When we hear this word we are probably reminded of car and industry emissions, petrol leakages or toxic waste in rivers. These terms are wide and may refer to many substances that are a threat to our health or the environment. A variety of classifications apply to pollutants; they may refer to toxicity, concentration or even source and fate in the environment.
Recently there has been a growing interest in “contaminants of emerging concern” or “emerging contaminants“. In this wide group we include substances we still don’t know much about or substances which are not monitored in the environment. This usually happens because said substance has been recently synthesized or maybe there were no analytic tools in the past that allowed their detection in really low concentrations.
Don’t you think we are talking about substances unknown to the general public!
Examples of emerging contaminants are:
- Pharmaceuticals (antibiotics, analgesics, anti-inflammatories, psychiatric drugs…)
- Personal care products (UV protection products, fragrances…)
- Tensioactives (detergents, emulsifiers…)
- Nitrosamines (present in cosmetics, tobacco, and elastic products as condoms and balloons)
- Flame retardants (used to prevent combustion or spread of flames)
- Fuel additives, plastifiers…
These pollutants are found persistently in our wastewater and the problematic lies in the inability of typical wastewater treatment plants to handle their removal. While we await for the European regulation (currently ongoing preparation), many countries have drafted their own criteria and researchers have been working in new solutions.
What are microbes to do with this issue?
Good question. There are chemo-physical treatment systems (tertiary treatments) able to eliminate most of the emerging contaminants from water at elevated energy costs. However, the use of biological systems promises an efficient and sustainable alternative to be applied in treatment plants. In this occasion we will briefly see some systems and in future publications we will dig deeper in what makes them work.
Microalgae in the treatment of urban wastewater have been studied for a while as alternative to activated sludges that are part of conventional treatments. Aside from consuming organic matter and inorganic pollutants, some microalgae can be used to degrade emerging pollutants such as hormones present in contraceptive pills (present in wastewater after human excretion).
Fungi in the treatment of hospital wastewater are being studied nowadays, after proving useful in the treatment of urgan wastewater. Hospital wastewater has higher concentration of pollutants and fungi are able to degrade some of them through their enzymes and specialized metabolism. As a curiosity, white rot fungi found growing on decaying wood are the best candidates for this job!
Bacteria are found everywhere generally in higher amounts than microalgae and fungi. Their diverse metabolisms are most useful when used in combination with microalgae and fungi. As wastewater is a great source of diverse bacteria, sometimes researchers just need to stimulate the growth of specific families in the bioreactors. In other cases, specific strains can be employed to degrade compounds of interest.
Pollutants can be either 1) degraded or just 2) removed from the system of interest.
- The first option is the optimal. Unfortunately, finding species able to degrade each pollutant is not always possible. Bacteria, fungi and algae can degrade pollutants through detoxifying mechanisms but sometimes they can use them as food to obtain energy and carbon!
- Through mechanisms as adsorption and absorption (that capture substances at the outer or inner part of the cell) we can extract pollutants from water. Microalgae have been widely studied in this aspect but it is always required to establish a good residue management protocol, as the growing biomass will contain increasing amounts of pollutant.
Love and hate, two sides of the same coin.
We have hinted in many posts that microorganisms cannot be simply classified as “good” or “bad”. Again, we have another example; certain microbe that was correlated to antibiotic removal in a bioreactor was also causing oportunistic infections in the hospital! [ref 1, pag 101-103]