Comparison of Sludge Granule and UASB Performance by Adding Chitosan in Different Forms

Abstract

This study prepared chitosan with the same properties, i.e. molecular weight and degree of deactivation in different forms, i.e. solution, bead and powder, and compared their effectiveness in enhancing granulation and UASB performance, A natural polymer chitosan in the form of freely moving polymeric chains was found to enhance sludge granulation and the efficiency of UASB system. The UASB with chitosan addition had a 9-59% lower effluent COD, 5-7% higher COD removal, up to 25% higher biogas production rate, 21-39% lower biomass washout, 37% larger particle size and 4 day longest sludge retention time. The differences are significant (P<0.05). However, chitosan in the form of bead and powder did not help enhance granulation process and UASB performances significantly. It was concluded that the size of the particles serving as inert nuclei and the chance of contact between the inert nuclei and biomass were very important. Surprisingly, even though chitosan powders had the net positive charges, their role in reducing electrostatic interaction between negatively charged bacteria was not prominent.