Model of Estimated Energy from Bio-methane Generated with Hydraulic Fracturing Wastewater and Beef Cattle Manure

Wastewater from hydraulic fracturing (HF) and manure from beef cattle production are two of the largest waste streams in the Texas Panhandle. Bio-methane, also known as renewable natural gas (RNG), is the cleaned or upgraded biogas that has been generated in anaerobic digesters. The cleaned or upgraded product can be used to generate electricity, heat, steam, replace or supplement natural gas, and can be upgraded to biofuel for use in vehicles. The objective of this research was to simulate the annual amount of energy that can be produced from these two waste streams. Data from a laboratory biogas generation study was used in the development of a dynamic systems model. Substrate combinations of manure mixed with produced and flowback water (PFW), well water (WW), and a 50/50 mix of the two, were evaluated at four moisture contents (MC; 65, 70, 80, and 90%). Manure was harvested from the West Texas A&M University Research Feedlot. The PFW was collected from a HF operation in the Texas Panhandle. Regression analyses were used to predict methane production based on MC for each water type. Regression model statements from the biogas study data were used in the energy estimation model, which simulated feedyard manure production and potential methane production from anaerobic digestion (AD). The model then simulates the amount of energy that can be generated from bio-methane. The optimum MC for PFW was 65%, with simulated results of 28,650 L of fuel and 47,600 kWh of electricity annually. This amount is approximately half of fuel (51,500 L) and electricity (95,100 kWh) that can be produced with well water and manure at 90% MC. The best option for using PFW in anaerobic digestion is to dilute it with well water at 65% MC. This combination results in simulated amounts of 49,400 L of alternative fuel and 88,700 kWh of electricity.