Freeze concentration, a nature-inspired water treatment technology, also referred to as freeze desalination or cryopurification, is a promising technology for treating contaminated water (Yin et al. 2017; Najim 2022). The process relies on the principle that the structure of ice crystal does not accommodate impurities/salts meaning that they are rejected by the growing ice as water freezes (Shonet 1987). The ice produced through cryopurification is separated from the concentrated solution and then melted to obtain pure water (Najim 2022). The application of cryopurification has several benefits over other common contaminated water treatment and desalination methods (Najim and Krishnan 2023). The energy consumption comparison between cryopurification and conventional evaporative technology showed that cryopurification is energetically more favourable by about 70%, which can be even higher in northern climates. For industrial applications of cryopurification at or near the polar regions, a natural weather advantage is in effect (Najim and Krishnan 2022; Xu et al. 2022; Najim 2022). Most importantly, little to no chemicals are involved in the process of water treatment by freezing and the cost is 2–10 times lower than other methods such as reverse osmosis, evaporative methods, nanofiltration, and distillation according to available literature data (Youssef et al. 2014; Xu et al. 2022).
It was reported based on laboratory tests and field data that freezing technology Is capable of effectively removing several impurities from wastewater and mine-impacted water including metals and heavy metals, such as nickel, cobalt, manganese, chromium, and others (Hasan and Louhi-Kultanen 2016; Melak et al. 2016; Wijewardena 2018; Popugaeva et al. 2021, 2023; Tongshuai et al. 2022). Among cryopurification cons there is a concentrated solution (brine), a by-product of the cryopurification process, that could harm the environment due to its high contaminant concentration. As an alternative to brine disposal, brine treatment promotes the reduction of pollution, minimization of waste volume, and production of freshwater with high recovery rates. Cryopurification could be combined with other water purification methods, for example, with membrane distillation. Such hybridization (integration of cryopurification with other water treatment methods) has the potential to make cryopurification more beneficial compared to the separate design. In addition, the process can also be integrated with biochemical processes such as microbial fuel cell (MFC). MFC is a process that uses bio-electrochemical processes for voltage generation and shows a potential for heavy metal remediation. The system uses organic substrates and the microorganism’s catalytic activity to generate electricity (Dutta and Kundu 2018). Single-chamber and dual-chamber MFCs are the main configurations of MFCs. The first one is also known as air cathode MFC and is composed of one chamber for microbial degradation and one cathode exposed to air. The second type has two chambers, the anode processes the organic matter, and the cathode is exposed to catholyte solutions such as potassium ferricyanide, and they are separated by a proton exchange membrane (Logan 2008; Munoz-Cupa et al. 2021; Obileke et al. 2021). Single-chamber MFC is a configuration that has been utilized for cadmium, chromium, zinc, and copper removal from mining wastewater. (Abourached et al. 2014; Wang et al. 2016; Peng et al. 2017; Vélez-Pérez et al. 2020; Xie et al. 2020). Moreover, dual-chamber MFC has been used for recovery of cadmium, copper, and vanadium (Aiyer 2020), also, zinc was treated in the cathode chamber (Fradler et al. 2014). Additionally, inorganic sulfur compounds in mining wastewater have been investigated for electricity generation using MFC technology (Sulonen et al. 2014; Ni et al. 2016). Furthermore, mining wastewater has been treated by dual-chamber MFC using catholyte reduction in the cathode chamber with different mixtures of microbial cultures in the anode chamber (Ai et al. 2020; Alexandre et al. 2022). However, these processes emphasize in the treatment of organic and sulfur compounds in the wastewater from the mining industry.
In addition, bacterial cultures for metal remediation have been found in the Yukon Territory. Some of these micro-organisms are anaerobic that interact in the metal fixation in soils from Zn-Pb deposits (Gadd et al. 2017; Nielsen et al. 2019). The main cultures used and found in the northern territories are composed of sulfate reduction bacteria. These types of bacteria are composed of different cultures such as Acidithiobacillus ferrooxidans, Pseudomonas putida, Bacillus subtilis, and Desulfovibrio desulfuricans that can be used for the removal of different metals such as iron and chromium (Dixit et al. 2015; Makhalanyane et al. 2016). Other microorganisms with metal reduction characteristics have been investigated such as Geobacter and Shewanella oneidensis is a gram-negative bacterium, that uses extra cellular electron transport (EET) for metal removal and bioelectrochemical processes such as MFC. Additionally, S. oneidensis is a facultative bacterium that can grow under aerobic and anaerobic conditions. This characteristic facilitates the application of the bacterium with different environmental conditions (Min et al. 2017; Yin et al. 2022).
In this work, Faro Mine’s water was used as a feed solution to test a novel approach of mine-impacted water treatment: cryopurification in combination with the MFC process towards zinc removal. With a critical analysis of studies performed before, the green water treatment approach could offer significant advantages over conventional treatment approaches including energy efficiency, no chemical pre-treatment, and zero waste generation (i.e. brine). Notably, this approach could be especially beneficial in northern climates due to natural cold temperature conditions promoting cryopurification. The Faro Mine’s water has elevated zinc concentrations that are up to almost 25–30 times above the effluent quality standard of 0.5 mg/L (The Government of Canada 2022). Taking this into the account, the objectives of this research work are: (i) to remove zinc from the Faro Mine water in a set of laboratory experiments on cryopurification below or close to the effluent quality standard and (ii) to eliminate the waste product of cryopurification experiments (i.e. brine) by treating brine solution using the MFC process. It is anticipated that this approach could be a sustainable water treatment solution at the Faro Mine site or other mine or industrial sites in Canada’s North.