Chemical Cleaning of Membranes in a Long-Term Operated Full-Scale MBR for Restaurant Wastewater Treatment

Abstract

Chemical cleaning was investigated for a membrane bioreactor (MBR) treating restaurant wastewater. Test results showed that membrane foulants were comprised of inorganic and organic substances. Sparingly soluble salts containing Mg, Al, Ca, and Fe were the major components of the inorganic foulants, and protein was likely to be the organic foulant with high hydrophobicity. It was also found that the chemical cleaning could modify the contact angle of the membranes, and the membranes became more hydrophobic than the virgin membrane after chemical cleaning. 2% sulfuric acid, 3% sodium hydroxide, and 4% sodium hypochlorite with 66.0%, 59.0%, and 56.3% flux recovery efficiency showed better performance than others.

Keywords:

• chemical cleaning
• membrane bioreactor
• membrane fouling
• microfiltration
• restaurant wastewater

ACKNOWLEDGEMENTS

Financial support of this work by the National Natural Science Foundation of China (Grant No. 51008217) and by the Science and Technology Commission of Shanghai Municipality (Grant No. 09dz1204200 and 10231201300) is gratefully acknowledged.

Notes

^a Values are given as mean value ± standard deviation except for oil (number of measurements: n = 29).

^a Values are given as mean value ± standard deviation except for oil (n = 29).

^a Not available, as organic acids were used as the extracting solution. (A) sodium hydroxide cleaning; (B) oxalic acid cleaning; (C) citric acid cleaning; (D) sodium hypochlorite cleaning; (E) hydrochloric acid cleaning; (F) hydrogen peroxide cleaning; (G) sulfuric acid cleaning. (The DOC analyses in eluents were measured in optimum concentration after 600-min soaking.)

^a Not available, as sodium hydroxide and sodium hypochlorite were used as the extracting solution. (A) sodium hydroxide cleaning; (B) oxalic acid cleaning; (C) citric acid cleaning; (D) sodium hypochlorite cleaning; (E) hydrochloric acid cleaning; (F) hydrogen peroxide cleaning; (G) sulfuric acid cleaning. (The element analyses in eluents were measured in optimum concentration after 600-min soaking.)