Project Summary

MEMA is designed to measure methane released from the sediment of lakes in the form of bubbles. This is the dominant pathway of methane emissions from water reservoirs – an unusually large source of greenhouse gasses – that is understudied in part due to difficulty of measurement. As the time of design, there was no commercially available sensor array that could *actively* measure the concentration of methane being released in this form. Passive traps were being used to collect finite amounts of gas, which was then brought back to the lab for analysis – a very labor intensive process that gets more intensive during active seasons, requiring daily sampling and processing. This device collects volume and concentration measurements in-the-field, and vents gas when trap gets full, allowing for continuous in-field measurement.

Engineering Thesis Report

Abstract

Water reservoirs are increasingly recognized as a significant anthropogenic source of methane (CH4) production and emissions, CH4 being the second most prevalent greenhouse gas (GHG) after CO2. The dominant emission pathway for CH4 in lacustrine environments is ebullition (bubbling).

A survey of current ebullition measurement methods reveals a technology gap; the ability to measure ebullition rates and CH4 content simultaneously and affordably with high temporal and spatial resolution is not currently available. Characterizing and modeling methane ebullition in water reservoirs is key to quantifying lacustrine methane emissions and providing a basis for potential mitigation efforts.

This report documents the development and assessment of a Methane Ebullition Measurement Apparatus (MEMA) designed for in-situ, autonomous, ebullition-rate and methane-concentration measurement in lacustrine environments. MEMA is designed to be affordable and easily replicable in-house by environmental research scientists with limited manufacturing resources, emphasizing low per-unit cost for maximum unit replication and spatial coverage. Documentation of the device’s build materials, supplier list, physical design, and control code have all been made publicly available to aid in replication efforts.

Conclusion

A functional, in-situ, autonomous methane ebullition measurement device was successfully designed and constructed using affordable materials and accessible tools, with field and laboratory tests demonstrating its integrity and accuracy.

CH4 Concentration Range and Accuracy	5-100% +/- 5%
Maximum Volume Measurement Rate	1 Sample/Sec.
Maximum CH4 Sampling Rate	1 Sample/ 15 Min.
Volume Measurement Only Battery Life	5 Days
Maximum Sampling Rate Battery Life	48 Hours
Hourly CH4 Sampling Battery Life	4 Days
Material Cost	$823/Unit

MEMA constitutes a novel ebullition measurement device, in terms of its dual ebullition-rate and CH4-concentration measurement capabilities and its relative affordability and replicability. Resources pertaining to MEMA’s materials, construction, programming, and data interpretation are all publicly available (Github Repo) to aid in further design replication, improvement, and testing.

MEMA Thesis Download

MEMA Github Repo