Microalgae create a highway for carbon sequestration in livestock wastewater: Carbon sequestration capacity, sequestration mechanisms, influencing factors, and prospects

Greenhouse gas emissions from the livestock industry are recognized as a major environmental issue. This includes emissions from livestock wastewater. However, the common methods used for carbon sequestration (CS) rarely involve treatment of livestock wastewater, due to an absence of standardized emission points and difficulties in gas collection. To remedy this knowledge gap, this review discusses the sequestration capacity, technical classification, mechanisms, and factors influencing carbon sequestration by microalgae (MCS) in livestock wastewater. First, the carbon emission characteristics of livestock farm are discussed, concluding that, compared with those from enteric fermentation, emissions from waste management are characterized by dispersed emission points, lack of obvious emission patterns, and difficulties in gas collection. Secondly, the use and potential of MCS in livestock wastewater are summarized, with emphasis on the mechanisms involved (both heterotrophic and autotrophic MCS). It was found that development of the heterotrophic microalgal mechanism or combining the use of autotrophic microalgae with bacteria was key to the effective use of MCS for treating livestock wastewater. Finally, physical and chemical factors directly influencing MCS, as well as biological factor (species), were found to determine the potential of MCS. Furthermore, a model for recycling MCS in livestock farms is proposed, providing a novel solution to the achievement of carbon neutrality, resource recycling and ecological environmental protection.