Effect of food wastewater on biomass production by a green microalga Scenedesmus obliquus for bioenergy generation

Lipid-rich particles of processed food waste for microalgae harvest through lipid-enriched floating biomat formation

Food waste was collected from the campus canteen and lipid-rich particles (LRP) phase was evaluated to harvest Tetradesmus obliquus. Box-Behnken design showed the highest harvest efficiency (HE) of 84.69 % in run#1 (LRP = 30 %; initial OD680 = 1.75; and harvest time = 6 h). Numerical optimization ramps suggested 24.15 % (v/v) LRP ratio, initial OD680 3.00, and harvest time 3.82 h for maximum HE. Two flocs were observed, a precipitate at the bottom (B-Floc) and a floating biomat (F-Floc). Experimental results showed HE of 88.3 %, with 67 % and 33 % of the harvested biomass forming F-Floc and B-Floc, respectively. Pre-heating of LRP in a boiling water bath for 10 min (HFB-T10) promoted F-Floc proportion up to 91.6 %. In addition, HFB-T10 showed the highest FAMEs yield of 11.17 g/L of the total used volume, which was significantly higher than that of the centrifuged cells and heat-untreated biomat. Moreover, HFB-T10 showed better iodine value and cetane number of the produced biodiesel.

Marine diatom algae cultivation in simulated dairy wastewater and biomass valorization

Liquid byproducts and organic wastes generated from dairy processing units contribute as the largest source of industrial food wastewater. Though bacteria-mediated treatment strategies are largely implemented, a more effective and innovative management system is needed of the hour. Thus, the current study involves the cultivation of centric diatoms, Chaetoceros gracilis, and Thalassiosira weissflogii in simulated dairy wastewater (SDWW) formulated using varying amounts of milk powder with artificial seawater f/2 media (ASW). The results revealed that cell density and biomass productivity were highest in the 2.5% SDWW treatment cultures of both the strains, the maximum being in C. gracilis (7.5 × 106 cells mL - 1; 21.1 mg L-1 day-1). Conversely, the total carotenoid, chrysolaminarin, and phenol content were negatively impacted by SDWW. However, a considerable enhancement in the total lipid content was reported in the 2.5% SDWW culture of both species. Furthermore, the fatty acid profiling revealed that though the total polyunsaturated fatty acid (PUFA) content was highest in the control setups, the total mono polyunsaturated fatty acid (MUFA) content was higher in the 5% SDWW setups (30.66% in C. gracilis and 33.21% in T. weissflogii). In addition to it, in the cultures utilizing energy from external carbon sources provided by SDWW, the biodiesel produced was also enhanced owing to the heightened cetane number. Thus, the current study evidently highlights the organic carbon acquisition potential of marine diatoms with the scope of providing sustainable biorefinery.

A critical review on phycoremediation of pollutants from wastewater-a novel algae-based secondary treatment with the opportunities of production of value-added products

Though the biological treatment employing bacterial strains has wide application in effluent treatment plant, it has got several limitations. Researches hence while looking for alternative biological organisms that can be used for secondary treatment came up with the idea of using microalgae. Since then, a large number of microalgal/cyanobacterial strains have been identified that can efficiently remove pollutants from wastewater. Some researchers also found out that the algal biomass not only acts as a carbon sink by taking up carbon dioxide from the atmosphere and giving oxygen but also is a renewable source of several value-added products that can be extracted from it for the commercial use. In this work, the cleaning effect of different species of microalgae/cyanobacteria on wastewater from varied sources along with the value-added products obtained from the algal biomass as observed by researchers during the past few years are reviewed. While a number of review works in the field of phycoremediation technology was reported in literature, a comprehensive study on phycoremediation of wastewater from different industries and household individually is limited. In the present review work, the efficiency of diverse microalgal/cyanobacterial strains in treatment of wide range of industrial effluents along with municipal wastewater having multi-pollutants has been critically reviewed.

Phycoremediation of milk processing wastewater and lipid-rich biomass production using Chlorella vulgaris under continuous batch system

This study compiles the results of phycoremediation of milk processing wastewater (MPWW) and production of lipid-rich Chlorella vulgaris biomass using a continuous batch system operated for 12-wks. After a 4-wks interval, a new MPWW was loaded photobioreactor to provide appropriate nutrient supply to algae. Results indicated that MPWW supported the algal growth efficiently and the maximum algal growth was recorded in the ranges of 400.36 to 421.58 mg L^-1 during 4-wk's of the cultivation cycle. Average reduction in total nitrogen, TN (45.82-69.18%); nitrate, NO₃ (93.32-94.54%); total ammonium nitrogen, TAN (92.94-94.54%); sulphate, SO₄^-2 (85.13-87.34%); total phosphorus (75.09-78.78%); and biochemical oxygen demands, BOD (89.53-92.40%) was recorded during 12-wks phycoremediation of MPWW. Harvested algal biomass (dry weight basis, DW) exhibited a significant content of total sugar (45.5%) and total lipid (39.7%). The lipid profiling results indicated the presence of palmitic acid (39.9%), oleic acid (21.08%), linoleic acid (13.13%), and other C18 compounds in algal biomass, suggesting the suitability of MPWW for Chlorella vulgaris cultivations. Algal biomass exhibited a high heating value (MJ/Kg of DW) in the range of 17.3 to 25.1, comparable to other lignocellulose biomass to be used for bioenergy purposes. Results of this study indicate that MPWW could be utilized as a valuable medium for Chlorella vulgaris cultivation under a circular economy approach: wastewater treatment and bioenergy feedstock production. The effect of controlled environmental conditions on algal growth behavior and lipid composition in biomass, while using MPWW as a medium, could be investigated in future studies.

Outdoor phycoremediation and biomass harvesting optimization of microalgae Botryococcus sp. cultivated in food processing wastewater using an enclosed photobioreactor

Microalgae cultivation is well known as a sustainable method for eco-friendly wastewater phycoremediation and valuable biomass production. This study investigates the feasibility and kinetic removal of organic compounds and nutrients from food processing wastewater (FPW) using Botryococcus sp. in an enclosed photobioreactor. Simultaneously, response surface methodology (RSM) via face-centered central composite design (FCCCD) was applied to optimize the effects of alum and chitosan dosage and pH sensitivity on flocculation efficiency. The maximum growth rate of Botryococcus sp. cultivated in FPW was 1.83 mg day^-1with the highest removal of chemical oxygen demand (COD), total organic carbon (TOC), and total phosphorus (TP) after 12 days of phycoremediation of 96.1%, 87.2%, and 35.4%, respectively. A second-order polynomial function fits well with the experimental results. Both coagulant dosage and pH significantly (p < 0.05) affect the flocculation efficiency of Botryococcus sp. biomass cultivated in FPW. The highest flocculation efficiency (92.4%) was obtained at a dosage of 166 mg L^-1and pH 12 for alum coagulant, while 94.9% flocculation efficiency was achieved with optimum chitosan dosage and pH of 30 mg L^-1and 5.54, respectively. In general, Botryococcus sp. shows a great removal efficiency of FPW contamination, whereas RSM provides excellent analysis for biomass harvesting optimization using a flocculation technique.

Algal-based system for removal of emerging pollutants from wastewater: A review

The bioremediation of emerging pollutants in wastewater via algal biotechnology has been emerging as a cost-effective and low-energy input technological solution. However, the algal bioremediation technology is still not fully developed at a commercial level. The development of different technologies and new strategies to cater specific needs have been studied. The existence of multiple emerging pollutants and the selection of microalgal species is a major concern. The rate of algal bioremediation is influenced by various factors, including accidental contaminations and operational conditions in the pilot-scale studies. Algal-bioremediation can be combined with existing treatment technologies for efficient removal of emerging pollutants from wastewater. This review mainly focuses on algal-bioremediation systems for wastewater treatment and pollutant removal, the impact of emerging pollutants in the environment, selection of potential microalgal species, mechanisms involved, and challenges in removing emerging pollutants using algal-bioremediation systems.

Phycoremediation of wastewater for pollutant removal: A green approach to environmental protection and long-term remediation

Surface and water bodies in many parts of the world are affected due to eutrophication, contamination and depletion. The approach of wastewater treatment using algae for eliminating nutrients and other pollutants from domestic wastewater is growing interest among the researchers. However, sustainable treatment of the wastewater is considered to be important in establishing more effective nutrient and pollutant reduction using algal systems. In comparison to the conventional method of remediation, there are opportunities to commercially viable businesses interest with phycoremediation, thus by achieving cost reductions and renewable bioenergy options. Phycoremediation is an intriguing stage for treating wastewater since it provides tertiary bio-treatment while producing potentially valuable biomass that may be used for a variety of applications. Furthermore, the phycoremediation provides the ability to remove heavy metals as well as harmful organic substances, without producing secondary contamination. In this review, the role of microalgae in treating different wastewaters and the process parameters affecting the treatment and future scope of research have been discussed. Though several algae are employed for wastewater treatment, species of the genera Chlamydomonas, Chlorella, and Scenedesmus are extensively utilized. Interestingly, there is a vast scope for employing algal species with high flocculation capacity and adsorption mechanisms for the elimination of microplastics. In addition, the algal biomass generated during phycoremediation has been found to possess high protein and lipid contents, promising their exploitation in biofuel, food and animal feed industries.

C. vulgaris growth batch tests using winery waste digestate as promising raw material for biodiesel and stearin production

The recovery of high added value compound from waste stream is fundamental to keep biotechnological processes sustainable. In this study, anaerobic digestion of two highly produced organic waste was integrated with microalgae-based processes both to treat liquid digestate and recover high value compounds. Chlorella vulgaris growth was assessed for lipids accumulation and subsequent recovery, using two types of digestate: organic waste and sewage sludge digestate (DIG-OFMSW) and wine lees digestate (DIG-WL). Growth tests were carried out in batch mode and results showed a slightly higher final biomass concentration from DIG-WL (1.36 ± 0.09 g l^-1) compared to DIG-OFMSW (1.05 ± 0.13 g l^-1) and a clearly different lipids accumulation yield (28.86 ± 0.05% in DIG-WL compared to 6.1 ± 0.2% of DIG-OFMSW, on total solids). Lipid characterization showed a high oleic acid accumulation (69.52 ± 0.50%w/w in DIG-WL) that positively influence biodiesel properties and a low linolenic acids content (below 0.30%w/w) that comply with European law EN14214 for biodiesel (linolenic acid content lower than 12%w/w). In addition, due to the high concentration of palmitic and stearic acids detected at the end of test, this oil can be used as new substrate to produce stearin, normally produced from palm oil.

Reuniting the Biogeochemistry of Algae for a Low-Carbon Circular Bioeconomy

Given their advantages of high photosynthetic efficiency and non-competition with land-based crops, algae, that are carbon-hungry and sunlight-driven microbial factories, are a promising solution to resolve energy crisis, food security, and pollution problems. The ability to recycle nutrient and CO₂ fixation from waste sources makes algae a valuable feedstock for biofuels, food and feeds, biochemicals, and biomaterials. Innovative technologies such as the bicarbonate-based integrated carbon capture and algae production system (BICCAPS), integrated algal bioenergy carbon capture and storage (BECCS), as well as ocean macroalgal afforestation (OMA), can be used to realize a low-carbon algal bioeconomy. We review how algae can be applied in the framework of integrated low-carbon circular bioeconomy models, focusing on sustainable biofuels, low-carbon feedstocks, carbon capture, and advances in algal biotechnology.

Cultivation of energy microalga Chlorella vulgaris with low-toxic sludge extract

Chlorella vulgaris was cultivated in different proportions of activated sludge extracts, which was from the treatment of synthetic wastewater containing tetrachlorophenol. The growth period of C. vulgaris could be shortened for about 10 days when sludge extract was mixed into BG11 culture substrate, and the growth of C. vulgaris was promoted during the period of adaptation and logarithmic period. In the stable and decay period, when the proportion of sludge extract increased to 50%, cell proliferation was inhibited. There was an evident positive correlation between the total and average amount of starch polysaccharide with sludge concentration. When C. vulgaris was cultivated with pure sludge extracts, the total amount of starch and polysaccharide was up to 103 and 125 mg/L. Therefore, the low-toxic sludge extracts were more beneficial to the accumulation of carbohydrates. In the 100% sludge extracts culture medium, chlorophyll-a in C. vulgaris was accumulated to 30.2 mg/L on the 25th day. Through the analysis of algal cells' ultrastructures, it was shown that the photosynthesis was strengthened greatly with low-toxic sludge extracts. The results show that the rich heterotrophic carbon source in the sludge extract can be used as an excellent medium for Chlorella. It provides new ideas for the harmless utilization of surplus sludge as a resource. At the same time, the use of nutrients in the sludge extract to cultivate Chlorella is of great significance to low-cost algae cultivation.

Evaluation of Chlorella vulgaris and Scenedesmus obliquus growth on pretreated organic solid waste digestate

In this research Scenedesmus obliquus and Chlorella vulgaris growth was tested on digestate sludge obtained from the anaerobic co-digestion treatment of the organic fraction of municipal solid waste (OFMSW) together with waste activated sludge (WAS). Digestate was diluted 1:10 and tested in three batch experimental conditions: with no pre-treatments (noPT), after centrifugation (AC) and after filtration (AUF), in order to evaluate microalgae limiting growth factors. The best growth was obtained by C. vulgaris on digestate AC compared to S. obliquus, reaching 479 ± 31 cell million ml^-1 and 131 ± 12 cell million ml^-1 respectively. Ammonia removal evaluated in C. vulgaris and S. obliquus cultures was 99.2% ± 0.3 and 98.146% ± 0.008 in AC condition, respectively. Considering that AUF showed similar microalgae growth values, the digestate pretreatment for microalgae growth, could be limited to centrifugation.

Treatment of Wastewaters by Microalgae and the Potential Applications of the Produced Biomass—A Review

The treatment of different types of wastewater by physicochemical or biological (non-microalgal) methods could often be either inefficient or energy-intensive. Microalgae are ubiquitous microscopic organisms, which thrive in water bodies that contain the necessary nutrients. Wastewaters are typically contaminated with nitrogen, phosphorus, and other trace elements, which microalgae require for their cell growth. In addition, most of the microalgae are photosynthetic in nature, and these organisms do not require an organic source for their proliferation, although some strains could utilize organics both in the presence and absence of light. Therefore, microalgal bioremediation could be integrated with existing treatment methods or adopted as the single biological method for efficiently treating wastewater. This review paper summarized the mechanisms of pollutants removal by microalgae, microalgal bioremediation potential of different types of wastewaters, the potential application of wastewater-grown microalgal biomass, existing challenges, and the future direction of microalgal application in wastewater treatment.

Remediation of Aquaculture Wastewater Using the Microalga Chlorella sorokiniana

The aquaculture industry requires solutions to several environmental challenges in order to become sustainable, including adequate wastewater management. Aquaculture wastewater (AWW) is rich in nitrogen, phosphorus, organic carbon, and other elements essential for microalgae. Due to the potential for AWW to be used as a microalgal growth medium and the potential of Chlorella sorokiniana to remediate wastewater, the growth of this species in AWW was evaluated. The microalgal growth in AWW was compared to the growth in a modified BG11 growth medium containing similar nutrient concentrations as the AWW. The effect of pH regulation and air-lifting the cell suspension at different airflow rates was also studied. As a result, it was found that C. sorokiniana can grow successfully in AWW; however, its cultivation required pH regulation. This microalga species can reach a biomass concentration of up to 476 mg/L and a biomass productivity of 140 mg/L/day. Furthermore, up to 78% of the nitrogen, 77% of the phosphorus, 70% of the magnesium, 90% of the zinc, and 99% of the nickel contained in the AWW were assimilated by the microalgae. The results of this study show that microalga cultivation in wastewater has great potential to reduce contamination while generating economic benefits.

Phycoremediation coupled biomethane production employing sewage wastewater: Energy balance and feasibility analysis

In the present work Chlorella pyrenoidosa, Scenedesmus abundans and Anabaena ambigua have been evaluated for their biomass, phycoremediation efficiency and biomethane production potential by cultivating them in the primary treated sewage waste water (PTSWW) under controlled conditions. By the end of 25-day experiment, up to 52-88% reduction was observed in the nutrient concentration from the 3:1 ratio of PTSWW. Co-digestion of microalgal biomass (dry) with cow dung was performed to estimate biomethane potential. Biogas yield of 618-925 ml g^-1 VS with 48-65% of methane content was obtained employing the microalgal species cultivated in PTSWW. Microalgae appeared notably competent at nutrient sequestration from PTSWW with significant microalgal biomass productivity for biogas production. Energy balance studies revealed the feasibility of coupling the remediation with energy generation. High photosynthetic rate and biomass generation ability along with nutrient confiscation supports employment of microalgae as a potential next generation biofuel source with waste management.

Interactions between Microalgae and Bacteria in the Treatment of Wastewater from Milk Whey Processing

Milk whey processing wastewaters (MWPWs) are characterized by high COD and organic nitrogen content; the concentrations of phosphorus are also relevant. A microalgal-based process was tested at lab scale in order to assess the feasibility of treating MWPW without any dilution or pre-treatment. Different microalgal strains and populations were tested. Based on the obtained results, Scenedesmus acuminatus (SA) and a mixed population (PM) chiefly made of Chlorella, Scenedesmus, and Chlamydomonas spp. were grown in duplicate for 70 days in Plexiglas column photobioreactors (PBRs), fed continuously (2.5 L culture volume, 7 days hydraulic retention time). Nutrient removal, microalgae growth, photosynthetic efficiency, and the composition of microalgal populations in the columns were monitored. At steady state, the microalgal growth was similar for SA and PM. The average removal efficiencies for the main pollutants were: 93% (SA), 94% (PM) for COD; 88% (SA) and 90% (PM) for total N; and 69% (SA) and 73% (PM) for total P. The residual pollution levels in the effluent from the PBRs were low enough to allow their discharge into surface waters; such good results were achieved thanks to the synergy between the microalgae and bacteria in the CO2 and oxygen production/consumption and in the nitrogen mineralization.

Current practices and challenges in using microalgae for treatment of nutrient rich wastewater from agro-based industries

Considerable research activities are underway involving microalgae species in order to treat industrial wastewater to address the waste-to-bioenergy economy. Several studies of wastewater treatment using microalgae have been primarily focused on removal of key nutrients such as nitrogen and phosphorus. Although the use of wastewater would provide nutrients and water for microalgae growth, the whole process is even more complex than the conventional microalgae cultivation on freshwater media. The former one adds several gridlocks to the system. These gridlocks are surplus organic and inorganic nutrients concentration, pH of wastewater, wastewater color, total dissolved solids (TDS), microbial contaminants, the scale of photobioreactor, batch versus continuous system, harvesting of microalgae biomass etc. The present review discusses, analyses, and summarizes key aspects involved in the treatment of wastewaters from distillery, food/snacks product processing, and dairy processing industry using microalgae along with sustainable production of its biomass. This review further evaluates the bottlenecks for individual steps involved in the process such as pretreatment of wastewater for contaminants removal, concentration tolerance/dilutions, harvesting of microalgae biomass, and outdoor scale-up. The review also describes various strategies to optimize algal biomass and lipid productivities for various wastewater and photobioreactor type. Moreover, the review emphasizes the potential of co-cultivation of microorganism such as yeast and bacteria along with microalgae in the treatment of industrial wastewater.

Comparative Appraisal of Biomass Production, Remediation, and Bioenergy Generation Potential of Microalgae in Dairy Wastewater

The present study is a trail to integrate the phycoremediation and bioenergy production from microalgal species cultivated in the dairy wastewater (DWW). Higher biomass productivities for Chlorella pyrenoidosa (24.44 ± 8.02 mg L-1d-1), Anabaena ambigua (23.64 ± 5.69 mg L-1d-1) and Scenedesmus abundans (18.72 ± 2.06 mg L-1d-1) were recorded in 3:1 DWW over the control. The microalgal species have effectively reduced the BOD by 56%, COD by 77%, nitrate by 88%, and phosphate by 85% following 25 days of the cultivation in the 3:1 DWW. The total lipid content was 10.36, 13.13, and 16.93% of dry matter of biomass in C. pyrenoidosa, A. ambigua, and S. abundans, respectively following 25 days of cultivation in the 3:1 ratio of DWW. The biochemical characterization revealed that the protein content was 21.8% in C. pyrenoidosa, 17.73% in A. ambigua and 34.06% in S. abundans. The estimation of theoretical methane potential suggested that the microalgal species have the desirable possibility of biogas generation. The results have marked the achievability of an integrated process for the remediation and bioenergy production by the employment of microalgal species.

An integrated approach for microalgae cultivation using raw and anaerobic digested wastewaters from food processing industry

An integrated approach has been proposed to produce microalgal biodiesel using both raw wastewater (RW) and anaerobically digested wastewater (ADW) of food processing industry without addition of extra nutrients or carbon source for cultivation besides obtaining effluent discharge permissible limits of TN, TP, and COD. Three microalgae species cultivated with following different combinations: RW, ADW, RW + ADW, and glucose + ADW. Results indicated that the addition of RW as a carbon source in ADW significantly enhanced BP, LP, and TN removal as compared to the ADW alone. The runs with RW + ADW removed COD, TN, and TP by 89%, 84%, and 70%, respectively. Sc. obliquus showed highest biomass and lipid productivities (211 and 27.5 mg L^-1 d^-1) for RW + ADW. The addition of RW or glucose in ADW significantly lowered PUFA contents to 5-15% CDW (as against 35-50% with ADW) for Chl. sorokiniana and Sc. obliquus.

Characterization of additional zinc ions on the growth, biochemical composition and photosynthetic performance from Spirulina platensis

In this study, the effect of various initial Zn²⁺ concentration additionally on microalgae growth and biochemical composition were investigated. The Spirulina platensis biomass of each concentration reached the maximum at the end of the cultivation. However, high levels could severely inhibit the growth of microalgae. Fluorescence activity occurred changes in response to heavy metal stress. Moreover, biochemical composition in Spirulina platensis altered under zinc stress, and the highest contents of phycocyanin (PC), Chlorophyll-a (Chl-a), Carotenoid and zinc accumulation were obtained. The proportion of saturated and polyunsaturated fatty acids increased constantly in response to Zn²⁺ exposure. Overall, this study indicated that the use of Spirulina platensis is a viable method for treating zinc containing wastewater and harvested microalgae can be processed into high-zinc products.

Investigation on the feasibility of Chlorella vulgaris cultivation in a mixture of pulp and aquaculture effluents: Treatment of wastewater and lipid extraction

In this study, feasibility of Chlorella vulgaris cultivation in pulp wastewater (PWW) diluted with lake water (LW) and aquaculture wastewater (AWW) was investigated. The best ratios of PWW and AWW (PAWW) viz., 80% PWW:20% AWW and 60% PWW:40% AWW were selected as microalgal culture medium. Algal growth was investigated with and without addition of macro and micronutrients to the cultivation medium. The highest dry algal weight was observed as 1.31 g/L in 60% PWW:40% AWW without adding micronutrients. Nutrients and organic compounds removal efficiencies by microalga were studied in PAWW. Protein, carbohydrate and lipid percentage of harvested microalga from wastewater and Bold's Basal Medium (BBM) solution were analyzed. Fatty acids analysis revealed that C16 and C18 are the major fatty acids in C. vulgaris cultivated in BBM and PAWW. The results of this study revealed that C. vulgaris is a potential candidate for PAWW treatment and lipid and carbohydrate accumulation.

Past, current, and future research on microalga-derived biodiesel: a critical review and bibliometric analysis

Microalga-derived biodiesel plays a crucial role in the sustainable development of biodiesel in recent years. Literature related to microalga-derived biodiesel had an increasing trend with the expanding research outputs. Based on the Science Citation Index Expanded (SCI-Expanded) of the Web of Science, a bibliometric analysis was conducted to characterize the body of knowledge on microalga-derived biodiesel between 1993 and 2016. From the 30 most frequently used author keywords, the following research hotspots are extracted: lipid preparation from different microalga species, microalga-derived lipid and environmental applications, lipid-producing microalgae cultivation, microalgae growth reactor, and microalga harvest and lipid extraction. Other keywords, i.e., microalga mixotrophic cultivation, symbiotic system between microalga and other oleaginous yeast, microalga genetic engineering, and other applications of lipid-producing microalga are future focal points of research. Graphical abstract.

Tofu whey wastewater is a promising basal medium for microalgae culture

Tofu whey wastewater (TWW) is an abundant, nutrient riched and safety wastewater and is regarded as an excellent alternative medium in fermentation. In this study, the feasibility of algal cultivation using TWW as the basal medium was investigated. Results indicated that through simple pH adjustment, TWW presented a better culture performance at autotrophic, heterotrophic, and mixotrophic modes compared with that of regular green algae medium, BG-11. The biomass productivities of Chlorella pyrenoidosa at each trophic mode were 4.76, 1.97, and 2.08 times higher than that cultured in BG-11 medium, respectively. Although a comparative or even lower lipid and protein content was obtained, much higher lipid and protein productivities were obtained in TWW compared to that of BG-11. The algal biomass accumulated in TWW can be used to produce high-value products. Therefore, TWW is a better alternative medium for efficient algal culture.

Prospects, recent advancements and challenges of different wastewater streams for microalgal cultivation

Microalgae are recognized as one of the most powerful biotechnology platforms for many value added products including biofuels, bioactive compounds, animal and aquaculture feed etc. However, large scale production of microalgal biomass poses challenges due to the requirements of large amounts of water and nutrients for cultivation. Using wastewater for microalgal cultivation has emerged as a potential cost effective strategy for large scale microalgal biomass production. This approach also offers an efficient means to remove nutrients and metals from wastewater making wastewater treatment sustainable and energy efficient. Therefore, much research has been conducted in the recent years on utilizing various wastewater streams for microalgae cultivation. This review identifies and discusses the opportunities and challenges of different wastewater streams for microalgal cultivation. Many alternative routes for microalgal cultivation have been proposed to tackle some of the challenges that occur during microalgal cultivation in wastewater such as nutrient deficiency, substrate inhibition, toxicity etc. Scope and challenges of microalgal biomass grown on wastewater for various applications are also discussed along with the biorefinery approach.

Pretreatment of brewery effluent to cultivate Spirulina sp. for nutrients removal and biomass production

Due to the low concentration of nitrate and high contents of organics, brewery effluent was not suitable for the cultivation of Spirulina sp. This work changed the nutrient profile of brewery effluent effectively by dilution, addition of nitrate, and anaerobic digestion. The result showed that the optimum dilution rate and NaNO₃ addition for brewery effluent were 20% and 0.5 g/L, respectively. Spirulina sp. grown in pretreated brewery effluent produced 1.562 mg/L biomass and reduced concentrations of nutrients to reach the permissible dischargeable limits. In addition, Spirulina sp. grown in pretreated brewery effluent had much higher protein content and oil content. So the appropriate treatment converted brewery effluent into a nutrient balanced medium for algae cultivation and alleviated the potential environmental problems. Pretreatment procedure developed in this work is an effective way to realize the sustainable utilization of brewery effluent and produce algal biomass with valuable nutrients.

Effect of flue gas CO2 on the growth, carbohydrate and fatty acid composition of a green microalga Scenedesmus obliquus for biofuel production

Effect of various flue gas CO₂ concentrations (5%, 10% and 14.1%) on growth rate and biochemical properties of a green microalga Scenedesmus obliquus was investigated. S. obliquus showed the highest biomass production and growth rate (0.36 g L^-1 and μ_max = 1.00 day^-1), total inorganic carbon removal (35.8 mg L^-1), lipid productivity (9.9 mg L^-1 day) and carbohydrate productivity (10.3 mg L^-1 day) with 14.1% CO₂ after 8 days of cultivation. Fatty acid methyl ester analysis revealed that the palmitic and oleic acid contents were increased up to 5% and 7% with 14.1% CO₂, respectively. Application of flue gas CO₂ enhanced the growth along with lipid and carbohydrate productivity of S. obliquus, which can be exploited for reducing the CO₂ concentration.

Nitrogen and phosphorus removal coupled with carbohydrate production by five microalgae cultures cultivated in biogas slurry

In this study, five microalgae strains were cultured for their ability to survive in biogas slurry, remove nitrogen resources and accumulate carbohydrates. It was proved that five microalgae strains adapted in biogas slurry well without ammonia inhibition. Among them, Chlorella vulgaris ESP-6 showed the best performance on carbohydrate accumulation, giving the highest carbohydrate content of 61.5% in biogas slurry and the highest ammonia removal efficiency and rate of 96.3% and 91.7mg/L/d respectively in biogas slurry with phosphorus and magnesium added. Additionally, the absence of phosphorus and magnesium that can be adverse for biomass accumulation resulted in earlier timing of carbohydrate accumulation and magnesium was firstly recognized and proved as the influence factor for carbohydrate accumulation. Microalgae that cultured in biogas slurry accumulated more carbohydrate in cell, making biogas slurry more suitable medium for the improvement of carbohydrate content, thus can be regarded as a new strategy to accumulate carbohydrate.

Improving pollutants removal by microalgae Chlorella PY-ZU1 with 15% CO2 from undiluted anaerobic digestion effluent of food wastes with ozonation pretreatment

In order to purify various pollutants (3108mg COD/L, 2120mg NH3-N/L) in the undiluted anaerobic digestion effluent of food wastes (UADEFW), ozonation pretreatment was employed to improve pollutants removal by microalgae mutant Chlorella PY-ZU1 with 15% CO2. Ozonation pretreatment broke CC bonds and benzene rings of refractory organics such as unsaturated fatty acids and phenols in UADEFW and degraded them into low-molecular-weight organics such as methanoic acid and methanal, but excessive ozone induced the accumulation of toxic by-products. The microalgal growth rate and biomass yield markedly increased to the peaks of 456mg/L/d and 4.3g/L, respectively, when the UADEFW was pretreated with 2mg-O3/mg-C of ozone. The removal efficiencies of NH3-N, TP and COD reached 99%, 99% and 68%, respectively. The lipid and carbohydrate contents of microalgal biomass increased because of the relative lack of nitrogen when microalgae was cultured with 15% CO2 to purify the UADEFW with ozonation pretreatment.

Application of acid mine drainage for coagulation/flocculation of microalgal biomass

A novel application of acid mine drainage (AMD) for biomass recovery of two morphologically different microalgae species with respect to AMD dosage, microalgal cell density and pH of medium was investigated. Optimal flocculation of Scenedesmus obliquus and Chlorella vulgaris occurred with 10% dosage of AMD at an initial pH 9 for both 0.5 and 1.0 g/L cell density. The flocculation efficiency was 89% for S. obliquus and 93% for C. vulgaris. Zeta potential (ZP) was increased from -10.66 to 1.77 and -13.19 to 1.33 for S. obliquus and C. vulgaris, respectively. Scanning electron microscope with energy-dispersive X-ray of the microalgae floc confirmed the sweeping floc formation mechanism upon the addition of AMD. Application of AMD for the recovery of microalgae biomass is a cost-effective method, which might further allow reuse of flocculated medium for algal cultivation, thereby contributing to the economic production of biofuel from microalgal biomass.