6.2.3 Clay Minerals Assisted Adsorption
Due to varying levels of nitrogen, magnesium, iron and other minerals, clay minerals, which are composed of hydrated aluminium phyllosilicates and cations like iron, magnesium, alkali, and alkaline earth metals, show different removal efficiencies (Shahid et al., 2021). Studies conducted by Paolo et al. (2012) and Zhao et al. (2012) have demonstrated that modifying their cation exchange capacity and specific surface area can enhance their efficiency. Maraschi et al. (2014) showed that modified zeolites are able to achieve up to 99% removal of fluoroquinolones from water. Natural clay has shown to remove ECs such as amoxicillin and trimethoprim. Additionally, enrofloxacin and fluoroquinolone were also removed using zeolites (Maraschi et al. 2014). Wu et al. (2012) and Wu et al. (2010) used montmorillonite to adsorb ciprofloxacin and found removal efficiencies of 35% and 100% under various conditions. Fischer et al. (2020) demonstrated effective adsorption of 21 different ECs on the surfaces of several zeolite-based adsorbents. Other studies reported high ciprofloxacin and ampicillin removal efficiencies using zeolite and alum-based adsorbents (Rahardjo et al., 2011; El-Shafey et al., 2012). Their low cost and abundance in nature make them a desirable option for large-scale water treatment.
6.2.4 Hydrothermal carbonization (HTC) of biomass
Hydrothermal carbonisation (HTC) is a thermochemical conversion process without redrying, converting wet biomass into hydrochar, a solid material rich in carbon rich (Babeker & Chen, 2021). This process reduces the oxygen and hydrogen content of the biomass while doing so in an aqueous environment at 180–250 °C under autogenous pressure (Wang et al., 2018). Hydrochar gained attention because of its potential as a precursor for activated carbon, which is widely used in wastewater management, soil remediation, and as fuel. In addition to the commonly used lignocellulose biomass, HTC can be applied to an array of derived waste, such as solid municipal waste, algae, and sewage sludge (Kambo & Dutta, 2015). The degree of coalification and reaction severity of the raw biomass are controlled by hydrothermal parameters, notably temperature and residence time (Wiedner et al., 2013). According to Azzaz et al. (2020), the oxygen functional groups in hydrochar react with organic molecules and heavy metals. Ma et al. (2021) demonstrated hydrochar had an adsorption amount of 145 mg/g for tetracycline and 74.2 mg/g for ciprofloxacin. In order to remove tetracycline, copper, and Zinc, Deng et al. (2020) produced hydrochar which demonstrated adsorption amounts of 361.7, 214.7, and 227.3 mg/g, respectively. In a recent study, Qin et al. (2023) reported PO₄³⁻ modified hydrochar had an adsorption capacity of 119.61 mg/g for lead and 98.38 mg/g for ciprofloxacin. Based on the feed stock, pyrolysis and carbonisation parameters, as well as activation/modification methods, hydrochar’s phosphate adsorption capacities range from 14 to 386 mg g−1 (Shyam et al., 2022). A recent review (Jalilian et al., 2024) goes into further detail about the application hydrochar and modified hydrochar in treating wastewater, CO2adsorption, removing pharmaceuticals, heavy metals, and organic dyes (both cationic and anionic). The biggest advantage of HTC is the conservation of energy that would have been spend in predrying, as well as the utilization of organic waste to produce hydrochar which is useful for bioremediation.