## 3 Results and Discussion
### Concentration and Removal of PhACs and Antibiotics in Assamra WWTP  
A total of 15 PhACs (excluding antibiotics) and one stimulant were detected in influent and effluent of Assamra WWTP. The combined concentration of PhACs (excluding antibiotics and caffeine; \(\sum\)PhACs) was 20,668-31,485 ng L\({}^{-1}\) in the influent and 4032-4394 ng L\({}^{-1}\) in the effluent, showing a significant reduction effect of treatment in Assamra WWTP (Figure 2, Table S4 in SI). The influent contained high levels of caffeine (27,737-53,223 ng L\({}^{-1}\)), but these were reduced effectively in Assamra WWTP, resulting in a concentration of 64-273 ng L\({}^{-1}\) in the effluent. Caffeine is highly biodegradable and can be used as an indicator of residual bioactivity [40]. The dominant PhACs in influent were paracetamol (anti-inflammatory; 14,891-24,309 ng L\({}^{-1}\)) which comprised 74% of \(\sum\)PhACs, carbamazepine (anti-epileptic; 2365-3020 ng L\({}^{-1}\)), which comprised 11% of \(\sum\)PhACs, atenol (beta-blocker; 1723-1952 ng L\({}^{-1}\)), which comprised 7% of \(\sum\)PhACs, and metformin (anti-diabetic), which comprised 4% of \(\sum\)PhACs. In the effluent, carbamazepine was the dominant PhAC (3138-3352 ng L\({}^{-1}\)), comprising 78% of \(\sum\)PhACs, followed by metoprolol (beta-blocker; 10% of \(\sum\)PhACs). The removal rate of the dominant substances during WWTP treatment was: 99% for paracetamol, \(-\)22% for carbamazepine, 95% for atenol, and 97% metformin (Figure 3). Poor removal has been reported previously for carbamazepine and hydrochloride in WWTPs in Spain [41]. [PERSON] et al. also reported poor removal of carbamazepine in WWTPs in Canada [42]. Other studies investigating the removal of PhACs in middle-income countries (e.g., Jordan) report low removal efficiencies (<50%) for a number of PhACs, including carbamazepine [30]. Bisoprolol (beta-blocker) was present in higher effluent concentrations than influent (10-fold increase). Beta-blocker i.e bisoprolol is generally difficult to remove from wastewater [43]. The overall removal rate in Assamra WWTP was 81%-87% for \(\sum\)PhACs and 99% for caffeine. The concentrations of all measured substances are shown in Table S4. In a previous study, [PERSON] et al. [30] found that carbamazepine concentration was high in Assamra WWTP influent (1100 ng L\({}^{-1}\)) and effluent (850 ng L\({}^{-1}\)), resulting in low removal of the substance (23%). That study also reported a high occurrence of caffeine (156,000 ng L\({}^{-1}\)) and its metabolite (1,7-dimethylxanthine; 10,500 ng L\({}^{-1}\)) in influent, but high removal in Assamra WWTP plant (>99%), and very high concentrations (36,700 ng L\({}^{-1}\)) of paracetamol in influent, but efficient removal in the WWTP (99%). The results in the present study confirm these findings of [PERSON] et al. [30]. Of the 18 antibiotics targeted in the analysis, only five substances were detected in the influent and six in the effluent of Assamra WWTP. These were clarithromycin, erythromycin, ofloxacin, metronidazoleazole, and sulfamethoxazole in the influent, and these five plus ciprofloxacin in the effluent (Figure 4). Ofloxacin (fluorquinolones class) showed the highest concentration in wastewater effluent, followed by erythromycin (macrolides class) and metronidazoleazole (antiprotozoan class) (Figure 4, Table S5 in SI). None of the target substances in the penicillin class (amoxicillin, ampicillin, benzylpenicillin) was detected in the influent or effluent samples. This result is surprising since [PERSON] et al. [2] reported  
Figure 3: Efficiency (%) of Assamra wastewater treatment plant in removing pharmaceutically active compounds (PhACs, excluding antibiotics) from the wastewater. S1, S2 = parallel samples.