Monitoring and troubleshooting of non-filamentous settling and dewatering problems in an industrial activated sludge treatment plant

A large industrial activated sludge wastewater treatment plant had temporar y problems with settling and dewatering of the sludge. Microscopical invest igations revealed that the poor settling properties were not due to presenc e of filamentous bacteria, but poor floc properties. In order to characteri se the changes in floc properties that led to settling and dewatering probl ems and to find reasons for this taking place, a comprehensive monitoring p rogram was conducted during more than one year. The monitoring program incl uded various measurements of floc settleability, floc strength and sludge d ewaterability. The monitoring program revealed that a deterioration of the floc strength and the settling properties in the process tanks was closely connected to downstream dewatering problems and poor effluent quality. Part icularly severe problems were observed a few weeks after the production at the factory had started after summer closedown. Possible reasons for the ch anges in floc properties in the process tanks were found by a) analysing ch ange in wastewater composition by evaluating the different production lines in the industrial plant, b) evaluating the operation of the plant, and c) performing short-term laboratory experiments testing factors that could pot entially affect floc properties (absence of oxygen, presence of sulphide, d etergents, etc). Among several measured parameters, the use of floc strengt h measurements in particular proved useful to monitor the activated sludge floc properties at this industrial plant. The described strategy can be use ful in general to find and solve many solid/liquid separation problems in a ctivated sludge wastewater treatment plants.