Mechanism and performance of algal pond assisted constructed wetlands for wastewater polishing and nutrient recovery

The limitation of oxygen and carbon source restricted the TN removal in constructed wetland (CW). Algal pond (AP) could produce oxygen and fix CO₂ to improve C/N ratio in water. Therefore, an AP-CW system was established under laboratory conditions to deeply explore the effect of nutrient load distribution and microalgae addition in CWs on pollutant removal. This study showed that AP-CW could remove 49.7% TN and 90.0% TP with no carbon addition in CWs. The significant removal of NH₄-N by AP advanced the location of denitrification in CWs. To enhance TN removal, different dosage of microalgae were intermittently added at 20 and 10 cm respectively below the inlet of the vertical flow CW1 and CW2, where the rest NH₄-N has been almost oxidized into nitrate. The addition of microalgae influenced the microflora and effluent quality. Microalgae dosage in denitrification area significantly increased the absolute abundance of Σnir. The best TN removal of AP-CW could reach 91.3% when 8 g (dry weight) microalgae was added. However, unlike previous knowledge, microalgae as an organic carbon source would also release N and P during decomposition, leading to increased nutrients in the effluent. The optimal dosage of microalgae was 1 g/5 d in this study. The position and amount of microalgae addition in CWs should be adjusted based on water property and element flow to achieve the best pollutant removal and biomass harvest.

Freshwater Microalgae as Promising Food Sources: Nutritional and Functional Properties

A number of researchers have predicted that the current food crisis is predicted to worsen in 2050. The prediction of this crisis is aligned with climate change causing increases in some basic foodstuff prices. Therefore, everyone should prepare to consume alternative foods at an early stage. Alternative foods have been widely developed, one of which involves microalgae. However, the type of microalgae produced by some countries on a large scale consists of only oceanic/seawater microalgae. This will have an impact on and hinder development in countries that do not have these resources. Therefore, it is necessary to explore the use of microalgae derived from freshwater. Unfortunately, freshwater microalgae are still rarely investigated for use as alternative foods. However, there is considerable potential to utilize freshwater microalgae, and these algae are very abundant and diverse. In terms of nutritional properties, compared to oceanic / seawater microalgae, freshwater microalgae contain nearly the same protein and amino acids, lipids and fatty acids, carbohydrates, and vitamins. There are even more species whose composition is similar to those currently consumed foods, such as beef, chicken, beans, eggs, and corn. In addition to dietary properties, freshwater microalgae also have functional properties, due to the presence of pigments, sterols, fatty acids, and polyphenols. Given the potential of freshwater microalgae, these aquatic resources need to be developed for potential use as future food resources.

Assuaging Microalgal Harvesting Woes via Attached Growth: A Critical Review to Produce Sustainable Microalgal Feedstock

Third-generation biofuels that are derived from microalgal biomass have gained momentum as a way forward in the sustainable production of biodiesel. Such efforts are propelled by the intention to reduce our dependence on fossil fuels as the primary source of energy. Accordingly, growing microalgal biomass in the form of suspended cultivation has been a conventional technique for the past few decades. To overcome the inevitable harvesting shortcomings arising from the excessive energy and time needed to separate the planktonic microalgal cells from water medium, researchers have started to explore attached microalgal cultivation systems. This cultivation mode permits the ease of harvesting mature microalgal biomass, circumventing the need to employ complex harvesting techniques to single out the cells, and is economically attractive. However, the main bottleneck associated with attached microalgal growth is low biomass production due to the difficulties the microalgal cells have in forming attachment and populating thereafter. In this regard, the current review encompasses the novel techniques adopted to promote attached microalgal growth. The physicochemical effects such as the pH of the culture medium, hydrophobicity, as well as the substratum surface properties and abiotic factors that can determine the fate of exponential growth of attached microalgal cells, are critically reviewed. This review aims to unveil the benefits of an attached microalgal cultivation system as a promising harvesting technique to produce sustainable biodiesel for lasting applications.

Microalgae Cultivation in Palm Oil Mill Effluent (POME) Treatment and Biofuel Production

Palm oil mill effluent (POME) is the wastewater produced during the palm oil sterilization process, which contains substantial amounts of nutrients and phosphorous that are harmful to the environment. High BOD and COD of POME are as high as 100,000 mg/L, which endanger the environment. Effective pre-treatment of POME is required before disposal. As microalgae have the ability of biosorption on nutrients and phosphorous to perform photosynthesis, they can be utilized as a sustainable POME treatment operation, which contributes to effective biofuel production. Microalgae species C. pyrenoidosa has shown to achieve 68% lipid production along with 71% nutrient reduction in POME. In this study, a brief discussion about the impacts of POME that will affect the environment is presented. Additionally, the potential of microalgae in treating POME is evaluated along with its benefits. Furthermore, the condition of microalgae growth in the POME is also assessed to study the suitable condition for microalgae to be cultivated in. Moreover, experimental studies on characteristics and performance of microalgae are being evaluated for their feasibility. One of the profitable applications of POME treatment using microalgae is biofuel production, which will be discussed in this review. However, with the advantages brought from cultivating microalgae in POME, there are also some concerns, as microalgae will cause pollution if they are not handled well, as discussed in the last section of this paper.

Municipal Wastewater: A Sustainable Source for the Green Microalgae Chlorella vulgaris Biomass Production

The need to reduce the costs associated with microalgae cultivation encouraged scientific research into coupling this process with wastewater treatment. Thus, the aim of this work was to assess the growth of Chlorella vulgaris (Chlorophyta) in different effluents from a municipal wastewater treatment plant (WWTP), namely secondary effluent (SE) and sludge run-off (SR). Assays were performed, under the same conditions, in triplicate with 4 dilution ratios of the wastewaters (25%, 50%, 75% and 100%) with the standard culture medium bold basal medium double nitrated (BBM2N) as a control. The capability of C. vulgaris for biomass production, chlorophyll synthesis and nutrients removal in the SE and SR was evaluated. The 25% SE and 25% SR showed increased specific growth rates (0.47 and 0.55 day−1, respectively) and higher biomass yields (8.64 × 107 and 1.95 × 107 cells/mL, respectively). Regarding the chlorophyll content, the 100% SR promoted the highest concentration of this pigment (2378 µg/L). This green microalga was also able to remove 94.8% of total phosphorus of SE, while in 50% SR, 31.2% was removed. Removal of 73.9% and 65.9% of total nitrogen in 50% and 100% SR, respectively, was also observed. C. vulgaris growth can, therefore, be maximized with the addition of municipal effluents, to optimize biomass production, while cleansing the effluents.

Molecular tools and applications of Euglena gracilis: From biorefineries to bioremediation

Euglena gracilis is a promising source of commercially important metabolites such as vitamins, wax esters, paramylon, and amino acids. However, the molecular tools available to create improved Euglena strains are limited compared to other microorganisms that are currently exploited in the biotechnology industry. The complex poly-endosymbiotic nature of the Euglena genome is a major bottleneck for obtaining a complete genome sequence and thus represents a notable shortcoming in gaining molecular information of this organism. Therefore, the studies and applications have been more focused on using the wild-type strain or its variants and optimizing the nutrient composition and cultivation conditions to enhance the production of biomass and valuable metabolites. In addition to producing metabolites, the E. gracilis biorefinery concept also provides means for the production of biofuels and biogas as well as residual biomass for the remediation of industrial and municipal wastewater. Using Euglena for bioremediation of environments contaminated with heavy metals is of special interest due to the strong ability of the organism to accumulate and sequester these compounds. The published draft genome and transcriptome will serve as a basis for further molecular studies of Euglena and provide a guide for the engineering of metabolic pathways of relevance for the already established as well as novel applications.

Pilot scale wastewater treatment, CO2 sequestration and lipid production using microalga, Neochloris aquatica RDS02

In present investigation carried out large-scale treatment of tannery effluent by the cultivation of microalgae, Neochloris aquatica RDS02. The tannery effluent treatment revealed that significant reduction heavy metals were chromium-3.59, lead-2.85, nickel-1.9, cadmium-10.68, zinc-4.49, copper-0.95 and cobalt-1.86 mg/L on 15th day of treatment using N. aquatica RDS02. The microalgal biosorption capacity q _max rate was Cr-88.66, Pb-75.87, Ni-87.61, Cd-60.44, Co-52.86, Zn-84.90 and Cu-54.39, and isotherm model emphasized that the higher R ² value 0.99 by Langmuir and Freundlich kinetics model. The microalga utilized highest CO₂ (90%) analyzed by CO₂ biofixation and utilization kinetics, biomass (3.9 mg/mL), lipid (210 mg mL^-1), carbohydrate (102.75 mg mL^-1), biodiesel (4.9 mL g^-1) and bioethanol (4.1 mL g^-1). The microalgal-lipid content was analyzed through Nile red staining. Gas chromatography mass spectrometric (GCMS) analysis confirmed that the presence of a biodiesel and major fatty acid methyl ester (FAME) profiling viz., tridecanoic acid methyl ester, pentadecanoic acid methyl ester, octadecanoic acid methyl ester, myristic acid methyl ester, palmitic acid methyl ester and oleic acid methyl ester. Fourier transform infrared (FTIR) analysis confirmed that the presence of a functional groups viz., phenols, alcohols, alkynes, carboxylic acids, ketones, carbonyl and ester groups. The bioethanol production was confirmed by high-performance liquid chromatography (HPLC) analyze.

Non-suspended microalgae cultivation for wastewater refinery and biomass production

Non-suspended microalgae cultivation technology coupled with wastewater purification has received more scientific attention in recent decades. Since the non-suspended microalgae cultivation is quite different from the suspended ones, the following issues are compared in this study such as advantages and disadvantages, pollutant removal mechanisms and regulations, influential factors, and microalgae biomass accumulation. The analysis aims to support the further application of this technology. The median removal rates of COD, TN, TP, NH₄⁺-N and NO₃^--N were 91.6%, 78.2%, 87.5%, 93.2% and 81.7%, respectively, by non-suspended microalgae under the TN & TP load rates up to 150 mg·L^-1·d^-1. The main pathway for TN & TP removal is microalgae cell absorbance. Light intensity, pollutant composition and microalgae metabolic types are the major factors that influence pollutant removal and the lipid content of microalgae. Meanwhile the mechanism concerning how macro-outer conditions influence the micro-environment and further growth of non-suspended microalgae requires more investigation.

Exploration of green integrated approach for effluent treatment through mass culture and biofuel production from unicellular alga, Acutodesmus obliquus RDS01

This study deals with the open pond (OP) pilot scale treatment of cassava effluent and enhancement of Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) enzyme through CO₂ utilization by the microalga, Acutodesmus obliquus RDS01. The cassava effluent treatment (ET) revealed maximum reduction of ammonia (96.8%), calcium (94.6%), chloride (95.2%), chlorine (98.5%), inorganic phosphate (94.6%), magnesium (96.8%), nitrate (96.89%), organic carbon (95.9%), organic phosphorus (96.3%), potassium (97.9%), sodium (97.1%), and sulfate (95.4%) on 15^th day using A. obliquus. The microalga produced highest RuBisCO enzyme activity (90%), CO₂ utilization efficiency (95%), biomass (8.9 gL^-1), lipid (176.65 mg mL^-1), carbohydrate (96.78 mg mL^-1), biodiesel (4.1 mL g^-1), and bioethanol (3.7 mL g^-1) during OP treatment. The isolated RuBisCO gene (rbcL) was used to construct the protein model by homology modeling. The microalgal-lipid content was analyzed through thin layer chromatography, the biodiesel produced was analyzed using Fourier-transform infrared spectroscopy and gas chromatography mass spectrometry (GCMS). The bioethanol production was confirmed by high performance liquid chromatography and GCMS analyses. A. obliquus produced of 98.75% biodiesel and 96.83% bioethanol in the OP pilot scale treatment A. obliquus. Overall, the microalga A. obliquus could act as an effective CO₂ capturing and bioremediation agent in the cassava ET, and also for the biodiesel and bioethanol can be produced.

Bioproducts From Euglena gracilis: Synthesis and Applications

In recent years, the versatile phototrophic protist Euglena gracilis has emerged as an interesting candidate for application-driven research and commercialisation, as it is an excellent source of dietary protein, pro(vitamins), lipids, and the β-1,3-glucan paramylon only found in euglenoids. From these, paramylon is already marketed as an immunostimulatory agent in nutraceuticals. Bioproducts from E. gracilis can be produced under various cultivation conditions discussed in this review, and their yields are relatively high when compared with those achieved in microalgal systems. Future challenges include achieving the economy of large-scale cultivation. Recent insights into the complex metabolism of E. gracilis have highlighted unique metabolic pathways, which could provide new leads for product enhancement by genetic modification of the organism. Also, development of molecular tools for strain improvement are emerging rapidly, making E. gracilis a noteworthy challenger for microalgae such as Chlorella spp. and their products currently on the market.

Phycoremediation resultant lipid production and antioxidant changes in green microalgae Chlorella Sp

In this investigation, we report on the treatment of tannery wastewater using microalgae Chlorella species to produce lipid and fatty acid as well as changes in antioxidant metabolism during the treatment. The variation in growth, production of pigments, antioxidant metabolism, lipid and fatty acids, and nutrient removal from wastewater during the remediation were observed. Surprisingly, a profuse growth was found in 50% diluted tannery wastewater (TW), which supported to accumulate high yield of lipid (18.5%) and unsaturated fatty acids (50.05%). The antioxidant activity of microalgae in both the concentrations (50% and 100% TW) were viz., lipid peroxidation 1.6 ± 0.1 and 2.3 ± 0.02nmol MDA mg^-1 protein, SOD 10.3 ± 0.4 and 15.7 ± 0.9 U mg^-1 protein, CAT 0.17 ± 0.036 and 0.52 ± 0.06 U mg^-1 protein, and APX 7.2 ± 0.8 and 11.2 ± 09 U mg^-1 protein respectively, which point out that the free radical scavenging mechanism against heavy metal stress. Maximum phycoremediation of heavy metals observed from both concentrations during the healthy growth period were Cr - 73.1, 45.7%, Cu - 90.4, 78.1%, Pb - 92.1, 52.2%, and Zn - 81.2, 44.6%, respectively. This study proved the potential use of Chlorella for heavy metal and nutrient removal from tannery wastewater. Moreover, an unaffected growth with high antioxidant activity of this species promises a sustainable lipid and fatty acid contents for biofuel production.

Assessing Nutrient Removal Kinetics in Flushed Manure Using Chlorella vulgaris Biomass Production

The utilization of dairy wastewater for producing algal biomass is seen as a two-fold opportunity to treat wastewater and produce algae biomass, which can be potentially used for production of biofuels. In animal agriculture system, one of the major waste streams is dairy manure that contains high levels of nitrogen and phosphorus. Furthermore, it is produced abundantly in California's dairy industry, as well as many other parts of the world. We hypothesized that flushed manure, wastewater from a dairy farm, can be used as a potential feedstock after pretreatment to grow Chlorella vulgaris biomass and to reduce nutrients of manure. In this study, we focused on investigating the use of flushed manure, produced in a dairy farm for growing C. vulgaris biomass. A series of batch-mode experiments, fed with manure feedstock and synthetic medium, were conducted and corresponding C. vulgaris production was analyzed. Impacts of varying levels of sterilized manure feedstock (SMF) and synthetic culture medium (SCM) (20-100%) on biomass production, and consequential changes in total nitrogen (TN) and total phosphorus (TP) were determined. C. vulgaris production data (Shi et al., 2016) were fitted into a model (Aslan and Kapdan, 2006) for calculating kinetics of TN and TP removal. Results showed that the highest C. vulgaris biomass production occurs, when SMF and SCM were mixed with ratio of 40%:60%. With this mixture, biomass on Day 9 was increased by 1,740% compared to initial biomass; and on Day 30, it was increased by 2,456.9%. The production was relatively low, when either only SCM or manure feedstock medium (without pretreatment, i.e., no sterilization) was used as a culture medium. On this ratio, TN and TP were reduced by 29.9 and 12.3% on Day 9, and these reductions on Day 30 were 76 and 26.9%, respectively.

Phycoremediation of Tannery Wastewater Using Microalgae Scenedesmus Species

A number of microalgae species are efficient in removing toxicants from wastewater. Many of these potential species are a promising, eco-friendly, and sustainable option for tertiary wastewater treatment with a possible advantage of improving the economics of microalgae cultivation for biofuel production. The present study deals with the phycoremediation of tannery wastewater (TWW) using Scenedesmus sp. isolated from a local habitat. The test species was grown in TWW under laboratory conditions and harvested on the 12th day. The results revealed that the algal biomass during the growth period not only reduced the pollution load of heavy metals (Cr-81.2-96%, Cu-73.2-98%, Pb-75-98% and Zn-65-98%) but also the nutrients (NO3 >44.3% and PO4 >95%). Fourier Transform Infrared (FTIR) spectrums of Scenedesmus sp. biomass revealed the involvement of hydroxyl amino, carboxylic and carbonyl groups. The scanning electron micrograph (SEM) and Energy Dispersive X-ray Spectroscopic analysis (EDS) revealed the surface texture, morphology and element distribution of the biosorbent. Furthermore, the wastewater generated during wet-blue tanning process can support dense population of Scenedesmus sp., making it a potential growth medium for biomass production of the test alga for phycoremediation of toxicants in tannery wastewaters.