BRIDGE Projects

Principal Investigator

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Team Members - CEB

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Fellowship Members - CEB

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Abstract

Most wastewater treatment plants (WWTP) in the world went, go or will go through the well-known phenomenon of filamentous bulking, that is, the failing of the sedimentation and of the thickening processes due to the overgrowth of filamentous. Excessive growth of certain filamentous bacteria can also lead to the formation of scums, known as foaming. The two phenomena are the most common referred causes of malfunctioning of activated-sludge WWTP and have attracted increasing attention of the scientific community. The identification of the causing agent of such problems is crucial to determine its problem: by acting upon the factor favoring the problematic species, one can expect to control its overgrowth. On the other hand, knowing the causes of the occurring filamentous overgrowth does not ensure the success of the operation. Several cases of bulking and foaming were studied along the 2-year sampling of the PROTOFILWW (PTDC/AMB/68393/2006) project and the causes identified. Yet, in several cases, there was no possibility of changing the conditions of the respective WWTP, often by economical or logistic constraints. So, despite the merit of the ethical solutions, that is, “acting upon the causes”, these cannot always be implemented. Other control measures urge. Even if not for universal application, the knowledge of the potential of other solutions can be of high prospective to potentially prevent pollution of natural resources. This approach can be of particular interest in the cases where filamentous overgrowth has been long neglected conducting to the existence of almost pure cultures of a filamentous bacterial strain in the aeration tank of activated-sludge. In these cases, changes of operational conditions will not alter the situation. The use of agents to directly control the growth of specific bacteria has always attracted attention, from medicine to bioremediation, from the production of energy and bioactive compounds to the control of diseases in food. However, bacteria resistant to most or all available antibiotics are rapidly emerging and spreading throughout the world. The excessive use of antibiotics in agrofood and in animal husbandry contributed to the occurrence and maintenance of antibiotic resistant pathogens, until reaching the WWTP and after them, the natural environments. Due to the increased resistance of microorganisms to chemical antimicrobials, the in-use concentrations of disinfectants are raising, leading to the augment of disinfectant residues on the wastewater systems. These residues can interfere with the microbial flora of WWTP by affecting the susceptible filamentous bacterial strains and selecting bacteria resistant to them. In fact, resistance will certainly increase as the drug persists, especially at low levels and for long periods of time. Few studies report the impact of chemical disinfectants in the performance of WWTP, a subject that this project intends to face. The study of the effect of quaternary ammonium compounds and aldehyde-based biocides (two primary antimicrobial chemical groups used in medicine and indoor biocides) on the filamentous populations of activated sludge can be of high interest and lead to potential measures to overcome specific problems in activated-sludge, caused by the overgrowth of specific bacterial populations, namely filamentous strains. On the other hand, knowing the effects of those compounds on the overall communities of such systems is of utmost interest to prevent the mortality of the essential depurating organisms. The use of bacteriophages has also great potential, but almost no investigation has been carried on the hypothesis of using bacteriophages to control the filamentous overgrowth in activated-sludge. Bacteriophages, or phages, were discovered almost 100 years ago by Twort in 1915 and independently by d’Herelle in 1917. There was great hope for their use in bacterial disease therapy, but the poor understanding of the heterogeneity and ecology of both phage and host bacteria led to a succession of badly designed and executed experiments and field trials. Nevertheless, phages have been used successfully as therapeutic agents in Eastern Europe and the former Soviet Union for many years.

Acknowledgements

Este trabalho é financiado por Fundos FEDER através do Programa Operacional Factores de Competitividade - COMPETE e por Fundos Nacionais através da FCT - Fundação para a Ciência e a Tecnologia.