1.2.1 Research Objectives
Operational parameters that influence floc blanket performance include: raw water turbidity, coagulant dose, upflow velocity in the floc blanket, height of the floc blanket, and extent of flocculation of the suspension entering the floc blanket. Bulk properties of the floc blanket, including solids concentration and bulk density, are parameters that could be related to performance. Understanding how operational parameters affect floc blanket performance is critical for application at a full-scale clarifier. Without floc blanket observation and operational control of dosing, complete loss of the floc blanket has been observed (AWWA/ASCE, 1990).
The focus of this research was to investigate parameters affecting floc blanket performance given constant raw water turbidity and alum dose. Although conditions of constant dose have been used by other investigators on a pilot and laboratory-scale (Miller & West, 1968; Zhang et al. 2006), this research was unique with respect to the wide range over which parameters were varied and the inclusion of both flocculation and tube settlers in the experimental apparatus. Continuous monitoring of effluent turbidity from both tube settlers (used to mimic lamellar plate settlers) as well as from the floc blanket clarifier, and quantification of the energy dissipation rate and residence time in the flocculator and floc blanket clarifier were also distinguishing features of this research.
The research objectives were to characterize floc blanket performance with respect to each of the variables listed above and to develop an understanding of the underlying mechanisms that affect floc blanket performance. The experiments that were conducted benefited from use of process control software developed by Weber-Shirk (2008) to automate operation of the laboratory-scale plant as well as to monitor and record influent and effluent turbidity readings.