Case Study; Viscous Bulking – Importance of Nutrient Monitoring.

The determination of nutrient deficiency for a wastewater treatment plant utilizing an activated sludge process is extremely important. The limitation of one or several nutrients can be linked to filamentous bulking and Viscous Bulking (Jenkins). During an incident late in 1999 at the Detroit Wastewater Treatment Plant (DWWTP), the activated sludge (SVI) had shown a significant increase over time without a concurrent change in the filamentous count. This lead to an investigation during 2000 for a relationship between nutrient deficiency and episodes of non-filamentous or “Viscous Bulking”. Initiated in January 2000 in response to the bulking incident of 1999, this study was undertaken to determine if the DWWTP activated sludge systems periodically suffers nutrient limiting conditions adversely impacting the Settled Volume Index (SVI) or other treatment conditions. Nutrients investigates were oxygen, nitrogen, carbon and phosphorus.Four periods of rising SVIs were found in 2000 to be a result of bio-polymer production in the floc particles. This was verified through microscopic examination of India ink reverse staining techniques. The production of bio-polymer appears to have occurred in response to a substantial loss of soluble phosphate, to levels less than 0.2 mg/L, and biodegradable organics in the influent stream to the activated sludge process. This finding not only assisted in the operation of the secondary system but also enabled a chemical cost saving by the alteration of the feed rate of iron salts to the primary system. The result was an increase in the soluble phosphate feed to the secondary system correcting the viscous bulking conditions.