Silica removal from rice straw for animal feed application

Abstract

The large production of rice straw (731 ton/season) could eventually lead to uncontrolled air pollution due to open burning activity. Although rice straw has been used as animal feed since in the 1980s, it has failed to provide sufficient amount of protein for daily ruminant growth (about 15-20%). Hence, this study explored the use of rice straw waste for animal feed that can provide the amount of protein needed for daily ruminant growth. Moreover, as silica has been discovered as the main hurdle in animal feed processing, the rice straw sample was treated with alkaline hydrogen peroxide (AHP) via batch and continuous systems. Besides reducing the silica content, it is also aimed to maximize the protein content of the treated rice straw. Meanwhile, in the continuous system, a single column packed bed with up-flow system was adapted before carrying out further biological treatment with the fungi, Neurospora sitophila for cell protein production. Other than that, physical and chemical characterizations of rice straw sample (obtained from Seberang Perak, Malaysia) were conducted before and after pretreatment processes to determine the effectiveness after each pretreatment process. From the results obtained, a kinetic study was carried out to investigate the removal behavior for each system. From the characterization analysis, the rice straw sample was found to contain a high level of silica (20%) and lignin (20%), but very low-level protein content (6-7%). Besides, the batch process of pretreatment with AHP, as well as the effects of different parameters (i.e. AHP concentrations, particle sizes of rice straw, and temperature) had been studied. From the batch process, the optimum condition obtained was at 60C with application of 10% of AHP solution for sample with < 0.5mm particle size. At this condition, more than 83.8% of silica removal, 80% of delignification, and 7.88% of reduced sugar production were achieved. On the other hand, as for the continuous AHP pretreatment process, and followed by biotreatment of Neurospora sitophila (edible fungus) in the single column, it was found that 84% of silica was removed with 80% of delignification and 8% of reduced sugar production with 10% AHP solution in a 7cm treated and compacted rice straw bed at room temperature. Furthermore, the protein content in the pretreated rice straw increased by a whopping 80%. Meanwhile, the kinetic study revealed that both the batch and the continuous silica removal processes were highly influenced by mass transfer, in comparison to the other steps. Hence, it can be concluded that this study has depicted that the selected processes for silica removal and protein enhancement of local rice straw are indeed suitable for animal feed production. Additionally, the kinetic study has been proven beneficial in understanding the attributes of the removal process.