Taiwan has more than 7,400 pig farms and 5.5 million pigs. The annual output value is about US$2.3 billion, accounting for 43% of the livestock industry. It is one of the most important agricultural economic sectors in Taiwan. However, due to the large number of herds, a huge amount of pig manure and urine are continuously discharged from the livestock farms. If they are not treated very well, it will seriously affect the environment and ecology. Pig manure contains a large amount of degradable solids, which is a high concentration organic wastewater. This high concentration organic wastewater undergoes a typical anaerobic fermentation process called three-step piggery wastewater treatment (TPWT), and biogas will be generated during the treatment process. Biogas is a combustible gas and its main component is methane, which accounts for 50 to 65% of the volume of biogas. In this study, a commercial scale of two stage anaerobic digestion (AD) treatment is established in central Taiwan. The processes followed the order of regulation, 1st AD, 2nd AD, sedimentation, aeration, and final sedimentation. The most different matter between two-stage AD and TPWT is in the solid-liquid separation process, the two-stage AD can treat wastewater without the solid-liquid separation in a higher solid content. The removal efficiency of chemical oxygen demand (COD) in two-stage AD is 95.7%, which is 12.4% higher than anaerobic fermentation of 83.3% in TPWT. The biogas production or biogas power generation has the benefits of reducing greenhouse gas (GHG) emissions, saving energy expenditure, and improving the quality of discharged water to promote the sustainable operation of the livestock environment. It has been used in overseas pig farming for many years and is one of the best applications of circular economy and biomass energy.
Keywords: Bio-circular economy, biogas production, pig manure, bio-electricity, greenhouse gas emissions.