A process to prepare a synthetic filter material containing nutrients for biofiltration

In this study, an optimal process to prepare a synthetic filter material (poly(vinyl alcohol) (PVA)/peat/KNO3 composite bead) containing nutrients was developed for biofiltration. The optimal preparing condition was that each of the peat and PVA aqueous solutions contains 6.4 g KNO3 and the nitrogen content in the boric and phosphate aqueous solutions must retain higher than 3.94 and 1.52 g N/l, respectively. The equilibrium amount of water-soluble nitrogen dissolved out of the prepared composite bead was between 7.95 and 8.21 mg N/g dry solid. The path of water-soluble nitrogen dissolving out of the A-type bead was the water-soluble nitrogen dispersed in the peat phase initially diffused into the outer PVA phase and then it diffused out of the bead surface. And the path of water-soluble nitrogen dissolving out of the H-type bead was the water-soluble nitrogen dispersed in both the peat and PVA phases simultaneously diffused into the outer PVA phase and out of the bead surface, respectively. The microbial growth rate kg of the H-type composite bead was higher than that of the A-type composite bead approximately 1.09–1.58 times, and its value was between 0.100 and 0.417 day−1 as the composite bead was immersed in 0–0.896 M KNO3 solution. The maximum value of kg appeared at the composite bead immersed in 0.384 M KNO3 solution and was higher than that of the compost by a factor approximately 1.49. The percentage of removed volatile organic compounds (VOCs) remained at more than 98% during the biofilter operating 230 days as the composite bead was immersed in KNO3 aqueous solution before packing. This composite bed was without the further addition of nutrients during this operating period. It was proved that this composite bead was superior to the compost as a filter material.