Abstract
The fate of representative indicator and pathogenic bacteria on ultrafiltration (UF)-membrane surfaces treating secondary wastewater effluent, as well as their reaction to common biofouling-removal techniques was investigated. Field-condition experiments showed that the number of heterotrophic bacteria, fecal coliforms, E. coli and Salmonella on membrane surface increased rapidly and continuously until the end of the experiment, reaching 9, 6.5, 6, and 2.4 logs, respectively. Similar results were obtained under controlled laboratory conditions. However, the increase in the bacterial numbers was dependent on the supply of fresh wastewater. Quantitative real-time PCR verified the behavior of attached E. coli cells, although the numbers were 1–2 logs higher compared to the standard culture-based method. The number of attached bacteria was positively correlated to increases in DNA and protein content and negatively correlated to the membrane flux. In-situ membrane cleaning using sodium hypochlorite significantly reduced the number of attached bacteria. However, the effect was temporary and affected bacterial cell cultivability rather than viability. Taken together, these findings suggest that, under the studied conditions, indicator and pathogenic bacteria can initiate rapid biofilm development, persist on UF membrane surfaces, and survive membrane cleaning with sodium hypochlorite.
Highlights
Water scarcity has become a global problem in arid and semiarid regions
The objectives of this study were to investigate whether these bacteria can persist on the UF membrane surface following UF as part of the formed biofilm and how these bacteria react to techniques designed to control biofilm development
The numbers of bacteria in the UF reject were less than those of the UF feed suggesting that bacterial cells were still attached to the membrane surface
Summary
Water scarcity has become a global problem in arid and semiarid regions. The increasing demand for clean water has prompted the reuse of domestic wastewater and use of seawater as alterative water resources. Integration of membrane-filtration techniques in water treatment has become an attractive and popular solution to meet this challenge[1,2,3] Among these techniques, ultrafiltration (UF) is considered the preferred technology for reclaiming wastewater and for pretreatment of wastewater and seawater prior to the reverse-osmosis (RO) stage[4]; this is because the UF process reduces colloidal, organic, and biofouling on RO membranes[5,6]. Biofouling, which is a biofilm phenomenon, is a multistage process initiated by membrane conditioning via adsorption of macromolecules originally existing in the feed, such as proteins, humic acids, and polysaccharides, and the secretion of extracellular polymeric substances (EPS) by the microorganisms Such membrane conditions facilitate attachment of one or more bacterial species to the membrane surface, followed by their growth and multiplication while utilizing the feed water nutrients, resulting in biofilm formation[2,12,13]. The objectives of this study were to investigate whether these bacteria can persist on the UF membrane surface following UF as part of the formed biofilm and how these bacteria react to techniques (sodium hypochlorite treatment) designed to control biofilm development
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