Influence of Source Characteristics, Chemicals and Flocculation on Non-Settleable Solids and Chemically Enhanced Primary Treatment

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The overall objective of this research was to investigate various methods and parameters to increase the efficiency of Chemically Enhanced Primary Treatment (CEPT). To understand the methods of improving efficiency, non-setteable solids (NSS) was selected as the controlling parameter that influenced efficiency of CEPT. Parameters and source characteristics that increase NSS results in poorer CEPT performance, while parameters and characteristics that decrease NSS improves CEPT performance. Several parameters were evaluated including clarification process parameter, chemical type and dose, and influent source characteristics. While rapid mix intensity did not affect NSS, flocculation impacted NSS considerably. A minimum flocculation time of approximately 15 minutes was needed without chemicals. This flocculation time could be reduced with iron and polymer addition for optimized CEPT performance. Coagulants such as ferric salts were mainly responsible for reducing NSS and improving CEPT performance. Both ferric and ferrous salts were useful, although ferrous was less efficient in reducing NSS and improving CEPT performance. Some of the source characteristics that influenced NSS concentration include influent TSS (total suspended solids), influent turbidity and influent total COD (chemical oxygen demand). A higher concentration of the influent constituents led to higher NSS concentration, suggesting that NSS represented a
somewhat fixed fraction or percent of these influent constituents. A new parameter was introduced to measure relative particle size. The specific particle surface area (SPSA) was found to correlate with percent NSS in the effluent. A higher SPSA is a result of more smaller sized non-settleable colloidal particles, thus leading to an increase in percent NSS. This lumped SPSA parameter was a surprisingly good gauge of influent characteristics impacting percent NSS in the effluent and warrants further study. In summary, there are several characteristics that affect NSS and several parameters that could be used to control NSS to improve CEPT as demonstrated by this study.

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