Improving secondary clarifier performance and capacity using a structured diagnostic approach

The causes of high effluent suspended solids (ESS) from secondary clarifier s are often incorrectly identified resulting in improperly focused remedial actions that do not yield the desired results. In this paper we demonstrat e a structured diagnostic approach that allows relatively rapid problem iso lation and resolution. A sequence of tests, procedures or observations are described that allow problems to be classified into one or more of the foll owing categories: (1) denitrification or rising sludge, (2) high sludge bla nkets, (3) flocculation or breakup problems, and (4) hydraulic problems. Th e following tools are used in the approach: (1) direct observation, (2) bla nket detection, (3) measurement of sludge thickening properties, (4) solids flux or state point analysis, (5) dispersed suspended solids (DSS) test, ( 6) flocculated suspended solids (FSS) test, (7) dye testing, and (8) hydrod ynamic modeling. The structured diagnostic approach has been applied and re fined by the authors over nearly three decades and has proven extremely use ful in rapidly identifying the least-cost technology for reducing ESS. Case examples are presented where the structured diagnostic approach is used to isolate the problems and identify the most appropriate remedy.