The Impact of Cake Compressibility In Coagulation-Microfiltration of Natural Organic Matter (NOM)

The impact of cake compressibility in coagulation-microfiltration of

Natural Organic Matter (NOM)

Gema Sakti Raspati^a*, Thomas Meyn^a, and TorOve Leiknes^a

^a Department of Hydraulic and Environmental Engineering

 Norwegian University of Science and Technology (NTNU) - Norway

Tel: +47-73594746 Fax: +47-73591298;

^*email: gema.s.raspati@ntnu.no

Compressibility of the coagulated materials has been found as one of the major limiting factors in coagulation-membrane filtration that can compromise the performance and the economics of a treatment system [1, 2]. Inline coagulation (IC) was proposed as an alternative to the conventional tank coagulation (TC) setup for coagulation-microfiltration (MF) process of water containing NOM with advantages in terms of simplicity of the setup without compromising the separation performance. It was found that removal efficiency was dependent to the dose of coagulant regardless to the applied configuration of the coagulant step [3]. However, at the same time the trans-membrane pressure (TMP) increase in filtration cycles was found higher in IC than that in TC.  Although the nature of the membrane fouling was backwash-reversible, it is necessary to investigate the reason for such a phenomenon to be able to optimize the IC configuration. Filtration data from the previous study of IC-MF (Metawater Co., Ltd.) [3] using aluminium-based coagulant (PAX-18, Kemira) and the current study using iron-based coagulant (PIX-111, Kemira) in a same molar dose of the coagulant treating water containing 6.90±0.23 mg C/L NOM will be presented. Different IC configurations in terms of the applied G-values and the coagulant types produced similar removal efficiency of around 69.1±1.1 % of the dissolved organic carbon. The behavior of cake material during filtration experiments was assessed by applying resistance-in-series model. The specific properties of cake layer i.e. compressibility index (i) and zero pressure specific cake resistance (alpha_o) were obtained from fitting specific cake resistance and trans-cake pressure with power-law model. Figure 1 and 2 depict the behavior of the two parameters.

Figure 1. Compressibility index as a function of filtration cycles	Figure 2. alphao as a function of filtration cycles

Figure 1 and 2 showed the impact of different configurations on the parameters that representing the cake compressibility and, thus, affecting the filtration behavior.  Iron-based coagulant seems to give higher compressibility indices compared to the aluminium-based coagulant. On contrary, alpha_o values of the aluminium –based coagulant were higher than that of the iron-based coagulant. In order to exemplify the physical meaning of this behavior, the result of floc size measurements using camera-based instrument (XPT-C, Prozesstechnik GmbH) will be included in the presentation to elaborate the calculation-based result as presented above.

Reference

[1] P.A. Belter, E.L. Cussler, W.-S. Hu, Bioseparations: downstream processing for biotechnology, Wiley, New York, 1988.

[2] A. Van Nieuwenhuijzen, J. Van der Graaf, Handbook on particle separation processes, in, IWA Publishing, 2012.

[3] T. Meyn, J. Altmann, T. Leiknes, In-line coagulation prior to ceramic microfiltration for surface water treatment - minimisation of flocculation pre-treatment, Desalination and Water Treatment, DOI: 10/5004/dwt.2012.2590, 2012.