Disposal of wastewater often results in high nutrient loading into aquatic environments, which may lead to favorable conditions for undesirable phytoplankton blooms. Microalgae are efficient in removing nitrogen, phosphorus, and toxic metals from wastewater under controlled environments. If key nutrients in the wastewater stream can be used to grow microalgae for biofuel production, the nutrients can be removed, thus significantly reducing the risk of harmful phytoplankton overgrowth. This review paper summarizes the major nutrient components of different wastewater streams, the mechanisms of algal nutrient uptake, nutrient removal performance of various species of microalgae when cultured in wastewater, and current microalgae production systems. Finally, new algae cultivation technologies applicable for biofuel production and nutrient recovery in polluted water bodies are discussed.

Nutrient recovery from wastewater streams by microalgae: Status and prospects

http://biodiesel.persiangig.com/Cultivation/(3)Microalgae%20biofuels-%20A%20critical%20review%20of%20issues,%20problems%20and%20the%20way%20forward%20Review%20Article.pdf

Microalgae biofuels: A critical review of issues, problems and the way forward

https://openscholar.dut.ac.za/bitstream/10321/1400/1/rawat__kumar__mutanda___bux_2013_aplplied_energy.pdf

Biodiesel from microalgae: A critical evaluation from laboratory to large scale production

The economically significant production of carbon-neutral biodiesel from microalgae has been hailed as the ultimate alternative to depleting resources of petro-diesel due to its high cellular concentration of lipids, resources and economic sustainability and overall potential advantages over other sources of biofuels. Pertinent questions however need to be answered on the commercial viability of large scale production of biodiesel from microalgae. Vital steps need to be critically analysed at each stage. Isolation of microalgae should be based on the question of whether marine or freshwater microalgae, cultures from collections or indigenous wild types are best suited for large scale production. Furthermore, the determination of initial sampling points play a pivotal role in the determination of strain selection as well as strain viability. The screening process should identify, purify and select lipid producing strains. Are natural strains or stressed strains higher in lipid productivity? The synergistic interactions that occur naturally between algae and other microorganisms cannot be ignored. A lot of literature is available on the downstream processing of microalgae but a few reports are available on the upstream processing of microalgae for biomass and lipid production for biodiesel production. We present in this review an empirical and critical analysis on the potential of translating research findings from laboratory scale trials to full scale application. The move from laboratory to large scale microalgal cultivation requires careful planning. It is imperative to do extensive pre-pilot demonstration trials and formulate a suitable trajectory for possible data extrapolation for large scale experimental designs. The pros and cons of the two widely used methods for growing microalgae by photobioreactors or open raceway ponds are discussed in detail. In addition, current methods for biomass harvesting and lipid extraction are critically evaluated. This would be novel approach to economical biodiesel production from microalgae in the near future. Globally, microalgae are largest biomass producers having higher neutral lipid content outcompeting terrestrial plants for biofuel production. However, the viscosities of microalgal oils are usually higher than that of petroleum diesel.

Biodiesel from microalgae: a critical evaluation from laboratory to large scale production. Appl Energy

Economic and technical problems related to the reduction of petroleum resources require the valorisation of renewable raw material Recently, microalgae emerged as promising alternative feedstock that represents an enormous biodiversity with multiple benefits exceeding the potential of conventional agricultural feedstock Thus, this comprehensive review article spots the light on one of the most interesting microalga Chlorella vulgaris It assembles the history and a thorough description of its ultrastructure and composition according to growth conditions The harvesting techniques are presented in relation to the novel algo-refinery concept, with their technological advancements and potential applications in the market

/pdf/morphology-composition-production-processing-and-5458j8vfab.pdf

Morphology, composition, production, processing and applications of Chlorella vulgaris: A review

Lipid production of Chlorella vulgaris cultured in artificial wastewater medium

With rapid urbanization and infrastructure investment, wastewater treatment plants (WWTPs) in Chinese cities are putting increased pressure on energy consumption and exacerbating greenhouse gas (GHG) emissions. A carbon footprint is provided as a tool to quantify the life cycle GHG emissions and identify opportunities to reduce climate change impacts. This study examined three mainstream wastewater treatment technologies: Anaerobic–Anoxic–Oxic (A–A–O), Sequencing Batch Reactor (SBR) and Oxygen Ditch, considering four different sludge treatment alternatives for small-to-medium-sized WWTPs. Following the life cycle approach, process design data and emission factors were used by the model to calculate the carbon footprint. Results found that direct emissions of CO2 and N2O, and indirect emissions of electricity use, are significant contributors to the carbon footprint. Although sludge anaerobic digestion and biogas recovery could significantly contribute to emission reduction, it was less beneficial for Oxygen Ditch than the other two treatment technologies due to its low sludge production. The influence of choosing “high risk” or “low risk” N2O emission factors on the carbon footprint was also investigated in this study. Oxygen Ditch was assessed as “low risk” of N2O emissions while SBR was “high risk”. The carbon footprint of A–A–O with sludge anaerobic digestion and energy recovery was more resilient to changes of N2O emission factors and control of N2O emissions, though process design parameters (i.e., effluent total nitrogen (TN) concentration, mixed-liquor recycle (MLR) rates and solids retention time (SRT)) and operation conditions (i.e., nitrite concentration) are critical for reducing carbon footprint of SBR. Analyses of carbon footprints suggested that aerobic treatment of sludge not only favors the generation of large amounts of CO2, but also the emissions of N2O, so the rationale of reducing aerobic treatment and maximizing anaerobic treatment applies to both wastewater and sludge treatment for reducing the carbon footprint, i.e., the annamox process for wastewater nutrient removal and the anaerobic digestion for sludge treatment.

Carbon footprint analyses of mainstream wastewater treatment technologies under different sludge treatment scenarios in China.

BACKGROUND

Microalgae biodiesel has attracted considerable attention, however, low lipid content has significantly restricted its development Many research studies have demonstrated that nutrient deficiency is an important factor stimulating lipid accumulation in algal cells This present study investigated the combined effects of nitrogen, phosphorus, and carbon on algal lipid accumulation by Chlorella vulgaris in mixotrophic culture



RESULTS

Phosphorus at 02 g L−1 concentration inhibited Chlorella vulgaris growth but did not influence lipid accumulation High concentration of NaNO3 (375 g L−1) inhibited both algal growth and lipid accumulation Nitrogen sufficiency can stimulate lipid accumulation Glucose limitation restricted both biomass production and lipid accumulation, resulting in lipid content decrease even under nitrogen sufficiency CO2 was unable to satisfy the carbon demand for lipid accumulation when glucose was exhausted in mixotrophic culture The initial C:N ratio of culture medium played an important role in algal lipid accumulation Lipid content was maintained at 76–113% when the initial C:N of culture was less than 50, while it increased significantly to 239% with initial C:N of culture increased to 927



CONCLUSION

Superior lipid accumulation requires limiting nitrogen concentration in the medium solution High initial C:N ratio greater than 86 was found to be beneficial for algal lipid accumulation © 2014 Society of Chemical Industry

Combined effects of carbon, phosphorus and nitrogen on lipid accumulation of Chlorella vulgaris in mixotrophic culture

The invention provides a method for detecting microalgae oil, belonging to the field of oil detection The method solves the technical problems that the needed sample is large and the consumed time is long in the existing weighing method The method comprises the following steps: 1, diluting microalgae culture solution to obtain diluent; 2, detecting the fluorescence intensity of the dyed diluent; 3, centrifuging the diluent, and detecting the fluorescence intensity of the dyed supernate; 4, detecting the fluorescence intensity of the undyed diluent; and 5, computing the maximum difference of the fluorescence intensity, and computing the content of the microalgae oil according to a fluorescence intensity-oil content standard curve The method is applied to detecting the unicellular algae such as the chlorella, the scenedesmus, the spirulina, the diatom, the dinoflagellate, the chrysophyceae, the euglenophyta, the stonewort and the like, and is applied to detecting the macro algae which is preprocessed by cell discruption

Method for detecting microalgae oil

Microalgae harvesting is a relatively costly process in microalgae biodiesel production. In this study, electrocoagulation-flotation (ECF) was employed to harvest microalgae (Chlorella vulgaris). Higher current density achieved higher collection efficiency, but also resulted in higher energy consumption and increased levels of dissolved aluminium. At the same ratio of current density to initial cell density, collection efficiency decreased from 99.0% of 0.24 g L−1 to 30.5% of 1.17 g L−1 when the electrolysis time was 20 min. For stirring and aeration, the highest collection efficiency was 98.4%, obtained by stirring at 50 rpm for 20 min. This efficiency was nearly equal to the highest collection efficiency for aeration: 98.3% for 50 mL min−1 aeration at 30 min. Acidic and neutral culture conditions were beneficial due to the positively charged aluminium species in the culture; higher collection efficiencies (more than 98%) occurred with pH levels of 5–7 after 20 min. The lowest energy consumption of 0.61 kW h kg−1 was achieved at pH 5. In this research, ECF exhibited higher collection efficiency (99.4%) as compared to the 93.5% collection efficiency of chemical flocculation (Al2(SO4)3).

Dawei Zhang

Papers

Lipid production of Chlorella vulgaris cultured in artificial wastewater medium

Carbon footprint analyses of mainstream wastewater treatment technologies under different sludge treatment scenarios in China.

Combined effects of carbon, phosphorus and nitrogen on lipid accumulation of Chlorella vulgaris in mixotrophic culture

Method for detecting microalgae oil

Factors affecting microalgae harvesting efficiencies using electrocoagulation-flotation for lipid extraction