Optimizing Anaerobic Digestion at Ambient Temperatures: Energy Efficiency and Cost Reduction Potential in Panama

Abstract

Anaerobic digestion (AD) is usually carried out at mesophilic temperatures (25–45 °C) in most countries, whether in temperate or tropical climates, which results in the need for heat injection and consequently increases costs. In this regard, batch AD tests were conducted at 25, 28, and 35 °C, with 25 °C being the lowest ambient temperature in Panama, using thickened secondary sludge (TSS) and digested secondary sludge (DSS) from the Juan Diaz wastewater treatment plant (WWTP) to determine the Biochemical Methane Potential (BMP). The AD study generated maximum mean BMP values of 163 mL CH4/g VS for DSS and 289.72 mL CH4/g VS for codigestion at 25 °C. The BMP value of DSS at 25 °C showed that it can still be used for energy generation, using the lowest ambient temperature recorded in Panama City. Likewise, trials at 25 °C showed a 43.48% reduction in the electrical energy produced compared to that generated at 38 °C in WWTP. This results in a reduction in energy, as the use of heat could be omitted and the energy costs required for the process are covered. In this regard, the novelty of this work lies in its investigation of anaerobic digestion at ambient temperatures, which represents a departure from conventional practices that typically require higher temperatures. By exploring the feasibility of anaerobic digestion within the temperature range of 25–35 °C, this study offers a novel approach to optimizing energy efficiency and reducing costs associated with elevated temperatures.