Methane

Livestock operations significantly contribute to global methane (CH₄) emissions, a potent greenhouse gas. This occurs primarily through enteric fermentation (a digestive process in ruminant animals that produce methane) and manure management. This review synthesizes the current understanding of the sources of methane within livestock farming systems. It focuses on the primary drivers of these emissions, namely methane production during ruminant digestion and emissions from manure handling. The review also explores the concept of methane sinks, highlighting the processes that remove methane from the atmosphere and their role in the global methane cycle. While natural methane sinks exist, their capacity to offset methane emissions from livestock operations is limited. This review therefore discusses a range of mitigation approaches, categorized into animal and feed management, diet manipulation, rumen manipulation, and advanced technologies. Synthesizing these elements provides a clear understanding of the challenges and opportunities in addressing livestock-related methane emissions. Effective strategies should aim to reduce methane production without negatively impacting animal productivity and health. This emphasizes that addressing sustainable livestock production requires integrated approaches that simultaneously tackle climate change mitigation.

This study evaluated the effects of ammonium sulfate [(NH₄)₂SO₄] addition and land-use history on greenhouse gas emissions (CH₄, CO₂, N₂O) and inorganic nitrogen dynamics (NH₄⁺ and NO₃⁻) in Brazilian Cerrado soils. The objective was to determine how fertilization interacts with native and agricultural soils to regulate key biogeochemical processes. Soil samples from native and agricultural areas were collected in four regions (Araras, Sorocaba, Itirapina, and Brasília), representing contrasting pedoclimatic conditions and soil textures under different cropping systems. Samples were incubated under controlled conditions, with greenhouse gas fluxes analyzed by gas chromatography and inorganic nitrogen concentrations determined by colorimetric methods. Nitrogen fertilization inhibited CH₄ consumption in native and agricultural soils and reversed fluxes to emissions in sandy soils. CO₂ emissions increased in native soils but decreased in agricultural soils, suggesting effects of soil fertility and carbon stocks. N₂O emissions increased mainly in native soils, reflecting intensified nitrification and denitrification, whereas agricultural soils responded heterogeneously. Nitrogen addition altered NH₄⁺ and NO₃⁻ consumption, indicating enhanced oxidation and microbial assimilation. These results demonstrate that land-use history influences soil biogeochemical responses to nitrogen, underscoring the importance of site-specific fertilization in mitigating emissions and promoting sustainability in the Cerrado.

Whey and its permeates constitute highly organic, low-alkalinity dairy streams whose management remains suboptimal in many processing facilities. This narrative review integrates recent evidence on the anaerobic digestion (AD) of whey, linking substrate composition and biodegradability with microbial pathways, inhibition mechanisms, biogas quality, and techno-economic and environmental feasibility in industrial settings. Data for sweet whey, acid whey, and their permeates are synthesized, with emphasis on operational windows, micronutrient requirements, and co-digestion or C/N/P/S balancing strategies that sustain resilient methanogenic communities. Options for biogas conditioning and upgrading towards combined heat and power, boiler applications, and compressed or liquefied biomethane are examined, and selection criteria are proposed based on impurity profiles, thermal integration, and methane-recovery performance. Finally, critical R&D gaps are identified, including mechanistic monitoring, bioavailable micronutrition, modular upgrading architectures, and the valorization of digestate as a recovered fertilizer. This review provides an integrated framework to guide the design and operation of technically stable, environmentally verifiable, and economically viable whey-to-biomethane schemes for the dairy industry.