Analysis of organic matter causing membrane fouling in drinking water treatment

Abstract

A study was conducted on characteristics of membrane-fouling matter and chemical cleaning of fouled membranes. The membranes were those used for the filtration of raw water taken from the Lake Kitaura, Ibaraki, Japan. Analysis of the molecular weight distribution of extracted foulants by ultrafilters showed that 23% of organic matter was in the fraction exceeding a molecular weight of 100,000 daltons and 33% between 10,000 to 100,000 daltons. Analysis by gel permeation chromatography (GPC) revealed a void peak and five peaks at a molecular weight of less than 6,000 daltons. Assessment by Fourier transform infrared spectroscopy( FTIR) and pyrolysis gas chromatography mass spectrometry (Py-GC-MS) revealed that organic fouling matter contained polysaccharides, proteins, amino sugars and aromatic compounds that constitute humic substances. A comparison of the apparent molecular weight distribution and the FTIR spectra of both the raw water and fouled membrane extracts revealed the attachment of membrane-fouling matter nonexistent in the raw water, which was considered to be extracellular organic matter. Chemical cleaning of fouled membranes suggested that sodium hypochlorite and hydrogen peroxide were effective for the recovery of membrane permeability. In most of the experiments, the higher the cleaning temperature is between 5°C and 40°C, the more effective the chemical cleaning. However, chemical cleaning by a mixture of 1%-NaOCl and 4%-NaOH showed a comparable cleaning efficiency at 5°C as chemical cleaning at 40°C after two hours.