## 2 Pharmaceuticals and Personal Care Products (PPCPs) in the Ecosystems
### Combined Chemical Engineering-Biological Methods
#### 2.3.1 Bioreactors
* Photobioreactors  
Photosynthetic microorganisms, such as microalgae and cyanobacteria, can, simultaneously, remove nutrients and produce biomass from atmospheric CO\({}_{2}\) and solar radiation (photoautotrophic growth). However, some of these microorganisms are able to grow under mixotrophic condition by using organic compounds as a partial carbon source [298]. Therefore, microalgae photobioreactors have been described as an efficient tool for PPCPs and other emerging pollutants in wastewaters [299]. For large scale applications, continuous raceways (Figure 6) are the most viable types of photobioreactors for microalgae-based micropollutant removal due to their low cost and simple operation and maintenance [300; 301]. Raceways consist in shallow channels (approximately 0.30 m), equipped with paddle wheels to keep water flowing and avoid settling. Because of it their open design, the microbial community is usually a dynamic consortium, changing its microbial population along time. [302] measured the removal of 52 different pharmaceuticals by a mixed microalgae culture grown in a pond, initially inoculated with _Tetradesmus dimorplus_. Their results showed a large variability in removal efficiency, ranging from >90% for nine compounds to <10% for 18 compounds. Aeration time improves microalgae activity [303]. A raceway system where microalgae and bacterial species are grown symbiotically is usually referred to as high rate algal pond (HRAP). In these systems, the photosynthesis process developed by microalgae supply the oxygen that is required by aerobic bacteria that, in turn, can degrade the organic pollutants. Therefore, the costly aeration that is necessary to support aerobic growth can be avoided. The metabolites from bacterial degradation of the contaminants and growth promoters synthesized by bacteria, such as vitamin B\({}_{12}\) and indoleacetic acid, can act as promoters for the growth of algae. Algal exudates are the main carbon sources (carbohydrate, protein, and lipid) for bacteria. In addition, the cell surfaces of microalgae can provide a stable habitat for the bacteria [238]. Thereby, cyanobacterial/algal photosynthesis provides oxygen, a key electron acceptor to the pollutant-degrading heterotrophic bacteria. In turn, bacteria support photoautotrophic growth of the partners by providing carbon dioxide and other stimulatory means [304]. The synergistic relationship in _Chlorella_-bacterial microcosms, substantially improves the removal of aromatic pollutants [305]. Competitive interaction between algae and bacteria also exists, so it is substantial to increase the number of consortium studies, in order to select the most effective systems. An HRAP containing _Stigeoclonium_ sp., _Chlorella_ sp., _Monoraphidium_ sp. and diatoms as predominant species, showed a very high removal efficiency (>95%) for CFN, acetaminophen, IBU, methyl dihydroasmonate, hydrocinnamic acid and oxybenzene for a HRT of four days. When HRT increased to eight days, other pollutants, such as ketoprofen, 5-methyl benzotriazole, galaxolide and TCS were removed to an extent higher than 95% [103]. In the above study, other important pharmaceuticals reached lower degree of degradation: DFC (92%), NPX (89%) and CBZ (62%). Other results also showed that HRAP are efficient alternatives for the treatment of wastewaters containing emerging and PPCPs micropollutants. For example, high removal (98%) of anti-inflammatory drugs (IBU, paracetamol, salicylic acid, and CDN) and diuretics, such as hydrochloride(84%) and furosemide (100%). However, the removal degree for several antibiotics (azithromycin, ciprofloxacin, ofloxacin and erythromycincin) and anxiolytics (lorazepam) were <48% and <57%, respectively [250]. Tetracycline can also be removed (>99%) from real wastewaters by HRAP operating at seven days of HRT under summer conditions [106].