Harvesting Of Microalgal Biomass Research Articles

The Crucial Impact of Microbial Growth and Bioenergy Conversion on Treating Livestock Manure and Antibiotics Using Chlorella sorokiniana

The residual antibiotics in livestock excreta (LE) have been regarded as a potential threat to the ecosystem and human society. Some photoautotrophic microalgae, however, were found to metabolize them during active biomass photosynthesis. This study investigates how the strength of the antibiotics impacts the overall biodiesel yield and composition of the harvested microalgal biomass grown from LE. The microalgal growth results demonstrate that increasing the concentration of residual antibiotics suppresses the microalgal growth rate from 0.87 d−1 to 0.34 d−1. This 61% lower biomass production rate supports the proposition that the kinetic impact of antibiotics may slow lipid synthesis. Moreover, the analytical results of fatty acid methyl ester (FAME) demonstrate that amoxicillin substantially reduces the C16:0 content by over 96%. This study evidences that the functional group similarity of amoxicillin may competitively inhibit the esterification reaction by consuming methanol. This explanation further highlights that residual antibiotics interfere with microalgal lipid synthesis and its transesterification. Moreover, it was confirmed that the presence of residual antibiotics may not affect the major nutrient removal (total nitrogen: 74.5~78.0%, total phosphorus: 95.6~96.8%). This indicates that residual antibiotics inhibit the metabolism associated with carbon rather than those associated with nitrogen and phosphorus, which is connected to the decrease in the biodiesel yield. Overall, these results reveal that the frequent abuse of antibiotics in livestock may harm the eco-friendly conversion of waste-into-bioenergy strategy.

Production of biomethane, biohydrogen, and volatile fatty acids from Nordic phytoplankton biomass grown in blended wastewater

Upgrading carbon-negative microalgal biomass to biofuels and value-added products presents a three-pronged solution for waste treatment, carbon capture, and economically viable bioenergy production. Acidogenesis and methanogenesis are versatile processes at the core of anaerobic digestion systems, facilitating the conversion of diverse biogenic substrates into energy and a wide range of biobased products. The present study was conducted to integrate acidogenesis and methanogenesis for coproduction of biohydrogen, biomethane, and volatile fatty acids from Nordic phytoplankton consortia. For this purpose, microalgal consortia was cultivated in a raceway pond equipped with high surface area structures. Harvested microalgal biomass was subjected to thermoalkaline (2% NaOH solution at 121 °C) and enzymatic (cellulase) pretreatments. The hydrolysates of the pretreated biomass were inoculated with thermally treated sludge for acidogenic fermentation and with mixture of untreated sludge and cow dung (1:1 v/v ratio) for anerobic digestion. The acidogenic process produced a significant amount of biohydrogen (maximum 164.8 mL bioH2/VSload) along with volatile fatty acids (maximum 7.9 g COD/L), while methanogenesis resulted in biomethane production of maximum 210.7 mL bioCH4/VSload, accompanied by an ammonium recovery of 1278 mg NH4+/L. These maximum yields were all achieved by enzymatic pretreatment of the biomass fraction harvested from high surface area brush head structures inserted in the raceway pond. These results have important implications for designing phytoplankton cultivation systems and upstream pathways to optimize energy production from carbon-negative phytoplankton biomass.

Treatment of mixed wastewater by vertical rotating microalgae-bacteria symbiotic biofilm reactor

A novel vertical rotating microalgae-bacteria symbiotic biofilm reactor was built to treat the mixed wastewater containing municipal and soybean soaking wastewater. The reactor was operated in both sequential batch and semi-continuous modes. Under the sequential batch operation mode, the maximum removal rates for Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), and Ammonia Nitrogen (NH4+-N) of the mixed wastewater were 95.6 %, 96.1 %, 97.6 %, and 100 %, respectively. During the semi-continuous operation, the water discharge indices decreased gradually and eventually stabilized. At stabilization, the removal rates of COD, TN, and NH4+-N achieved 98 %, 95 %, and 99.9 %, respectively. The maximum biomass productivity of the biofilm was 2.69 g·m−2·d-1. Additionally, the carbohydrate, protein and lipid comprised approximately 22 %, 51 % and 10 % of the dry weight of Chlorella. This study demonstrates the great potential of the microalgae-bacteria symbiotic biofilm system to treat food and domestic wastewater while harvesting microalgal biomass.

Hydrothermal liquefaction of freshwater microalgae biomass using Fe3O4 nanoparticle as a catalyst

ABSTRACT Harvesting microalgal biomass using economic and ecological magnetic nanoparticles has been a promising approach due to its superior efficiency, low operating costs, scalable performance, and environmental safety. In this study, we have investigated the efficient harvesting of freshwater microalgae Chlorella sorokiniana (UUIND6) by using synthesized magnetic nanoparticles (Fe3O4). Simultaneously, the harvested microalgae biomass has been applied for hydrothermal liquefaction. Fe3O4 nanoparticles accrued in the magnetically harvested microalgae biomass have played a catalytic role in the hydrothermal liquefaction process under the varied parameters of temperature (250‒350°C), concentration (0.5‒1.5%), and retention times (30‒60 min). The results have revealed an efficient harvesting of microalgae biomass of ~ 83% in 60 min to be used for hydrothermal liquefaction. The response surface methodology was applied to maximize the yield of biochar and bio-oil. It was observed that the maximum biochar of 71.2% was obtained at 250°C using 0.5% Fe3O4 catalysts (Fe3O4) in 45 min. However, the maximum amount of bio-oil of 28% was obtained at 350°C using 1.5% Fe3O4 catalysts in 45 min. This study presents an economical pioneering approach to produce biochar and bio-oil from microalgae biomass for biofuel as well as ecologically safe applications.

Performance Evaluation of Ceramic Membrane Based Process for Microalgal Biomass Harvesting: Analyzing the Effect of Membrane Pore Sizes, Process Optimization and Fouling Behavior

Microalgal biofuel emerges as a potential resource of renewable energy in view of global energy demand and increasing greenhouse gases. However, substantial challenges of efficient up-concentrating of biomass act as a bottleneck in large scale production of biofuel. The study is aimed towards unravelling the obstacles encountered during dewatering of biomass from mixed-microalgae consortia using ceramic membrane based process with varying pore sizes in the microfiltration (MF) and ultrafiltration (UF) range. For clay and alumina based MF membrane, 1.2 µm pore size (average) and for alumina supported nano-alumina coated UF membrane, ∼0.01 µm pore size (average) was used. The effect of various recirculation parameters was studied for process optimization. Resistance-in-series model was employed for analyzing fouling behavior of the membranes. MF membrane was observed to have better harvesting efficiency than the UF counterpart in terms of productivity (124.41). Optimum permeate flux of microalgal suspension was found to be 315.29 L.m−2.h−1 for MF membrane. Regeneration of membranes by air assisted backpulsing process showed up to 97.71% of flux recovery for MF membrane. Volume reduction factor/ membrane area (371) was found to be considerably high compared to various reported studies. The study highlighted efficient harvesting of microalgae using indigenously developed ceramic MF membrane integrated filtration towards cost-effective production of biofuel.

Swollen-state preparation of chitosan lactate from moulted shrimp shells and its application for harvesting marine microalgae Nannochloropsis sp.

Chitosan lactate (CSS) has been widely used for academic and industrial applications due to its biocompatibility, biodegradability, and high biological activity. Unlike chitosan, which is generally soluble only in acid solution, CSS can be directly used by dissolving in water. In this study, CSS was prepared from moulted shrimp chitosan at room temperature by a solid-state method. Chitosan was first swollen in a mixture of ethanol and water, making it more susceptible to reacting with lactic acid in the next step. As a result, the prepared CSS had a high solubility (over 99 %) and zeta potential (+ 99.3 mV) and was comparable to the commercial product. The preparation method of CSS is facile and efficient for a large-scale process. In addition, the prepared product exhibited a potential flocculant for harvesting Nannochloropsis sp., a marine microalga widely used as a popular food for larvae. In the best condition, the CSS solution (250 ppm) at pH 10 showed the highest recovery capacity (∼ 90 % after 120 min) for harvesting Nannochloropsis sp. Besides, the harvested microalgal biomass showed excellent regeneration after 6 culture days. This paper's findings suggest a circular economy in aquaculture by producing value-added products from solid wastes, which can minimize the environmental impact and move towards sustainable zero-waste.

Effective and sustainable bioremediation of molybdenum pollutants from wastewaters by potential microalgae

Due to industrialization and growing population have greatly affected the quality of natural water resources globally. Molybdenum is a harmful metal that can cause serious health issues when exposed to >10 ppm levels. Several industries routinely discharged it, hence posing the environmental problems. For discharged industrial effluents, there are not any environmentally friendly and sustainable treatment method have developed for removing molybdenum hazards. The objective of this study was to design a green, sustainable approach for removing the molybdenum pollutant and to offset the treatment cost by obtaining values from microalgal by-products. Chlorella sorokiniana TU5 and Picochlorum oklahomensis, two fast-growing microalgal strains, were used for molybdenum treatment. The maximum removal efficiency was 115.65 mg L−1 with biomass and lipid yield of 2.35 g L−1 and 579.3 mg L−1, respectively, after 14 days of growth and further exposure to molybdenum pollutant. The molybdenum removal capacity was further increased by optimizing crucial factors, pH and temperature before removing biomass from the aqueous phase. Zeta potential study helped to determine the pH range that appropriately facilitate the strongest possible ionic bonds, leading to the enhanced molybdenum adsorption. In order to verify molybdenum adsorption and comprehend the dominating and quantitative interactions, FTIR was carried out to analyze the reactive groups in the algal cell surface. The current work analyses to control external parameters for improving the adsorption efficiency during harvesting of microalgal biomass, which efficiently improved the removal of molybdenum (V) from the liquid phase. The proposed technique aims to improve the bioremediation efficiency of molybdenum and other inorganic contaminants at an industrial scale by using microalgal treatment.

A sustainable vanadium bioremediation strategy from aqueous media by two potential green microalgae

Globally, environmental concerns are rapidly growing due to increasing pollution levels. Vanadium is a hazardous heavy metal that poses health issues with an exposure concentration of about 2 ppm. It is regularly discharged by some industries and poses an environmental challenge. There are no sustainable green treatment methods for discharged effluents to mitigate vanadium threats to humans and the environment. In this study, the goal was to develop a green, sustainable method for removing vanadium and to utilize the produced biomass for biofuels, thus offsetting the treatment cost. Microalgae Chlorella sorokiniana SU1 and Picochlorum oklahomensis were employed for vanadium (III) treatment. The maximum removal was 25.5 mg L−1 with biomass and lipid yields of 3.0 g L−1 and 884.4 mg L−1 respectively after 14 days of treatment. The vanadium removal capacity by microalgae was further enhanced up to 2–2.7 folds while optimizing the key parameters, pH, and temperature before removing biomass from the liquid phase. FTIR is used to analyse the reactive groups in algal cell walls to confirm vanadium adsorption and to understand the dominant and quantitative interactions. Zeta potential analysis helps to find out the most suitable pH range to facilitate the ionic bonding of biomass and thus maximum vanadium adsorption. This study addresses regulating external factors for enhancing the removal performance during microalgal biomass harvesting, which significantly enhances the removal of vanadium (III) from the aqueous phase. This strategy aims to improve the removal efficiency of microalgal treatment at an industrial scale for the bioremediation of vanadium and other inorganic pollutants.

Development of an Energy-Efficient Rapid Microalgal Cell-Harvesting Method Using Synthesized Magnetic Nanocomposites

Due to high consumption and non-renewable nature of fossil fuels, rapid development of potential renewable energies such as biofuel derived from microalgae is necessary for achieving the goals of sustainable growth and carbon neutrality. However, the high energy consumption required for microalgal biomass harvesting is regarded as a major obstacle for large-scale microalgal biofuel production. In the present study, the marine green microalgae Tetraselmis sp. was used to investigate a rapid and energy-efficient biomass collection method among different methods such as gravity sedimentation, auto-flocculation (at target pH), flocculation by polymers followed by magnetic separation, and centrifugation. The results showed that sufficient high cell densities of microalgae were obtained under the optimized growth conditions after 21 days of cultivation, and the microalgae could be easily flocculated and collected by magnetic separation using synthesized magnetic nanocomposites. The results also showed that among the different methods, magnetic separation was more efficient for biomass harvesting because of its simple and fast processing steps as well as low energy consumption. However, further investigation on different target microalgal species and their cultivation conditions, such as salinity and medium pH, will be required before application for large-scale biofuel production in the future.

Comprehensive insights into conversion of microalgae to feed, food, and biofuels: Current status and key challenges towards implementation of sustainable biorefineries

Microalgae have been promoted as important feedstocks for producing biofuels and bioproducts. However, their production on a large scale would require a large amount of water and nutrients. Considering the importance of food security and the high economic value of microalgal biomass, food and feed applications should be prioritized if microalgae are grown using conventional water resources. Nevertheless, microalgae can also be grown in nutrient-rich wastewater streams while producing valuable biomass and treating harmful effluents. Because of health issues, food and feed applications of microalgal biomass grown using waste resources are not allowed; hence, it can be used as a feedstock for biofuel production. In line with that, this review first briefly discusses the applications of microalgae in food, feed, and wastewater treatment and then summarizes the efforts put into utilizing microalgal biomass to produce biofuels through different pathways. These technologies, including thermochemical (200–1300 °C), biochemical (25–55 °C), and chemical (25–200 °C) conversion methods, are critically discussed. The pros and cons of using different microalgal conversion technologies are outlined to identify possible future directions for the field. Different microalgal biomass harvesting methods are also reviewed, and the process conditions are summarized. Parameters affecting technology selection, such as energy costs, reaction time, and technological sophistication, are also explored and presented. In general, microalgal biofuels still face many challenges in replacing traditional fossil fuels. Future work should focus on maximizing the yield and quality of microalgal biofuels while enhancing their economic viability.

A rapid, efficient and eco-friendly approach for simultaneous biomass harvesting and bioproducts extraction from microalgae: Dual flocculation between cationic surfactants and bio-polymer

Microalgal biomass harvesting and cell disruption are the main bottlenecks for downstream processing of microalgae such as high-value bioproducts extraction and biofuels production. In this study, we evaluated the performance of dual flocculation between cationic surfactants and bio-polymer of chitosan for simultaneous biomass harvesting and bioproducts extraction from Chlorella sorokiniana microalgae. First, the effects of individual natural flocculants of chitosan and two cationic surfactants: cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) on biomass harvesting were studied. Next, the synergistic effect of dual flocculation between the cationic surfactants and chitosan on harvesting efficiency, time and flocculant dosage was investigated. Finally, we evaluated the potential of high value bioproducts extraction from microalgae after the individual and dual flocculation processes. Zeta potential analysis and microscopic images were employed to achieve mechanistic understanding. Maximum biomass harvesting efficiencies of 85 %, 88 % and 78 % were achieved using individual flocculants of chitosan, CTAB and DTAB, under their optimum dosages of 100, 400 and 4000 mg/L, respectively. A significant synergistic effect of dual flocculation between chitosan (C) and cationic surfactants on biomass harvesting efficiency (CTAB-C: 99 % and DTAB-C: 97 %), settling time (CTAB-C: 2 min and DTAB-C: 5 min) and optimum dosage of surfactants (CTAB-C: 100 mg/L and DTAB-C: 1000 mg/L) was observed. The synergistic effect was associated with multiple flocculation mechanisms of charge neutralization and bridging induced by cationic surfactants and chitosan, respectively. Furthermore, bioproducts recovery efficiencies of 12 %, 25 % and 15 % of cell dry weight were achieved for protein, carbohydrate and lipid, respectively by using dual flocculation of CTAB surfactant and chitosan at much lower dosage of 100 mg/L.

Harvesting of Microalgal Biomass Using Moringa Oleifera as Natural Coagulant: A Cost-Effective Approach

Microalgae has been considered one of the most promising 3rd generation biofuel sources. Nevertheless, the commercialization of this biomass has not been successful in developing countries due to the energy-intensive harvesting process. The aim of the present study is to find a suitable coagulant which is locally available, costeffective, non-toxic, and environmentally friendly. In this regard, Moringa Oleifera (MO) seed powder, locally known as Shojne in Bangladesh, is used as natural coagulant to fulfil the present crisis. However, the harvesting efficiency and coagulant properties of MO were evaluated through jar-test, where wastewater grown microalgae, cultured in a photobioreactor (PBR), was used. This study optimized the harvesting parameters such as coagulant dose, mixing rate, and mixing time. As those parameters have a significant impact on the microalgae harvesting process. Low mixing rate and mixing time have better performance with coagulant dose varied from 10-70 mg/L. The highest harvesting efficiency of 83% microalgae recovery was achieved at 20 rpm for 10 minutes with coagulant dose of 70 mg/L. The MO seeds are recommended to be prospective coagulants for both water treatment and microalgae harvesting. Journal of Engineering Science 13(1), 2022, 51-59

A circular approach for the efficient recovery of astaxanthin from Haematococcus pluvialis biomass harvested by flocculation and water reusability

Flocculation has been proved an efficient method for microalgal biomass harvesting, but some coagulant agents may have adverse effects on microalgae growth, making the reuse of the medium unfeasible. In this study, Haematococcus pluvialis was harvested by different flocculants, and the feasibility of the reuse of the culture medium was evaluated. Results suggested that both inorganics, polyaluminum chloride (PA) and ferric chloride (FC), and organics, extracted from Moringa oleifera seed (MSE) and chitosan (CH) resulted in efficient flocculation – flocculation efficiency above 99 %. However, using PA and FC had adverse effects on the astaxanthin recovery from haematocysts – losses of 58.6 and 73.5 %, respectively. Bioflocculants in the reused medium also had higher growth performance than inorganic ones. Furthermore, bioflocculants in reused medium increase the contents of β-carotene, astaxanthin, and linolenic acid. This investigation demonstrated that using MSE and CHI for harvesting H. pluvialis enables the water reusability from a flocculated medium.

Arthrospira sp. mediated bioremediation of gray water in ceramic membrane based photobioreactor: process optimization by response surface methodology

Direct discharge of raw domestic sewage enriched with nitrogenous and phosphorous compounds into the water bodies causes eutrophication and other environmental hazards with detrimental impacts on public and ecosystem health. The present study focuses on phycoremediation of gray water with Arthrospira sp. using an innovative hydrophobic ceramic membrane-based photobioreactor system integrated with CO2 biofixation and biodiesel production, aiming for green technology development. Surfactant and oil-rich gray water collected from the domestic kitchen was used wherein, chloride, sulfate, and surfactant concentrations were statistically optimized using response surface methodology (RSM), considering maximum microalgal growth rate as a response for the design. Ideal concentrations (mg/L) of working parameters were found to be 7.91 (sulfate), 880.49 (chloride), and 144.02 (surfactant), respectively to achieve optimum growth rate of 0.43 gdwt/L/day. Enhancement of growth rate of targeted microalgae by 150% with suitable CO2 (19.5%) supply and illumination in the photobioreactor affirms its efficient operation. Additionally, harvested microalgal biomass obtained from the process showed a biodiesel content of around 5.33% (dry weight). The microalgal treatment enabled about 96.82, 87.5, and 99.8% reductions in BOD, COD, and TOC, respectively, indicating the potential of the process in pollutant assimilation and recycling of such wastewater along with value-added product generation.

Transcriptome analysis of potential flocculation-related genes in Streptomyces sp. hsn06 with flocculation activity on Chlorella vulgaris biomass.

Chlorella vulgaris is a biomass energy provider with promising potential to help alleviate the energy crisis. Streptomyces sp. hsn06, as an actinomycete, can harvest C. vulgaris biomass safely and efficiently through flocculation activity, and proteins contribute greatly to the flocculation effect. However, potential flocculation protein-related genes are unclear. The mycelia of strain hsn06 after culture with glucose as the sole carbon source exhibited significantly higher flocculation activity as well as higher protein contents than those cultured with starch as the carbon source. To further explore the flocculation mechanism, the mycelia of strain hsn06 with distinct flocculation activities after culture with different carbon sources were examined by transcriptome analysis. We found that 403 genes were differentially up-regulated in mycelia cultured with glucose, compared to those cultured with starch as the carbon source. Five significantly differentially expressed protein-related genes were determined and confirmed by qRT-PCR, which indicated that three of the selected genes were potential flocculation-related genes. These results advance our understanding of potential flocculation-related genes during the harvesting of microalgal biomass.

Promotion effect of bacteria in phycosphere on flocculation activity of Aspergillus niger on Synechocystis biomass

The cyanobacterium Synechocystis with high scientific research value and application potential to aquaculture is hard to harvest its biomass. Bioflocculation is an economical and efficient method for harvesting microalgal biomass. In this study, Aspergillus niger 7806F3, a fungus that showed high flocculation activity on Synechocystis cells, was selected to assess its potential for the harvest of microalgal biomass. The analyses of flocculation activity and flocculation mechanism indicated that mycelial pellets of Aspergillus niger 7806F3 exhibited high flocculation activity on Synechocystis biomass through charge neutralization mechanism, and proteins of mycelial pellets participated in the flocculation activity. The flocculation activity of strain 7806F3 on aseptic algal culture indicated that bacteria in the phycosphere can promote the flocculation effect of strain 7806F3 on algal cells. Bacterial community analysis indicated that the addition of mycelial pellets changed the bacterial community diversity in the Synechocystis phycosphere, increasing the abundance of genus Pseudomonas in the phycosphere. Finally, Pseudomonas sp. Algal4 was isolated from the Synechocystis phycosphere and confirmed with the ability to promote the flocculation activity of strain 7806F3 on Synechocystis cells. This study not only provides a method to harvest Synechocystis biomass, but also confirms the promotion effect of bacteria in phycosphere on flocculation activity, which provided a new understanding for the interaction between the algae and bacteria in the phycosphere.

Dual nutrient heterogeneity modes in a continuous flow photobioreactor for optimum nitrogen assimilation to produce microalgal biodiesel

The impact of different nitrogen sources on the microalga, Chlorella vulgaris, was studied in a newly developed microalgal-bacterial photobioreactor via a dual nutrient heterogeneity mode. The mechanisms of nitrogen transformation and valorisation were unveiled, and subsequently, optimized via dual nutrient heterogeneity feeding modes comprising of various NH4+-N and NO3−-N concentrations. The nitrogen-assimilation mechanism from the microalgal-bacterial consortium was found to reduce microalgal growth inhibition, stemming at high NH4+-N concentrations. Accordingly, the total nitrogen removal efficiency was enhanced from 40.91% to 96.38% accompanied with maximum microalgal biomass production of up to 792 mg/L at a balanced or higher NH4+-N loading from mixed nitrogen environment. The harvested microalgal biomass contained high lipid accumulation of approximately 30% when fed with optimum NH4+-N and NO3−-N loadings at 60 and 58 mg/d, respectively. At this mixed nitrogen species loadings, high unsaturated fatty acid methyl esters (FAME) were attained. Indeed, the major FAME species (97%–100%) fell within the C16-18 range, signifying biodiesel characteristics conformity to the requirements for quality biodiesel application. Therefore, the dual heterogeneity modes of balanced NH4+-N and NO3−-N loadings into photobioreactor could offer effective microalgal nitrogen assimilation for sustainable wastewater treatment and microalgae-based biodiesel production simultaneously.

Bioflocculation of Euglena gracilis via direct application of fungal filaments: a rapid harvesting method

The high cost and environmental impact of traditional microalgal harvesting methods limit commercialization of microalgal biomass. Fungal bioflocculation of microalgae is a promising low-cost, eco-friendly method but the range of fungal and microalgal species tested to date is narrow. Here, eight non-pathogenic, filamentous fungi were screened for their ability to self-pelletize and flocculate Euglena gracilis (ca.50 µm motile microalga) in suspension. Self-pelletization was tested under various rotational speeds, and species which formed pellets (Ø > 0.5 cm) were selected for harvesting tests. Filaments of each species were combined with E. gracilis at various ratios based on dry weight. Harvesting efficiency was determined by measuring the change in cell counts over time, and settling of the flocs was evaluated by batch settling tests. Three fungal species, Ganoderma lucidum, Pleurotus ostreatus, and Penicillium restrictum, were able to reliably flocculate and harvest 62–75% of the microalgae while leaving it unharmed. The results demonstrated that self-pelletization, harvesting, and settling were dependent on the fungal species. The fungi to algae ratio also had significant but contrasting effects on harvesting and settling. In balancing the needs to both harvest and settle the biomass, the optimal fungi to algae ratio was 1:2. The application of fungal filaments to microalgae in suspension produced readily settling flocs and was less time-consuming than other commonly used methods. This method is especially attractive for harvesting microalgal biomass for low-value products where speed, low cost, and cell integrity is vital.

Integrating anaerobic digestion and microalgae cultivation for dairy wastewater treatment and potential biochemicals production from the harvested microalgal biomass

Utilizing wastewaters as feedstock for microalgal cultivation has the dual benefits of water-saving and low nutrient costs, with simultaneous remediation of pollutants and generation of value-added biochemical products. This study employed two different strategies to treat raw dairy wastewaters with moderate and high chemical oxygen demand (COD) levels. For moderate-COD dairy wastewater, the wastewater was directly utilized as feedstock for algal cultivation, in which the effects of wastewater dilution ratios and algal inoculum sizes were investigated. The results show that the microalga strain used (Chlorella sorokiniana SU-1) was capable of obtaining a high biomass concentration of 3.2 ± 0.1 g/L, accompanied by 86.8 ± 6%, 94.6 ± 3%, and 80.7 ± 1%, removal of COD, total phosphorus (TP) and total nitrogen (TN), respectively. Meanwhile, the obtained microalgal biomass has lipids content of up to 12.0 ± 0.7% at a wastewater dilution ratio of 50% and an inoculum size of 2 g/L. For high-COD dairy wastewater, an integrated process of anaerobic digestion and microalgal phycoremediation was employed, and the effect of inoculum sizes was also studied. The inoculum size of 2 g/L gave highest biomass production of 4.25 ± 0.10 g/L with over 93.0 ± 2.0% removal of COD, TP, and TN. The harvested microalgal biomass has lipids and protein content of 12.5 ± 2.2% and 18.0 ± 2.2%, respectively. The present study demonstrated potential microalgal phycoremediation strategies for the efficient COD removal and nutrients recovery from dairy wastewater of different COD levels with simultaneous production of microalgal biomass which contains valuable components, such as protein and lipids.

Effective harvesting of Scenedesmus using quaternary ammonium chitosan and xanthan gum: Formation of mega flocs with oppositely charged polyelectrolytes

Microalgae are a promising sustainable source of biomass while large-scale harvesting of microalgal biomass is a major technological and economic challenge. In this study, a flocculation method and mechanism for the formation of compact mega flocs was developed using two oppositely charged polyelectrolytes, quaternary ammonium chitosan (N-[(2-hydroxy-3-trimethyl ammonium) propyl] chitosan, HTCC) and xanthan gum (XG). With 8 mg/L HTCC and 16 mg/L XG, Scenedesmus cells could be flocculated into mega flocs with diameters larger than 5 mm and were harvested by 500-μm-pore-sized sieves with an efficiency over 95%. The flocs were generated within 12 s and resisted strong hydraulic shear (stirring at 960 rpm), reducing energy consumption and handling time for the subsequent separation. With HTCC or XG alone, the harvest efficiency was consistently lower than 30%. The flocculation mechanism was investigated by changing the order in which the HTCC, XG, and Scenedesmus cells were added, and by fluorescence staining, scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the mega flocs were formed by the crosslinking of HTCC and XG, based on their long-chain molecular structure and electrostatic interaction. Scenedesmus cells were enmeshed in the polymer matrix of HTCC and XG and then aggregated into large flocs. Thus, an effective, eco-friendly, and sustainable flocculation strategy for microalgae biomass was developed using the biodegradable components HTCC and XG.