PPCPs (Table 15.1). Among them, the antimicrobial TCS may be considered as a
hygienic PCP, whereas the other compounds represent PhACs (Hochstrat et al.
2015; Hofmann and Schlosser 2016). Another classification approach, which is
based on the biological effect mechanism of certain micropollutants, refers to the
compounds causing interferences with the endocrine system of vertebrates as endocrine disrupting chemicals (EDCs). Among the aforementioned micropollutants,
EE2, BPA, NP, and (possibly) also TCS exhibit endocrine activities, and, therefore,
they are also referred to as EDCs (Ahmed et al. 2017; Hofmann and Schlosser 2016;
Jahangiri et al. 2017; Table 15.1).
As a precondition for the function of any biological treatment technology, both
anthropogenic and naturally occurring chemicals can only be biologically degraded
under favorable conditions (Kolvenbach et al. 2014). New catabolic pathways,
which are directed against the existing chemicals and the new ones in order to
detoxify and/or utilize them as growth substrates, are known to be constantly
evolving especially in bacteria (Kolvenbach et al. 2014). However, typically very
low environmental concentrations of micropollutants make them only poor growth
substrates for microbes, which is not in favor of the evolution of productive
microbial degradation pathways typically found in bacteria (Harms et al. 2011;
Hochstrat et al. 2015). Moreover, too low concentrations of potentially toxic pollutants may not adversely affect organisms and thus might not drive the evolution of
degradative pathways aimed at detoxification (Kolvenbach et al. 2014). Furthermore, micropollutants usually occur in a mixture, whereas pollutant-degrading
microbes such as bacteria are often more or less compound-specific (Harms et al.
2011). Degradation rates of those polluting chemicals, which are susceptible to
potentially existing, sufficiently promiscuous enzymes, may remain infinitely low
at too low environmental concentrations (Kolvenbach et al. 2014). Depending on the
nature of a chemical, these obstacles may become even more complicated by
physicochemical constraints related to bioavailability and bioaccessibility
(Kolvenbach et al. 2014). Altogether, the aforementioned limitations largely contribute to the insufficient performance of conventional biological (waste)water
treatment technologies towards micropollutants.
Besides too low pollutant concentrations, also too high loads of toxic contaminants and/or other extreme conditions of waters represent a second group of scenarios that also may hamper or even stop the efficient treatment by conventional
biological technologies. The examples include acidic olive oil mill wastewaters
contaminated with recalcitrant and toxic phenolic and lipid compounds; and colored
and frequently alkaline effluents from the textile and dyestuff industries, which
contain highly concentrated mixtures of structurally diverse, recalcitrant, often
toxic, and sometimes potentially carcinogenic dyes and pigments together with
high loads of different inorganic additives. Furthermore, highly toxic molassesbased wastewaters polluted with melanoidin-type high molecular weight compounds. and toxic pulp and paper bleach plant effluents of the alkaline extraction
stage (containing phenolic wastes) and of chlorine-mediated bleaching processes
(polluted with various chloroaromatic and chloroaliphatic compounds, and further
colored substances) are also well-known to be inhibitory to conventional biological
340
D. Schlosser
hygienic PCP, whereas the other compounds represent PhACs (Hochstrat et al.
2015; Hofmann and Schlosser 2016). Another classification approach, which is
based on the biological effect mechanism of certain micropollutants, refers to the
compounds causing interferences with the endocrine system of vertebrates as endocrine disrupting chemicals (EDCs). Among the aforementioned micropollutants,
EE2, BPA, NP, and (possibly) also TCS exhibit endocrine activities, and, therefore,
they are also referred to as EDCs (Ahmed et al. 2017; Hofmann and Schlosser 2016;
Jahangiri et al. 2017; Table 15.1).
As a precondition for the function of any biological treatment technology, both
anthropogenic and naturally occurring chemicals can only be biologically degraded
under favorable conditions (Kolvenbach et al. 2014). New catabolic pathways,
which are directed against the existing chemicals and the new ones in order to
detoxify and/or utilize them as growth substrates, are known to be constantly
evolving especially in bacteria (Kolvenbach et al. 2014). However, typically very
low environmental concentrations of micropollutants make them only poor growth
substrates for microbes, which is not in favor of the evolution of productive
microbial degradation pathways typically found in bacteria (Harms et al. 2011;
Hochstrat et al. 2015). Moreover, too low concentrations of potentially toxic pollutants may not adversely affect organisms and thus might not drive the evolution of
degradative pathways aimed at detoxification (Kolvenbach et al. 2014). Furthermore, micropollutants usually occur in a mixture, whereas pollutant-degrading
microbes such as bacteria are often more or less compound-specific (Harms et al.
2011). Degradation rates of those polluting chemicals, which are susceptible to
potentially existing, sufficiently promiscuous enzymes, may remain infinitely low
at too low environmental concentrations (Kolvenbach et al. 2014). Depending on the
nature of a chemical, these obstacles may become even more complicated by
physicochemical constraints related to bioavailability and bioaccessibility
(Kolvenbach et al. 2014). Altogether, the aforementioned limitations largely contribute to the insufficient performance of conventional biological (waste)water
treatment technologies towards micropollutants.
Besides too low pollutant concentrations, also too high loads of toxic contaminants and/or other extreme conditions of waters represent a second group of scenarios that also may hamper or even stop the efficient treatment by conventional
biological technologies. The examples include acidic olive oil mill wastewaters
contaminated with recalcitrant and toxic phenolic and lipid compounds; and colored
and frequently alkaline effluents from the textile and dyestuff industries, which
contain highly concentrated mixtures of structurally diverse, recalcitrant, often
toxic, and sometimes potentially carcinogenic dyes and pigments together with
high loads of different inorganic additives. Furthermore, highly toxic molassesbased wastewaters polluted with melanoidin-type high molecular weight compounds. and toxic pulp and paper bleach plant effluents of the alkaline extraction
stage (containing phenolic wastes) and of chlorine-mediated bleaching processes
(polluted with various chloroaromatic and chloroaliphatic compounds, and further
colored substances) are also well-known to be inhibitory to conventional biological
340
D. Schlosser