Analysis of the microbial community structure and function in a paper mill water system

[摘要] English: Microbiological studies of wastewater treatment systems generally rely on methods that are dependent on the culturability of the microorganisms being investigated. However, it has recently been estimated that less than 1 % of all microorganisms are culturable on synthetic media and under artificial conditions. The numbers of microorganisms are, therefore, largely underestimated. Due to the limitation of the conventional microbiological methods, numerous alternative assays have been proposed. These assays include the analysis of the functional and structural diversities of microbial communities in situ. A study was, therefore, undertaken at the Sappi Cape Kraft paper mill, Milnerton, Cape Town, South Africa, to evaluate the applicability of these alternative monitoring techniques in industrial systems. Microbial contamination at the plant are substantially enhanced due to the reuse of water and the use of recycled fibre for the production of fluting and linerboard. The influence of the production of various paper grades, biocide application and monthly shuts on the functional diversity of the microbial communities within the water system was determined. Results obtained during this study indicated that different microbial communities developed during the production of the different paper grades. A difference in the functional diversity of the planktonic and the sessile communities was evident after a change in the production grade. The shift in the functional diversity of the microbial community present in the planktonic phase was evident almost immediately upon a change in the board grade. Although a shift in the functional diversity of the microbial community within the sessile phase was also evident, the response was significantly delayed. The effect of different biocide dosages was also monitored in the planktonic and the sessile phases. No clear trends concerning the period of time after a shutdown could be observed in the planktonic phase, although a change could be observed in the sessile phase. It was concluded that the analysis of the functional diversity was sensitive enough to detect shifts in the community and to differentiate between microbial communities within the same system. The shifts could be ascribed to changes in the operational parameters in the water system. The influence of the process parameters on the structural diversity of the microbial community was also determined using signature lipid biomarkers. The ratio of diglyceride fatty acids to phospholipid fatty acids provided an estimate of the nonviable to viable microorganisms in the water system. A high biomass mortality was generally observed throughout the one year period of evaluation. The high ratios of trans to cis C18:1 obtained during this study were also indicative of stressed microbial communities. Based on the presence of signature lipid biomarkers, it was concluded that a large diversity of microorganisms was present in both the sessile and planktonic phases. The same trends in the number of cultured cells and the counts obtained with PLFA analysis were observed in all samples. Differences in the abundance and groups of specific fatty acids were detected due to the production of different board grades. These results confirmed the shift in the microbial community, as was detected on the basis of substrate utilisation profiles. Based on the results obtained during this study, it is evident that the application of signature lipid biomarkers provided substantially more information on the microbial communities than conventional culturing. Due to these positive results, the new techniques were applied to characterise the functional and structural diversities of the microbial communities during two microbial audits at the Sappi Cape Kraft paper mill. The first audit was performed to assess the efficiency of the current microbiological control programme at the mill and to make recommendations for the improvement of the microbial control. The second audit was performed to evaluate the effect of subsequent changes made to the microbial control programme. Due to the indication that resistance to the current biocides had developed, alternative biocides were recommended for future use in the system. A large diversity of microorganisms was detected in the various unit operations using phospholipid fatty analysis. Cluster analysis of the functional diversity of the various microbial communities indicated that groups of unit operations could be closed using separate biocide dosage programmes. It may thus be concluded that the application of these alternative techniques provided substantial information concerning the microbial function and structure in situ. This information assisted in the implementation of an alternative microbiological control programme at the paper mill, which resulted in a significant reduction in the microbiological associated problems.

[发布机构] University of the Free State