Produced water (PW), the largest waste stream generated in oil and gas industries, has the potential to be a harmless product rather than being a waste. Biological processes using microorganisms have proven useful to remediate PW contaminated by petroleum hydrocarbons, complex organic chemicals, and solvents. In particular, the bioremediation of PW using algae is an eco-friendly and low-cost approach due to algae’s ability to utilize certain pollutants as nutrient sources. Therefore, the utilization of PW as an algal growth medium has a great potential to eliminate chemicals from the PW and minimize the large volumes of freshwater needed for cultivation. Although several reviews describing the bioremediation of PW have been published, to the best of our knowledge, no review has exclusively focused on the algae-based PW treatment. Therefore, the present review is dedicated to filling this gap by portraying the many different facets of the algae cultivation in PW. Several algal species that are known to thrive in a wide range of salinity and the critical steps for their cultivation in hypersaline PW have been identified. Overall, this comprehensive review highlights the PW bioremediation using algae and brings attention to utilizing PW to grow biomass that can be processed to generate biofuels and useful bioproducts.

Solid waste generation has been projected to increase worldwide. Presently, the most applied methodology to dispose of solid waste is landfilling. However, these landfill sites, over time release a significant quantity of leachate, which can pose serious environmental issues, including contamination of water resources. There exist many physicochemical and biological landfill leachate treatment schemes with varying degrees of success. With an increasing focus on sustainability, there has been a demand for developing eco-friendly, green treatment schemes for landfill leachates with viable resource recovery and minimum environmental footprints. Microalgae-based techniques can be a potential candidate for such a treatment scenario. In this article, research on microalgae-based landfill leachate treatments reported in the last 15 years have been summarized and critically reviewed. The scale-up aspect of microalgae technology has been discussed, and the related critical factors have been elucidated. The article also analyzes the resource recovery potential for microalgal techniques with respect to leachate treatment and explores possible methodologies to minimize the environmental footprints of the microalgae-based treatment process. The future research potential in the area has been identified and discussed.

Produced water (PW) is the largest waste stream generated by the oil and gas industry. Traditional treatment of PW burdens the industry with significant expenses and environmental issues. Alternatively, microalgal-based bioremediation of PW is often viewed as an ecologically safe and sustainable platform for treating PW. Moreover, the nutrients in PW could support algal growth. However, significant dilution of PW is often required in algal-based systems due to the presence of complex chemical contaminants. In light of these facts, the current work has investigated the potential of cultivating Galdieria sulphuraria and Chlorella vulgaris in PW using multiple dilutions; 0% PW, 5% PW, 10% PW, 20% PW, 50% PW and 100% PW. While both algal strains can grow in PW, the current results indicated that G. sulphuraria has a higher potential of growth in up to 50% PW (total dissolved solids of up to 55 g L⁻¹) with a growth rate of 0.72 ± 0.05 g L⁻¹ d⁻¹ and can achieve a final biomass density of 4.28 ± 0.16 g L⁻¹ in seven days without the need for additional micronutrients. Additionally, the algae showed the potential of removing 99.6 ± 0.2% nitrogen and 74.2 ± 8.5% phosphorus from the PW.

This study aims to evaluate the potential of using a thermophilic acidophilic red alga, Galdieria sulphuraria for effective on-site treatment of municipal landfill leachate (LL). This study focused on evaluating the effects of LL dilution, nitrogen loading, and initial algal biomass density on the overall treatment efficiency, and evaluated the long-term performance of the system using 5-day growth cycles. This study confirmed that optimal conditions for G. sulphuraria biomass production are 20% strength LL, a lower initial biomass concentration of 0.25 g L⁻¹, and the addition of N at twice the level of initial media. Furthermore, the results indicated G. sulphuraria’s ability to grow in elevated NH₄-N concentration (>950 mg L⁻¹) and provide nitrogen removal rates of up to 40 mg L⁻¹ d⁻¹. In addition, the long-term running experiment showed that the proposed algal-based system could be applied in semi-continuous mode to achieve bioremediation. Overall, the results obtained from this study can be used to develop the necessary process parameters to implement large-scale algal-based systems for landfill leachate treatment.

The algae-based landfill leachate (LL) treatment system has been proved promising for nutrient recycling and biomass production at lab- or small-scale photobioreactors (PBRs). However, many assessment tools such as techno-economic analyses (TEAs) usually utilize parameters from small-scale experiments as input data to predict the potential performance of commercial large-scale or full-scale bioreactors. Reliability of using data from lab-scale for commercial large-scale estimation is still uncertain. This study compared the performance of three photobioreactor systems that differed simultaneously in scale, geometry, light intensity, mixing mode, and aeration: 0.125 L small-scale flask, 1 L medium-scale tubular PBR, and 15 L wall-shaped PBR for real LL treatment. The 1 L medium-scale tubular photobioreactor outperformed the other two systems in biomass growth rate and the rates of nitrogen and phosphorus removal, even though all three systems removed nearly all NH₄-N and PO₄-P (≈100%) within two weeks. Possible reasons for this better performance include stronger illumination, a bubbling aeration mode, the reactor shape (which improves mixing), and higher surface area to volume ratio × light intensity. According to these results, using relatively small-scale flask experimental data for predictive analysis of industrial-scale algal systems could be inadequate. In this study, volumetric optical radiation (VOR) serves as a promising preliminary descriptive indicator to reflect the overall performance of an algal-based treatment system.