Microalgae: A potential bioagent for treatment of emerging contaminants from domestic wastewater.

Water crisis around the world leads to a growing interest in emerging contaminants (ECs) that can affect human health and the environment. Research showed that thousands of compounds from domestic consumers, such as endocrine disrupting chemicals (EDCs), personal care products (PCPs), and pharmaceuticals active compounds (PhAcs), could be found in wastewater in concentration mostly from ng L-1 to µg L-1. However, generally, wastewater treatment plants (WWTPs) are not designed to remove these ECs from wastewater to their discharge levels. Scientists are looking for economically feasible biotreatment options enabling the complete removal of ECs before discharge. Microalgae cultivation in domestic wastewater is likely a feasible approach for removing emerging contaminants and simultaneously removing any residual organic nutrients. Microalgal growth rate and contaminants removal efficiency could be affected by various factors, including light intensity, CO2 addition, presence of different nutrients, etc., and these parameters could greatly help make microalgae treatment more efficient. Furthermore, the algal biomass harvests could be repurposed to produce various bulk chemicals such as sustainable aviation fuel, biofuel, bioplastic, and biochar; this could significantly enhance the economic viability. Therefore, this review summarizes the microalgae-based bioprocess and their mechanisms for removing different ECs from different wastewaters and highlights the different strategies to improve the ECs removal efficiency. Furthermore, this review shows the role of different ECs in biomass profile and the relevance of using ECs-treated microalgae biomass to produce green products, as well as highlights the challenges and future research recommendations.

Microalgal bioremediation of brackish aquaculture wastewater.

Rapid aquaculture industry development contributed to a major increase in aquaculture wastewater generation. In the context of a circular economy, aquaculture wastewater treatment should simultaneously recover nutrients from the wastewater. Among many treatment methods, bioremediation using microalgae could be a cost-effective and environmentally friendly system that can be applied to treat aquaculture wastewater and simultaneously produce high-value microalgal biomass. This study explored the feasibility of treating brackish wastewater (0.8 % NaCl) generated from a Qatari commercial tilapia farm by microalgae. At first, 10 strains were grown using wastewater from the local farm in an indoor experiment. Based on nitrogen assimilation, biomass yield, biomass quality, and ease of harvesting, 4 candidate strains (Haematococcus sp., Neochloris sp., Monoraphidium sp., and Nostoc sp.) were shortlisted for outdoor growth experiments. Although Nostoc sp. could not grow outdoor in the wastewater, the other three strains were able to assimilate at least 70.5 % of the total nitrogen in the wastewater. Haematococcus sp. and Neochloris sp. could be harvested using self-settling, whereas Monoraphidium required an energy-intensive tangential flow filtration membrane process. Hence, the overall energy requirement for bioremediation, including biomass dewatering, for Haematococcus sp., Neochloris sp., and Monoraphidium sp. were determined as 0.64, 0.78, and 5.68 MJ/m3, respectively. Neochloris sp. had almost twice the biomass yield compared to Haematococcus sp. - suggesting that Neochloris sp. could be a potential candidate for aquaculture wastewater treatment.

A comparative physicochemical property assessment and techno-economic analysis of biolubricants produced using chemical modification and additive-based routes.

Several edible and non-edible oil sources are currently being developed as renewable basestocks for biolubricant production. However, these feedstocks possess undesirable physicochemical properties limiting their lubricant applications. Chemical modification and additive-based routes could be used to modify their properties -suitable for different biolubricant applications. The first part of this study compares how the selected modifications affect the properties of the basestocks. Next, the techno-economic analysis (TEA) was conducted to study 4 selected biolubricants and a potential biolubricant derived from marine microalgae biomass. Oxidative stabilities of chemically modified biolubricants followed the order of epoxidation> triesterification> estolide. Pour points of triesters showed minimal increments and reduced for estolides, whereas epoxidation increased pour points. Estolides exhibit maximum kinematic viscosity increment among chemical modification routes, followed by TMP-transesterification and epoxidation. The oxidative stability of chemically modified biolubricants was higher than additized biolubricants; conversely, the viscosity increments and pour point reductions for additized biolubricants were higher than chemically modified biolubricants. TEA results show that the unit cost for producing 1-kg estolide was the highest among the chemical modification routes. The unit cost per kilogram of jatropha biolubricant produced using the additive-based route was lower than chemically modified biolubricants. Due to a high microalgal oil feedstock cost, the unit cost per kilogram of additized microalgae oil biolubricant was more than the unit cost of additized Jatropha oil. The techno-economic feasibility of biolubricant production from marine microalgal oil could be improved by adopting a biorefinery approach.

Haematococcus pluvialis Microalgae Extract Inhibits Proliferation, Invasion, and Induces Apoptosis in Breast Cancer Cells.

Breast cancer (BC) is the most common malignant cancer in females worldwide. Drug resistance, toxicity, and the failure of current therapies to completely cure BC has challenged conventional medicine. Consequently, complementary alternative medicine has become popular due to its safety and efficacy. Haematococcus pluvialis (H. pulvialis) is a green microalga living in fresh water, and its crude extract is rich of bioactives, including carotenoids, known to inhibit cancer cell growth. In the present study, we investigated the effects of a methanol crude extract called "T1" of H. pulvialis on cell growth and migration/invasion of the BC cell line MDA-MB-231 in comparison to the fibroblast control cells. TI significantly suppressed BC cell growth, inhibited migration and invasion and induced apoptosis. Interestingly, apoptosis was mediated by a significant loss of mutant p53 protein, and increased Bax/Bcl2 ratio. Our findings support our hypothesis that T1 exerts its anti-cancer effects by inhibiting BC invasion and inducing apoptosis mediated, at least, via the p53/Bax/Bcl2 pathway. Ongoing experiments aim to identify the molecular mechanisms underpinning T1-inhibited BC cell invasion using pre-designed metastasis gene-based array method.

Industrial sludge valorization and decontamination via lipid extraction and heavy metals removal using low-cost protic ionic liquid.

Sludge is a heterogenous organic-rich matter that comprise of highly valuable biopolymers along with various contaminants including heavy metals. Sludge valorization as a renewable resource and inexpensive feedstock is key for sludge realization in circular economy context. This study presents the use of low-cost protic ionic liquid (PIL) as an integrated process medium to decontaminate heavy metal contaminated industrial sludge while selectively extract the lipid content. The treatment process focused on the use of 1-methylimidazole chloride for its higher heavy metal extraction performance compared to other screened ionic liquids (ILs). The treatment was also able to selectively extract lipids from industrial sludge, leaving a protein/carbohydrate rich solid product. Process temperature was shown to have a key impact on the biopolymers' fractionation. Operating at temperatures above 120 °C resulted in higher recovery of proteins in the lipid-rich fraction, compromising the quality of the lipid stream. Variation of the PIL acid/base (a/b) ratio also had a significant impact on the deconstruction of the sludge biopolymers, with a/b ratio of 1 resulting in highest recovery of all biopolymers. Optimal water concentration as co-solvent was found at 30 wt%, with lipid recovery reaching 60% and heavy metals extraction ranging between 29 and 89%.

Potential of microalgae as a sustainable feed ingredient for aquaculture.

An increase in fish consumption, combined with a decrease in wild fish harvest, is driving the aquaculture industry at rapid pace. Today, farmed seafood accounts for about half of all global seafood demand for human consumption. As the aquaculture industry continues to grow, so does the market for aquafeed. Currently, some of the feed ingredients are coming from low-value forage fishes (fish meal) and terrestrial plants. The production of fish meal can't be increased as it would affect the sustainability and ecosystem of the ocean. Similarly, increasing the production of terrestrial plant-based feed leads to deforestation and increased freshwater use. Hence, alternative and environmentally sustainable sources of feed ingredients need to be developed. Microalgae biomasses represent potential feed source ingredients as the cell metabolites of these microorganisms contain a blend of essential amino acids, healthy triglycerides as fat, vitamins, and pigments. In addition to serving as bulk ingredient in aquafeed, their unique array of bioactive compounds can increase the survivability of farmed species, improve coloration and quality of fillet. Microalgae has the highest areal biomass productivities among photosynthetic organisms, including fodder crops, and thus has a high commercial potential. Also, microalgal production has a low water and arable-land footprint, making microalgal-based feed environmentally sustainable. This review paper will explore the potential of producing microalgae biomass as an ingredient of aquaculture feed.

Enhancing the electrocoagulation process for harvesting marine microalgae (Tetraselmis sp.) using interdigitated electrodes.

Marketable value of algal biomass has been increasing in recent years due to its wide range of applications. This study investigates the performance of a novel cylindrical interdigitated electrode array in electrocoagulation for the harvesting of marine microalgae (Tetraselmis sp.). The new electrode array is expected to exert a dielectrophoretic (DEP) force which would assist in the harvesting of the microalgae in the electrocoagulation process. Through numerical investigation, the induction of dielectrophoretic force was confirmed in the new electrode array. In this study, 10 min electrolysis time was found to be sufficient to harvest 82.4% microalgae with 1 cm electrode distance and 50 mA/cm2 current density. Furthermore, decreasing the electrode distance to 0.5 cm increased the algal harvesting efficiency to 96.18%. Energy analysis showed that the proposed electrode array shows 38% lower specific energy consumption than the conventional flat sheet electrode array.

Outdoor scale-up of Leptolyngbya sp.: Effect of light intensity and inoculum volume on photoinhibition and -oxidation.

The effect of light intensity and inoculum volume on the occurrence of photooxidation for Leptolyngbya sp. QUCCCM 56 was investigated, to facilitate the transition from small-scale laboratory experiments to large-scale outdoor cultivation. Indoor, the strain was capable of growing at light intensities of up to 5600 µmol photons/m2 /s, at inoculation densities as low as 0.1 g/L (10% inoculation volume vol/vol). Levels of chlorophyll and phycocyanin showed a significant decrease within the first 24 h, indicating some level of photooxidation, however, both were able to recover within 72 h. When cultivated under outdoor conditions in Qatar during summer, with average peak light intensities 1981 ± 41 µmol photons/m2 /s, the strain had difficulties growing. The culture recovered after an initial adaptation period, and clear morphological differences were observed, such as an increase in trichome length, as well as coiling of multiple trichomes in tightly packed strands. It was hypothesized that the morphological changes were induced by UV-radiation as an adaptation mechanism for increased self-shading. Furthermore, the presence of contaminating ciliates could have also affected the outdoor culture. Both UV and contaminants are generally not simulated under laboratory environments, causing a mismatch between indoor optimizations and outdoor realizations.

Potential utilization of waste nitrogen fertilizer from a fertilizer industry using marine microalgae.

This study investigated the feasibility of microalgal biomass production using waste nitrogen fertilizers (WNFs) generated by the Qatar Fertiliser Company (QAFCO). From the plant, three types of WNFs (WNF1, WNF2, and WNF3) were collected; WNF1 and WNF2 had high solubility (e.g., 1000 g/L) whereas WNF3 had low solubility (65 g/L). For a lower dosage (i.e., 100 mg N/L) of these WNFs, >98% of nitrogen was soluble in water for WNF1 and WNF2; however, 52 mg N/L was soluble for WNF3. Nitrogen content in these wastes was 44, 43, and 39% for WNF1, WNF2, and WNF3, respectively. As these WNFs were used as the sole nitrogen source to grow Tetraselmis sp., Picochlorum sp., and Synechococcus sp., Tetraselmis sp. could utilize all the three WNFs more efficiently than other two strains. The biomass yield of Tetraselmis sp. in a 100,000 L raceway pond was 0.58 g/L and 0.67 g/L for mixed WNFs (all WNF in equal ratio) and urea, respectively. The metabolite profiles of Tetraselmis sp. biomass grown using mixed WNFs were very similar to the biomass obtained from urea-added culture - suggesting that WNFs produced Tetraselmis sp. biomass could be used as animal feed ingredients. Life cycle impact assessment (LCIA) was conducted for six potential scenarios, using the data from the outdoor cultivation. The production of Tetraselmis sp. biomass in QAFCO premises using its WNFs, flue gas, and waste heat could not only eliminate the consequences of landfilling WNFs but also would improve the energy, cost, and environmental burdens of microalgal biomass production.

A novel electrocoagulation electrode configuration for the removal of total organic carbon from primary treated municipal wastewater.

In this paper, the removal of total organic carbon (TOC) from a primary treated municipal wastewater using a new electrode configuration in electrocoagulation was evaluated. The used electrode configuration induces a dielectrophoretic (DEP) force by using an asymmetrical aluminum electrode with an alternating current power supply. The impact of applied current, electrolysis time, and interelectrode distance on the removal efficiency of TOC were evaluated. The experimental results showed that the maximum removal efficiency of TOC was obtained at 30 min electrolysis time, 600 mA applied current, and 0.5 cm interelectrode distance. Under these operating conditions, the TOC removal was 87.7% compared to 80.5% using symmetrical aluminum electrodes with no DEP effect. The energy consumption at the selected operating conditions was 3.92 kWh/m3. The experimental results were comparable with the simulation results done by COMSOL Multiphysics software.

Effect of the induced dielectrophoretic force on harvesting of marine microalgae (Tetraselmis sp.) in electrocoagulation.

In this study, a new electrocoagulation electrode configuration has been investigated in order to induce dielectrophoretic (DEP) force for the enhanced harvesting of marine microalgae (Tetraselmis sp.). Asymmetrical aluminum electrodes with an alternative current power supply were used. The impact of electrode configuration, current density and electrolysis time were evaluated. A maximum algal harvesting efficiency of 90.9% was achieved using 7.1 mA/cm2 current density and 10 min electrolysis time. The energy consumption was found to be 4.62 kWh/kg of microalgae. The major significance of using the new electrode configuration was found in the aluminum content in the harvested biomass which decreased by 52% compared to the conventional symmetrical electrocoagulation electrodes.

Energy recovery and nutrients recycling from municipal sewage sludge.

Hydrothermal Liquefaction (HTL) could be a promising and better alternative to other techniques for energy recovery from municipal sewage sludge (MSS). However, the nutrients (i.e., N, and P) recovery potential from the byproducts, generated in the HTL of MSS, needs to be studied so that a comprehensive sludge management practice could be adopted. In this study, HTL process temperature (275-400 °C), and reaction time (30-120 min) were first investigated for biocrude yield and release of the nutrients to the aqueous phase liquid (APL) and biochar. The maximum energy recovery (i.e., 59%) and maximum energy return on investment (i.e., 3.5) were obtained at 350 °C and 60 min of holding time. With the increase in HTL reaction time, the concentration of nitrogen in the APL increased (5.1 to 6.8 mg/L) while the concentration of phosphorus decreased (0.89 to 0.22 mg/L); the opposite was observed for the biochar. The nutrient recycling efficiency from the APL using microalgae was found to be strain-specific; nitrogen recycling efficiency by Picochlorum sp. and Chlorella sp. were 95.4 and 58.6%, respectively. The APL, derived from 1 kg MSS, could potentially produce 0.49 kg microalgal biomass. Since the concentrations of various metals in the biochar samples were substantially lower compared to their concentrations in raw MSS, the application of biochar as a soil conditioner could be very promising. Overall, net positive energy could be recovered from MSS using the HTL process, while the nutrients in the APL could be used to cultivate specific microalgae, and biochar could be applied to enhance the soil quality.

A feasibility study of utilizing hydrothermal liquefaction derived aqueous phase as nutrients for semi-continuous cultivation of Tetraselmis sp.

The feasibility of substituting 50% nutrients by aqueous phase liquid (APL), derived from hydrothermal liquefaction of Tetraselmis sp. biomass, in a semi-continuous cultivation of Tetraselmis sp. was studied. Growth experiments were conducted in indoor photobioreactor and outdoor raceway tank for three consecutive cycles. At the end of exponential growth pahse, 75% of the culture was harvested, and the supernatant was returned to the cultivation system. For control cultures, fresh nutrients were added; however, for the experimental cultures, an appropriate volume of APL was added to replace half of the nutrients. Either indoor or outdoor, the growth rate and biomass yield in APL-added cultures were either equal or slightly better compared to control culture; although APL had little to no effect on the metabolite content of Tetraselmis sp., metabolites profile of Tetraselmis sp. varied between APL-added and control cultures. Nevertheless, 50% nutrients requirements for microalgae cultivation could be replaced by APL.

The effect of culture salinity on the harvesting of microalgae biomass using pilot-scale tangential-flow-filter membrane.

In this study, the effect of culture salinity (4-6% NaCl) on the harvesting of two microalgal strains (i.e., Picochlorum sp., and Tetraselmis sp.) was investigated using pilot-scale TFF membranes. The cultures of these two strains were collected from their respective continuous cultivation in 2, 25,000 L raceway ponds. For both strains, an increase in culture salinity aggravated the membrane fouling and hence negatively influenced the permeate flux rate, biomass concentrating factor, and energy requirement in biomass harvesting. For the TFF membranes, an increase in 1% NaCl salinity, the volume of processed permeate reduced by 30-44 %, the energy consumption per unit volume of permeate increased by 3-63%, and the biomass concentrating factor reduced by 47-61%.

Effect of harvesting methods on the energy requirement of Tetraselmis sp. biomass production and biocrude yield and quality.

A halo-tolerant Tetraselmis sp. was grown in a 100,000 L raceway pond in the Qatari desert environment. As the biomass density reached 0.679 g/L, after 7 days, five different harvesting methods (i.e., cross-flow filtration, electrocoagulation, and coagulation-flocculation by FeCl3, NaOH, and alum) were applied to harvest the biomass. Hydrothermal liquefaction, for all the harvested biomass, was conducted at 350 °C for 30 mins in 10 mL Swagelok unions. The biocrude yield from cross-flow processed biomass (i.e., control) was 50.8%. Biocrude yield from electrocoagulation and alum processed biomass were 62.7% and 60.4% respectively where aluminum could have a catalytic effect. Biocrude yield from FeCl3 and NaOH processed biomass were 42.9% and 19.8% respectively. The total fraction of alkenes and alkanes was higher in the biocrude obtained from alum-harvested biomass, compared to other biocrude samples. However, the transition of metal species from biomass to biocrude was very low in all the biocrudes.

Factors affecting the induction of UV protectant and lipid productivity in Lyngbya for sequential biorefinery product recovery.

With objective to design cyanobacterial biorefinery, taking Lyngbya as a model organism, a detail sequential protocol has been developed for production of UV protectant and lipids. This study addresses ultra violet radiations (UVR), exposure time of UVRT, nitrogen stress, salinity, oxidative stress to produce UV protectant and lipid in cyanobacteria. To evaluate these parameters a design of experiment (DOE; using a 2 k design) was performed. Based on chemical solubility property of UV protectant in form of mycosporine like amino acid (MAAs) and lipids were extracted. Quantitative and qualitative assay of UV protectant was confirmed by spectrophotometric scanning and Fourier-transform infrared spectroscopy and lipid through fatty acid methyl esters analysis. Nitrogen abundance and high oxidative stress is helpful in the synthesis of UV protectant. This study concluded, UV exposure is good strategy to induce synthesis of UV protectant and saturated lipid productivity. This biorefinery approach encourages economical and environmentally sustainable options.

Long-term semi-continuous cultivation of a halo-tolerant Tetraselmis sp. using recycled growth media.

In this study, a halotolerant Tetraselmis sp. was selected for 11-month outdoor semi-continuous cultivation in one sq. m raceway tank in the Qatari desert. A fraction of the culture was harvested using ferric chloride, and the growth media was returned to the tank. The recycling of culture media continued till the culture salinity reached 8% NaCl; 90% culture was then harvested, and the remaining culture fraction was used as inoculum for a new cultivation cycle. The growth of Tetraselmis sp. was not affected by incremental salinity although the intracellular metabolites varied; the average biomass productivity was 17.8 g/m2/d. Harvesting efficiency was slightly affected by the increase in salinity. Iron content in the harvested biomass was in the range of 1.5-3.3%, and acidic solution (pH = 1.48) was able to recover 91.3% iron from the harvested biomass. Nonetheless, Tetraselmis sp. could be grown continuously throughout the year in Qatar's climate condition.

Microalgae harvesting by pH adjusted coagulation-flocculation, recycling of the coagulant and the growth media.

Coagulation-flocculation can be considered as one of the least energy intensive microalgae biomass harvesting processes. However, cost of the coagulant and biomass contamination are two critical issues that need to be considered. In this study, ferric chloride (72-96mg/L) was used to effectively harvest Scenedesmus sp. (530mg/L) - grown in BG-11 media and wastewater. Reducing the culture pH below 6.5, greatly improved the harvesting efficiency. Acidic solution (pH 1.0) was very effective to recover (almost 90%) the associated iron from the harvested biomass. Scenedesmus sp. was able to grow in the supernatant and utilize the residual iron in it. Iron extracted solution, with a supplementation of 9.8mg/L ferric chloride, was able to achieve similar harvesting efficiency. The potential recovery of iron from the harvested biomass and its reuse in the harvesting can improve the biomass quality for subsequent downstream processing while reducing the cost.

A comparative study of the growth of Tetraselmis sp. in large scale fixed depth and decreasing depth raceway ponds.

In this study, an alternative approach was proposed where excess seawater would be added only during inoculation (DD) rather than daily addition (FD). Growth and metabolite contents of Tetraselmis sp. weren't affected for daily increase of 2% NaCl salinity. Tetraselmis sp. was then cultured in DD and FD pond. In DD pond, initial culture depth was 23.5cm and its depth reduced as no water was added; for FD pond, everyday sterilized seawater was added to maintain 20cm depth. DD pond had higher biomass productivity compared to FD pond, until DD pond was deeper than FD pond; metabolite content and FAME profile of Tetraselmis sp. were also similar in both cultures. Therefore, considering the simplicity in operation, halo tolerant microalgae can be grown in DD pond method.