The optimization of waste recycling and material flow cost in zero-emission intensive pig farming

Reducing greenhouse gas emissions and minimizing waste recovery costs are essential in intensive pig farming. In this study, an integrated system combining commercial intensive pig farming, rice cultivation, and biochar production in the same area leading to zero emissions goal was implemented in the Southeast region, Vietnam. Biochar from rice straw was combined with sludge after biodigester to produce nutrient-rich organic fertilizer for later use at the farm. The rice field at the farm used treated wastewater and organic fertilizer with purpose to avoid the use of chemical fertilizers. Biogas plays a role as an effective fuel for biochar production, household activities, and electricity generation for the farm. In addition, the modified Material Flow Cost Analysis (MFCA) tool was used to assess the hidden costs and greenhouse gas emissions of recycling waste solutions within the farming system. The total raw material cost of the fattening production stage is 8219 USD, the cost of sick and dead pigs is allocated to 10 % of the cost of commercial pigs, and the biogas output is about 7300 m3, part of which is used for electricity generation, and 400 tons of organic fertilizer can be sold out each month. In addition, the higher nutrient content (total N and P) in the wastewater reused for rice cultivation is 121 and 95 mg/L, which reduces chemical fertilizer costs by 10 %. The self-produced organic fertilizer also contains high nutritional value, with total C and N of 25.3 and 1.9, respectively. The study results indicate that waste recovery costs were minimized in the integrated system, reducing greenhouse gas emissions into the environment and reusing nutrients from intensive pig farming waste, moreover, the system can indicate which material flow-related measures are suitable for saving costs and reducing environmental impacts.