Physiological and biochemical evaluation of pure cultures of problematic filamentous bacteria isolated from activated sludge

Abstract

Since the development of the activated sludge process, bulking and foaming have been a major problem affecting treatment efficiency. Filamentous bacteria have long been known to be the primary cause of bulking and foaming problems in activated sludge wastewater treatment systems. Attempts to cure filamentous bulking and foaming have thus far not shown great success in effective long-term control measures due to a lack of understanding of these organisms. Chemical methods such as chlorination and the use of hydrogen peroxide are still used to cure bulking but are only effective as interim measures. This could be due to the main factors stimulating filamentous bacterial growth not being changed by these methods for curing bulking and also, a lack of in-depth understanding of filamentous bacteria by scientists. It is therefore important to gain a proper understanding of these bacteria on the basis of their physiological, biochemical and growth characteristics. For all this to be successfully attained, filamentous bacteria need to be studied in pure culture so as to facilitate a better understanding of bulking and foaming and the control thereof during wastewater treatment. The aim of this study was therefore, to isolate and cultivate problematic filamentous bacteria and determine the physiological, biochemical and morphological traits of these organisms in pure culture, with the purpose of being able to integrate these findings to in situ analysis. Using four different isolation techniques, a total of 14 isolates from 7 different wastewater systems were obtained and evaluated for a range of physical, chemical, redox and substrate conditions. Results of the study indicate that filamentous survival and proliferation in BNR systems is largely due to varied phosphate uptake capacities and widespread ability to denitrify both nitrate and nitrite. Lipid hydrolysis is also a major component of filamentous bacterial metabolism with hydrolysis of other large compounds, as revealed by Biolog, such as starch, dextrin, proteins/peptides, Tween 40, Tween 80 and nucleosides indicating an affinity for larger slowly biodegradable substrates. They also strive on a variety of amino acids and sugars. The results obtained in this study revealed that filamentous bacteria are more diverse and complex in their biochemistry and physiology hence the difficulty in achieving long- term optimal control of filamentous bulking in activated sludge. It was concluded that filamentous bacteria have the ability to survive during times of starvation where growth factors are limiting and, this may be attributed to their ability to store storage compounds such as PHB, glycogen and polyP. The filaments' ability to store storage compounds and denitrify, suggests that they may in fact play significant roles in denitrification and EBPR. It is also concluded from this study that the filamentous bacteria under study are sensitive to aromatic compounds and that they have an affinity for slowly biodegradable polymers such as lipids, nucleosides, proteins/ peptides, dextrin and starch. Also concluded is that, the use of Biolog for biochemical profiling! fingerprinting of filamentous bacteria is useful, however, due to the possibility that some organisms may in fact, not grow and! or may give negative results on some and! or all substrates, other strategies. for biochemical profiling be established and used in this regard. Identification and evaluation of filamentous bacteria based on morphological traits is limiting and requires development and optimization of in situ techniques, such as DNAIRNA based probes and micro autoradiography. Bulking and BNR are elaborate and still not fully understood. The filaments' ability to take up phosphates and denitrify means that an advanced understanding of the roles they play in BNR systems and AA- bulking (Anoxic- Aerobic) is still required. Physiological and biochemical fingerprinting of pure cultures of filamentous bacteria is an important basis to understanding these organisms, and establishing potential bulking and foaming criteria for in situ evaluation and verification. It is from a study such as this that the main goal of curing bulking and gaining an enhanced understanding of BNR may be achieved.