Algal Biomass Concentration Research Articles

The impact of rainfall events on dissolved oxygen concentrations in a subtropical urban reservoir

Understanding controls of dissolved oxygen (DO) concentrations in reservoirs is important as they are important for fisheries and a significant driver of greenhouse gas emissions. The latter is of global significance as IPCC inventories now require greenhouse gas emissions from artificial reservoirs to be included. Declines in dissolved oxygen (DO) concentrations in lakes and reservoirs have been linked to climate change and human activity. However, these effects can vary widely in any given region under various meteorological conditions. There is a clear need to know how changes in weather patterns affect DO in reservoirs by changing internal processes. Based on a six-year (2016–2021) high-frequency (twice a week) dataset from a shallow urban reservoir (Xinglinwan Reservoir) in subtropical China, the long-term (six years) and short-term (8–72-h) drivers of DO concentrations in surface waters were evaluated. Over the past six years, the concentration of DO has gradually decreased in the reservoir from 2016 to 2021. Multivariate adaptive regression spline (MARS) models were developed to identify the key factors explaining variability in DO and partial least squares path models (PLS-PM) were used to explore the short-term relationships between DO and environmental variables in rainy and dry (non-rain) periods, separately. We identified three key drivers operating on different time scales. First, the long-term decline of DO in Xinglinwan Reservoir from 2016 to 2021 was best explained by anthropogenic nutrient inputs. Second, rainy periods prior to sampling reduced DO concentrations indirectly by affecting the algal biomass and nutrient concentrations. This effect varied in complexity with the duration of the rainfall period. Third, water temperature best explained DO concentrations during dry periods, while wind reduced DO by reducing algal biomass. We conclude that anthropogenic nutrient and organic matter inputs drive long-term oxygen declines in urban subtropical reservoirs, while meteorological factors determine short-term variability in DO concentrations.

Advanced treatment and Resource recovery of brewery wastewater by Co-cultivation of filamentous microalga Tribonema aequale and autochthonous Bacteria

To use unicellular microalgae to remove waste nutrients from brewery wastewater while converting them into algal biomass has been explored but high-cost treatment and low-value biomass associated with current technologies have prevented this concept from further attempts. In this study, a filamentous microalga Tribonema aequale was introduced and the alga can grow vigorously in brewery wastewater and algal biomass concentration could be as high as 6.45 g L−1 which can be harvested by a cost-effective filtration method. The alga together with autochthonous bacteria removed majority of waste nutrients from brewery wastewater. Specifically, 85.39% total organic carbon (TOC), 79.53% total dissolved nitrogen (TN), 93.38% ammonia nitrogen (NH3–N) and 71.33% total dissolved phosphorus (TP) in brewery wastewater were rapidly removed by co-cultivation of T. aequale and autochthonous bacteria. Treated wastewater met the national wastewater discharge quality, and resulting algal biomass contained large amounts of high-value products chrysolaminarin, palmitoleic acid (PLA) and eicosapentaenoic acid (EPA). It is anticipated that reduced cost of algal harvesting coupled with value-added biomass could make T. aequale as a promising candidate for brewery wastewater treatment and resource utilization.

Eco-friendly products for sorption of fenamiphos, imidacloprid, and oxamyl pesticides from water and their detection by UV/VIS spectrophotometry

The present study evaluates the efficiency of the dry biomass of the microalgae Spirogyra porticalis and Nannochloropsis oculata for the removal of fenamiphos, imidacloprid, and oxamyl pesticides from water. The influence of incubation time, pesticide concentration, and algal biomass concentration on the degradation of pesticides were considered in the study. A rapid UV-Vis spectrophotometry method was developed and validated for the analysis and quantification of pesticides in the context of bioremediation with microalgae. The optimum conditions were obtained at 15 min, 50 mg/L pesticide concentration and 900 mg/L algal biomass with the response of 67.27% and 68.67 for fenamiphos by S. porticalis and N. oculata, respectively. For Imidacloprid, the optimum conditions were obtained at 15 min, 50 mg/L pesticide concentration and 900 mg/L algal biomass with the response of 28.20% and 35.55 for fenamiphos by S. porticalis and N. oculata, respectively. With the same, previse conditions the response of 65.71 and 81.31% for oxamyl by S. porticalis and N. oculata, respectively. This study confirmed that removing pesticides by the microalgae S. porticalis and N. oculata are both active and biomass of algae dependent. Consequently, these algae biomass exhibited a potential reduction of pesticides in contaminated water samples.​

Recovery of Chlorella biomass using Fe3O4 and Fe3O4@SiO2 magnetic nanoparticles: isotherm and thermodynamic characteristics of adsorption

AbstractHarvesting microalgae by centrifugation and filtration is very costly, affecting technical and economical feasibility of downstream processing of algal biomas to bioproducts. Flocculation is a potential technique for recovery of algae biomass. Particularly, flocculation using magnetic nanoparticles offers high separation efficiency due to their high surface area and magnetic properties. In this work, the synthesized magnetic nanoparticles including Fe3O4 and Fe3O4@SiO2 were used to harvest C. sorokiniana TH01 from aqueous suspension. The effects of pH, adsorbent dosage, algal biomass concentration, temperature and reaction time on harvesting performance were investigated. It was revealed that the optimal C. sorokiniana TH01 harvesting conditions for Fe3O4 were pH of 5, adsorbent dosage of 0.5 g/L, biomass concentration of 2‐2.5 g/L, temperature 25oC and reaction time 20‐30 min. For Fe3O4@SiO2, the optimal conditions were pH of 7, adsorbent dosage of 0.6 g/L, with the same biomass concentration, temperature and reaction time as Fe3O4. Under the optimal conditions, Fe3O4 and Fe3O4@SiO2 can be regenerated up to three cycles with harvesting efficiency till remained over 55%. Adsorption of C. sorokiniana TH01 on Fe3O4 and Fe3O4@SiO2 exhibited the best fitness with Langmuir isortherm with R2 and maximal adsorption capacity estimated of 0.995 and 6.55 g/g and 0.9971 and 9.53 g/g, respectively. Thermodynamics study revealed that an adsorption of C. sorokiniana TH01 on Fe3O4 and Fe3O4@SiO2 was exothermic process. Furthermore, XRD, EDS, SEM, TGA and FT‐IR data confirmed the successful binding of microalgae cells on surfaces of Fe3O4 and Fe3O4@SiO2. The super‐magnetization intensities (> 22 emu/g) of the synthesized materials demonstrated an excellent separation capability with external magnetic devices.

Simultaneous utilization of CO2 and nitrate wastes from compact recirculating aquaculture system for improving algal biomass (Scenedesmus armatus) production

Tilapia cultivation in an air-tight culture tank of a recirculating aquaculture system (RAS) was conducted for 8 days to produce CO2 for growing Scenedesmus armatus in bubble column photobioreactors. The average CO2 concentrations in the headspace of the culture tank were determined at 925 ± 73.4 and 1619 ± 197.7 ppm for fish stocking densities of 3 and 10 kg/m3, respectively. These CO2 concentrations were higher than CO2 concentrations at the tank inlet (496 ± 13.9 ppm) exposed to the atmosphere. Using the captured CO2 and nitrate from the effluent of a commercial tilapia farm for cultivating S. armatus yielded higher algal biomass concentration (621 ± 41.2 mg/L) than using ambient air (410 ± 30.1 mg/L). Insufficient nitrate in RAS effluent is the limiting factor for CO2 utilization and algal biomass production. In conclusion, this study demonstrates the possibility of repurposing CO2 from RAS to enhance algal cultivation.

Cyanidiales-Based Bioremediation of Heavy Metals.

With growing urbanization and ongoing development activities, the consumption of heavy metals has been increasing globally. Although heavy metals are vital for the survival of living beings, they can become hazardous when they surpass the permissible limit. The effect of heavy metals varies from normal to acute depending on the individual, so it is necessary to treat the heavy metals before releasing them into the environment. Various conventional treatment technologies have been used based on physical, chemical, and biological methods. However, due to technical and economic constraints and poor sustainability towards the environment, the use of these technologies has been limited. Microalgal-based heavy metal removal has been explored for the past few decades and has been seen as an effective, environment-friendly, and inexpensive method compared to conventional treatment technology. Cyanidiales that belong to red algae have the potential for remediation of heavy metals as they can withstand and tolerate extreme stresses of heat, acid salts, and heavy metals. Cyanidiales are the only photosynthetic organisms that can survive and thrive in acidic mine drainage, where heavy metal contamination is often prevalent. This review focuses on the algal species belonging to three genera of Cyanidiales: Cyanidioschyzon, Cyanidium, and Galdieria. Papers published after 2015 were considered in order to examine these species' efficiency in heavy metal removal. The result is summarized as maximum removal efficiency at the optimum experimental conditions and based on the parameters affecting the metal ion removal efficiency. This study finds that pH, initial metal concentration, initial algal biomass concentration, algal strains, and growth temperature are the major parameters that affect the heavy metal removal efficiency of Cyanidiales.

Removal of fenamiphos, imidacloprid, and oxamyl pesticides from water by microalgal Nannochloropsis oculata biomass and their determination by validated HPLC method

The present study assessed the removal of fenamiphos, imidacloprid, and oxamyl pesticides from water using algal Nannochloropsis oculata biomass. Several factors, such as algal biomass concentration, incubation time, and pesticide concentration, were studied for their impact on pesticide removal. Analysis and quantification of pesticides by rapid HPLC have been developed and validated. The optimum conditions were obtained at 15 min, 50 mg/L of pesticide concentration, and 4,500 mg/L of the algal biomass with 92.24% and 90.43% removal for fenamiphos and imidacloprid, respectively. While optimum parameters of 10 min incubation, 250 mg/L of pesticide concentration, and 2,750 mg/L of the algal biomass exhibited 67.34% removal for oxamyl. N. oculata, marine microalgae, successively removed different concentrations of the tested pesticides from water, and the algal biomass showed a potential reduction of pesticides in polluted water samples.

Phosphorus uptake and accumulation in Chlamydomonas reinhardtii: Influence of biomass concentration, phosphate concentration, phosphorus depletion time, and light supply

The model microalga Chlamydomonas reinhardtii was cultivated under P depleted and P repleted conditions to test the influence of dissolved P concentration (0–20 mg-P·L−1), initial algal biomass concentration (0.17–0.57 g-DW·L−1), P-depletion time (1 h – 4 days) and light supply (continuous illumination versus darkness) on phosphate uptake rate (mg-P·h−1·L−1) and the cellular P content (as %P of dry cell mass). Dissolved P concentration positively influenced cellular P content, while biomass concentration and P-depletion time did not. Biomass concentration and P-depletion time instead positively influenced P uptake rates. Light supply neither influenced cellular P content nor P assimilation. These findings evidence that depleting the cells at high initial biomass concentration could enhance P removal during wastewater treatment in waste stabilization ponds. Practically, these findings imply that high P removal from wastewater could be achieved by exposing ‘concentrated’ P-depleted biomass to P-laden influent in a relatively short contact-time reactor and subsequently harvesting and removing the resultant P-rich biomass. This stage would be followed by normal biomass growth in larger ponds which depletes the remaining P, with this biomass being harvested and returned to the contact tank for P removal.

Towards enhancement of fungal hydrolytic enzyme cocktail using waste algal biomass of Oscillatoria obscura and enzyme stability investigation under the influence of iron oxide nanoparticles

Development of low-cost and economic cellulase production is among the key challenges due to its broad industrial applications. One of the main topics of research pertaining to sustainable biomass waste based biorefinaries is the development of economic cellulase production strategies. The main cause of the increase in cellulase production costs is the use of commercial substrates; as a result, the cost of any cellulase-based bioprocess can be decreased by employing a productive, low-cost substrate. The goal of the current study is to develop low-cost cellulase using the carbohydrate-rich, renewable, and widely accessible cyanobacteria algae Oscillatoria obscura as the production substrate. Maximum cellulase was produced utilising the fungus Rhizopus oryzae at substrate concentration of 7.0 g among various tested concentrations of algal biomass. Maximum production rates of 22 IU/gds FP, 105 IU/gds BGL, and 116 IU/gds EG in 72 h were possible under optimal conditions and substrate concentration. Further investigations on the crude enzyme's stability in the presence of iron oxide nanoparticles (IONPs) revealed that it was thermally stable at 60 °C for up to 8 h. Additionally, the crude enzyme demonstrated pH stability by maintaining its complete activity at pH 6.0 for 8 h in the presence of the optimal dose of 15 mg IONPs. The outcomes of this research may be used to investigate the possibility of producing such enzymes in large quantities at low cost for industrial use.

Reduction of algal wall-growth biofilm for the cultivation of Chlorococcum in photobioreactors using commercial surfactants and floating plastic media

During the cultivation of Chlorococcum humicola in photobioreactors (PBRs), significant biofilm formation occurred, leading to light limitation and lower productivity. This work presents the possibility of using commercial surfactants to reduce wall-growth biofilm in PBRs. Results confirm that sodium dodecyl sulfate (SDS) at 0.0082 mM can successfully control wall-growth biofilm in the cultivation of C. humicola more than CTAB and Triton X-100. The addition of SDS into 2-L PBRs, built from either acrylic or glass, results in 68–158 % and 28–43 % increases in algal biomass concentrations compared to those without SDS addition. PBRs applying with SDS at the start of the cultivation can be operated for 23 days without stopping aeration to remove biofilm. Both SDS and floating plastic media were effective in algal biofilm control when applying in 60-L PBRs. The addition of SDS is seen to offer a practical solution to reduce algal biofilm on both glass and acrylic surfaces and promote higher biomass concentration during the cultivation.

Algal Biomass-Loaded Hydrogel Scaffolds as a Biomimetic Platform with Antibacterial and Wound Healing Activities

The confluence of hydrogel scaffolds and dried algal biomass (AB), consisting of all the bioactive compounds, offers the possibility to facilitate wound healing while simultaneously instilling antibacterial benefits. For this purpose, a single-step synthesis of algal (Chlorella sorokiniana) biomass-loaded hydrogel scaffolds (AHS) was achieved. C. sorokiniana has been used in different areas for several years and has proved attractive to the pharmaceutical and cosmetic industries. Of note, the presence of phytochemicals and various bioactive compounds provides an added health benefit. Hitherto, we report AHS with accelerated wound healing along with potent anti-inflammatory and antibacterial properties. AHS consisting of different concentrations of AB was applied for 14 days on excisional wounds in mice. Microscopic analyses, assessment of proinflammatory and anti-inflammatory cytokines, and histological studies were performed to investigate wound healing. These scaffolds were extensively characterized and studied using Fourier transform infrared, X-ray diffraction, Raman, atomic force microscopy, transmission electron microscopy, scanning electron microscopy, swelling, rheological, thermal, and mechanical analyses. AHS have excellent biocompatibility in addition to significant antibacterial activity against Escherichia coli (99%) and Staphylococcus aureus (98%). We believe that the as-synthesized AHS have the potential to broaden the arsenal of more effective wound healing processes along with antibacterial activities.

Optimization of biohydrogen production from microalgae by response surface methodology (RSM)

In the present study, the design and fabrication of a micro-photobioreactor to produce the bio-hydrogen are aimed. Furthermore, the optimization of variables affecting hydrogen production was optimized using the response surface methodology (RSM). A quadratic model was used to predict the behavior of samples. The central composite design was applied using 20 treatments and 6 replications in the central points. Independent variables for evaluation included sulfur concentration (0.5–1%), run time (5–120 h) and algal biomass concentration (50–100 g/L). The results suggested that test length had a significant impact on hydrogen production and that sulfur content and biomass concentration had no significant effect on hydrogen production but did cause a little increase. The experimental values of response variable in these optimal conditions match the predicted values. Optimal conditions to produce bio-hydrogen were identified as the sulfur concentration of 0.75%, run time of 101.96 h, and biomass concentration of 53.31 g/L for maximum production of bio-hydrogen (66.32 mL g-VS−1). In conclusion, the response surface methodology can predict the production and extraction of bio-hydrogen in photobioreactors.

Optimization of light intensity and photoperiod for growing Chlorella sorokiniana on cooking cocoon wastewater in a bubble-column bioreactor

Previous studies showed that cooking cocoon wastewater (CCW) could be used as a medium alternative directly to cultivate Chlorella sorokiniana (FACHB-275) in a bubble-column bioreactor. In order to further improve culture conditions and enhance algal biomass production, impacts of light intensity and photoperiod on biomass concentration, nutrient removal, and chemical compositions of C. sorokiniana were investigated in this work when this alga grew on CCW in the bioreactor. Results showed that the maximum values of algal biomass concentration and productivity of 3.96 g/L and 516.1 mg/L/d, respectively, were achieved when C. sorokiniana was cultivated in the bioreactor for 7 days under a light intensity of 150 μmol/m2/s and photoperiod of 16L:8D. And the optimal light intensity and photoperiod for biomass production were 104.3 μmol/m2/s and 15.3L:8.7D, respectively, which were anaylzed by a quadratic model. Correspondingly, removal efficiencies of ammonium, total nitrogen, total phosphorus, and chemical oxygen demand were 93.12, 80.79, 93.08, and 69.08%, respectively. In addition, chemical compositions in this alga varied with the changes of light conditions (i.e., light intensity and photoperiod), suggesting that a desirable chemical composition could be obtained by regulating the light conditions. These results would be helpful to large-scale cultivation of this alga in CCW using photobioreactors.

Experimental Study of the Quantitative Impact of Flow Turbulence on Algal Growth

Flow turbulence has been widely accepted as one of the essential factors affecting phytoplankton growth. In this study, laboratory cultures of Microcystis aeruginosa in beakers were carried out under different turbulent conditions to identify the quantitative relationship between the algal growth rate and the turbulent intensity. The turbulent intensity (represented by energy dissipation rate, ε) was simulated with the software FLUENT. Daily measurement of the two parameters (algal biomass and chlorophyll-a concentration) was carried out during the experimental period to represent the algal growth rate. Meanwhile, the rates of photosynthetic oxygen evolution and chlorophyll fluorescence intensity were calculated to investigate the photosynthetic efficiency. The results indicated that the growth rate of Microcystis aeruginosa became higher in the turbulent environment than in the still water environment under the designed experimental conditions. The peak growth rate of Microcystis aeruginosa occurred when ε was 6.44 × 10−2 m2/s3, over which the rate declined, probably due to unfavorable impacts of strong turbulence. In comparison, the maximum rate of photosynthetic oxygen evolution occurred when ε was 0.19 m2/s3. Based on the findings of this study, an exponential function was proposed in order to incorporate the effect of flow turbulence into the existing algal growth models, which usually just consider the impacts of nutrient availability, illumination, and temperature.

A novel acrylic acid-Schizochytrium sp. bio-based polymer: Design, synthesis, and properties

The innovative synthesis of a bio-based poly(acrylic acid) (PAA) and Schizochytrium sp. was performed for the first time. Schizochytrium sp. whole biomass (SCZ) and the insoluble cell fraction (cell wall) (FIP) were used as precursors for the synthesis of the copolymer. Infrared spectroscopy, thermogravimetry, and scanning electron microscopy were performed to determine copolymer formation, thermal properties, and morphology. The new hybrid biopolymers’ thermal and mechanical properties were found to be dependent on microalgae biomass type and concentration. Transition temperature (Tg) of the hybrid PAA-SCZ biopolymers decreased when increasing microalgae percentage, while the opposite occurred for PAA-FIP. It was evaluated the maximum mechanical strength and elongation capacity of PAA-SCZ and PAA-FIP at room temperature and 50 °C. The elongation percentage of the obtained copolymer raised 2–7 times upon increasing the algal biomass concentration. Flexibility increased 3–4 fold when using FIP instead of SCZ. The entire biomass and the cell wall induced structural changes in the hybrid biopolymers similar to those observed in elastomers. A hydrolytic assessment revealed a high swelling capacity (30000 %) for PAA-SCZ hybrid polymer when exposed to physiological conditions (pH 7.4). In terms of these new properties, they can be suitable for biological and environmental applications.

Acid hydrolysis conditions for the production of fine chemicals from Gracilaria birdiae alga biomass

Gracilaria birdiae is a tropical agarophytes species of red seaweed that is rich in carbohydrates and presents a great potential for mariculture and economic use. However, it is still understudied as a potential renewable resource. In this study, the hydrolysis conditions of G. birdiae algal biomass, reaction time, and sulfuric acid concentration for obtaining monosaccharides, organic acids, and furanic compounds were optimized. Glucose and galactose concentrations were found to be more affected by algal biomass concentration, while the production of 5-hydroxymethylfurfural (5-HMF) and organic acid were most affected by sulfuric acid concentration. The most suitable conditions to produce glucose (28.56 ± 0.72 g·L−1) and galactose (108.03 ± 1.32 g·L−1) were at 121 °C, with sulfuric acid 1.3 mol·L−1, 841.59 g·L−1 of algal biomass and time of 20 min. For cellobiose (25.39 ± 0.43 g·L−1), the condition was sulfuric acid 0.6 mol·L−1, 680 g·L−1 of biomass, and 10 min. For 5-HMF (19.82 ± 0.43 g·L−1), it was sulfuric acid 0.6 mol·L−1, 680 g·L−1 of biomass and 30 min. Finally, for levulinic (38.88 ± 0.58 g·L−1) and formic acids (26.75 ± 0.54 g·L−1) and, the best conditions were sulfuric acid 2.0 mol·L−1, 680 g·L−1 of biomass and 30 min. Thus being, Gracilaria birdiae is a promising renewable resource to produce fine chemicals and fermentable compounds by optimizing its acid hydrolysis conditions.

Artificial neural network and techno-economic estimation with algae-based tertiary wastewater treatment

In this study, secondary-treated (ST) wastewater effluents supplemented with different nutrient sources were employed for microalgae cultivation in outdoor pilot-scale pools operated under natural environmental conditions. The BG11-supplemented wastewater showed a high algal biomass concentration = 0.79 ± 0.04 g/L, with NO3−, NH4+, and PO43− removal efficiencies = 83.20 ± 2.90 %, ≈ 100 %, and 93.50 ± 3.28 %, respectively. The corresponding lipid, protein, and carbohydrate contents of microalgae were 25.60 ± 0.80 %, 29.00 ± 0.88 %, and 18.40 ± 1.00 % w/w dry cell weight (DCW) basis, respectively. The ranges of protein and carbohydrate contents of lipid-extracted biomass were 25–40 % and 17–23 %, respectively. A three-layer feed-forward back-propagation artificial neural network (ANN) was used to predict the microalgae DCW, based on six inputs, i.e., temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), NO3−, and PO43-. The optimized ANN architecture (6–10 – 1), with the Levenberg-Marquardt training algorithm, achieved the highest predictive performance (R2: 0.983). Based on the ANN sensitivity analysis, the environmental factor’s relative importance arranged as NO3− > PO43- > pH ≈ DO > temperature > EC. The nutrient removal ability and biochemical composition of microalgae were expressed regarding capital and operational costs, and profits. The payback period of the wastewater-based algal cultivation system was shorter than the project’s lifetime, implying a sustainable and feasible application.

Evaluation of the effect of reaction time on nutrients removal from secondary effluent of wastewater: Field demonstrations using algal-bacterial photobioreactors.

Real field demonstrations to assess the removal efficiency of nutrients and organic matter from domestic wastewater were carried out using algal-bacterial photobioreactors. The reactors which consisted of three basins of 200 L were fed with secondary effluent of domestic wastewater and operated under natural day light/dark cycles. The results demonstrated that reaction time (RT) has a substantial role on the whole process performance. Whereas inoculation with nitrifiers affected the process only in some aspects. The enhancement in the dissolved oxygen production rate (1.15 mg O2. L−1.h−1) was in alignment with growing higher algal biomass concentrations due to the increase in RT. COD removal rates were significantly increased (p < 0.05) with increasing the RT, and removal rates of 27%, 46% and 50% were obtained under RTs of 2, 3 and 4hrs. respectively. Meanwhile, 30%, 84% and 95% of the phosphorus was removed under the same studied RTs. No significant effect was recorded due to the addition of nitrifying bacteria on the removal of both COD and phosphorus. Ammonium (NH4+-N) removal rates were also increased with increasing RT and by the addition of nitrifiers, such that removal rates of 13%, 21% and 31% were obtained in basins inoculated with nitrifiers, but 11%, 14% and 19.5% were obtained in non-inoculated basins under RT of 2, 3, and 4 hrs. respectively. These results provide some new insights into algal-bacterial symbiosis systems under real field conditions which could be helpful for further process development.

Development and Applications of Attached Growth System for Microalgae Biomass Production

With realizing the potential of algal biomass as a good natural resource for the harnessing of valuable bioproducts, algal biomass production has gained a lot of interest in recent years. However, due to some limitations such as low harvesting efficiency, higher nutrient supply, and high water requirement, the production of algal biomass is uneconomical. Over the past several years, researchers are continuously working on growing algae as a biofilm for easy microalgae harvesting, concentration of algal biomass to a great extent, and requiring less quantity of water as compared to other microalgae cultivation methods. Most of the documented studies have been carried out on either use of algal biomass for tertiary treatment of wastewater or cultivation and harvesting of algal biomass for biofuel production. Limited research studies have documented other applications of the algal biofilm system. The present review paper summarizes the current knowledge on various factors affecting microalgae growth, development of algal biofilm, and operation of algal biofilm systems to help properly understand and optimize these factors for better economics, more positive environmental impacts, and successful potential applications of the attached growth systems. The important factors include the structure of algal biofilms, EPS matrix, supporting materials, nutrient availability, environmental conditions, and biofilm thickness and harvesting frequency. The potential applications such as wastewater treatment, CO2 sequestration, microalgae–microbial fuel cell, large-scale biomass production, and water quality improvement are also discussed.

High methylmercury uptake by green algae in Lake Titicaca: Potential implications for remediation

Anthropogenic pressure in the high altitude lakes such as Titicaca and Uru (Bolivia) may favor the production of methylmercury (MeHg) known to accumulate in trophic chains. Periphyton associated with emerged aquatic plants (totoras) from the lake shores accumulates and demethylates MeHg providing a potential cost-effective water treatment technique. In this laboratory study, we measured the MeHg uptake kinetics of a consortium of green algae isolated from Lake Titicaca totora's periphyton. The most abundant algal consortium, composed of Oedogonium spp., Chlorella spp., Scenedesmus spp., was exposed to rising MeHg concentrations (from 5 to 200 ng·L−1) to assess their maximum potential capacity for MeHg accumulation. Various algal biomass concentrations were tested to choose the optimal one. Results provided a net MeHg uptake rate by this algal consortium of 2.38 amol ng−1·h−1·nM−1 (the total uptake was 2863 ng MeHg·g−1) for an initial concentration of 200 ng MeHg·L−1 with an algal biomass concentration of 0.02 g·L−1. This initial MeHg concentration is 1000 times higher than the one measured in the eutrophic Cohana Bay of Lake Titicaca, which shows the high accumulation potential of these green algae. Our data suggest that periphyton has a high potential for the treatment of Hg contaminated waters in constructing wetlands in the Andean Altiplano.