also be of relevance to overcome oxygen transfer limitation and enhance the removal
of pharmaceuticals. Results from a total of six publications, covering aerated variations of SF, HSSF and hybrid systems, showed that the removal of the compounds
diclofenac, ibuprofen, naproxen, caffeine, atenolol and metoprolol was favoured by
the higher availability of dissolved oxygen in aerated systems, thus pointing towards
the upregulation of aerobic biodegradation pathways [64, 66–70]. Acetaminophen is
normally easily biodegraded and no differences to non-aerated controls were
observed [70].
By now it is clear that removal efficiency depends on design, pointing towards the
need to better understand removal mechanisms and operational factors that condition
the removal.
3 Removal Mechanisms and Processes
3.1 Mechanisms and Processes Overview
Constructed wetlands are known for their complex ecosystem allowing for a multitude of biological and physicochemical processes. By selecting the most adequate
design (or combination of designs in case of hybrid systems) and operational
conditions, one has the possibility to shape the water treatment as a function of the
quality/strength of the incoming water to the CW. Therefore, the removal processes
in CWs are pollutant and design dependent.
The main removal processes in CWs are photodegradation, sedimentation, volatilization, sorption and biological degradation [29]. Nitrogen processes comprise
volatilization, ammonification, nitrification, nitrate-ammonification, denitrification,
fixation, plant/microbial uptake (assimilation), ammonia adsorption, organic nitrogen burial, anaerobic ammonia oxidation (anammox). Nevertheless, the major
processes just change nitrogen speciation, only few processes ultimately remove
total nitrogen from the wastewater [71]. Degradable carbon compounds are rapidly
utilized in wetland carbon processes. At the same time, a variety of wetland
decomposition processes produce carbon [29]. The assessment of organic carbon
removal, usually documented as COD and BOD, for conventional wastewater
treatment has been documented for 70 years [72]. When it comes to organic
chemicals (e.g. PCBs, PAHs, pesticides) studies only started in the early 2000s. A
comprehensive analysis of the removal processes of organic micropollutants was
prepared by Imfeld and Braeckevelt [73]. More recently, pharmaceuticals removal
processes have been discussed by several of the available review papers mentioned
in the previous section [27, 28, 50, 57, 60, 62]. Phosphorus transformations include
peat/soil accretion, adsorption/desorption, precipitation/dissolution, plant/microbial
uptake, fragmentation and leaching and mineralization and burial [71]. However,
removal of phosphorus in all types of CWs can be limited, sometimes requiring
additional measures, e.g. usage of special substrates or inclusion of a chemical
precipitation step. Regarding particles, normally assessed as total suspended solids
Constructed Wetlands and Phytoremediation as a Tool for Pharmaceutical Removal
395
of pharmaceuticals. Results from a total of six publications, covering aerated variations of SF, HSSF and hybrid systems, showed that the removal of the compounds
diclofenac, ibuprofen, naproxen, caffeine, atenolol and metoprolol was favoured by
the higher availability of dissolved oxygen in aerated systems, thus pointing towards
the upregulation of aerobic biodegradation pathways [64, 66–70]. Acetaminophen is
normally easily biodegraded and no differences to non-aerated controls were
observed [70].
By now it is clear that removal efficiency depends on design, pointing towards the
need to better understand removal mechanisms and operational factors that condition
the removal.
3 Removal Mechanisms and Processes
3.1 Mechanisms and Processes Overview
Constructed wetlands are known for their complex ecosystem allowing for a multitude of biological and physicochemical processes. By selecting the most adequate
design (or combination of designs in case of hybrid systems) and operational
conditions, one has the possibility to shape the water treatment as a function of the
quality/strength of the incoming water to the CW. Therefore, the removal processes
in CWs are pollutant and design dependent.
The main removal processes in CWs are photodegradation, sedimentation, volatilization, sorption and biological degradation [29]. Nitrogen processes comprise
volatilization, ammonification, nitrification, nitrate-ammonification, denitrification,
fixation, plant/microbial uptake (assimilation), ammonia adsorption, organic nitrogen burial, anaerobic ammonia oxidation (anammox). Nevertheless, the major
processes just change nitrogen speciation, only few processes ultimately remove
total nitrogen from the wastewater [71]. Degradable carbon compounds are rapidly
utilized in wetland carbon processes. At the same time, a variety of wetland
decomposition processes produce carbon [29]. The assessment of organic carbon
removal, usually documented as COD and BOD, for conventional wastewater
treatment has been documented for 70 years [72]. When it comes to organic
chemicals (e.g. PCBs, PAHs, pesticides) studies only started in the early 2000s. A
comprehensive analysis of the removal processes of organic micropollutants was
prepared by Imfeld and Braeckevelt [73]. More recently, pharmaceuticals removal
processes have been discussed by several of the available review papers mentioned
in the previous section [27, 28, 50, 57, 60, 62]. Phosphorus transformations include
peat/soil accretion, adsorption/desorption, precipitation/dissolution, plant/microbial
uptake, fragmentation and leaching and mineralization and burial [71]. However,
removal of phosphorus in all types of CWs can be limited, sometimes requiring
additional measures, e.g. usage of special substrates or inclusion of a chemical
precipitation step. Regarding particles, normally assessed as total suspended solids
Constructed Wetlands and Phytoremediation as a Tool for Pharmaceutical Removal
395