Search

Acid mine drainage (AMD) is a multi-factor pollution formed from complex chemical, physical, and biological interactions that takes place under ambient conditions in abandoned and active mines. Over the years, researchers have been investigating ways to mitigate its potential impact on the environment through various treatment technologies. The aim of this review was to critically analyze the broad spectrum of treatment methods that have been engaged in published literature on the remediation of AMDs. Adsorption treatment using zeolites, fly ash, biochar activated carbon, clay-based minerals and biomass-based adsorbents was discussed. Given an appropriate choice of adsorbent, ions in AMD can be reduced between 50% and 99%. Membrane separation processes like nanofiltration, reverse osmosis and hybrid systems were discovered to be more effective than adsorption and can effect over 90% rejection at optimized conditions. Biological processes showed a far wider range of performance amongst all treatment types due to the selectivity in performance of the different micro-organisms used although Advanced Oxidation Process (AOPs) have been shown to achieve>80% ions removal. In all biological processes studied ranging from wetlands to bioreactors, algal bioreactors seemed the most effective in this domain. Most of these treatment technologies are corrective while preventive techniques can be explored to prevent the production of AMD. Despite the positive outcomes of the different types of treatment, they have associated technical issues. It is recommended that more preventive techniques be explored to reduce the production of AMD. The review discussed how AMD treatment would affect environmental protection and water resource management.

Acetaminophen (ACT) is an effective and widely available analgesic and antipyretic used in medical practice. It can get into water from veterinary use, medical waste and pharmaceutical effluents. The aim of this review was to elaborate on the recent progress on ACT adsorption from water, present the findings in a structured written report and identify interesting new foundations for further work. ZnAl/biochar had the highest potential of removing ACT and can adsorb more than its weight of the pollutant ( q max > 1000 mg/g). The Langmuir and Freundlich isotherm models and the pseudo-second-order kinetics model were best-fits in most cases (usually at R2 > 0.99 threshold). It was observed that the key mechanisms of ACT uptake are π-π interactions, hydrogen bonds and electrostatic interaction. For most of the adsorbents, a >30% ACT removal efficiency was achievable after the 4 cycles. Effects as salting-out, electrostatic screening, and accumulation of moieties at sorbent-sorbate interfaces due to the competitive adsorption of ions and co-pollutants are profound in the uptake of ACT from aqueous solutions. Future perspectives were discussed in the area of process costing, adsorbent regeneration, mechanistic investigations and fixed-bed column adsorption.

The intensification of urbanisation and industrial activities significantly exacerbates the distribution of toxic contaminations into the aqueous environment. Persistent organic pollutants (POPs) have received considerable attention in the past few decades because of their persistence, long-distance migration, potential bioaccumulation, latent toxicity for humans and wildlife. There is no doubt that POPs cause serious effects on the global ecosystem. Therefore, it is necessary to develop a simple, safe and sustainable approach to remove POPs from water bodies. Among other conventional techniques, the adsorption process has proven to be a more effective method for eliminating POPs and to a larger extent meet discharge regulations. Nanomaterials can effectively adsorb POPs from aqueous solutions. For most POPs, a70% adsorptive removal efficiency was achieved. The major mechanisms for POPS uptake by nano-adsorbents includes electrostatic interaction, hydrophobic (van der Waals, π-π and electron donor-acceptor) interaction and hydrogen bonding. Nano-adsorbent can sustain a90% POPs adsorptive removal for about 3 cycles and reuseable for up to 10 cycles. Challenges around adsorbent ecotoxicity and safe disposal were also discussed. The present review evaluated recent research outcomes on nanomaterials that are employed to remove POPs in water systems.

Besides the techno-economic feasibility of the circular economy, the environmental sustainability of the value chain is a crucial issue in further development and commercialisation. One such process that is techno-economically feasible and eco-friendly is waste pyrolysis. The utilisation of its major product (pyrolysis oil) is however hindered due to low heating value, low chemical instability, high oxygenated compounds content, high water content and high sulphur content. Its positive influence of the circular economy initiative can be improved by reducing its sulphur content by regenerative desulphurisation. This study aimed to review the research efforts on the regenerative desulphurisation of pyrolysis oil. There are various approaches such as adsorptive desulphurisation, extractive desulphurisation, bio-desulphurisation, hydrodesulphurisation, oxidative desulphurisation and precipitative desulphurisation to diminish sulphur content in fuels. Looking at the percentage sulphur reduction, all techniques had wide variations based on the nature of the employed technique and the effect of the process factors. Desulphurisation of pyrolysis oil will reduce the dependence on fossil fuels as a major source of energy for transportation and industrialisation. It will lead to a rapid increase in plastics and municipal solid waste recycling. This is because higher pyrolysis oil usage will result in need for more wastes to be pyrolysed. The review recommends that improved government participation, industry partnership, improved waste collection systems and better data retrieval systems are new areas that can be focused on to help in the achievement of the circular economy initiative in this regard.