Comparison of optional process configurations and operating conditions for ceramic membrane MF coupled with coagulation/flocculation pre-treatment for the removal of NOM in drinking water production

Abstract

The increase of Natural Organic Matter (NOM) in natural water sources, partly caused by progressing climate change issues, is a growing concern for drinking water production.In recent years, membrane technology like Reverse Osmosis (RO) or Nanofiltration (NF) has been successfully applied as a robust solution for NOM removal to produce potable water. However, coagulation/flocculation pre-treatment, combined with Microfiltration (MF) ceramic membrane filtration is nowadays seen as an alternative, less-energy-consuming membrane process for NOM removal. In this study different coagulants have been used under varying coagulation/flocculation conditions to investigate the respective impact on membrane filtration performance.Three alternative coagulation/flocculation configurations were compared. It is shown that NOM was efficiently removed independently on the chosen configuration or coagulant type. Similar and low membrane fouling rates were observed for all tests. Residual metal concentration was found to be the limiting permeate quality parameter, which limits the options of operating conditions. Furthermore, the compact inline pipe flocculator configuration has the potential of designing more compact full-scale units, using less space compared to conventional sand filtration units or even membrane filtration plants using classical tank coagulation/flocculation configurations.

Micro‐coagulation effects on direct ultrafiltration of challenging raw river water

“…On the other hand, Boulestreau and Miehe noted that an excessive coagulant dose had a negative effect on membrane filterability. Finally, Meyn and Leiknes stated that both overdosing and underdosing coagulant in comparison with its optimal requirements caused increased irreversible fouling. Wang et al attributed these effects to incomplete particle aggregation, due to the larger repulsion forces caused by the high charge imbalances.…”

Optimization of Coagulation Pretreatment Conditions in a Ceramic Membrane System

“…Membrane fouling was quantified in this study as the rate of transmembrane pressure gain per hour. TMP data before and after each backwash cycle were extracted from the unfiltered logged pressure data by following procedures described by Meyn and Leiknes (2010) and Zhu et al (2012). This was the pressure immediately before the membrane feed pumps were stopped for the backwash sequence and 1 min after backwash to account for the pump ramp‐up period.…”

“…Coagulation pretreatment. Coagulation pretreatment has been demonstrated as an effective pretreatment solution for microfiltration not only for controlling fouling but also for removing contaminants smaller than the membrane pores (Meyn & Leiknes 2010, Huang et al 2009, Meyn et al 2008, Loi‐Brügger et al 2006, Fiksdal & Leiknes 2006, Matsushita et al 2005, Matsui et al 2003, Bérubé et al 2002, Judd & Hillis 2001). However, understanding coagulation chemistry and the factors that control the coagulation process is important for its successful implementation as a pretreatment stage.…”

“…Lehman et al (2008) observed that with inline flocculation, the decline in specific flux was only 9% from the initial flux, while the specific flux decline was about 22% with the two‐stage coagulation/flocculation. Meyn and Leiknes (2010) compared three ceramic coagulant mixing schemes and their impact on dissolved organic carbon (DOC) removal, membrane fouling rate, and residual coagulant concentrations. The first was a conventional rapid mix and flocculation stage with a retention time of 21 min, the second was only a rapid mix stage with a retention time of 7 min, and the third was an inline static mixer with a retention time of 45 s. Using a constant dose of 10 mg/L as iron (Fe) (0.18 mM Fe) at pH 5 for all configurations, the authors observed that the DOC removal was approximately 80% for all configurations.…”

Preface

“…On the one hand, dosing of a coagulant decreases considerably membrane fouling and, on the other hand, increases the otherwise low NOM removal of porous membranes. In the study of Meyn & Leiknes (2010), different coagulants have been used under varying coagulation/flocculation conditions to investigate the respective impact on the performance of a ceramic MF. Papers investigating other types of hybrid process are included in this issue.…”