Estimation of methane emission from an urban wastewater treatment plant applying inverse Gaussian model.

The methane (CH4) emissions from urban sources are increasing, and they depend on the processes and technologies applied in each one. Thus, studying them individually to quantify their emissions and understand their behavior to design CH4 mitigation strategies is meaningful. Although many studies have been carried out in different cities worldwide, the complex methodologies and technologies applied are not readily available in developing countries. The main objective of this work is to apply a simple and inexpensive methodology to collect air samples in urban areas using syringes with a three-way stopcock. Considering the baseline concentration in different urban zones, the WWTP contribution to atmospheric CH4 concentration was assessed. Moreover, it was possible to estimate the CH4 emission rate from the source by applying the inverse Gaussian model. The atmospheric CH4 concentrations inside and around the WWTP varied from 2.04 to 32.78 ppm. Most of the highest concentrations were found inside the WWTP; however, high concentrations were found up to 500 m from its center. The values in the urban zones were between 2.06 and 3.52 ppm, consistently higher in the area with the highest population density. Finally, considering the WWTP as a single source and according to the operational and atmospheric conditions during the studied period, the mean CH4 emission rate from this source was 2.08E + 04 µg s-1. The proposed sampling methodology could be applied to estimate CH4 emission rates from fixed sources in areas with overlapping sources.

Extending the Collection Duration of Breath Samples for Enteric Methane Emission Estimation Using the SF6 Tracer Technique.

The daily sample collection protocol of the sulphur hexafluoride (SF6) tracer technique for the estimation of methane (CH4) emissions from ruminants may not be practical under extensive grazing systems. Here, under controlled conditions, we evaluated extended periods of sampling as an alternative to daily sample collections. Eight rumen-fistulated cows were housed and fed lucerne silage to achieve common daily feed intakes of 6.4 kg dry matter per cow. Following SF6 permeation tube dosing, eight sampling lines were fitted to the breath collection harness, so that a common gas mix was available to each line. Half of the lines collected samples into PVC yokes using a modified capillary system as commonly used in New Zealand (NZL), and half collected samples into stainless steel cylinders using a ball-bearing flow restrictor as used in Argentina (ARG), all within a 10-day time frame, either daily, across two consecutive 5-day periods or across one 10-day period (in duplicate). The NZL system had greater sampling success (97.3 vs. 79.5%) and yielded more consistent CH4 emission estimates than the ARG system. Emission estimates from NZL daily, NZL 5-day and NZL 10-day samplings were 114, 110 and 111 g d(-1), respectively. Extended sample collection protocol may be feasible, but definitive evaluation of this alternative as well as sample collection systems is required under grazing situations before a decision on recommendation can be made.

Methane Emission and Milk Production of Dairy Cows Grazing Pastures Rich in Legumes or Rich in Grasses in Uruguay.

Understanding the impact of changing pasture composition on reducing emissions of GHGs in dairy grazing systems is an important issue to mitigate climate change. The aim of this study was to estimate daily CH4 emissions of dairy cows grazing two mixed pastures with contrasting composition of grasses and legumes: L pasture with 60% legumes on Dry Matter (DM) basis and G pasture with 75% grasses on DM basis. Milk production and CH4 emissions were compared over two periods of two weeks during spring using eight lactating Holstein cows in a 2 × 2 Latin square design. Herbage organic matter intake (HOMI) was estimated by chromic oxide dilution and herbage organic matter digestibility (OMD) was estimated by faecal index. Methane emission was estimated by using the sulfur hexafluoride (SF6) tracer technique adapted to collect breath samples over 5-day periods. OMD (0.71) and HOMI (15.7 kg OM) were not affected by pasture composition. Milk production (20.3 kg/d), milk fat yield (742 g/d) and milk protein yield (667 g/d) were similar for both pastures. This may be explained by the high herbage allowance (30 kg DM above 5 cm/cow) which allowed the cows to graze selectively, in particular in grass sward. Similarly, methane emission expressed as absolute value (368 g/d or 516 L/d) or expressed as methane yield (6.6% of Gross Energy Intake (GEI)) was not affected by treatments. In conclusion, at high herbage allowance, the quality of the diet selected by grazing cows did not differ between pastures rich in legumes or rich in grasses, and therefore there was no effect on milk or methane production.