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.