The relevance of critical flux and backwash intervals parameters for the design of ultrafiltration process in the treatment of eutrophic reservoirs: A pilot study for the development of a full-scale project

Abstract

The determination of the critical flux and backwash intervals for ultrafiltration process still remains valid for the design and long-term operation of new water treatment systems. In this study, an ultrafiltration pilot plant was installed at the Gavião Water Treatment Plant, in the Fortaleza city, state of Ceará, Brazil, under the following experimental conditions: flows of 2.5 m3·h−1, 5 m3·h−1, 7.5 m3·h−1 and 10 m3·h−1, backwash intervals of 30, 40, 50, 60 and 70 min and operation in wet and dry seasons. Each condition was maintained constant for at least 160 min. The aim of the study was to evaluate the critical operational parameters for the design of large-scale treatment units. The results showed that the critical operating parameters were 84 kPa and 30 L·m−2·h−1 with a backwash interval of 65 min for dry season, and 67 kPa and 24.8 L·m−2·h−1 with a backwash interval of 55 min for wet season. The highest number of retained cells (9.5 × 1011) was associated with the lowest flux rate (24.8 L·m−2·h−1), and the dominance of Planktothrix sp. may have led to a slightly faster fouling rate. However, the retention of the most abundant filamentous genera Planktothrix sp. and Raphidiosis sp. did not decrease the permeate flow under optimized operation conditions. The study resulted in an operation with linear flux, maximizing the permeate volume and obtaining critical parameters, which is very important for the design of real scale treatment plants. In addition, the obtained results demonstrate the relevance of assays for the project optimization.