Risks of Perfluoroalkyl and Polyfluoroalkyl substances (PFAS) for sustainable water recycling via aquifers

The prediction of the fate of perfluoroalkyl and polyfluoroalkyl substances (PFAS) in water recycling with urban stormwater and treated wastewater is important since PFAS are widely used, persistent, and have potential impacts on human health and the environment. These alternative water sources have been utilized for water recycling via aquifers or managed aquifer recharge (MAR). However, the fate of these chemicals in MAR schemes and the potential impact in terms of regulation have not been studied. PFAS can potentially be transported long distances in the subsurface during MAR. This article reviews the potential risks to MAR systems using recycled water and urban stormwater. To date, there are insufficient data to determine if PFAS can be degraded by natural processes or retained in the aquifer and become suitable pre-treatment or post-treatment technologies that will need to be employed depending upon the end use of the recovered water. The use of engineered pre-treatment or post-treatment methods needs to be based on a ‘fit for purpose’ principle and carefully integrated with the proposed water end use to ensure that human and environmental health risks are appropriately managed

Recovery of metals from waste lithium ion battery leachates using biogenic hydrogen sulfide

Lithium ion battery (LIB) waste is increasing globally and contains an abundance of valuable metals that can be recovered for re-use. This study aimed to evaluate the recovery of metals from LIB waste leachate using hydrogen sulfide generated by a consortium of sulfate-reducing bacteria (SRB) in a lactate-fed fluidised bed reactor (FBR). The microbial community analysis showed Desulfovibrio as the most abundant genus in a dynamic and diverse bioreactor consortium. During periods of biogenic hydrogen sulfide production, the average dissolved sulfide concentration was 507 mg L−1 and the average volumetric sulfate reduction rate was 278 mg L−1 d−1. Over 99% precipitation efficiency was achieved for Al, Ni, Co, and Cu using biogenic sulfide and NaOH, accounting for 96% of the metal value contained in the LIB waste leachate. The purity indices of the precipitates were highest for Co, being above 0.7 for the precipitate at pH 10. However, the process was not selective for individual metals due to simultaneous precipitation and the complexity of the metal content of the LIB waste. Overall, the process facilitated the production of high value mixed metal precipitates, which could be purified further or used as feedstock for other processes, such as the production of steel

Recent progress in biohydrometallurgy and microbial characterisation

Since the discovery of microbiological metal dissolution, numerous biohydrometallurgical approaches have been developed to use microbially assisted aqueous extractive metallurgy for the recovery of metals from ores, concentrates, and recycled or residual materials. Biohydrometallurgy has helped to alleviate the challenges related to continually declining ore grades by transforming uneconomic ore resources to reserves. Engineering techniques used for biohydrometallurgy span from above ground reactor, vat, pond, heap and dump leaching to underground in situ leaching. Traditionally biohydrometallurgy has been applied to the bioleaching of base metals and uranium from sulfides and biooxidation of sulfidic refractory gold ores and concentrates before cyanidation. More recently the interest in using bioleaching for oxide ore and waste processing, as well as extracting other commodities such as rare earth elements has been growing. Bioprospecting, adaptation, engineering and storing of microorganisms has increased the availability of suitable biocatalysts for biohydrometallurgical applications. Moreover, the advancement of microbial characterisation methods has increased the understanding of microbial communities and their capabilities in the processes. This paper reviews recent progress in biohydrometallurgy and microbial characterisatio

Ammonia recycling enables sustainable operation of bioelectrochemical systems

Ammonium (NH4+) migration across a cation exchange membrane is commonly observed during the operation of bioelectrochemical systems (BES). This often leads to anolyte acidification (pH 10) from the cathodic headspace to the acidified anolyte. Results indicated that current (110mA or 688Am-3 net anodic chamber volume) was sustained as long as the NH3 recycling path was enabled, facilitating continuous anolyte neutralization with the recycled NH3. Since the microbial current enabled NH4+ migration against a strong concentration gradient (~10-fold), a novel way of ammonia recovery from wastewaters could be envisaged

Integrating Microbial Electrochemical Technologies With Anaerobic Digestion for Waste Treatment

Microbial electrochemical technologies, or bioelectrochemical systems (BES), represent an emerging environmental technology capable of converting waste streams into valuable products by harnessing part of the residual energy content within the waste streams. The main feature of this technology lies in the use of solid-state electrodes to induce and control the microbial metabolism. It has been increasingly embraced as a versatile technology compatible with other established technologies for novel industrial and environmentally beneficial or sanitary applications. This chapter reviews and discusses various options for the integration of BES with anaerobic digestion (AD)—an established organic waste treatment technology—to maximize overall treatment efficiencies and the bioenergy recovery potential from waste streams. The principles of and examples of how BES could be integrated with AD are outlined and discussed, and used to consolidate the merit of integrating BES with AD for organic waste treatment

A new method for ranking potential hazards and risks from wastes

A quantitative approach for assessing hazards facilitates decision making on hazardous waste management practices. In this study, a scoring approach was developed to evaluate the physical, human health, environmental and amenity hazard aspects and risks (in case of exposure) of waste streams. The approach was based on the 15 hazard properties (HPs) defined in European Commission Waste Framework Directive 2008/98/EC and their related Globally Harmonised System of Classification and Labelling of Chemicals (GHS) hazard statement codes (H-codes). Additionally, amenity and other hazards including space requirement, odour, dust, vermin, visual impact, radioactivity and physical injury were considered. A score of 0–3 was assigned to each of the H-codes or amenity and other hazards. The scoring approach consisted of: 1) determining the waste composition; 2) searching H-codes based on waste composition and assigning H-codes to the associated HPs; 3) calculating the hazard score for each of the four hazard aspects; and 4) calculating the total score for each waste. Two methods were used to calculate the total hazard score for 29 hazardous wastes. The wastes were ranked over a hazard spectrum to indicate the potential degree of hazard. The new hazard scoring approach can be used for prioritising efforts in managing wastes. Keywords: Hazard; Method; Risk; Scoring; Wast

Microbially catalysed selenate removal in an inverse fluidised bed reactor

Selenate removal from mine waters is required to mitigate human and environmental health impacts. In this study, the performance of an inverse fluidised bed reactor (IFBR) for the biological removal of selenate from synthetic mine water (pH 6.0-7.0) was evaluated. A laboratory-scale IFBR was set up with floating biomass carriers. Selenate reducers were enriched from environmental samples and anaerobic sludge. The synthetic medium contained ~10 mM (~1.4 g L-1) selenate, nutrients and 10 mM ethanol as electron donor. During stable performance the bioreactor achieved 94 % removal of selenate representing a removal rate of 251 mg L-1 d-1 at a hydraulic retention time of 5 d. Selenite concentration remained < 1 mg L-1 during stable performance, and the formation of a red precipitate indicated that selenate was reduced to elemental selenium. The biological selenate reduction generated alkalinity, increasing the wastewater pH from 6.0 to 8.6. The redox potential gradually approached a value ranging from -300 mV to -400 mV against standard hydrogen electrode. Overall, the results showed that the IFBR can be used for removing selenate and acidity from mine waters. Moreover, it has potential to facilitate recovery of elemental selenium. Therefore, the bioprocess provides an opportunity to reduce the costs and liabilities associated with selenium containing mine drainage and the associated environmental impacts

Ano-cathodophilic biofilm catalyzes both anodic carbon oxidation and cathodic denitrification

Biocathodic denitrification using bioelectrochemical systems (BES) have shown promise for both wastewater and groundwater treatment. Typically, these systems involve anodic carbon oxidation and cathodic denitrification catalyzed by two electroactive biofilms located separately at an anode and a cathode. However, process efficiencies are often limited by pH drifts in the respective electrode-biofilms: acidification (pH 8.5) in the biocathode. Here, we describe for the first time a single electroactive biofilm that acts as a bioanode and a biocathode, alternately catalyzing anodic acetate oxidation (Coulombic efficiency (CE) 85.3%) and cathodic denitrification (CE 87.3%) (−400 mV Ag/AgCl). Our results indicate that the ano-cathodophilic biofilm denitrified autotrophically using the electrode (−200 to −600 mV Ag/AgCl) as a direct electron donor. Further, the alkalinity produced from cathodic denitrification partially (19%) neutralized the acidity of the anodic reaction. Switching the electrode potential to temporarily favor either an anodic or cathodic reaction may represent a unique method for removing carbon and nitrate from contaminated liquors. This study offers new insights into the development of sustainable BES-based nutrient removal processes

Sequential in situ hydrotalcite precipitation and biological denitrification for the treatment of high-nitrate industrial effluent

A sequential process using hydrotalcite precipitation and biological denitrification was evaluated for the treatment of a magnesium nitrate (Mg(NO3)2)-rich effluent (17,000 mg NO3−-N/L, 13,100 mg Mg/L) generated from an industrial nickel-mining process. The hydrotalcite precipitation removed 41% of the nitrate (7000 mg NO3−-N/L) as an interlayer anion with an approximate formula of Mg5Al2(OH)14(NO3)2·6H2O. The resultant solute chemistry was a Na–NO3–Cl type with low trace element concentrations. The partially treated effluent was continuously fed (hydraulic retention time of 24 h) into a biological fluidised bed reactor (FBR) with sodium acetate as a carbon source for 33 days (1:1 v/v dilution). The FBR enabled >70% nitrate removal and a maximal NOx (nitrate + nitrite) removal rate of 97 mg NOx-N/L h under alkaline conditions (pH 9.3). Overall, this sequential process reduced the nitrate concentration of the industrial effluent by >90% and thus represents an efficient method to treat Mg(NO3)2-rich effluents on an industrial scale

E-waste recycling and resource recovery: A review on technologies, barriers and enablers with a focus on Oceania

Electronic e-waste (e-waste) is a growing problem worldwide. In 2019, total global production reached 53.6 million tons, and is estimated to increase to 74.7 million tons by 2030. This rapid increase is largely fuelled by higher consumption rates of electrical and electronic goods, shorter life cycles and fewer repair options. E-waste is classed as a hazardous substance, and if not collected and recycled properly, can have adverse environmental impacts. The recoverable material in e-waste represents significant economic value, with the total value of e-waste generated in 2019 estimated to be US $57 billion. Despite the inherent value of this waste, only 17.4% of e-waste was recycled globally in 2019, which highlights the need to establish proper recycling processes at a regional level. This review provides an overview of global e-waste production and current technologies for recycling e-waste and recovery of valuable material such as glass, plastic and metals. The paper also discusses the barriers and enablers influencing e-waste recycling with a specific focus on Oceania