3.4.3 Wastewater Treatment Plant
Antibiotics have a main role in the environmental pollution through wastewater
treatment processes. Some of these pharmaceuticals may be eliminated from wastewater by adsorption onto solids; however, these can be released into the groundwater
by sludge application to land, landfill, or soil erosion, thus the removal of these
compounds are variable and depend mainly on the complexity of the environmental
matrices and the properties of individual compound, in terms of the ability of this
compound to be accumulated or degraded, and of the treatment unit in sludge
treatment plants (STPs), leading to removal of the individual drugs at any step of
treatment stages (Meakins et al. 1994; Diaz-Cruz et al. 2003). Several medicinal
compounds are degraded by biodegradation at both aerobic and anaerobic pathway,
in the presence of intra or/and extracellular enzymes excreted by bacterial cells
(Meakins et al. 1994). However, this process completely depends on the chemical
properties of these drugs. When a compound is composed of molecules with long,
highly branched side chain then biodegradation is not easy compared to those with
unbranched, short side chain. In addition, the biodegradation of aromatic and
saturated aliphatic compounds are less accessible than that of unsaturated and simple
aromatic compounds (Voulvoulis et al. 2016). For instance, in Germany, four
iodinated compounds (diatrizoate, iopamidol, iopromide, and iomeprol) were
detected in raw sewage as parent compounds, in aqueous phase, as these will not
be degraded or absorbed through the sewage treatment processes. The concentration
of these compounds is usually more than 1 μg L
À1 in raw sewage and final effluents,
except for iopamidol with concentration of 15 μg L
À1 (Voulvoulis et al. 2016). In
STP, the microbial community may adapt gradually to particular compounds like
clofibric acid, ibuprofen, and diclofenac and may degrade them efficiently over time;
however, clofibric acid shows more persistence and is highly mobile in sewage
treatment plant (Zwiener and Frimmel 2003). In conventional STPs, many factors
affect the removal of these compounds, i.e., sludge retention time (SRT), hydrolic
retention time (HRT), and temperature (Suarez et al. 2008).
In conventional wastewater treatment, after primary sedimentation, biological
treatment by activated sludge and trickling filters are used to eliminate drugs, similar
to that used to remove organic micropollutants by adsorption and biodegradation or
chemical degradation, and biotransformation. However, it was found that removal of
drugs by activated sludge is much greater than that of percolating filter, which is due
to the high efficient activity of bacteria in activated sludge. Nevertheless, WWTPs
are not fully designed to eliminate a very small amount of organic compounds;
therefore, activated sludge should have more attention for removal of biological
nutrients and pharmaceuticals.
Generally, the influent of contaminated water that enters the conventional municipal STPs undergoes three main treatment stages: preliminary, primary, and secondary steps; which then come out with final effluent that passes to the surface water
body to be reused indirectly for agricultural purposes; although some of chemical or
drug compounds usually exist at low concentrations ranging from 10
À3 to
3 Existence of Antibiotics in Wastewater as a Pollution Indicator
49
Antibiotics have a main role in the environmental pollution through wastewater
treatment processes. Some of these pharmaceuticals may be eliminated from wastewater by adsorption onto solids; however, these can be released into the groundwater
by sludge application to land, landfill, or soil erosion, thus the removal of these
compounds are variable and depend mainly on the complexity of the environmental
matrices and the properties of individual compound, in terms of the ability of this
compound to be accumulated or degraded, and of the treatment unit in sludge
treatment plants (STPs), leading to removal of the individual drugs at any step of
treatment stages (Meakins et al. 1994; Diaz-Cruz et al. 2003). Several medicinal
compounds are degraded by biodegradation at both aerobic and anaerobic pathway,
in the presence of intra or/and extracellular enzymes excreted by bacterial cells
(Meakins et al. 1994). However, this process completely depends on the chemical
properties of these drugs. When a compound is composed of molecules with long,
highly branched side chain then biodegradation is not easy compared to those with
unbranched, short side chain. In addition, the biodegradation of aromatic and
saturated aliphatic compounds are less accessible than that of unsaturated and simple
aromatic compounds (Voulvoulis et al. 2016). For instance, in Germany, four
iodinated compounds (diatrizoate, iopamidol, iopromide, and iomeprol) were
detected in raw sewage as parent compounds, in aqueous phase, as these will not
be degraded or absorbed through the sewage treatment processes. The concentration
of these compounds is usually more than 1 μg L
À1 in raw sewage and final effluents,
except for iopamidol with concentration of 15 μg L
À1 (Voulvoulis et al. 2016). In
STP, the microbial community may adapt gradually to particular compounds like
clofibric acid, ibuprofen, and diclofenac and may degrade them efficiently over time;
however, clofibric acid shows more persistence and is highly mobile in sewage
treatment plant (Zwiener and Frimmel 2003). In conventional STPs, many factors
affect the removal of these compounds, i.e., sludge retention time (SRT), hydrolic
retention time (HRT), and temperature (Suarez et al. 2008).
In conventional wastewater treatment, after primary sedimentation, biological
treatment by activated sludge and trickling filters are used to eliminate drugs, similar
to that used to remove organic micropollutants by adsorption and biodegradation or
chemical degradation, and biotransformation. However, it was found that removal of
drugs by activated sludge is much greater than that of percolating filter, which is due
to the high efficient activity of bacteria in activated sludge. Nevertheless, WWTPs
are not fully designed to eliminate a very small amount of organic compounds;
therefore, activated sludge should have more attention for removal of biological
nutrients and pharmaceuticals.
Generally, the influent of contaminated water that enters the conventional municipal STPs undergoes three main treatment stages: preliminary, primary, and secondary steps; which then come out with final effluent that passes to the surface water
body to be reused indirectly for agricultural purposes; although some of chemical or
drug compounds usually exist at low concentrations ranging from 10
À3 to
3 Existence of Antibiotics in Wastewater as a Pollution Indicator
49