Characteristics of physicochemical adsorption of soluble matter by particles formed in a fluidized pellet bed reactor.

To investigate the mechanism of soluble matter removal by a fluidized pellet bed (FPB) reactor, an experimental study was conducted using a laboratory-scale FPB device for treating synthetic wastewater under a condition of no activated sludge seeding and no dissolved oxygen supply so that the physicochemical functions of the FPB reactor could be evaluated. By using polyaluminium chloride and polyacrylamide as coagulants, it was found that most of the substances in the synthetic wastewater could not be effectively removed by conventional coagulation and sedimentation. A similar condition was observed in the start-up period of the FPB operation. However, as a steady FPB was formed usually after about 10 hours' operation, the influent COD, ammonia nitrogen and total phosphorous could be quickly and effectively entrapped by the fluidized grown particle layer. Because these substances were not coagulable under normal conditions, adsorption might have performed an important role in their removal. Through an adsorption experiment using the grown pellets as adsorbent and glucose as adsorbate without dosing coagulants, it was found that the process followed well the Freundlich adsorption isotherm. The adsorption was also confirmed to be reversible by a washing experiment. A scanning electron microscopy coupled with energy dispersive spectroscopy analysis of the pellets before and after washing showed that the elements of carbon and phosphorous in the outer layer of the pellets were easily desorbed. The study results can provide an explanation, other than the coagulation mechanism, for the removal of soluble matter by the FPB. [ABSTRACT FROM AUTHOR]