The mechanism of nutrients dissolved out of a synthetic composite bead filter material in a biofilter

In this study, an optimal process to prepare a synthetic material having nutrient (PVA/peat/KNO(3) composite bead) is developed. The equilibrium water-soluble nitrogen content in the composite bead prepared by this process is 8.25-10.06 mg N/g dry solid. The mass-transport process for the water-soluble nitrogen dissolved out of the composite bead was also investigated. The dissolved out process occurs in two stages: external mass transport occurs in the early stage and the intraparticle diffusion process occurs in the long-term stage. The rate of water-soluble nitrogen dissolved out in both stages is concentration dependent. The path of nitrogen dissolved out is that the nitrogen dispersed in the peat and PVA phases simultaneously diffused into the outer PVA phase and out of the bead surface. The moisture holding capacity of the composite bead bed is better than the compost bed. The percentage of removed volatile organic compounds (VOCs) can remain at levels higher than 99% for a longer time (about 230 d) as the composite bead immersed in a KNO(3) aqueous solution before packing with an optimal concentration of KNO(3) aqueous solution of 0.384 M. The rate of nitrogen dissolved out in the intraparticle diffusion process could be used as an index to predict the microbial growth rate in the biofilter.