Selection of ventilation rates on dead pig composting

Routine mortality of animals is an inevitable consequence in animal production, the major disposal routes used in China are on-farm burial, incineration and rendering. None of these routes has been widely extended due to perceived environmental risks. On-farm burial poses a potential contamination threat to groundwater. A health risk from incineration arises from toxic emissions, such as dioxins and furans. The main environmental concerns associated with rendering relate to carcass collection and transport. The disposal of mortalities has become more of an issue for animal farming systems in recent years. Many countries are moving to alternative methods of carcass disposal. One alternative is composting, which has been proved to be a viable option for mortality disposal. However there is a lacking of information on dead pig composting in China. On-farm experiments of dead pig composting were conducted to investigate the much-needed alternative for intensive swine production, where dead pig disposal has become a serious problem. Twelve composting bins (1m L×1m W×1m H) were used, and three ventilation rates of 300, 200 and 100 L/m3.min were applied and designated as treatments 1 to 3, with each treatment containing 4 composting bins (as 4 replicates). Three dead pigs with a total weight of 30-32 kg were put together in the center of each bin. The lower and upper parts and surrounding of the dead pigs inside each bin were filled with a mixture of corn stalk and pig manure. The trial was conducted in a suburb of Beijing during the summer season. Both the mixture and dead pig residues were moved out of the composting bin every 2 weeks in order to measure the weights of dead pigs. Soon after measurement, the materials were put back with dead pig residue at a layer in the center. Results showed that: the average temperatures over 55℃ were 19、19 and 34d for the 3 treatments respectively, so that there was no significant difference among treatments. The degradation rates (in wet base) of a dead pig after 6w fermentation were 95.5±1.4%、94.7±1.7% and 95.0±0.8%, respectively. By then only the skeleton was left, and a significant difference (P<0.05) in the weights of dead pigs （wet base）between treatment 1 and treatment 3 was detected. The number of E. Coli could meet the demands of related national standards after 7 d, and all E. Coli were thoroughly killed after 2 w of composting. Each characteristic parameter of composting mixture from different treatments demonstrated the same trend，but no significant difference in each parameter among treatments was found. The contents of organic matter (dry base) in the composting mixture were 47%-48%, with a sum of total nitrogen and phosphorus (dry base) of 5.7%-6.4% at end of the trials, i.e. after 6w composting. Both values were higher than the corresponding indexes required by the Chinese Agricultural Standard of Organic Fertilizer. Composting was proved to be a viable and practical option for farmers to dispose of dead pigs. In view of the above results and the operational costs of aeration, the ventilation rate of no more than 100 L/m3.min and composting period of 6 w are recommended for dead pig composting in bins. Composting can dispose of dead pigs safely and practically, and turn mortalities into organic fertilizer, which offer a new and promising technology for on-farm dead pig disposal.