Exploration of microalgal species for simultaneous wastewater treatment and biofuel production

Low-Cost Greywater Treatment Using Polyculture Microalgae-Microalgal Growth, Organics, and Nutrient Removal Subject to pH and Temperature Variations During the Treatment

Organics and nutrient removal studies are rarely done using polyculture microalgae, and that too in outdoor conditions, as they are often not deemed effective for wastewater treatment purposes. This study examined the organics and nutrient removal efficiency of polyculture microalgae cultivated in greywater. The reactor was operated in outdoor conditions. Hence, it was subjected to natural pH and temperature variations. A growth rate of 0.05 g L-1 day-1 was observed for temperatures up to 37 °C, beyond which the growth rate declined by 0.07 g L-1 day-1. During the treatment, the pH of the system was observed to be between 7.4 and 8.4. However, the growth rate would again pick up (0.05 g L-1 day-1) when the pH and temperature moved towards the optimum range, indicating that the polycultures adapt very quickly to their environment. The maximum biomass concentration reached 0.82 gL-1. The highest removal efficiency of organic carbon, ammonia, and phosphate was 80.7, 61.9, and 58.4%, respectively. Nitrate and nitrite concentrations remained ≤ 1.3 mgL-1 and ≤ 2 mgL-1, respectively, indicating the absence of nitrification/denitrification and ammonia volatilization. The mass balance of microalgae indicated that the primary removal mechanism of nitrogen and phosphorus removal was assimilation by the microalgae. The study proved polyculture microalgae to be as effective as some monoculture species in wastewater treatment, which require costlier controlled growth conditions. The high organics and nutrient removal by polycultures in outdoor conditions could pave the way to reducing wastewater treatment costs.

Application of Response Surface Methodology (RSM) in the statistical evaluation of biodiesel production from the neutral lipids of the Coelastrella-Nannochloropsis consortium

The paramount challenge in economically workable microalgal biodiesel production is the selection of a competent catalyst to improve the fatty acid methyl ester yield with desirable fatty acid composition. Though countless researchers have explored different homogeneous and heterogeneous catalysts to improve the transesterification efficacy, achieving greater biodiesel production from the neutral lipids of the microalgal consortium using a statistical tool, response surface methodology is scarce. Thus, the present study applied Response surface methodology to statistically analyze the biodiesel production from the neutral lipids of the indigenous Coelastrella-Nannochloropsis consortium (CNC) on the way to commercial feasibility. Onset of the study, the neutral lipids and acid value of the CNC were determined to be 18.74% and 2.73%, respectively. The transesterification of the neutral lipids of CNC was optimized through the coded factors in the RSM for various reaction parameters as combined influence viz., (i) Catalyst dose: methanol volume, (ii) Catalyst dose: reaction time; (iii) Catalyst dose: reaction temperature, (iv) Time: temperature, (v) time: methanol volume, (vi) temperature: methanol volume. Based on the ANOVA, coefficient determination, 2% KOH, 2 h time, 70 °C temperature, and 9 mL methanol volume were ascertained to be optimal values to accomplish 92% biodiesel production. Further, the biodiesel has desirable palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic acids, with palmitic acid as the prevalent fatty acid contributing 16-18%. In addition, the tested fuel properties of CNC biodiesel satisfy international biodiesel standards.

Realization process of microalgal biorefinery: The optional approach toward carbon net-zero emission

Increasing carbon dioxide (CO2) emission has already become a dire threat to the human race and Earth's ecology. Microalgae are recommended to be engineered as CO2 fixers in biorefinery, which play crucial roles in responding climate change and accelerating the transition to a sustainable future. This review sorted through each segment of microalgal biorefinery to explore the potential for its practical implementation and commercialization, offering valuable insights into research trends and identifies challenges that needed to be addressed in the development process. Firstly, the known mechanisms of microalgal photosynthetic CO2 fixation and the approaches for strain improvement were summarized. The significance of process regulation for strengthening fixation efficiency and augmenting competitiveness was emphasized, with a specific focus on CO2 and light optimization strategies. Thereafter, the massive potential of microalgal refineries for various bioresource production was discussed in detail, and the integration with contaminant reclamation was mentioned for economic and ecological benefits. Subsequently, economic and environmental impacts of microalgal biorefinery were evaluated via life cycle assessment (LCA) and techno-economic analysis (TEA) to lit up commercial feasibility. Finally, the current obstacles and future perspectives were discussed objectively to offer an impartial reference for future researchers and investors.

Strategies and challenges to enhance commercial viability of algal biorefineries for biofuel production

The rise in energy consumption would quadruple in the coming century and the, existing energy resources might be insufficient to meet the demand of the growing population. An alternative and sustainable energy resource is therefore needed to address the fossil fuel deficiency. The utility of microalgae strains in the aspect of biorefinery has been in research for quite some time. Algal biorefinery is an alternate way of renewable energy however even after decades of research it still suffers from commercialization bottlenecks. The current manuscript reviews the scenarios where the innovation needs an ignition for its commercialization. This review discusses the prospects of up-scale cultivation, and harvesting algal biomass for biorefineries. It narrates algal biorefinery hurdles that can be solved using integrated technology approach, life cycle assessment and applications of nanotechnology. The review also sheds light upon the ties of algal biorefineries with its economic viability.

Sustainable approach for biodiesel production and wastewater treatment by cultivating Pleusrastrum insigne in wastewater

The globalized modern world has been confronted with some of the most challenging problems, most of which arise from human activities. Overexploitation of fossil fuels which leads to energy and environmental crisis, and loss of aquatic ecosystem due to improper disposal of household and industrial waste into water bodies constitute some of the biggest emerging global problems. In this study, an unconventional and sustainable approach to produce biodiesel was analyzed by growing Pleurastrum insigne in different wastewater. The growth of P. insigne in wastewater in turn resulted in up to 93.61% reduction in biological oxygen demand, 58.62% reduction in total phosphorus content, and up to 76.61% total nitrogen removal in the wastewater. The total lipid content of the organism was highest in wastewater sample 6 (30.47%). The fatty acid profile also showed a high percentage of C16 and C18 fatty acids which are desirable fatty acids for a high-grade fuel. Production of biodiesel conforming to international standards was predicted from P. insigne cultivated in wastewater confirming the effectiveness of combining wastewater treatment and biodiesel production. Novelty statement: Pleurastrum insigne has never been studied before for phytoremediation of wastewater and biodiesel production. This novel research highlighted the application of P. insigne in wastewater treatment and the viable scope in biodiesel production. This work aimed to provide a significant contribution in reducing the cost of production of biodiesel from microalgae while shedding new light on an eco-friendly approach to wastewater treatment.

Adsorption of sulfamethoxazole via biochar: The key role of characteristic components derived from different growth stage of microalgae

Converting microalgal biomass residues into biochar (BC) after microalgal wastewater treatment is a popular approach that can produce an adsorbent to treat refractory organic pollutants. Moreover, the adsorption efficiency via BC is closely associated with the surface morphology, which may be determined by the composition of the microalgal biomass. However, the intrinsic relationship and advanced mechanism between the adsorption efficiency and microalgal composition have not been thoroughly investigated. In this work, four microalgal BCs were prepared from Chlamydomonas sp. QWY37 (CBC) after collection from four different growth stages of microalgal biomass during wastewater treatment. The adsorption performance for sulfamethoxazole indicates that the CBC collected in the mid-log phase (CBC_L-M) possessed the best adsorption capacity (287.89 mg/g) owing to the higher decomposition of the microalgal cellular protein concentration (70%). Meanwhile, a higher protein content contributed to the largest specific surface area (42.16 m²/g), maximum pore volume (0.037 cm³/g) and abundant surface functional groups of the CBC_L-M. Furthermore, based on the theoretical calculation of the structural analysis, the adsorption mechanism was a multilayer adsorption process in accordance with the Freundlich isotherm. Additionally, the strong hydrogen bond, electron donor-acceptor interaction and electrostatic attraction were the main adsorption mechanisms due to the carboxyl/ester functional groups. The results of this research provide a novel perspective on the reasonable harvest of microalgal biomass for BC fabrication and large-scale implementation of microalgal BC in future applications.

Sustainability and carbon neutrality trends for microalgae-based wastewater treatment: A review

As the global economy develops and the population increases, greenhouse gas emissions and wastewater discharge have become inevitable global problems. Conventional wastewater treatment processes produce direct or indirect greenhouse gas, which can intensify global warming. Microalgae-based wastewater treatment technology can not only purify wastewater and use the nutrients in wastewater to produce microalgae biomass, but it can also absorb CO₂ in the atmosphere or flue gas through photosynthesis, which demonstrates great potential as a sustainable and economical wastewater treatment technology. This review highlights the multifaceted roles of microalgae in different types of wastewater treatment processes in terms of the extent of their bioremediation function and microalgae biomass production. In addition, various newly developed microalgae cultivation systems, especially biofilm cultivation systems, were further characterized systematically. The performance of different microalgae cultivation systems was studied and summarized. Current research on the technical approaches for the modification of the CO₂ capture by microalgae and the maximization of CO₂ transfer and conversion efficiency were also reviewed. This review serves as a useful and informative reference for the application of wastewater treatment and CO₂ capture by microalgae, aiming to provide a reference for the realization of carbon neutrality in wastewater treatment systems.

Calcium ions-effect on performance, growth and extracellular nature of microalgal-bacterial symbiosis system treating wastewater

Microalgal-bacterial symbiosis (MABS) system treating wastewater has attracted great concern because of its advantages of carbon dioxide reduction and biomass energy production. However, due to the low density and negative surface charge of microalgae cells, the sedimentation and harvesting performance of microalgae biomass has been one limitation for the application of MABS system on wastewater treatment. This study investigated the performance enhancement of microalgae harvesting and wastewater treatment contributed by calcium ions (i.e., Ca²⁺) in the MABS system. Results showed that a low Ca²⁺ loading (i.e., 0.1 mM) promoted both COD and nutrients removal, with growth rates of 11.95, 6.53 and 1.21% for COD, TN and TP compared to control, and chlorophyll a was increased by 64.15%. Differently, a high Ca²⁺ loading (i.e., 10 mM) caused removal reductions by improving the aggregation of microalgae, with reduction rates of 34.82, 3.50 and 10.30% for COD, NH₄⁺-N and TP. Mechanism analysis indicated that redundant Ca²⁺ adsorbed on MABS aggregates and dissolved in wastewater decreased the dispersibility of microalgae cells by electrical neutralization and compressed double electric layer. Moreover, the presence of Ca²⁺ could improve extracellular secretions and promoted flocculation performance, with particle size increasing by 336.22%. The findings of this study may provide some solutions for the enhanced microalgae biomass harvest and nutrients removal from wastewater.

Bioprospecting of marine microalgae from Kaohsiung Seacoast for lutein and lipid production

A bioprospecting study was conducted from Seawater samples collected at Kaohsiung Seacoast, Taiwan. The current research was aimed to isolate potential lutein-producing strain, evaluate and optimize the best cultivation mode, lutein accumulation stage, lutein-extraction method, and condition to recover maximum lutein (main product) and lipid (byproduct). Biorefinery is the latest approach worldwide to extract multi-products for cost-effectiveness. Selected isolate among several isolates, identified as Chlorella sorokiniana Kh12 and exploited under biorefinery concept for lutein and lipid extraction. Kh12 cultivated under mixotrophy: 2X-(HT)-9k yielded maximum biomass (3.46 g L^-1) and lutein (13.69 mg g^-1) which is among the higher yields reported so far. Among various tested solvents, methanol was the best extractor. Bead milling was most effective to disrupt algal cell walls, seven minutes of milling was best for maximum lutein (7.56 mg g^-1) extraction. Kh12 could be a promising candidate for commercial lutein and lipid co-production based on the outcome.

Biological Approaches Integrating Algae and Bacteria for the Degradation of Wastewater Contaminants-A Review

The traditional approach for biodegradation of organic matter in sewage treatment used a consortium of bacterial spp. that produce untreated or partially treated inorganic contaminants resulting in large amounts of poor-quality sludge. The aeration process of activated sludge treatment requires high energy. So, a sustainable technique for sewage treatment that could produce less amount of sludge and less energy demanding is required for various developed and developing countries. This led to research into using microalgae for wastewater treatment as they reduce concentrations of nutrients like inorganic nitrates and phosphates from the sewage water, hence reducing the associated chemical oxygen demand (COD). The presence of microalgae removes nutrient concentration in water resulting in reduction of chemical oxygen demand (COD) and toxic heavy metals like Al, Ni, and Cu. Their growth also offers opportunity to produce biofuels and bioproducts from algal biomass. To optimize use of microalgae, technologies like high-rate algal ponds (HRAPs) have been developed, that typically use 22% of the electricity used in Sequencing Batch Reactors for activated sludge treatment with added economic and environmental benefits like reduced comparative operation cost per cubic meter, mitigate global warming, and eutrophication potentials. The addition of suitable bacterial species may further enhance the treatment potential in the wastewater medium as the inorganic nutrients are assimilated into the algal biomass, while the organic nutrients are utilized by bacteria. Further, the mutual exchange of CO2 and O2 between the algae and the bacteria helps in enhancing the photosynthetic activity of algae and oxidation by bacteria leading to a higher overall nutrient removal efficiency. Even negative interactions between algae and bacteria mediated by various secondary metabolites (phycotoxins) have proven beneficial as it controls the algal bloom in the eutrophic water bodies. Herein, we attempt to review various opportunities and limitations of using a combination of microalgae and bacteria in wastewater treatment method toward cost effective, eco-friendly, and sustainable method of sewage treatment.

Shining a Light on Wastewater Treatment with Microalgae

Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition.

Bioprocesses for the recovery of bioenergy and value-added products from wastewater: A review

Wastewater and activated sludge present a major challenge worldwide. Wastewater generated from large and small-scale industries, laundries, human residential areas and other sources is emerging as a main problem in sanitation and maintenance of smart/green cities. During the last decade, different technologies and processes have been developed to recycle and purify the wastewater. Currently, identification and fundamental consideration of development of more advanced microbial-based technologies that enable wastewater treatment and simultaneous resource recovery to produce bioenergy, biofuels and other value-added compounds (organic acids, fatty acids, bioplastics, bio-pesticides, bio-surfactants and bio-flocculants etc.) became an emerging topic. In the last several decades, significant development of bioprocesses and techniques for the extraction and recovery of mentioned valuable molecules and compounds from wastewater, waste biomass or sludge has been made. This review presents different microbial-based process routes related to resource recovery and wastewater application for the production of value-added products and bioenergy. Current process limitations and insights for future research to promote more efficient and sustainable routes for this under-utilized and continually growing waste stream are also discussed.

Mitigation of self-shading effect in embedded optical fiber in Chlorella sorokiniana immobilized polyvinyl alcohol gel beads

The addition of optical fibers to improve light penetration into microalgae-immobilized poly (vinyl) alcohol (PVA) gel beads is proposed herein. Live/dead staining in combination with confocal laser scanning microscopy analysis revealed greater light penetration in Chlorella sorokiniana-immobilized PVA gel beads with optical fibers (PVA-OF) than in C. sorokiniana-immobilized PVA gel beads (PVA-NOF). The improved light penetration had positive effects on the initial nutrient removal efficiency, which resulted in a 1.2-fold higher initial nutrient removal efficiency in PVA-OF than in PVA-NOF. The use of polymeric PVA materials is effective for maintaining structural integrity. The findings demonstrate a methodology for mitigating self-shading effects in microalgae immobilized on opaque polymeric materials.

Algae-mediated processes for the treatment of antiretroviral drugs in wastewater: Prospects and challenges

The prevalence of pharmaceuticals (PCs), especially antiretroviral (ARV) drugs in various aquatic ecosystems has been expansively reported, wherein wastewater treatment plants (WWTPs) are identified as the primary point source. Consequently, the occurrence, ecotoxicity and treatment of ARV drugs in WWTPs have drawn much attention in recent years. Numerous studies have shown that the widely employed activated sludge-based WWTPs are incapable of removing ARV drugs efficiently from wastewater. Recently, algae-based wastewater treatment processes have shown promising results in PCs removal from wastewater, either completely or partially, through different processes such as biosorption, bioaccumulation, and intra-/inter-cellular degradation. Algal species have also shown to tolerate high concentrations of ARV drugs than the reported concentrations in the environmental matrices. In this review, emphasis has been given on discussing the current status of the occurrence of ARV drugs in the aquatic environment and WWTPs. Besides, the current trends and future perspectives of PCs removal by algae are critically reviewed and discussed. The potential pathways and mechanisms of ARV drugs removal by algae have also been discussed.

The Upcoming 6Li Isotope Requirements Might Be Supplied by a Microalgal Enrichment Process

Lithium isotopes are essential for nuclear energy, but new enrichment methods are required. In this study, we considered biotechnology as a possibility. We assessed the Li fractionation capabilities of three Chlorophyte strains: Chlamydomonas reinhardtii, Tetraselmis mediterranea, and a freshwater Chlorophyte, Desmodesmus sp. These species were cultured in Li containing media and were analysed just after inoculation and after 3, 12, and 27 days. Li mass was determined using a Inductively Coupled Plasma Mass Spectrometer, and the isotope compositions were measured on a Thermo Element XR Inductively Coupled Plasma Mass Spectrometer. The maximum Li capture was observed at day 27 with C. reinhardtii (31.66 µg/g). Desmodesmus sp. reached the greatest Li fractionation, (δ⁶ = 85.4‰). All strains fractionated preferentially towards ⁶Li. More studies are required to find fitter species and to establish the optimal conditions for Li capture and fractionation. Nevertheless, this is the first step for a microalgal nuclear biotechnology.

Enhancement of Biomass and Lipid Productivities of Scenedesmus sp. Cultivated in the Wastewater of the Dairy Industry

Microalgae are photoautotrophic microorganisms capable of producing compounds with potential bioenergetic applications as an alternative energy source due to the imminent exhaustion of fossil fuels, their impact on the environment, and the constant population increase. The mass cultivation of these microorganisms requires high concentrations of nutrients, which is not profitable if analytical grade culture media are used. A viable alternative is the use of agro-industrial wastewater, due to the metabolic flexibility of these microorganisms and their ability to take advantage of the nutrients present in these substrates. For the reasons mentioned above, the effect of the cultivation in wastewater from cheese processing on the growth parameters and biomass composition of Scenedesmus sp. was evaluated, and its nutrient removal capacity determined. A high lipid concentration was obtained in the cultures with the dairy effluent (507.81 ± 19.09 mg g−1) compared to the standard culture medium, while the growth parameters remained similar to the control medium. Scenedesmus sp. achieved high percentages of nutrient assimilation of the wastewater used (88.41% and 97.07% for nitrogen and phosphorus, respectively). With the results obtained, the feasibility of cultivating microalgae in agro-industrial wastewater as an alternative culture medium that induces the accumulation of compounds with potential bioenergetic applications was verified.