A Comprehensive Study to Reduce Polymer Usage at Austin's Biosolids Management Plant

The City of Austin experienced a substantial increase in polymer usage for thickening and dewatering operations between 2004 and 2007. The acidification of sludge in pipelines and storage tanks prior to thickening likely resulted in increased polymer demand at the thickeners. One main reason for the increase in polymer usage at the belt presses was suspected to be an increase in extracellular polymer substances caused by a drastic change in digester operation on four of the eight digesters. Continued foaming issues in all eight digesters underscore the sustained high usage of polymer seen after the initial increase. On site experiments showed that the flow equalization basin was not equalizing concentration which resulted in the need for conservative use of polymer at the thickeners. Bench-scale experiments revealed that the belt press was not being fed an optimal dilution of polymer, and bench scale anaerobic digester experimental results suggested that the digesters should be fed a lower influent solids concentration to improve sludge dewaterability. Finally, a full-scale lithium tracer test revealed that over 25% of the volume in the digester was dead space. The results ultimately led to a list of recommendations for reducing polymer usage at the plant.