The low removal results of Nevirapine (Figure 3) could be attributed to its persistent nature (Wood et al. 2015). An in-vitro investigation of the removal rate of Nevirapine carried out by Vankova showed that Nevirapine has low biodegradability (up to 3%) in a closed bottle system (Vankova 2010). However, K'Oreje and co-workers have reported a much higher average removal percentage of 37% from a conventional aerobic wastewater treatment plant in Kenya (K'Oreje et al. 2016). Comparable results were also reported in South Africa by Abafe et al. (2018), who reported an average removal percentage of 32% from a municipal WWTP in the KwaZulu-Natal province. On the contrary, K'Oreje et al. (2016) also reported an increase in nevirapine concentrations at the outlet from another WWTP in Kenya (850 ng/L at the inlet and 1,000 ng/L at the outlet) and attributed this increase in concentration to the de-conjugation of the hydroxylated metabolites of nevirapine in the WWTP. Tenofovir was the second least biodegraded drug from the MBBR, with 74% removal efficiency (Figure 4). Like Nevirapine, Tenofovir has been reported to be persistent in the environment. Al-Rajab et al. (2010) in London have shown that Tenofovir is relatively persistent in soils with no evidence of transformation products. After introducing the drug to varying temperatures in treated soils (range 4 °C to 30 °C and autoclaved), mineralization in the soil increased with temperature and did not occur in autoclaved soil, suggesting a microbial-based degradation (Al-Rajab et al. 2010). Although this hypothetical finding addresses the compound's biodegradability by microorganisms, several studies have reported the detection of Tenofovir in WWTP effluents and surface waters, confirming the refractory nature of this drug (Schoeman et al. 2015; Wood et al. 2015; Mlunguza et al. 2019). Even though Nevirapine and Tenofovir were the least biodegradable antiretroviral drugs investigated in this study, the MBBR presents a promising alternative when compared to findings reported for conventional wastewater treatment plants (Table 2).

Table 2

Antiretroviral drug removal efficiency of different wastewater treatment plants

ARVCountryRemoval Percentage (%)References
Nevirapine South Africa 15 Schoeman et al. (2015)  
South Africa (Northern WWTP) 19 Abafe et al. (2018)  
South Africa (Decentralized) Abafe et al. (2018)  
South Africa (Phoenix) 32 Abafe et al. (2018)  
Kenya (Nyalenda) 37 K'Oreje et al. (2016)  
Kenya (Kisat) K'Oreje et al. (2016)  
Kenya (Dandora) −76 K'Oreje et al. (2016)  
MBBR 62 This study 
Efavirenz South Africa 27–71 Schoeman et al. (2015)  
South Africa (Decentralized) Abafe et al. (2018)  
South Africa (Nothern) −37 Abafe et al. (2018)  
South Africa (Phoenix) 41 Abafe et al. (2018)  
Kenya (Nyalenda) 67 K'Oreje et al. (2016)  
Kenya (Kisat) 89 K'Oreje et al. (2016)  
Kenya (Dandora) 87 K'Oreje et al. (2016)  
MBBR 94 This study 
Tenofovir MBBR 74 This study 
Ritonavir South Africa (Decentralized) 53 Abafe et al. (2018)  
South Africa (Northern WWTP) 43 Abafe et al. (2018)  
South Africa (Phoenix WWTP) 71 Abafe et al. (2018)  
MBBR 95 This study 
Emtricitabine MBBR  95 This study 
ARVCountryRemoval Percentage (%)References
Nevirapine South Africa 15 Schoeman et al. (2015)  
South Africa (Northern WWTP) 19 Abafe et al. (2018)  
South Africa (Decentralized) Abafe et al. (2018)  
South Africa (Phoenix) 32 Abafe et al. (2018)  
Kenya (Nyalenda) 37 K'Oreje et al. (2016)  
Kenya (Kisat) K'Oreje et al. (2016)  
Kenya (Dandora) −76 K'Oreje et al. (2016)  
MBBR 62 This study 
Efavirenz South Africa 27–71 Schoeman et al. (2015)  
South Africa (Decentralized) Abafe et al. (2018)  
South Africa (Nothern) −37 Abafe et al. (2018)  
South Africa (Phoenix) 41 Abafe et al. (2018)  
Kenya (Nyalenda) 67 K'Oreje et al. (2016)  
Kenya (Kisat) 89 K'Oreje et al. (2016)  
Kenya (Dandora) 87 K'Oreje et al. (2016)  
MBBR 94 This study 
Tenofovir MBBR 74 This study 
Ritonavir South Africa (Decentralized) 53 Abafe et al. (2018)  
South Africa (Northern WWTP) 43 Abafe et al. (2018)  
South Africa (Phoenix WWTP) 71 Abafe et al. (2018)  
MBBR 95 This study 
Emtricitabine MBBR  95 This study 

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