System for Quantifying Methane, Carbon Dioxide, and Hydrogen Sulfide Emissions in Low-Cost Digesters Inoculated with Horse Manure

Abstract

Methane CH₄ and carbon dioxide CO₂ are the primary gases produced during anaerobic digestion AD, followed by what is referred to as “other gases,” a highly variable group depending on the type of organic matter being digested. However, one of the most notable and common gases is hydrogen sulfide (H₂S), a gas that, while not a greenhouse gas, is well-known for its corrosive effects and its impact on health and the environment [1].
To quantify gas emissions associated with the treatment of horse manure at the Cavalry Canton of the National Army of Colombia, a direct monitoring system was implemented. Over 45 days, measurements of CH₄, CO₂, and H₂S were conducted using sensors such as the MQ-4, TGS 2611, SEN 0219, and MQ-136, respectively. The measurement ranges of the instruments used were: (200 – 10,000 ppm, 500 – 12,500 ppm, 0 – 5000 ppm, and 0 – 200 ppm), with detection levels of: (10 ppm, 0.1 – 0.65 ppm, 40 ppm, 30 ppm). These instruments were placed in three key scenarios: the manure storage site, the biodigester outlet, and under controlled laboratory conditions. The objective was to generate a detailed analysis of the behavior of these emissions.
As a result, theoretical estimates of CH₄ and CO₂ equivalents were calculated for the Cavalry Canton. These theoretical estimates were compared with the data obtained from the monitoring and showed reductions ranging from 8 to 87 % for CH₄, 58 to 67 % for CO₂, and 33 to 65 % for H₂S. These figures highlight the effectiveness of the implemented system in detecting gas emissions of interest from horse manure management, significantly contributing to environmental sustainability.