Table 6.
Pros and cons of treatment methods.
| Treatment method | Advantages | Disadvantages |
|---|---|---|
| Chlorination | It is low in cost (Pillay and Olanirano, 2016; Anthony et al., 2020; Barbosa et al., 2021) | When E. coli is exposed to chlorine it induces a specific set of proteins, making them less susceptible to disinfection (Ateba et al., 2020) |
| Chlorine diffuses into the intracellular component of the cell causing impairment to the cell membrane and cytoplasm (Anthony et al., 2020) | It does not permanently damage ARB/ARG and it results in high regrowth of bacteria (Pillay and Olanirano, 2016; Anthony et al., 2020) | |
| EC | Eco-friendly and affordable (Crini and Lichtfouse, 2019; Chen et al., 2020a). | A higher current density would have to be applied for EC to achieve a higher removal efficiency of ARGs (Chen et al., 2020a). |
| pH control is not necessary (Crini and Lichtfouse, 2019) | Requires post-treatment to remove high concentrations of iron ions and the sludge treatment is costly (Crini and Lichtfouse, 2019) | |
| Membrane | It traps undissolved ARGs (Anthony et al., 2020) | There is minimal ARG removal when dissolved ARGs pass through the pores (Anthony et al., 2020) |
| Anaerobic membrane bioreactors (AnMBRs) do not require energy for aeration and they produce less solids than aerobic system (Kappell et al., 2018). | Ultrafiltration tends to be non-destructive in nature, resulting in the retentate water having higher concentrations of ARBs and ARG than the influent, resulting in fouling (Ebomah and Okoh, 2020; Wallmann et al., 2021) | |
| AnMBRs produce methane that could be recovered for energy (Kappell et al., 2018). | Removal efficiency of membrane systems depends on the shape of the ARB, i.e., round shaped ARBs will be efficiently retained while rod shaped ARBs will be unretained on the permeate (Anthony et al., 2020) | |
| No chemicals required (Crini and Lichtfouse, 2019) | Investment costs are often too high for small and medium industries. With high energy requirements, maintenance and operation costs (Crini and Lichtfouse, 2019) | |
| Limited flow rates (Crini and Lichtfouse, 2019) | ||
| Ozone | Gram negative bacteria are more susceptible to ozone (Anthony et al., 2020). | Gram-positive bacteria are less susceptible to ozone (Anthony et al., 2020). |
| It induces oxidative stress responses in surviving wastewater populations (Jager et al., 2018) | The reduction efficiency of oxidative treatments is different in different species because of the presence of anti-oxidative mechanisms in those species. The disinfection efficiency of ozone depends on the water quality, the contact time and the ozone concentration (Jager et al., 2018). | |
| The oxygen radicals interact with the cell surface (Ebomah and Okoh, 2020; Wallmann et al., 2021) | The oxygen radicals rarely oxidize the interior contents of the cells (Wallmann et al., 2021) | |
| Generation of ozone on-site (no storage-associated dangers) (Crini and Lichtfouse, 2019) | Short half-life (Crini and Lichtfouse, 2019) | |
| UV | UV inactivates ARGs by impairing the synthesis of RNA and DNA replication and leading to cell death (Barbosa et al., 2021) | UV tends to reduce the absolute abundance and increase the relative abundance of some ARGs and it also induces bacteria into VBNC state (Jia et al., 2021) |
| UV causes a selective change in the inhibition zone diameters of ARBs (Hasan Abusaiba and Al-Harmoosh, 2020; Wallmann et al., 2021) | tet genes are more resistant to UV treatment (Jager et al., 2018) | |
| UV light cannot interpenetrate wastewater that has high turbidity (Jager et al., 2018) |