Operating Cost Reduction of In-line Coagulation/Ultrafiltration Membrane Process Attributed to Coagulation Condition Optimization for Irreversible Fouling Control

Sung Yoo

doi:10.3390/w10081076

Abstract

This study examined the optimum coagulation conditions for reducing irreversible fouling during the in-line coagulation/ultrafiltration (UF) membrane process and assessed the decrease in operating cost. The coagulation conditions that generated charge-neutralization, sweep-flocculation, and under-dosing mechanisms were obtained by a jar-test, and a pilot-scale in-line coagulation/UF membrane process was operated under the coagulation conditions. Charge-neutralization and sweep-flocculation mechanisms reduced irreversible fouling effectively, and the under-dosing mechanism was able to reduce irreversible fouling only when flocs of a certain size or larger were formed. This revealed that floc size was a more important factor in reducing irreversible fouling than floc structure, and once initial cake layers were created by flocs of a fixed size, the structure of formed cake layers had only a minor effect on irreversible fouling. Regarding reduction in operating cost, 0.5 mg/L and 3 h, which were necessary to produce an under-dosing mechanism, were deemed the optimum coagulant dosage and coagulant injection time, respectively, to reduce irreversible fouling. In order to analyze the operating cost reduction effect, a pilot plant was operated under optimum operating conditions, and the total operating cost was approximately 11.2% lower than without in-line coagulation.

Highlights

The increase in contamination of the drinking water resource by the industrialization has accelerated the introduction of advanced treatment processes [1]
To determine optimal coagulation conditions in order to reduce irreversible fouling during the in-line coagulation, first, a jar test was conducted to select a proper coagulation dosage, which resulted in charge-neutralization, sweep-flocculation, and under-dosing mechanisms
Zeta potential of raw water was −23 m V and, overall, zeta potential increased as the coagulation dosage increased and pH decreased (Figure 2a). This occurred because the increase in the dosage of coagulant, which is a positive ion, resulted in further destabilization of natural organic matters (NOM), which is a negative ion, as well as colloidal material

Summary

Introduction

The increase in contamination of the drinking water resource by the industrialization has accelerated the introduction of advanced treatment processes [1]. The membrane filtration process is one of the advanced treatment processes that has attracted attention because of its ease of operation, requirement of a relatively small area, and its stability in obtaining effluent [2,3]. Many studies have been performed and hybrid processes have been proposed in which coagulation, powdered activated carbon (PAC), granular activated carbon (GAC), ion exchange resin, and oxidation are combined as a pretreatment process [7,8] Of these proposed pretreatment processes, the coagulation process is relatively inexpensive and easy to execute, and is widely applied to the membrane filtration process for water treatment, as it is excellent in removing natural organic matter (NOM) and colloidal material, which are major pollutants in water [9,10]

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Conclusion