Understanding the influence of nutrient levels on biofouling control is an important requirement for management strategies in a recirculating cooling water system. Nutrient limitation may be one way to control biofouling development without increasing biocide dosing. Therefore, this study was carried out to investigate the effects of nutrient levels on biofouling characteristics and to identify the preponderant bacteria in the batch tests with a simulated cooling water system. The biofouling characteristics were assessed by varying the biofoulant mass and the bacteria respiratory activity, which was estimated by measuring oxygen uptake rates. According to the results obtained in nutrient factor experiments, the biofouling could be better controlled at carbon, nitrogen and phosphorus concentrations of 30 mg N/L, 8 mg N/L and 1.0 mg P/L, respectively. Increasing carbon concentrations shortened the biofouling initial growth period and resulted in higher biofoulant mass. The preponderant bacteria strains involved in biofouling under two culture conditions were identified by applying both physiological and biochemical tests and further molecular biology techniques with phylogenetic affiliation analysis. Enterobacter (family Enterobacteriaceae), Staphylococcus (family Micrococcaceae), Bacillus (family Bacillaceae), Proteus (family Enterobacteriaceae), Neisseria (family Neisseriaceae) and Pseudomonas (family Pseudomonadaceae) were dominant in the conditions of lower carbon concentration (30 mg/L). Enterobacter are autotrophs, but the other five bacteria are all heterotrophs. In the conditions of higher carbon concentration (70 mg/L), Klebsiella (family Enterobacteriaceae), Enterobacter and Microbacterium (family Microbacteriaceae) were dominant; Enterobacter and Microbacterium are heterotrophs.
With the reducing of water resources, using advanced treated refinery wastewater as recirculating cooling water is an effective method to save water and to reduce the pollution of petroleum and petrochemical industry. However, the control of biofilm is a bottleneck in the application of this technology. To resolve the problem of biofilm formation and development, antimicrobial characteristics of chlorine dioxide and benzyldimethyldodecyl-ammonium chloride on biofilm at different substrate levels were investigated. Biofilm detachment ratio and TTC-dehydrogenase activity (DHA) were two indexes to discuss the antimicrobial effects. The results showed that at the high substrate level, the biofilms characteristics (biomass, the content of protein, polysaccharide and EPS) were the higher than those at the medium and low substrate levels, however biofilm's DHA at the medium substrate level (12.97 lgTF/(g h)) was higher than those at the medium substrate level (7.64 lgTF/(g h)) and low substrate level (1.94 lgTF/(g h). The difference of substrate level in the media resulted in different biofilm structure. By contrast with the control experiment, biofilm detachment ratios were all increased in three media with ClO 2 and BDMDAC addition. After ClO 2 addition, MITs were 30, 120 and 240 min and MIC was 1, 4 and 6 mg/L, respectively, at the low, medium and high substrate level. After BDMDAC addition, MITs in three media were all longer than those after ClO 2 addition, MIC was 200, 300 and 400 mg/L, respectively, at the low, medium and high substrate level.
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