In Dallas Fort Worth (DFW), sewage is treated with a combination of anaerobic digestion, effluent filtration and lime stabilization to create biosolids which are then composted, landfilled, or land applied. The current treatment procedure has certain concerns including emissions or accumulation of odors, pathogens, nutrients, metals, and pharmaceutical products.<br/> An alternative method, the Slurry Injection technique, enables the digestion of biosolids in the deep earth and can replace the current practice of wastewater treatment or disposal in a much more environmentally friendly and cost-efficient manner. By completely sequestering methane and CO2 into deep geologic formations which are produced as biosolids breakdown, reduces the greenhouse gas emissions and enables the operator to create greenhouse gas emission offset credits which can be marketed to offset the operating costs.<br/> The economic, environmental, and technical aspects of building a new biosolids slurry injection facility in DFW, includes both the surface construction requirements as well as the subsurface strata evaluation for containment assurance. For the subsurface aspects, a geomechanical and stress analysis is performed on the Atoka formation (near the city of Fort Worth) and it confirms a confining layer above and below the injection zone to keep the waste contained for permanent storage.

Carbon offset describes the environmental benefit from an initiative that avoids, reduces or removes greenhouse gases (GHGs) from the atmosphere. The Intergovernmental Panel on Climate Change has identified Carbon Dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O) as major constituent of the GHGs. Wastewater Treatment Facilities (WWTFs) among several other sectors is a neglected source for GHG emission. Considering the risk of rise in GHGs, United States along with other countries signed the Paris Agreement to respond to the global climate change threat in 2016. It is assessing projects to cut GHGs in exchange for emission credits that can be used to comply with goals they set under the United Nations pact. In order to curb the GHG emission by WWTFs, an innovative approach "Bioslurry Injection" (BSI) can be implemented to reduce the emission of the GHGs produced during the course of biological and chemical treatment of wastewater. The technology is inherited from the traditional drill cutting injection and Carbon sequestration technology implemented by the Oil and Gas industry since 1980's. The BSI operation has the ability to accept the feed from different treatment stages after the initial screening process to prepare the injection slurry and help in controlling the GHG emission at respective treatment stage along with managing the intake volume. The slurry can be prepared by mixing the treated biosolids with wastewater and injected into a pre-selected underground earth formation, where biosolids undergo anaerobic digestion and decompose into CO2 and CH4. An injection formation with sufficient capacity to accept the slurry is selected by conducting a detailed geomechanical and fracture simulation analyses. Along with the injection feasibility, the calculations of the amount of Carbon dioxide equivalent (CO2e) sequestrated underground by implementing BSI technique is presented in this paper. The sequestration of decomposed GHGs is an environmentally friendly activity that has proved to be economically beneficial due to its ability to earn carbon offsets. According to the new carbon law in the state of California the amount of CO2e eliminated from the atmosphere can be traded to earn carbon credits. TIRE facility through its ability to sequester and thus eliminate emission of the GHGs from the atmosphere can gain up to $1.5M worth of carbon credits per year providing both environmental and economic benefit. Also, low capital and operating cost for the BSI facility due to its compact surface requirement is an additional advantage along with reduced risk of spillage hazard when BSI facility is incorporated within the WWTF boundaries.

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A strong economy, industrial base, and low cost of living have led to a significant rise in population in the Greater Houston Metropolitan area of Texas, and with it, an increase in production of sewage and biosolids wastes. In the Houston area, sewage is treated with a combination of anaerobic digestion and lime stabilization to create biosolids which are then pelletized into fertilizer, composted, landfilled, or land applied. The Slurry Injection technique is an alternative treatment and disposal method, that can replace much of the capital costs associated with maintaining and expanding the wastewater treatment infrastructure in Houston at significantly lower capital cost. This technique utilizes the principles of Drill Cutting Injection which has been implemented in petroleum industry since mid 1980s for oil and gas waste management. A biosolids slurry injection facility of sufficient capacity to dispose of all the biosolids currently produced by the city of Houston could be installed for less than 1/10 of the nearly $526 million in capital currently budgeted by the city to expand the current system under the current rolling 5-year plan. A substantial reduction in greenhouse gases is achieved as well, by using the slurry injection technology as the Carbon Dioxide and Methane (which are prominenet greenhouse gases) produced by biosolids degradation is completely sequestered under deep geological formation and along with it the emissions produced during dewatering and transportation of biosolids is also eliminated. The City of Los Angeles’ Terminal Island Waste Water Treatment Plant facility has deployed the slurry injection technology since 2010. It currently disposes of approximately 20% of biosolids of the city of Los Angeles. This paper describes the economic and environmental aspects related to biosolids management and the formation evaluation carried out to inject the bioslurry in greater Houston. The study includes both the economics of the surface construction requirements as well as the science behind the subsurface strata evaluation for containment assurance. For the subsurface aspects, a geomechanical and stress analysis is performed on two different formations (the Frio and the Vicksburg). A significant confining layer is present above and below our targeted injection zones, which restrict and assure the injected waste remains contained. Also, hydraulic fracture simulation and analysis provides an assurance and the waste containment within the engineered subsurface strata/formation for permanent storage.

The United States Department of Energy (DOE) Carbon Storage Assurance Facility Enterprise (CarbonSAFE) focuses on developing geological storage sites that can accommodate more than 50 million metric tons of Carbon Dioxide (CO2) over 25 years period. Few formations can accept this volume of CO2 through one classic vertical injection well. Multiple injection wells are usually needed to handle the targeted CO2 volume, with well spacing of several miles to avoid any pressure interference between the injectors. Nebraska is among the largest ethanol-producing states in the USA, with 25 ethanol plants that produce more than 17 million metric tons of ethanol per year. These plants produce a significant volume of CO2 as a typical ethanol plant produces around 150,000 metric tons of CO2 annually. Several techniques have been proposed to capture and sequestrate the emitted CO2, including mineral carbonation and carbon geological storage. Among these techniques, carbon geological storage is the most feasible option, especially sequestration in deep saline aquifers because of the larger volume that can be stored underground, and lower cost compared to the other techniques. Most of the ethanol plants are located on the eastern side of the state, while geological evaluation suggests that thick aquifers that can handle the large volume of CO2 are located in the southwest area of the state. Due to the high cost of building more than 100 miles of pipeline to transport the CO2 from the source to the injection point (pipeline costs around one million dollars per mile), thin aquifers have been identified locally near the plants to receive the generated CO2 volume. However, conducting CO2 injection operations through multiple scattered wells will increase the anticipated cost, including pore space rights, well drilling cost, land acquisition, CO2 transportation between sites, multiple injection systems and high-pressure pumps, labor, and injection monitoring. Drilling horizontal wells can maximize the volume of CO2 that can be injected in a single well at lower injection pressure than a vertical well. The long horizontal section will expose a larger formation volume and increase the surface area available for CO2 to flow through. St. Peter formation has been identified as one of the thin candidate formations to inject CO2 in the eastern part of Nebraska. The injection modeling conducted in this study shows that a single horizontal well with a lateral of 2,000 to 3,000 ft can replace at least three classic vertical injection wells.