Settleability assessment protocol for anaerobic granular sludge and its application

Abstract

A simple method for settleability assessment of anaerobic granular sludge was proposed and its applicability as an operating parameter was evaluated in a lab-scale UASB reactor treating brewery wastewater. Based on the settleability protocol, the OLR was increased up to 28 kg COD·m -3·d-1 (67 kg COD·m-3 of granular bed volume-d-1) which corresponds to an HRT of 1 h. The results revealed that the protocol was sufficiently sensitive to define the settleability of the sludge samples and to accurately determine their allowable upflow velocities, resultant organic loading rates, and recycling ratios according to the settleability of the granular bed. Also, a series of graphical procedures with settling tests which are very easy to apply for settleability monitoring was improvised, capable of direct use as an operational and monitoring parameter of the granular bed with laboratory and full-scale reactors, without need for additional sludge bed control such as dosing of chemicals. In addition, this method was also found to be applicable to improve and monitor system performance according to high or low-strength wastewater characteristics. Image analysis of the granular biomass supported the suitability of this graphical method.