The causes of high effluent suspended solids (ESS) from secondary clarifiers are often incorrectly identified resulting in improperly focused remedial actions that do not yield the desired results. In this paper we demonstrate a structured diagnostic approach that allows relatively rapid problem isolation and resolution. A sequence of tests, procedures or observations are described that allow problems to be classified into one or more of the following categories: (1) denitrification or rising sludge, (2) high sludge blankets, (3) flocculation or breakup problems, and (4) hydraulic problems. The following tools are used in the approach: (1) direct observation, (2) blanket 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) hydrodynamic modeling. The structured diagnostic approach has been applied and refined by the authors over nearly three decades and has proven extremely useful 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.

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The near-field mixing of effluent from buoyant and nonbuoyant flows from outfalls discharging into a cross-flowing ambient current in trapezoidal channels has been investigated. A physical model was scaled to represent a typical large outfall into one of the connecting channels of the Great Lakes system. The discharged jet was measured in detail to determine the velocity and concentration fields. The excess velocities and concentrations were found to follow the Gaussian distribution. Empirical expressions for the jet trajectories, minimum dilutions, and plume widths were derived. A correction factor has been introduced to the concentration distribution to ensure mass conservation. The calibrated model was verified by comparison with field data and the results of other near-field models (PDS, MIT, and CORMIX).Resume : Le prCsent article rend compte des rtsultats d'une Ctude portant sur le melange en champ proche des effluents de panaches flottants et non flottants provenant d'exutoires se dtchargeant dans le courant transversal ambiant de canaux trapkzoidaux. Un modtle physique i l'tchelle a Ct C construit pour representer un exutoire type de grandes dimensions se dtchargeant dans l'un des canaux de raccordement du rCseau des Grands Lacs. Le jet de dtcharge a fait l'objet de mesures dCtaillCes afin de determiner la vClocitC et les champs de concentration. On a remarqut que les vtlocitts et les concentrations exctdentaires suivaient la distribution gaussienne. Des expressions empiriques ont t t t Clabortes pour les trajectoires des jets, les dilutions minimales et la largeur des panaches. Un facteur de correction a t t t appliqut i la distribution de la concentration afin d'assurer la conservation de la masse. Le modtle ttallonnC a Ct C compart aux donnkes sur le terrain ainsi qu'aux rtsultats d'autres modkles en champ proche (PDS, MIT et CORMIX).

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