The Determination of Settled Sludge Volume and Sludge Volume Index Using Process Methodologies

Abstract

One of the key analytical parameters used to assess the performance of typical municipal wastewater processes is the determination of the settled sludge volume (SV) within the aeration basin. Commonly, this measurement method is performed on a bench scale using a settlometer. This method is sensitive to sampling technique, agitation methods, variations in suspension, process temperature, dimensions of the settling column, and the amount of time between sampling and the start of the determination; all of which can significantly affect results 1 . The test is time-consuming and because of this it is typically performed only once per day.To help eliminate the difficulty in performing the SV measurement, an on-line instrument has been designed to continuously perform the measurement on-site. The methodology includes purging the previous sample, accepting a new sample, and performing the measurement. The instrument design includes a uniquely shaped settlometer vessel. This specially designed vessel increases the settling rate and reduces the analysis time. This decreased time has been correlated to the standardized laboratory methods for the 30-minute SV standard protocol across a wide number of samples. Thus, shortened cycle time for the process SV measurement is the result.Two on-line SV instruments were installed in the aeration basins of two different municipal wastewater plants. These installations provided data that can be compared directly to the utilities' laboratory values generated from their treatment process. These installations sites also provided the opportunity to calculate Sludge Volume Index (SVI) when the total suspended solids (TSS) measurements from the aeration basin are measured concurrently. The use of this process monitoring technology to determine the WEFTEC ® 2003 critical SVI of the wastewater plant provides information to allow plant performance to be controlled real-time.This paper presents comparisons between the SVI values generated using laboratory methods and the process methodology. These comparisons also demonstrate how the increased frequency of the process measurements provided additional details that were missed when less frequent laboratory analysis were performed. Data from these comparisons come from the two different water reclamation plants. The process control SVI data will be correlated to final effluent parameters such as effluent biological oxygen demand (BOD), and TSS. In addition, more practical application issues such as process instrument maintenance protocols will be discussed.

Modeling, Instrumentation, Automation, and Optimization of Wastewater Treatment Facilities

“…To experimentally obtain initial settling velocities representative of full-scale conditions, Giokas et al (2003) concluded that settling columns with height-to-diameter ratios greater than 12 should be used. Sadar et al (2003) reported that SVI data from an automated in-situ settleometer correlated with the data from a standard 2L settleometer.…”