As a result of the renewable nature of microalgae, combined with significant potential for application in various industries (such as bioenergy and nutrition), there is increasing interest in their commercial production. A key processing step is harvesting the microalgae and utilization of crossflow membrane technology is gaining interest. Published research shows biomass recoveries of 93%–100%, relatively low energy consumption, and the option to avoid chemical additives. This review discusses membrane harvesting performance, by examining the effect of microalgal physical characteristics, membrane and module types, and operational conditions. As membrane fouling is a major challenge to maintaining good performance, different strategies to control and mitigate fouling are also discussed.

The search for new and effective anticancer drugs from natural sources has been expanded beyond culture collections. It now includes the less explored eukaryotic and prokaryotic microalgae, bioprospected from both extreme and non-extreme freshwater environments. Microalgae exposed to abiotic stresses, found in a variety of ecosystems, have shown the ability to produce a series of unique metabolites, which help them adapt and survive. In particular, those found in extreme environments may be capable of producing metabolites that are novel and have potential cancer fighting properties. This review highlights current research into extracts and compounds from microalgae bioprospected from a range of freshwater environments, including extreme environments, and their potential in producing anticancer agents.

Microalgal genera Chlorella, Coccomyxa, Scenedesmus, and Dunaliella, bioprospected from freshwater or marine conditions have shown promising bioactivities. Some microalgae are adapted to thrive in extreme environments, including those with extreme salinity, pH, temperature, and/or heavy metals. Survival and growth under these conditions, as a characteristic of the natural environment or the result of anthropogenic impacts, has been associated with exaggerated production of protective bioactive secondary metabolites. Such microalgal metabolites have been associated with antimicrobial activity including antibacterial, antifungal, and antiviral. Extremophilic microalgae and the bioactive secondary metabolites produced from cultivation in extreme environments are not widely reviewed. The production of bioactive antimicrobial compounds in extremophilic microalgae due to exposure to a range of environmental stresses is reviewed.

Microalgae are a source of a range of natural products, including biofuels, but financial and technical limitations can make large-scale production challenging to commercialize. A significant limitation is the practical and economical bulk harvesting of microalgae from the cultivation medium. Based on chemical and energy demands, common harvesting processes can have high costs due to microalgae having a similar specific gravity as their medium, negative surface charges and significant variability between strains.Determining the cost-effectiveness of harvesting methods is complicated as many publications commonly quote harvesting as costing 20-30 % of the operational cost, regardless of the method of biomass production (e. g., open ponds, bioreactors, etc.) or the harvesting method selected. This non-specific statement does not reflect that specific harvesting methods will have different operational costs. This paper aims to provide a more accurate, method-specific cost analysis of the harvesting stage operating costs to help in the economic analysis of microalgae production systems. The four primary harvesting mechanisms currently used, centrifugation, flocculation, flotation, and filtration, are assessed for their energy and chemical consumption. Centrifugation, flocculation, flotation, and filtration had an average biomass recovery of 92 %, 95 %, 92 % and 91 % and an energy requirement range of 1-8 kWh m- 3, 0.1-6.7 kWh m- 3, 0.015-7.6 kWh m- 3 and 0.1-5.9 kWh m- 3, respectively. Furthermore, the operational costs, based on energy requirements and the use of flocculants, were 0.448-1.086 USD m- 3, 0.014-16.65 USD m- 3, 0.08-31.3 USD m- 3 and 0.013-0.791 USD m- 3, respectively. Finally, the biomass production costs were calculated as ranging between 0.02-0.177 USD kg-1, 0.006-35.05 USD kg 1, 0.169-26.95 USD kg- 1 and 0.02-3.00 USD kg- 1 for centrifugation, flocculation, flotation, and filtration microalgae harvesting technologies, respectively.

Oil crops account for approximately 23% of the world’s crop lands and are mainly used to produce animal feeds and edible oils. Livestock production is expected to double between 2017 and 2050, which would require significant oil crop expansion to meet feed demands. Alternatively, microalgae have significantly higher productivities and have been shown to produce desirable protein and lipids concentrations. Microalgae have been shown to produce protein (13.3%–58% dry weight, including all essential amino acids) at levels much higher than oilseeds, while also providing a source of essential vitamins and minerals. Additionally, the inclusion of bioactive compounds, including antimicrobials and antioxidants, could further improve the quality of microalgal animal feeds.

Controlling light exposure (wavelength and intensity) has been shown to increase the cellular production of antioxidants in some species of microalgae. However, these light stress studies do not typically examine extremophiles, which have been shown to produce antioxidants as a defense mechanism. This study aims to examine the effect of ultraviolet radiation (UVR) on the production of natural antioxidant compounds (carotenoids, chlorophyll a, and chlorophyll b) in extremophiles, with the ultimate goal of improving the feasibility of industrial CO2 mitigation. Three strains of microalgae were bioprospected from low pH (<4) mining impacted water bodies in Ontario, Canada. This study found that the bioprospected strains naturally produce higher levels of antioxidant compounds compared to culture collection strains. However, decreasing the pH, as would happen with industrial off-gas application, resulted in a decreased concentration of antioxidant compounds and activity, with the exception: strain M2 maintained high activities at both low and unregulated pH. Three UVR treatments were tested, consisting of 10 h of UVR exposure and different recovery periods. Treatments resulted in increased antioxidant concentrations in samples with initially low concentrations, with these concentrations continuing to increase for up to 48 h after UVR exposure. A concurrent increase in antioxidant activity was also determined based on ABTS radical scavenging activity and ferric reducing power. Furthermore, this study identifies a promising strain (M2) that could simultaneously produce health beneficial compounds and mitigate industrial CO2 emissions.

The utilization of microalgae to treat carbon dioxide (CO2)-rich industrial off-gas has been suggested as both beneficial for emissions reduction and economically favorable for the production of microalgal products. Common sources of off-gases include coal combustion (2-15% CO2), cement production (8-15% CO2), coke production (18-23% CO2), and ore smelting (6-7% CO2). However, industrial off-gas also commonly contains other acid gas components [typically nitrogen oxides (NOX) and sulfur dioxide (SO2)] and metals that could inhibit microalgae growth and productivity. To utilize industrial off-gas effectively in microalgae cultivation systems, a number of solutions have been proposed to overcome potential inhibitions. These include bioprospecting to identify suitable strains, genetic modification to improve specific cellular characteristics, chemical additions, and bioreactor designs and operating procedures.In this review, results from microalgae experiments related to utilizing off-gas are presented, and the outcomes of different conditions discussed along with potential solutions to resolve limitations associated with the application of off-gas.

Although the percentage of cancer survivors has increased over time, cancer remains the second leading cause of death worldwide. Chemotherapy, a common approach to treating cancer, has been successful with certain types of cancer, but has limitations resulting from cancer drug resistance. To address this, the search for new, effective drugs from natural sources has expanded beyond commonly investigated organisms to include less explored eukaryotic and prokaryotic microalgae from freshwater habitats. Due to their ability to adapt to very diverse ecosystems, these microorganisms possess enormous potential to produce novel compounds with biological activities, including anticancer properties. While there has been increasing research on marine microalgae, their freshwater counterparts have not been studied to the same extent. This review highlights the opportunity with extracts and compounds from freshwater microalgae from work examining culture collections in terms of their potential for providing novel anticancer drugs.

Oil crops account for approximately 23% of the world's crop lands and are mainly used to produce animal feeds and edible oils. Livestock production is expected to double between 2017 and 2050, which would require significant oil crop expansion to meet feed demands. Alternatively, microalgae have significantly higher productivities and have been shown to produce desirable protein and lipids concentrations. This review investigates the feasibility of substituting common oil crops with microalgae on a nutritional basis. Microalgae have been shown to produce protein (13.3–58% dry weight, including all essential amino acids) and lipid fractions (2.04–80% dry weight, including commonly deficient long-chain omega-3 fatty acids and other essential fatty acids) at levels much higher than oilseeds, while also providing a source of essential vitamins and minerals. Additionally, the inclusion of bioactive compounds, including antimicrobials and antioxidants, could further improve the quality of microalgal animal feeds and edible oils.

The cost of microalgae cultivation is one of the largest limitations to achieving sustainable, large-scale microalgae production of commercially desirable lipids. Utilizing CO2 as a 'free' carbon source from waste industrial flue gas emissions can offer wide-ranging cost savings. However, these gas streams typically create acidic environments, in which most microalgae cannot survive due to the concentration of CO2 and the presence of other acidic gasses such as NO2 and SO2. To address this situation, we investigated growth of a mixed acid-tolerant green microalgal culture (91% dominated by a single Coccomyxa sp. taxon) bioprospected at pH 2.8 from an acid mine drainage impacted water body. The culture was grown at pH 2.5 and fed with a simulated flue gas containing 6% CO2 and 94% N2. On reaching the end of the exponential growth phase, the culture was exposed to either continued light-dark cycle conditions or continual dark conditions. After three days in the dark, the biomass consisted of 28% of lipids, which was 42% higher than at the end of the exponential phase and 55% higher than the maximum lipid content achieved under light/dark conditions. The stress caused by being continually in the dark also favoured the production of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs; 19.47% and 21.04%, respectively, after 7 days) compared to 7-days of light-dark treatment (1.94% and 9.53%, respectively) and showed an increase in nitrogen content (C:N ratio of 6.4) compared to light-dark treatment (C:N ratio of 11.9). The results of the research indicate that use of acid tolerant microalgae overcomes issues using flue gasses that will create an acidic environment and that applying dark stress is a low-cost stressor stimulates production of desirable dietary lipids.

A potential commercial market for microalgal-produced antioxidants is a natural alternative to synthetic compounds that are possible carcinogens. Further, utilizing microalgae for carbon (CO2) capture from industrial off-gas could be environmentally beneficial for their mass production, but due to an increase in acidity of the growing media caused by acid gasses, microalgae able to survive at pH 3.0-4.0 while still producing antioxidant metabolites are needed. Two strains of green microalgae were bioprospected from acid mine drainage impacted water bodies (pH 2.9) in Canada. These and a culture collection strain Chlamydomonas reinhardtii (pH 7.0) were investigated for their antioxidant capacity and chlorophyll content while growing under low pH conditions. The isolates were identified as Coccomyxa sp. and Chlamydomonas sp. based on ITS sequences. The microalgae were grown at pH 3.0 and unregulated pH media for 28 d and their antioxidant potential evaluated with three complimentary assays. The results showed that C. reinhardtii did not grow at pH 3.0, and that Coccomyxa sp. had significantly higher antioxidant potential than Chlamydomonas sp. Both species also showed significantly higher antioxidant potential than C. reinhardtii when it was grown at pH 7.0.

Metal ore smelters have significant environmental footprints due to very high energy consumption and the resulting large quantities of waste heat. The industry recognizes, therefore, the need for implementation of changes to improve process economics by reducing primary energy consumption through recovery and repurposing of waste heat. However, when deciding the merit of a process modification, it should not only be based on economic gains (which have previously been highlighted), but also on environmental impacts. For the latter, life cycle assessment (LCA) is a well-established and useful tool. But across the mineral processing industry, LCA is not commonly incorporated into decision-making processes. We have investigated the environmental gains from introducing low-grade heat recovery and repurposing within a smelters’ sulphuric acid plant. An LCA model was developed to first assess the environmental impact of existing sulphuric acid making processes across four standard potentials (global warming, acidification, eutrophication, and relative human toxicity). The model was then used to examine the potential of installing heat pumps to capture waste heat from water cooling towers associated with sulphuric acid production and repurposing it to replace existing on-site electric heaters. The study found that replacing electric heaters made significant improvements in a range of environmental impacts. The results of the model show a potential 13% reduction in electricity consumption, with a 53% reduction from the mist precipitators in global warming, acidification, eutrophication, and relative human toxicity potential. The LCA comparison showed a potential 13% reduction in overall electricity consumption through the addition of low-grade heat capture using heat pumps, as well as a 5% reduction in heat load on the cooling towers. Together, this would lead to a 21% reduction in carbon dioxide equivalent emissions from the mist precipitators and cooling towers, as well as acidification, eutrophication, and relative human toxicity potential.

Sludges from pulp and paper mills represent a major ecological and environmental cost, and anaerobic digestion represents a method of waste reduction and energy recovery for these mills. This study compared methane production potential and microbial communities across 11 primary- and biosludges from five pulp and paper mills using various mill processes. We measured methane production from sludges in anaerobic batch reactor experiments over 64 days. Sludges were incubated with and without added substrate to test for organic substrate limitation versus inhibition of methanogens. Initial microbial communities and changes to community composition were determined using Illumina MiSeq for metabarcoding of bacterial and archaeal 16S rRNA genes. Mean methane production potential varied greatly between sludges (0.002-79 mL CH4 g-1 TS). Among primary sludges, kraft mill sludge produced more methane than other mill types. For these other mills, biosludge produced more methane than primary sludge, which had evidence of methanogen inhibition. Microbial communities and diversity were influenced by the initial community composition, and high methane production was only seen in sludges with high diversity. A number of sludges innately produced substantial methane and may be targets for further modelling and larger scale testing of anaerobic digestion.

The use of fossil fuel sourced diesel underground has various associated health and environmental hazards, and additional energy demand and costs associated with necessary ventilation. One way to reduce these impacts is by utilizing a biodieselblend, which generates lower levels of harmful emissions from underground equipment and can be produced regionally, reducing the impact of transportation. Furthermore, this would help allow use of existing machinery during transition towards more widespread electrification underground. Therefore, the concept of an integrated supply and use chain within the mining industry is examined based on biodiesel from acidophilic photosynthetic microalgae cultivated using CO 2 in smelter off-gas. A life cycle assessment (LCA) was conducted to compare the environmental impacts of production, transportation, and end-use of fossil fuel sourced diesel to biodieselblended fuel across four underground metal ore mine sites (Canada, Poland, Zambia, and Australia). The outcomes from assessing four key environmental impact potentials (global warming, eutrophication, acidification and human toxicity) demonstrate the advantages of using biodiesel-blends. The integration of biodiesel resulted in changes of -22.5–+22.8% (global warming), -6.1–+27.3% (eutrophication), -18.9–+26.3% (acidification), and -21.0–-3.6% (human toxicity). The results showed reduction across all potentials for two mines and reduction in human toxicity potential for all sites.

A household scale UVC/TiO2 based advanced oxidation process (AOP) reactor was developed for drinking water treatment. A 3D UVC absorption model to predict light energy absorbed by the photocatalyst coatings was developed and agreed with direct light irradiance measurements. The tubular reactor was used with and without titanium dioxide (TiO2) coated plates lining inside and was found to simultaneously inactivate a high initial concentration of Escherichia coli and degrade uracil, which was used as a synthetic water pollutant. The reactor, lined with replaceable TiO2 coated plates, degraded uracil by 34.2% and natural organic matter in raw lake water by 33.2% within 24 minutes. An additional low dose of hydrogen peroxide also demonstrated an advantage to a reactor without TiO2 coated plates. The electrical energy per order value was evaluated for this UVC/TiO2 reactor to be 8.13 kWh/m3, which is in the competitive range for a photocatalytic reactor. The UV/photocatalyst based AOP water treatment reactor design shows practical application potential for remote households and communities that do not have access to municipal water treatment.

A life-cycle assessment (LCA) model was developed to comparatively analyze the use of manual and automated mining equipment in underground copper mine sites. Processes and key variables that were determined to contribute to the environmental impact of operations were identified for six mine sites in a range of geographical locations around the world. Our model successfully calculated carbon dioxide (CO2 eq.) emissions to within 4.9% of the reported annual emissions from the site's respective companies. The implementation of automation was found to decrease global warming potential by a range of 11.4%–18.0% or 3.9–17.9 kg CO2 eq./t ore. The model was also used to estimate the average reductions across several impact potentials including, acidification (11.9%–17.8%), eutrophication (7.6%–13.7%), and human toxicity (16.0%–20.0%). World-wide the mining industry is moving toward introducing significantly more automation to enhance productivity and safety. This novel work demonstrates an important third dimension that can support this move, reduced environmental impact.

Microalgae are an abundant and diverse resource that can help ease the growing pressure on the food and dietary supplements industry. Microalgae can be used either as whole biomass to increase the overall food content of lipids, carbohydrates, and proteins. They can be also grown to produce high levels of specific metabolites that are extracted and purified, such as omega-3 fatty acids, antioxidants and phycobiliproteins. However, technological and economical barriers within downstream processing, in particular microalgae harvesting, continue to limit large-scale production. Harvesting can affect both process economics and the end-use market, as many existing methods involve large energy expenditures or use of potentially harmful chemicals which would not satisfy government regulations. This review discusses the requirements of harvesting microalgal dietary supplements, and provides a comparison of harvesting techniques currently used in industries, along with other promising methods that could be utilized in the future. Based on a comparison of methods, centrifugation remains a top choice despite energy costs, and flotation techniques that utilize promising bioflocculants that avoid the toxicity associated with traditional flocculants have significant potential for harvesting microalgae to produce dietary supplements.

The use of CO 2 rich industrial flue gases to support cultivation of microalgae to produce lipids for biofuel and other applications is an increasingly researched option. However, this approach presents a challenge, as whilst flue gasses typically contain 6-10% CO 2 , excessive medium acidification can be caused by the presence of NO x and SO 2 . The use of acidophilic or acid-tolerant species is a possible solution, but little is known about these microalgae. In this study we investigated the growth of a bioprospected acid-tolerant mixed photosynthetic green microalgae culture (91% dominated by a single Coccomyxa sp . taxon) at pH 2.5 and fed with a simulated flue gas containing 6% CO 2 and 94% N 2 . At the end of the exponential growth phase, lipid accumulation and profiles, and the elemental composition of biomass were analysed over one week during which biomass was exposed to either continued light-dark cycle conditions or continual dark conditions. After three days of dark stress, the biomass consisted of approximately 28% of lipids, which was 42% higher than at the end of the exponential phase and 55% higher than the maximum lipid content achieved under light/dark conditions. Oleic acid (C18:1), pentadecanoic acid (C15:0), and palmitic acid (C16:0) were the dominant fatty acids at the end of the exponential phase, and light-dark and dark-treated biomass, respectively. Dark stress conditions favoured polyunsaturated fatty acid production and showed an increase in nitrogen content. This suggests that the use of dark stress to stimulate production of desirable lipids is a no-cost alternative to other commonly used stressors.