Seasonal variation of organic matter characteristics and fluoride concentration in the Maji ya Chai River (Tanzania): Impact on treatability by nanofiltration/reverse osmosis

Azam Jeihanipour, Junjie Shen, Gudrun Abbt-Braun, Stefan A. Huber, Godfrey Mkongo, Andrea I. Schäfer

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The Maji ya Chai River in Northern Tanzania, a fluoride-rich tropical area, shows a seasonal variation of natural organic matter (NOM) and fluoride concentration. Water samples collected monthly during one year from two locations of the River were characterized. High levels of precipitation in the rainy seasons increased the total organic carbon (TOC) concentration to as high as 36 mgC L−1 and diluted the fluoride concentration from a dry season high of 24 mg L−1 to <4 mg L−1. A black water swamp in the Maji ya Chai River catchment was confirmed as the main source of NOM, fluoride, salinity, and inorganic carbon entering the River in the rainy season. The water samples were filtered by a number of nanofiltration/reverse osmosis (NF/RO) membranes to identify the retention mechanisms and the impact of varying water quality on treatability. While the denser membranes removed fluoride due to size exclusion, for the membranes with bigger pore radius charge repulsion was the dominant mechanism of fluoride retention. Regardless of the seasonal conditions a TOC concentration <2 mgC L−1 was achieved by all membranes at 50% recovery, as NF/RO membranes remove TOC mainly by size exclusion. Two swamp water samples, containing high TOC (79 and 183 mgC L−1), were filtered to determine the characteristics of NOM which permeate the NF/RO membranes. Liquid chromatography organic carbon detection (LC-OCD) was used to characterize the fractions in the permeates, consisting of about 1% of the original NOM. The average molecular weight of the permeate humic substances (HS) was more than four times larger than the membrane molecular weight cut-off. This suggests that large HS can permeate the NF/RO membranes through diffusion. Moreover, the relatively high aromaticity of the permeate HS (1.7–5.2 L mg−1 m−1) indicated the high content of hydrophobic-aromatic fractions.

Original languageEnglish
Pages (from-to)1209-1220
Number of pages12
JournalScience of the Total Environment
Volume637-638
Issue number2
Early online date22 May 2018
DOIs
Publication statusPublished - 1 Oct 2018

Keywords

  • Fluoride
  • Liquid chromatography organic carbon detection (LC-OCD)
  • Membrane filtration
  • Nanofiltration
  • Tropical natural organic matter
  • Water treatment

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution

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