Phosphorus flow analysis in maize cultivation: a case study in Thailand

Greenhouse gas emissions and carbon footprint of maize-based feed products for animal farming in Thailand

Due to the growing demand for livestock products both within the country and in foreign markets, there is a need to boost the production of maize-based animal feed in Thailand. However, greenhouse gas (GHG) emissions and the potential for reducing these emissions through the production of various types of animal feed remain ambiguous. Thus, this study is aimed at estimating GHG emissions from broiler, layer, and swine feed production in Thailand and identifying economic advantages of alternative methods to mitigate those emissions. Field surveys were carried out to quantify the input and output of energy and materials in 10 commercial feed mills so as to determine greenhouse gas emissions using proper emission factors. The scope of this study is based on the cradle-to-gate approach. The functional unit used for greenhouse gas evaluation was kg CO2-eq/t of feed. Total greenhouse gas emissions from broiler, layer, and swine feed production were found to be 650 ± 20, 706 ± 20, and 466 ± 20 kg CO2-eq/t of feed, respectively. Layer feed production created the highest greenhouse gas emissions, 1.09 and 1.52 times that of broiler and swine feed production, respectively. This is because layer feed required intensive fish meal (FM) as protein sources for improving egg quality. In broiler and swine feed production, the most significant emissions are attributed to the use of maize grain (MG) and soybean meal (SBM) as sources of carbohydrate and protein in those feeds. However, animal feed production operation at the existing condition still emits CO2 to the atmosphere as CO2 fixation efficiencies of 69.3, 67.5, and 75.9% for broiler, layer, and swine feed, respectively. From the sustainable resource consumption scenarios in broiler, layer, and swine feed production, approximately 39.6, 49.6, and 43.3% reduced carbon emissions could be achieved by using MG rotated with SB in the maize plantation phase and substituting FM, wheat grain and fossil fuel needed in the manufacturing process with SBM, locally-produced tapioca chips and biomass energy. Consequently, the potential cost savings of such replacements were determined to be 54.0, 62.5, and 29.7 USD/t of feed, respectively.

Enhancing anaerobic co-digestion of primary settled-nightsoil sludge and food waste for phosphorus extraction and biogas production: effect of operating parameters and determining phosphorus transformation

The study aimed to comprehensively determine P extraction efficiency and co-digestion of food waste (FW) and primary settled-nightsoil sludge (PSNS) process performance influenced by different hydraulic retention times (4, 7, 10, and 15 days) and mixture ratios of FW:PSNS in substrates (100:0, 75:25, 50:50, 25:75, and 0:100). P-transformation was evaluated to identify P fractionation in both supernatant and sludge accumulated in reactors. The results showed that anaerobic co-digestion was inhibited by the accumulation of undigested feedstock due to higher %PSNS found in AD4 (25FW:75PSNS) and AD5 (100PSNS). A more stable process was found in AD2 (75FW:25PSNS) under hydraulic retention time (HRT) 15 days in which COD removal efficiency and P release were 97.2 and 80.2%, respectively. This recommended condition allowed a high organic loading rate (OLR) at 12 gVS/L/day resulting in the highest biogas yield of 0.93 L/L/day. Distribution of P data demonstrated that most of P in feedstock was deposited and accumulated in sediment up to 97.8%. Poor biodegradability resulting from using shortened HRT led to high increased P-solid content in effluent. In addition, available P in effluents and accumulated P-solids in sediment obtained from the AcoD process has the potential to serve as sources for P recovery.