Long-term onsite monitoring of a sewage sludge drying pan finds methane emissions consistent with IPCC default emission factor

As the wastewater sector moves towards achieving net zero greenhouse gas (GHG) emissions, quantifying and understanding fugitive emissions from various sewage treatment steps is crucial for developing effective GHG abatement strategies. Methane (CH₄) emissions from a sludge drying pan (SDP) were measured at a wastewater treatment plant in Australia for more than a year, using a micrometeorological technique paired with open-path lasers. The emission rate was tightly associated with sludge additions, climatology, and operational processes. The mean emission rate during the 90 weeks after initial sludge addition was 2.3 (± 0.8) g m^-2 d^-1, with cumulative emissions of approximately 32 t of CH₄. A dynamic temporal pattern of emissions was observed, highlighting the importance of continuous (or near-continuous) measurements for quantifying SDP emissions. A Methane Correction Factor (MCF) expressed as a fraction of the measured chemical oxygen demand of the sludge, was determined to be 0.17 after 63 weeks (the median operational cycle duration at the facility). This is broadly consistent with, albeit slightly less than, the IPCC default value of 0.2 for shallow anaerobic lagoons. These emission measurements will support wastewater utilities that employ open air sludge drying processes to develop effective GHG abatement strategies.

Lignite effects on NH3, N2O, CO2 and CH4 emissions during composting of manure

Production of compost from cattle manure results in ammonia (NH₃) and greenhouse gas emissions, causing the loss of valuable nitrogen (N) and having negative environmental impacts. Lignite addition to cattle pens has been reported to reduce NH₃ emissions from manure by approximately 60%. However, the effect of lignite additions during the manure composting process, in terms of gaseous emissions of NH₃, nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) is not clear. This composting study was conducted at a commercial cattle feedlot in Victoria, Australia. Prior to cattle entering the feedlot, we applied 4.5 kg m^-2 of dry lignite to a treatment pen, and no lignite to a control pen. After 90 days of occupancy, the cattle were removed and the accumulated manure from each pen was used to form two separate compost windrows (control and treatment). During composting we collected manure samples regularly and quantified gaseous emissions of NH₃, N₂O, CO₂, and CH₄ from both windrows with an inverse-dispersion technique using open-path Fourier transform infrared spectroscopy (OP-FTIR). Over the 87-day measurement period, the cumulative gas fluxes of NH₃, N₂O, CO₂, and CH₄ were 3.4 (± 0.6, standard error), 0.4 (± 0.1), 932 (± 99), and 1.2 (± 0.3) g kg^-1 (initial dry matter (DM)), respectively for the lignite amended windrow, and 7.2 (± 1.3), 0.1 (± 0.03), 579 (± 50) and -0.5 (± 0.1) g kg^-1 DM, respectively for the non-lignite windrow. The addition of lignite reduced NH₃ emissions by 54% during composting, but increased total greenhouse gas (GHG) emissions by 2.6 times. Total N losses as NH₃-N and N₂O-N were approximately 11 and 25% of initial N for the lignite and non-lignite windrows, respectively. The effectiveness of retaining N was obvious in the first three weeks after windrow formation. A cost-benefit analysis indicated that the benefit of lignite addition to cattle pens by reduced NH₃ emission could justify the trade-off of increased GHG emissions.

Gas emissions during cattle manure composting and stockpiling

Manure composting is a common management practice for cattle feedlots, but gaseous emissions from composting are poorly understood. The objective of this study was to quantify ammonia (NH₃ ), nitrous oxide (N₂ O), carbon dioxide (CO₂ ), and methane (CH₄ ) emissions from windrow composting (turning) and static stockpiling (nonturning) of manure at a commercial feedlot in Australia. An inverse-dispersion technique using an open-path Fourier transform infrared (OP-FTIR) spectrometer gas sensor was deployed to measure emissions of NH₃ , N₂ O, CO₂ , and CH₄ over a 165-d study period, and 29 and 15% of the total data intervals were actually used to calculate the fluxes for the windrow and stockpile, respectively. The nitrogen (N) lost as NH₃ and N₂ O emissions represented 26.4 and 3.8% of the initial N in windrow, and 5.3 and 0.8% of that in the stockpile, respectively. The carbon (C) lost as CO₂ and CH₄ emissions represented 44 and 0.3% of the initial C in windrow, and 54.8 and 0.7% of that in the stockpile, respectively. Total greenhouse gas (GHG) emissions from the manure windrow were 2.7 times higher than those of the stockpiled manure. This work highlights the value that could be accrued if one could reduce emissions of NH₃ -N and N₂ O-N from composting, which would retain manure N content while reducing GHG emissions.

Using airborne technology to quantify and apportion emissions of CH4 and NH3 from feedlots

A novel airborne approach using the latest technology in concentration measurements of methane (CH4) and ammonia (NH3), with quantum cascade laser gas analysers (QCLAs) and high-resolution wind, turbulence and other atmospheric parameters integrated into a low- and slow-flying modern airborne platform, was tested at a 17 000 head feedlot near Charlton, Victoria, Australia, in early 2015. Aircraft flights on 7 days aimed to define the lateral and vertical dimensions of the gas plume above and downwind of the feedlot and the gas concentrations within the plume, allowing emission rates of the target gases to be calculated. The airborne methodology, in the first instance, allowed the emissions to be qualitatively apportioned to individual rows of cattle pens, effluent ponds and manure piles. During each flight, independent measurements of emissions were conducted by ground-based inverse-dispersion and eddy covariance techniques, simultaneously. The aircraft measurements showed good agreement with earlier studies using more traditional approaches and the concurrent ground-based measurements. It is envisaged to use the aircraft technology for determining emissions from large-scale open grazing farms with low cattle densities. Our results suggested that this technique is able to quantify emissions from various sources within a feedlot (pens, manure piles and ponds), as well as the whole feedlot. Furthermore, the airborne technique enables tracing emissions for considerable distances downwind. In the current case, it was possible to detect elevated CH4 to at least 25 km and NH3 at least 7 km downwind of the feedlot.

Non-interference measurement of CH4, N2O and NH3 emissions from cattle

A technique combining open-path Fourier transform infrared spectroscopy with an inverse-dispersion model was used to quantify methane (CH4), nitrous oxide (N2O) and ammonia (NH3) emissions from an isolated cattle pen in south-eastern Australia. Twenty-eight Angus steers (1-year old, initial average liveweight 404 kg) were fed a 60% grain diet and kept in a pen (20 × 20 m) for 41 days. Gas concentrations were measured downwind of the pen using an open-path Fourier transform infrared spectroscopy with a path length of 100 m, having a detection sensitivity of 2, 0.3 and 0.4 ppb for CH4, N2O and NH3, respectively. Daily emission rates were 232, 14 and 192 g/cattle.day for CH4, N2O and NH3, respectively. The measured CH4 emissions were in agreement with predictions based on Australian National Inventory recommendations, however, measured N2O and NH3 emissions were much higher than the predicted values. Extrapolation of our measurements would mean that CH4 and N2O emissions from beef feedlot cattle contribute 3.1% and 5.9% of the Australian agricultural CH4 and N2O emissions, respectively.