Measuring Livestock CH4 Emissions with the Laser Methane Detector: A Review

The handheld, portable laser methane detector (LMD) was developed to detect gas leaks in industry from a safe distance. Since 2009, it has also been used to measure the methane (CH4) concentration in the breath of cattle, sheep, and goats to quantify their CH4 emissions. As there is no consensus on a uniform measurement and data-analysis protocol with the LMD, this article discusses important aspects of the measurement, the data analysis, and the applications of the LMD based on the literature. These aspects, such as the distance to the animal or the activity of the animals, should be fixed for all measurements of an experiment, and if this is not possible, they should at least be documented and considered as fixed effects in the statistical analysis. Important steps in data processing are thorough quality control and reduction in records to a single point measurement or “phenotype” for later analysis. The LMD can be used to rank animals according to their CH4 breath concentration and to compare average CH4 production at the group level. This makes it suitable for genetic and nutritional studies and for characterising different breeds and husbandry systems. The limitations are the lower accuracy compared to other methods, as only CH4 concentration and not flux can be measured, and the high amount of work required for the measurement. However, due to its flexibility and non-invasiveness, the LMD can be an alternative in environments where other methods are not suitable or a complement to other methods. It would improve the applicability of the LMD method if there were a common protocol for measurement and data analysis developed jointly by a group of researchers.

Detection of Methane Eructation Peaks in Dairy Cows at a Robotic Milking Station Using Signal Processing

The aim of this study was to investigate the use of signal processing to detect eructation peaks in CH4 released by cows during robotic milking, and to compare recordings from three gas analysers (Guardian SP and NG, and IRMAX) differing in volume of air sampled and response time. To allow comparison of gas analysers using the signal processing approach, CH4 in air (parts per million) was measured by each analyser at the same time and continuously every second from the feed bin of a robotic milking station. Peak analysis software was used to extract maximum CH4 amplitude (ppm) from the concentration signal during each milking. A total of 5512 CH4 spot measurements were recorded from 65 cows during three consecutive sampling periods. Data were analysed with a linear mixed model including analyser × period, parity, and days in milk as fixed effects, and cow ID as a random effect. In period one, air sampling volume and recorded CH4 concentration were the same for all analysers. In periods two and three, air sampling volume was increased for IRMAX, resulting in higher CH4 concentrations recorded by IRMAX and lower concentrations recorded by Guardian SP (p < 0.001), particularly in period three, but no change in average concentrations measured by Guardian NG across periods. Measurements by Guardian SP and IRMAX had the highest correlation; Guardian SP and NG produced similar repeatability and detected more variation among cows compared with IRMAX. The findings show that signal processing can provide a reliable and accurate means to detect CH4 eructations from animals when using different gas analysers.

The Effect of Rice vs. Wheat Ingestion on Postprandial Gastroesophageal Reflux (GER) Symptoms in Patients with Overlapping GERD-Irritable Bowel Syndrome (IBS)

A randomized crossover study in twenty-one patients (18F, age 50 ± 13 years) with overlapping GERD-IBS was conducted to evaluate the effects of rice noodles (low FODMAPs) vs. wheat noodles (high FODMAPs) on typical GER symptoms, and the correlation between GERD symptoms and intestinal gas production. Results: Heartburn and regurgitation scores were highest in most patients (19/21) during the first 15 min after meals. At 15 min after lunch, wheat was significantly associated with more regurgitation and heartburn than rice. Also, at 15 min after breakfast, wheat aggravated more regurgitation than rice. Wheat ingestion was significantly associated with higher H2 and CH4 levels after lunch compared to rice, whereas gas levels before lunch were similar (p > 0.05). The area under the curve of H2 and CH4 concentration 15 min after a lunch of wheat moderately correlated with the regurgitation severity at 15-min (r = 0.56, p < 0.05). Conclusion: Wheat induced more GERD symptoms than rice in patients with overlapping GERD-IBS. This effect, immediately developed after lunch, was associated with more intestinal gas production. Thus, a low FODMAPs diet may relieve postprandial GERD symptoms in GERD patients with overlapping IBS. Wheat inducing more regurgitation than rice after breakfast suggests other mechanism(s) besides gut fermentation.

The Influence of Above-Ground Herbivory on the Response of Arctic Soil Methanotrophs to Increasing CH4 Concentrations and Temperatures

Rising temperatures in the Arctic affect soil microorganisms, herbivores, and peatland vegetation, thus directly and indirectly influencing microbial CH4 production. It is not currently known how methanotrophs in Arctic peat respond to combined changes in temperature, CH4 concentration, and vegetation. We studied methanotroph responses to temperature and CH4 concentration in peat exposed to herbivory and protected by exclosures. The methanotroph activity was assessed by CH4 oxidation rate measurements using peat soil microcosms and a pure culture of Methylobacter tundripaludum SV96, qPCR, and sequencing of pmoA transcripts. Elevated CH4 concentrations led to higher CH4 oxidation rates both in grazed and exclosed peat soils, but the strongest response was observed in grazed peat soils. Furthermore, the relative transcriptional activities of different methanotroph community members were affected by the CH4 concentrations. While transcriptional responses to low CH4 concentrations were more prevalent in grazed peat soils, responses to high CH4 concentrations were more prevalent in exclosed peat soils. We observed no significant methanotroph responses to increasing temperatures. We conclude that methanotroph communities in these peat soils respond to changes in the CH4 concentration depending on their previous exposure to grazing. This “conditioning” influences which strains will thrive and, therefore, determines the function of the methanotroph community.

Improved Membrane Inlet Mass Spectrometer Method for Measuring Dissolved Methane Concentration and Methane Production Rate in a Large Shallow Lake

Natural water bodies, such as lakes, rivers, and oceans, are important sources of atmospheric methane (CH4). Therefore, quantitative and accurate determination of the dissolved CH4 concentration in water is of great significance for studying CH4 emissions and providing an in-depth understanding of the carbon cycle. Headspace gas chromatography (HGC) is the traditional method for measuring CH4 in water. Despite its long success, it has a lot of problems in use, such as complex pretreatment and a long measurement time, and it is not suitable for the CH4 determination of a large number of samples. In view of these shortcomings, a more convenient and efficient method based on membrane inlet mass spectrometry (MIMS) for quantitative measurements of the dissolved CH4 concentration in water was established. In our study, the standard curves showed that the method had high accuracy, both at low and high CH4 concentrations. After a laboratory test, to evaluate the sensitivity of this method, samples were collected from a large shallow lake (Lake Taihu). Both the HGC method and MIMS method were used to determine the dissolved CH4 to compare these two methods. The small difference in CH4 concentration obtained from the MIMS and HGC methods and the significant correlation between the CH4 concentrations derived from the MIMS method with those derived from the HGC method showed that the MIMS method could replace the HGC method in the determination of dissolved CH4 in natural waters. In addition, we also measured the sediment CH4 production rates in three different areas of Lake Taihu using a laboratory incubation experiment. During the experiment, significant CH4 accumulations were observed, indicating that sediment CH4 production was an important source of dissolved CH4 in the water column. Our study concluded that the MIMS method was sufficient and a better alternative than the HGC method owing to its capacity to measure a broad range of values plus the fact that it was relatively easy to use with less manipulation of the samples.

The utility of concentration duration curve in CH4 and CO2 risk assessment

Current CH4 and CO2 risk assessment of comparing the single occurrence of worst-case concentration with trigger values of 5% and 1% respectively is often of low resolution but could be improved by the application of the concept of Concentration Duration Curve (CDC). With the aid of the Gasclam (In-borehole continuous gas monitor), four sites were monitored for CH4 and CO2 concentrations, and the time-series datasets used to construct CDC. The result shows that a 5% CH4 concentration is exceeded for 17, 41, 0, and 0% of the monitoring period in sites 1-4 respectively, whilst a 1% CO2 concentration was exceeded for 75, 75.5, 100, and 93% of the time in sites 1-4 respectively. The recorded worst case CH4 concentration are 11.5, 22.1, 2.7, and 1.56% in sites 1-4 respectively while that of CO2 concentration are 8.2, 15.5, 3.3, and 6.71% in sites 1-4 respectively This implies that treating risk in terms of a single occurrence of the worst-case ground-gas concentration rather than any sort of time-weighted function can be defective. While the concept of CDC can be useful in improving risk assessment due to CH4 and CO2, the worst-case ground-gas concentration may not occur during the monitoring period, therefore prediction is required. To predict the worst-case ground-gases concentration requires an understanding of the processes responsible for controlling gas concentration.

Spectroscopic Identification on CO2 Separation from CH4 + CO2 Gas Mixtures Using Hydroquinone Clathrate Formation

The formation of hydroquinone (HQ) clathrate and the guest behaviors of binary (CH4 + CO2) gas mixtures were investigated by focusing on an application to separate CO2 from landfill gases. Spectroscopic measurements show that at two experimental pressures of 20 and 40 bar, CO2 molecules are preferentially captured in HQ clathrates regardless of the gas composition. In addition, preferential occupation by CO2 is observed more significantly when the formation pressure and the CH4 concentration are lower. Because the preferential occupation of CO2 is found with binary (CH4 + CO2) gas mixtures regardless of the composition of the feed gas, a clathrate-based process can be applied to CO2 separation or concentration from landfill gases or (CH4 + CO2) mixed gases.