. Landfills that accept Construction and Demolition (C&D) waste introduces the mechanisms that produce hydrogen sulfide (H2S) in the landfill, which presents certain technical challenges in eliminating it.
Society, scientists, and technologists are making significant gains to recycle or reuse C&D waste materials and debris, but until a better solution emerges, C&D landfills will need to continue to safely dispose of waste and manage emissions as effectively as they can.
C&D Materials in the Waste Stream
Because most C&D wastes are considered zero-value materials, virtually all of it ends up in landfills. According to the EPA, 600 million tons of C&D debris was generated in the U.S. in 2018, an increase of more than 300 percent since the EPA started maintaining records in 1990. Of that, demolition represents more than 90 percent of the total waste generated, with each project generating approximately 155 pounds of waste per square foot. Construction debris represents less than 10 percent of the total. Empirical studies conducted by non-profit agencies and the industry analyst firm Transparency Market Research predict the yearly construction waste generated worldwide will nearly double to 2.2 billion tons by 2025.
C&D landfills typically rely on leachate being attenuated by natural soils and aquifers to prevent environmental contamination. Still, under landfill anaerobic conditions, gypsum-containing materials, such as plasters, drywall, ceiling tiles, partitions, and building blocks break down, and sulfates contained on those items are converted to H2S, dimethyl sulfide, and mercaptans. These vapors are collected via a network of pipes installed when the landfill is constructed. Of the three sulfur compounds, H2S is emitted from landfills at the highest rates and concentrations, which is problematic on several levels. H2S has a low odor threshold, is toxic to humans, and is corrosive in nature. Some landfill gases have a mean H2S concentration of around 4500 ppm.
Landfill Gas Desulfurization: The Technology
While federal- and state-level agencies and private enterprises seek solutions to landfill sulfur, industry has stepped in with a solution. Merichem Company’s LO-CAT™ process is a patented liquid redox system that uses a proprietary chelated iron solution to convert H2S to innocuous, elemental sulfur that can be used as an additive for fertilizer. LO-CAT does not use any toxic chemicals and does not produce any hazardous waste byproducts.
The first commercial installation of LO-CAT technology took place in 1980 for upstream and midstream oil and gas production. Over time, the LO-CAT process was improved and modified for expanded use in other markets and industrial segments, including landfills. The LO-CAT process has achieved H2S removal efficiencies of 99.9+ percent in various applications and industries.
Case Example: The Largest Landfill Gas Desulfurization Project in the U.S.
In August 2023, the largest solid waste landfill gas desulfurization project in the U.S. was launched two hours outside of Cleveland, OH, at the WIN Waste Innovations (WIN) Seneca County landfill in Fostoria, OH. It is one of two WIN Waste landfills in the state; the other is Tunnel Hill Reclamation in New Lexington. WIN Waste acquired the landfills in 2019 to expand its capability to responsibly manage the growing waste stream. In acquiring the landfills, the company also acquired the previous owners’ consent decree put in place by the Environmental Protection Agency of Ohio. The consent decree required the installation of a gas mitigation facility to remove H2S from the landfills’ gas, thereby preventing the emission of sulfur dioxide.
To meet the requirements of the consent decree, WIN Waste invested in in a technical solution that would serve both landfills and that could scale to grow with them. They also needed a solution that could be up and running in 24 months or less.
Merichem licensed, engineered, designed, and provided proprietary equipment for two LO-CAT H2S treatment trains for each landfill site based on the gas flow and sulfur generation provided as a design basis, WIN Waste’s reliability and operational efficiency objectives, and the projected growth model to meet the landfills’ future development. All four trains (two at each site) are designed to remove up to 4.5 long tons per day of elemental sulfur. The landfill gas stream flows at 4,500 standard cubic feet per minute per train and contains up to 4 percent H2S. Merichem’s liquid redox process removes more than 99 percent of the inlet H2S and virtually eliminates sulfur dioxide (SO2) emissions from the landfill gas. The design-build construction delivery was provided by ET Design Build of Atlanta.
The WIN Waste Innovations Seneca County landfill began removing H2S in August 2023, while WIN Waste’s Tunnel Hill landfill is expected to begin removing H2S before the end of the year.
These projects are the largest application of desulfurization technology for landfill gas resulting from solid waste in the U.S. The LO-CAT trains will ensure compliance requirements and allow for future facility growth.
Case Example: Post Hurricane C&D Landfill Management
After Hurricane Andrew struck southern Florida in 1992, the Broward County Central Sanitary Landfill & Recycling Center experienced a dramatic increase in C&D waste, which created a dramatic rise in H2S levels. The landfill planned to burn the landfill gas to generate up to 11 MW of power from three to five turbine powerplants, which made the H2S issue problematic. It caused odor problems in the surrounding residential area, corrosion in the compressors, and SO2 emission issues in the exhaust gas from the turbine generators. Of all combustion equipment, turbines have the lowest tolerance for H2S, 100 ppmv inlet, which was well below the levels in the landfill gas.
The landfill required a desulfurization system that could treat up to 15 million standard cubic feet per day (MMSCFD) of landfill gas containing up to 5,000 parts per million volume (ppmv) of H2S. The desulfurization technology had to be operational within 16 weeks of the building permit approval for the landfill to stay in environmental compliance with the SO2 emissions.
A LO-CAT system was designed to remove the hydrogen sulfide from the landfill gas before use in the turbines. It was fabricated, the site was prepared, and the equipment was delivered and installed at the landfill and put into commission in 1994. It has been operating since then, producing gas with less than 100 ppmv H2S.
Another Application Case Example: Landfill Biogas Conversion to Energy
As the world seeks clean alternatives to fossil fuels, energy companies are using biogas from municipal landfills to generate energy. Electric power generation is the most widely applied landfill gas-to-energy (LFGE) technology in the U.S.
Advanced treatment is required to produce high-BTU gas for injection into the production of alternative fuels. The H2S content in the biogas must be removed as a pretreatment of LFG for high-BTU to mitigate corrosion in the pipes, pumps, engines, gas storage tanks, and other power generation equipment and to reduce sulfur oxide emissions associated with LFG combustion.
LO-CAT is attractive for biogas applications because it is > 99 percent effective, the catalyst solution is non-toxic, and it operates at near ambient temperatures, so the media requires minimal heating or cooling. The byproduct of the LO-CAT process is an elemental sulfur cake that can be disposed of in the landfill or used as a fertilizer.
A Cleaner Landfill Environment
It was once believed that construction, renovation, and demolition debris would be used as clean fill, and the landfill cover would generate little or no gas or odors. There has been a long-standing challenge to find ways to capture or eliminate H2S, which has resulted in the development of technologies using a range of emerging materials, including ionic liquids, deep eutectic solvents, zeolites, carbon-based materials, metal-organic frameworks, polymeric membranes, biological methods, and advanced oxidation processes. The LO-CAT process boasts removal efficiencies of more than 99.9 percent, up to 100 percent turndown with no loss of H2S removal efficiency, and the lowest operating costs in the industry to safely convert H2S to elemental sulfur. The result is a cleaner landfill environment. | WA
Juan J. Gonzales, JM/MBA, BSChE is the Assistant Director of Sales at Merichem Company. As is a sales professional and department manager, he is an experienced Process Technology Licensing Director with a demonstrated history of working in the oil and energy industry. For more information, visit www.merichem.com.