It is essential to life for H2S to be removed from landfill gas. At peak performance, Merichem Technologies’ LO-CAT® has removal efficiencies of more than 99.9 percent, and the H2S is safely converted to elemental sulfur, creating an even cleaner environment around the landfill.
By Mark Knobloch
Disposal of solid wastes in America has reached epic proportions. In 2018 alone, homes, businesses, and institutions threw out more than 292 million ton of municipal solid waste (MSW). According to the U.S. EPA, Construction & Demolition (C&D) waste is expected to exceed 2.2 billion tons by 2025, as reported by industry analyst Transparency Market Research.
The Problem: A Dangerous Precedent
Today, more than 1,250 landfill facilities are in the U.S. According to the Environmental Research & Education Foundation (EREF), C&D waste is accepted at MSW landfills in 41 states. More than 30 percent of all materials delivered to construction sites end up as waste. Asphalt, bricks, concrete, shingles, and drywall, none of which are biodegradable, make up more than 75 percent of construction essentials that are moved to landfills. C&D waste is notable for the production of hydrogen sulfide (H2S) as a result of the biological conversion of sulfate from gypsum drywall. Degradation of the gypsum-based drywall produces significant concentrations of H2S, making it one of the most dangerous of the C&D wastes. The H2S in the anaerobic environment of a landfill creates noxious odors and potentially dangerous health concerns. When combusted, it can form sulfur oxides (SOx), which are harmful to the environment and can cause serious health effects. To alleviate the need for H2S treatment, the industry has developed desulfurization technologies that range from simplistic to complex and vary in efficacy.
Images courtesy of Merichem.
Flooding the Landfills
Construction fell off during the pandemic, plunging contractors into one of the most challenging times in their history, exacerbated by crippled supply chains. There was a decided decline in third-party landfill tons and industrial hauls, which showed a positive impact of the reduced volume of C&D debris on biosolids management.
The constraints of the pandemic eased beginning in 2021, and the construction industry recovered. In its rebound, construction output is expected to gain an annual average growth rate of 5.3 percent between 2025 and 2027, fueled by investments in key sectors, including energy, transportation, housing, and manufacturing. The processes of construction and demolition make cross-contamination of materials in waste streams inevitable. Without a country-wide, zero-waste strategy and/or a concerted recycling plan, C&D waste will continue to flood the nation’s landfills.
Gypsum: The Bad Actor
The Gypsum Association reports that more than 20 billion square feet of gypsum board is manufactured in North America annually for use in residential and commercial construction. Also known as drywall or wallboard, gypsum board has been mandated by consensus model building codes since the first half of the 20th century for its fire-retardant properties.
Although gypsum panels currently incorporate recycled paper facers, the remainder of the boards are made of a soft sulfate mineral composed of calcium sulfate dihydrate (CaSO4·2H2O) referred to as gypsum, and additives such as mica, clay, and resin. When treated as waste, it takes up substantial landfill space. Decaying gypsum leaches sulfate ions and organic matter, which sulfate-reducing bacteria (SRB) use to generate large concentrations of H2S. Many co-disposed wastes will also show some effect on H2S generation.
Even at concentrations as low as single-digit parts per billion H2S, emissions in communities surrounding C&D landfills produce offensive odors. Prolonged exposure to H2S may pose adverse health effects, especially in susceptible populations—the young, elderly, pregnant, and immune-compromised. The OSHA permissible exposure limit (PEL) for H2S is 20 ppm and is not to be exceeded at any time during an eight-hour period and a single period of 10 minutes if the concentration is 50 ppm. The National Institute for Occupational Safety and Health (NIOSH) reports that H2S environmental concentrations of 100 ppm are “Immediately Dangerous to Life or Health”, and concentrations greater than 500 ppm can cause one to collapse within five minutes. At concentrations exceeding 700 ppm, symptoms are immediate collapse and death within just one or two breaths. Various C&D landfills in Florida have measured concentrations as high as 12,000 parts per million by volume (ppmv).
The Future is Not Now
The current and future management of C&D waste is embodied by the mantra: “Reduce, Reuse, Recycle, and Rebuy.” It calls for practicing source reduction, salvaging, recycling, and reusing existing materials, and buying used and recycled materials and products.
The U.S. Federal Government and all 50 states have written laws, ratified by the World Health Organization (WHO), designed to keep C&D waste statistics within acceptable limits. They include a renewed focus on recycling and comprehensive waste management plans. Waste containment procedures are outlined to include the materials and equipment necessary to collect and transport C&D materials. They also include portable containers or trash enclosures as secondary containments to ensure minimal to no contact with surrounding areas when collecting or dumping discarded materials and transport to permitted facilities.
The internet is flush with examples of C&D waste management plans and guidelines for creating them. Implementation is another story. The construction industry erects and demolishes hundreds of new buildings and homes every day. Some companies believe that recycling/reuse puts them at an economic disadvantage. Those who do or will do so must engage in the promotion of culture change, which requires a substantial time investment.
For some companies, it is logistically complex to access recycling facilities. Those who do may find its waste ends up in a landfill, after all. Recycling companies without proximity to landfills that accept C&D waste have little option but to dump it.
Disaster Debris
Natural disasters have a history of filling landfills by virtue of mass destruction, with hurricanes being the most destructive. The debris left in the wake of catastrophic events often contains wood, plastic, metal, gypsum board, oil, electronics, and plaster—all commingled and contaminated.
Disasters such as hurricanes, floods, tornadoes, and fires typically generate quantities of debris much greater than the amount of waste many communities handle in a single year. If disaster cleanup is not prompt, damp debris can develop mold, which can start to propagate within 24 to 48 hours after water damage.
The Catalyst for Landfill Desulfurization: A Solution for Removing H2S
LO-CAT® by Merichem Technologies is a flexible hydrogen sulfide removal process applicable for all types of gas streams, including air, natural gas, CO2, amine acid gas, biogas, refinery fuel gas, as well as landfill gas. The LO-CAT process was introduced to the market in 1980 for oil and gas production and refining. Since then, the process has been continually improved and modified for use in other markets and has been continuously operating on landfill gas applications for more than 20 years.
LO-CAT is a patented, wet scrubbing, liquid redox system that uses a chelated iron solution to convert H2S to innocuous, elemental sulfur. It does not use any toxic chemicals and does not produce any hazardous waste byproducts. The catalyst is readily available, and since it is continuously regenerated in the process, catalyst use is minimized, making LO-CAT an economically viable solution for H2S removal.
The liquid catalyst adapts easily to variations in flow and concentration. Flexible operation allows a wide turndown in gas flow and H2S concentrations. Units require minimal operator attention.
The 20+ Year Case Example
In 1992, Hurricane Andrew slammed into South Florida before making a second U.S. landfall in Louisiana. At the time, it was considered the costliest and most damaging hurricane ever to hit the U.S., a record it maintained for 13 years.
A major U.S. waste handling company that operates a large landfill in Florida was presented with a massive increase in C&D waste from the storm. Inevitably, levels of H2S rose dramatically. The waste company evaluated several technologies for the H2S removal with concentrations reaching as high as 5,000 ppmv, for rates of 2 to 3 tons/day of sulfur in the landfill gas.
This became an issue for the landfill owners, who were planning to burn the landfill gas to generate up to 11 MW of power from three to five turbine power plants. Of all the combustion equipment, turbines have the lowest tolerance (maximum 100 ppmv) for H2S.
The owners implemented Merichem Technologies’ LO-CAT process to manage the H2S removal. The LO-CAT Process converted the gaseous H2S into solid elemental sulfur that could be used as an additive for fertilizer. The LO-CAT H2S Oxidation System was designed and delivered to the landfill in just 22 weeks. The unit was commissioned in 1994 and has been operating since, producing gas with less than 50 ppmv H2S.
After the Andrew storm, changes were made to the waste being accepted at the site. In addition to the planned opening of additional C&D waste sites, there was a projected increase in the gas flow and H2S levels over what the unit was treating and required an expansion of the capacity of the LO-CAT H2S Oxidation System.
In 2001, the landfill owners began evaluating options for expanding their capacity. They considered sending gas offsite for treatment and use, deploying a different technology for H2S removal to replace the existing LO-CAT H2S Oxidation System or expanding the existing LO-CAT system to handle the higher load.
A plan was implemented to expand the unit’s capacity to treat sour C&D waste gas. After several modeling exercises that considered the gas production and the anticipated H2S production and based on current and future expected waste types and amounts, a design basis was set. Several alternatives were considered, but none could offer the combination of a cost-competitive system with the experience and guarantees that compared to their operating experience with their existing LO-CAT Unit.
In 2002, the construction of a LO-CAT expansion system was initiated. It was designed to increase the sulfur handling capacity of the LO-CAT unit from 2.3 long tons/day up to 10.8 long tons/day, giving the unit the capacity to treat gas containing up to 33,350 ppmv H2S, thereby reducing it to less than 50 ppmv H2S. The expansion required tie-ins to the existing unit and gas lines during a planned plantwide maintenance turnaround. The tie-ins were successfully completed, and the unit started up in January 2003, resulting in reduced H2S emissions below the expected outlet conditions.
A Contemporary Case Example
In August 2023, the U.S.’s largest solid waste landfill gas desulfurization project was launched in central Ohio at the WIN Waste Innovations (WIN) Seneca County landfill in Fostoria, OH and the Tunnel Hill Reclamation facility near New Lexington, OH.
Merichem Technologies 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 a maximum of 4.5 long tons of elemental sulfur per day per train. Each train is capable of treating up to 4,500 standard cubic feet per minute of sour landfill gas containing up to 4.0 volume percent of 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 commenced operation later in the year. These projects are the largest application of desulfurization technology for landfill gas resulting from solid waste in the U.S.
A Cleaner Environment
In 2016, the International Journal of Epidemiology published findings that confirmed living within three miles of a landfill site can put health at risk. In a controlled study that took place from 1996 to 2008, just under 250,000 people were studied and evaluated for potential health effects of living near nine different landfills in the Lazio region of Italy. The results indicated a strong association between H2S used as a model for all pollutants co-emitted from the landfills and deaths caused by lung cancer. They also studied deaths and hospitalizations by respiratory diseases linked to inhalation exposure to endotoxins, microorganisms, and aerosols from waste collection and landfilling.
It is essential to life for H2S to be removed from landfill gas. At peak performance, LO-CAT has removal efficiencies of more than 99.9 percent, and the H2S is safely converted to elemental sulfur, creating an even cleaner environment around the landfill.
Today, there are more than 200 installations around the world that depend on the LO-CAT process to remove hydrogen sulfide from gas streams. LO-CAT is reliable, efficient, and economical and can be licensed with guarantees of H2S removal efficiency, sulfur removal capacity, and chemical consumption rates. | WA
Mark Knobloch is Technical Services Manager for Merichem Technologies. He is an accomplished project and process engineer in the oil and gas, and petrochemical engineering and construction industries. As the Technical Services Manager for Merichem Technologies, he oversees engineering specialists providing technical service support for pre-commissioning, start-up, and ongoing support of Merichem Technologies’ licensed treating processes. He is a certified PHA leader from the Process Safety Institute, has a HAZardous Waste Operations and Emergency Response (HAZWOPER) standards certification from OSHA, and is a Registered Professional Engineer with the State of Texas. Mark can be reached at (713) 428-5000 or e-mail [email protected].