The surging global population growth, coupled with socioeconomic development and improved living standards, has created a heightened demand for livestock and poultry products such as meat, eggs, and milk. This escalating demand has, in turn, spurred rapid growth in the livestock and poultry industry, exacerbating environmental issues, particularly the greenhouse effect.
Over the past five decades, China has witnessed significant growth in its animal husbandry sector, with a remarkable 13.3% increase in total output value. However, this expansion has led to the production of an enormous amount of livestock and poultry manure, amounting to a staggering 3.8 gigatons annually. This manure emits significant amounts of methane (CH4) and nitrous oxide (N2O), which have global warming potentials (GWPs) 23 and 298 times greater than carbon dioxide (CO2), respectively. Consequently, the management of livestock and poultry manure has emerged as a primary source of carbon emissions in agriculture.
In response to these challenges, the United Nations has introduced the 2030 Agenda for Sustainable Development, urging countries to adopt sustainable production practices, conduct scientific research, employ appropriate technologies, and implement effective management methods to reduce greenhouse gas emissions from livestock and poultry production by 30%. Achieving this goal hinges on decreasing carbon emission intensity and promoting renewable energy credits.
To provide a theoretical foundation for reducing carbon and other pollutant emissions from livestock and poultry production, several key components must be addressed. This includes developing accounting methods for carbon emissions and carbon footprint, identifying the factors and mechanisms influencing carbon emissions, and gradually establishing a methodology for carbon emission reduction. Shifting towards bioenergy generated from livestock and poultry manure can also reduce fossil energy consumption in daily life.
In line with a carbon-neutral strategy, Professor Zhidan Liu from China Agricultural University and his colleagues have conducted in-depth research on the manure management system of livestock and poultry. They have examined the emission patterns of greenhouse gases and other harmful substances during the stages of manure collection, storage, and treatment, and qualitatively assessed various manure management technologies in terms of their carbon-friendliness.
Diverging from previous reviews that focused primarily on resource recovery and technology in manure treatment, this work, now published in Frontiers of Agricultural Science and Engineering, delves deeper into the concept of coordinated pollution reduction and carbon reduction. It also highlights technologies for livestock and poultry manure management that align with pollution and carbon reduction objectives.
Moreover, the study summarizes the influencing factors and mechanisms of manure carbon emissions, and it analyzes the current status and potential development of carbon trading systems. The report presents suggestions and potential countermeasures for reducing livestock and poultry manure pollution.
The livestock and poultry manure management system encompasses three stages: collection, storage, and treatment. It recommends the use of dry collection technology during the collection stage and suggests strategies such as acidification, compaction, mulching, and the addition of regulators like biochar and storage tanks to reduce GHG emissions during storage.
Technologies employed in the waste treatment stage vary in principle, carbon-friendliness, and technical maturity. For open systems like composting, achieving source reduction of harmful gases requires further study. Although anaerobic digestion is environmentally friendly, its adoption is hindered by high investment costs and low efficiency in low-temperature CH4 production. Technologies like biochar and microalgae show promise for carbon emission reduction, but they necessitate detailed technical and economic evaluation.
The quantity of GHG emissions from the livestock and poultry manure management system is contingent on numerous factors, including regional distribution, temperature, season, livestock and poultry characteristics (such as type, age, weight, sex, health status, and physiological cycle), manure treatment details, feed characteristics, and social factors like the economy, policy, and population. To gauge the influence of each factor, in-depth factor decomposition research is imperative.
Various carbon emission and carbon footprint accounting methods are employed depending on the situation, each with its advantages and disadvantages. These methods encompass the mass balance method, actual measurement method, carbon emission factor method (OECD, IPCC), input-output method, and life cycle assessment methods. Due to the potential for subjective and objective errors, the application of Monte Carlo simulation post-carbon emission accounting can help mitigate accounting result uncertainties.
Finally, as a market-oriented energy-saving mechanism, carbon trading holds significant promise. Although China’s carbon market started relatively late, it has been expanding rapidly. The carbon trading market for livestock and poultry manure management presents ample potential for growth. Collaborative efforts in manure treatment technology, methodology, trading mechanisms, farming practices, economics, politics, dietary choices, and other aspects will pave the way for a robust carbon trading mechanism, expediting the realization of carbon neutrality.