Co-cultivation of activated sludge and microalgae for the simultaneous enhancements of nitrogen-rich wastewater bioremediation and lipid production

Microalgal-bacterial biofilms enhance pollutant removal coupling with eicosapentaenoic acid production in high-concentration ammonia‑nitrogen wastewater

Microalgal-bacterial biofilms have emerged as a promising approach for wastewater treatment. However, its potential to treat high-concentration ammonia‑nitrogen wastewater coupling with high-value fatty acid production remains unclear. Therefore, this study explored the efficiency of a microalgal-bacterial biofilm in treating high-concentration ammonia‑nitrogen wastewater and its ability to produce high-value fatty acids, with the activated sludge (bacteria) and microalgal-bacterial suspension as control. The results indicated that pollutant removal in the microalgal-bacterial biofilm system was the most efficient, with a 98.3 % removal efficiency for chemical oxygen demand, 87.46 % for ammonium nitrogen, and 20.6 % for phosphate. Coupling analysis of microbial community shift and nitrogen conversion genes showed that the relative abundance of Rhodanobacter and Nitrosomonas significantly increased in microalgal-bacterial biofilms, and the expression of nitrification-related genes (amo and hao) and denitrification-related genes (nasA,napA, narI, narV, nirK, and norB) increased compared to the control systems, which played an important role in nitrogen removal. The microalgal-bacterial biofilm system exhibited higher levels of fatty acid synthase and omega-6 fatty acid desaturation, resulting in a dry weight content and production of eicosapentaenoic acid (EPA) with 15.8,19.1 times greater than that achieved by the microalgal suspension system. These results present a foundation for application of pollutant removal in high ammonia nitrogen wastewater coupling with high-value acid production by microalgal-bacterial biofilms.

Insight into recent advances in microalgae biogranulation in wastewater treatment

Microalgae-based technology is widely utilized in wastewater treatment and resource recovery. However, the practical implementation of microalgae-based technology is hampered by the difficulty in separating microalgae from treated water due to the low density of microalgae. This review is designed to find the current status of the development and utilization of microalgae biogranulation technology for better and more cost-effective wastewater treatment. This review reveals that the current trend of research is geared toward developing microalgae-bacterial granules. Most previous works were focused on studying the effect of operating conditions to improve the efficiency of wastewater treatment using microalgae-bacterial granules. Limited studies have been directed toward optimizing operating conditions to induce the secretion of extracellular polymeric substances (EPSs), which promotes the development of denser microalgae granules with enhanced settling ability. Likewise, studies on the understanding of the EPS role and the interaction between microalgae cells in forming granules are scarce. Furthermore, the majority of current research has been on the cultivation of microalgae-bacteria granules, which limits their application only in wastewater treatment. Cultivation of microalgae granules without bacteria has greater potential because it does not require additional purification and can be used for border applications.

Effect of microalgae and bacteria inoculation on the startup of bioreactors for paper pulp wastewater and biofuel production

The use of microalgae and bacteria as a strategy for the startup of bioreactors for the treatment of industrial wastewater can be a sustainable and economically viable alternative. This technology model provides satisfactory results in the nitrification and denitrification process for nitrogen removal, organic matter removal, biomass growth, sedimentation, and byproducts recovery for added-value product production. The objective of this work was to evaluate the performance of microalgae and bacteria in their symbiotic process when used in the treatment of paper pulp industry wastewater. The experiment, lasting fourteen days, utilized four bioreactors with varying concentrations in mgVSS/L of microalgae to bacteria ratio (R1-100:100, R2-100:300, R3-100:500, R4-300:100) in the startup process. Regarding the sludge volumetric index (SVI), the results show that the R1 and R2 reactors developed SVI30/SVI10 biomass in the range of 85.57 ± 7.33% and 84.72 ± 8.19%, respectively. The lipid content in the biomass of reactors R1, R2, R3 e R4 was 13%, 7%, 19%, and 22%, respectively. This high oil content at the end of the batch, may be related to the nutritional stress that the species underwent during this feeding regime. In terms of chlorophyll, the bioreactor with an initial inoculation of 100:100 showed better symbiotic growth of microalgae and bacteria, allowing exponential growth of microalgae. The total chlorophyll value for this bioreactor was 801.46 ± 196.96 μg/L. Biological removal of nitrogen from wastewater from the paper pulp industry is a challenge due to the characteristics of the effluent, but the four reactors operated in a single batch obtained good nitrogen removal. Ammonia nitrogen removal performances were 91.55 ± 9.99%, 72.13 ± 19.18%, 64.04 ± 21.34%, and 86.15 ± 30.10% in R1, R2, R3, and R4, respectively.

Bioremediation potential of the Chlorella and Scenedesmus microalgae in explosives production effluents

This study explores microalgae-based bioremediation for treating black gunpowder production effluents, an understudied yet environmentally significant stream. Two native microalgae, Chlorella sp. MC18 (CH) and Scenedesmus sp. MJ23-R (SC), were assessed for growth kinetics and nutrient removal capabilities in culture media containing different proportions of untreated raw wastewater. Results show both species thrived in 100 % raw wastewater, displaying robust growth and substantial biomass production in parallelepiped-shaped photobioreactors. SC showed superior performance, with higher maximum specific growth rate (0.549 d-1), biomass yield (454.57 mg L-1) and biomass productivity (64.94 mg L-1 d-1) compared to CH (0.524 d-1, 380.60 mg L-1, 54.37 mg L-1 d-1, respectively). The use of 100 % raw wastewater as a culture medium eliminated the need for additional freshwater input, thus reducing the water footprint. The bioremediation process also resulted in a high removal efficiency in turbidity (>95 % CH, >76 % SC), total suspended solids (>93 % CH, >74 % SC), biochemical oxygen demand (BOD5) (>62 % CH, >93 % SC) and chemical oxygen demand (COD) (>63 % CH, >87 % SC), bringing the effluent into compliance with environmental regulations. Although nitrogen (>45 % CH, >57 % SC) and sulphate (>43 % CH, >35 % SC) removal efficiencies was high, potassium bioremediation was limited (<6 %). The proximate chemical composition of the microalgal biomass revealed different allocations to carbohydrates, lipids and proteins. The results suggest promising applications for biofuel production and aquaculture. This research highlights the potential of microalgae-based bioremediation for sustainable wastewater management in the explosives industry, contributing to the UN Sustainable Development Goals and promoting green industrial practices.

Advancements of microalgal upstream technologies: Bioengineering and application aspects in the paradigm of circular bioeconomy

Sustainable energy transition has brought the attention towards microalgae utilization as potential feedstock due to its tremendous capabilities over its predecessors for generating more energy with reduced carbon footprint. However, the commercialization of microalgae feedstock remains debatable due to the various factors and considerations taken into scaling-up the conventional microalgal upstream processes. This review provides a state-of-the-art assessment over the recent developments of available and existing microalgal upstream cultivation systems catered for maximum biomass production. The key growth parameters and main cultivation modes necessary for optimized microalgal growth conditions along with the fundamental aspects were also reviewed and evaluated comprehensively. In addition, the advancements and strategies towards potential scale-up of the microalgal cultivation technologies were highlighted to provide insights for further development into the upstream processes aimed at sustainable circular bioeconomy.

Strategy for the formation of microalgae-bacteria aggregates in high-rate algal ponds

This work studied the formation of aggregates used for wastewater treatment in high-rate algal ponds (HRAP). For this, the establishment of microalgae-bacteria aggregates in these systems was evaluated, considering strategies for the inoculation and start-up. Two HRAP were operated in parallel, at first in batch mode and then in continuous flow. The wastewater treatment was efficient, with removal rates around 80% for COD and N-ammoniacal. Volatile suspended solids and chlorophyll for the culture grew continuously reached a concentration of 548 ± 11 mg L^-1 and 7.8 mg L^-1, respectively. Larger photogranules were observed when the system was placed in a continuous regime. The protein fraction of extracellular polymeric substances was identified as a determinant in photogranules formation. During the continuous regime, more than 50% of the biomass was higher than 0.2 mm, flocculation efficiency of 78 ± 6%, and the volumetric sludge index of 32 ± 5 mL g^-1. The genetic sequencing showed the growth of cyanobacteria in the aggregate and the presence of microalgae from the chlorophytes and diatoms groups in the final biomass.

Pollutants removal, microbial community shift and oleic acid production in symbiotic microalgae-bacteria system

The functional interaction between microorganisms is key in symbiotic microalga-bacteria systems; however, evaluations of fungi and pathogenic microorganisms are not clear. In this study, the roles of three groups (i.e., microalgae-activated sludge (MAS), Microalgae, and activated sludge) in pollutant removal and biomass recovery were comparatively studied. The data implied that microalgal assimilation and bacterial heterotrophic degradation were the major approaches for degradation of nutrients and organic matter, respectively. According to 16S rRNA and internal transcribed spacer sequencing, the relative abundance of Rhodotorula increased remarkably, favoring nutrient exchange between the microalgae and bacteria. The abundances of two types of pathogenic genes (human pathogens and animal parasites) were reduced in the MAS system. The oleic acid content in the MAS system (51.2 mg/g) was 1.7 times higher than that in the Microalgae system. The results can provide a basis for practical application and resource utilization of symbiotic microalgae-bacteria systems.

Screening of microalgae species and evaluation of algal-lipid stimulation strategies for biodiesel production

Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15-35 mg/L and P:4-16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.

A review on algal-bacterial symbiosis system for aquaculture tail water treatment

Aquaculture is one of the fastest growing fields of global food production industry in recent years. To maintain the ecological health of aquaculture water body and the sustainable development of aquaculture industry, the treatment of aquaculture tail water (ATW) is becoming an indispensable task. This paper discussed the demand of environmentally friendly and cost-effective technologies for ATW treatment and the potential of algal-bacterial symbiosis system (ABSS) in ATW treatment. The characteristics of ABSS based technology for ATW treatment were analyzed, such as energy consumption, greenhouse gas emission, environmental adaptability and the possibility of removal or recovery of carbon, nitrogen and phosphorus as resource simultaneously. Based on the principle of ABSS, this paper introduced the key environmental factors that should be paid attention to in the establishment of ABSS, and then summarized the species of algae, bacteria and the proportion of algae and bacteria commonly used in the establishment of ABSS. Finally, the reactor technologies and the relevant research gaps in the establishment of ABSS were reviewed and discussed.

New concept of biodiesel production using food waste digestate powder: Co-culturing algae-activated sludge symbiotic system in low N and P paper mill wastewater

This paper aims to demonstrate an innovative process for the conversion of food waste digestate (FWD) powder into biofuel. The effects of different doses of FWD are investigated on microalgae-activated sludge (MAS) in treating pulp and paper mill wastewater (PPW) which generally contains insufficient nitrogen and phosphorus. FWD was added to adjust the initial N:P molar ratio in MAS at various levels (8:1 to 15:1). The highest Auxenochlorella protothecoides biomass achieved was 1.67 gL^-1 at a 13.45:1 N/P molar ratio of PPW. After 10 days of cultivation, Auxenochlorella protothecoides-activated sludge system removed 91.7 %, 74.6 %, and 91.5 % of total nitrogen, phosphorus, and sCOD respectively at D_0.836 gL^-1 DD. The highest lipid productivity was reported as 41.27 ± 2.43 mg L^-1 day^-1. Fatty acid methyl ester (FAME) analysis showed the presence of an appreciable percentage of balanced saturated and unsaturated fatty acids i.e. palmitic, oleic, and linoleic acid, rendering its potential as a feedstock for biodiesel production. Activated sludge induced flocculation of Auxenochlorella protothecoides was measured. The whole process establishes an effective means of circular economy, where the secondary source of recyclable nutrients i.e. FWD will be used as a source of N and P in PPW to obtain algal biodiesel from a negative value industrial wastewater.

Optimization of Microalgae–Bacteria Consortium in the Treatment of Paper Pulp Wastewater

The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH4+–N), nitrite nitrogen (NO2−–N), nitrate nitrogen (NO3−–N), phosphate phosphorus (PO43−–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH4+–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO43−–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

Heavy metal impact on lipid production from oleaginous microorganism cultivated with wastewater sludge

Using municipal wastewater sludge to produce microbial lipid is an effective way of resource recycling. Sludge contains heavy metals and may lead to negative impact on lipid production. However, relative study has not been reported. In this study, metal impact on Lipomyces starkeyi lipid accumulation was conducted. Results showed that Cd²⁺ had great impact on lipid accumulation, but other metals had no much impact. The maximum lipid content of L. starkeyi cultivated in 0.55 mg/L of Cd²⁺ was only 41% w/w, which was lower than the control (51% w/w). The inhibition on acetyl-CoA formation was observed when Cd²⁺ was in the medium. After removing metals from sludge, the lipid accumulation was only around half of the one without metal removal. It would be due to that not only the toxic metals in the sludge were removed as well as the metals such as Zn²⁺ which can enhance lipid accumulation.

Co-culture of microalgae-activated sludge in sequencing batch photobioreactor systems: Effects of natural and artificial lighting on wastewater treatment

Co-culture using microalgae-activated sludge in Sequencing Batch Photobioreactors (PBRs) was investigated for wastewater treatment performance. This study evaluated the effect of natural and artificial lighting conditons on treatment performance under consideration of energy consumption. The results found that the removal of nutrients and COD of natural lighting condition was only 10% and 13% lower than those of artificial lighting respectively. Generally, artificial lighting mode took an advantage in pollutants removal. However, standing at 0.294 kWh L^-1, the total energy consumption of natural lighting was over two times less than that of artificial lighting. It reveals the natural lighting system played a dominant role for cutting energy costs significantly compared to artificial lighting one (∼57%). As a practical viewpoint on energy aspect and treatment performance, a natural lighting PBR system would be a sustainable option for microalgae-activated sludge co-culture system treating wastewater.

Integrating bioremediation of textile wastewater with biodiesel production using microalgae (Chlorella vulgaris)

Microalgae-led wastewater treatment is a promising biorefinery approach to promote environmental and economical sustainability. In this study, Chlorella vulgaris (C. vulgaris) was employed for the bioremediation of textile wastewater (TWW) and biodiesel production. C. vulgaris is cultivated in undiluted and diluted TWW (50%). Cultivation in freshwater containing BG11 medium was set as a control. Results show the highest growth (1.62 ± 0.12 OD₆₈₀) in diluted TWW followed by BG11 medium (1.56 ± 0.15 OD₆₈₀) and undiluted TWW (0.89 ± 0.11 OD₆₈₀). The highest methylene blue decolorization of 99.7% was observed in diluted TWW as compared to 98.5% in undiluted TWW. Morever, COD removal efficiency was also higher (99.7 ± 4.2%) in diluted TWW than BG11 medium (94.4 ± 3.5%) and undiluted TWW (76.3 ± 2.8%). For all treatment, more than 80% nitrogen and phosphorous removal were achieved. Otther than this, fatty acids methyl ester (FAME) yield in diluted TWW was higher (11.07 mg g^-1) than the undiluted TWW (9.12 mg L^-1). Major FAME were palmitic acid (C16:0) and linolenoic acid (C18:3) which are suitable for biodiesel production. All these results suggest that C. vulgaris can be cultivated in both diluted and undiluted TWW for biodiesel production. However, cultivation in undiluted TWW is more favorable as it displaces the need for freshwater addition in the growth medium.

Microbial approaches for remediation of pollutants: Innovations, future outlook, and challenges

Environmental contamination with persistent organic pollutants has emerged as a serious threat of pollution. Bioremediation is a key to eliminate these harmful pollutants from the environment and has gained the interest of researchers during the past few decades. Scientific knowledge upon microbial interactions with individual pollutants over the past decades has helped to abate environmental pollution. Traditional bioremediation approaches have limitations for their applications; hence, it is essential to discover new bioremediation approaches with biotechnological interventions for best results. The developments in various methodologies are expected to increase the efficiency of bioremediation techniques and provide environmentally sound strategies. This paper deals with the profiling of microorganisms present in polluted sites using various techniques such as culture-based approaches and omics-based approaches. Besides this, it also provides up-to-date scientific literature on the microbial electrochemical technologies which are nowadays considered as the best approach for remediation of pollutants. Detailed information about future outlook and challenges to evaluate the effect of various treatment technologies for remediation of pollutants has been discussed.

Co-cultivation of microalga and xylanolytic bacterium by a continuous two-step strategy to enhance algal lipid production

To enhance microalgal lipid production, canonical two-step cultivation strategy that by transferring the microalgal cells grown in nutrient-replete medium to nutrient-depleted medium is widely used. However, the harvesting step during the transfer raises the production cost. To avoid the harvesting step, this study developed a continuous two-step (CTS) cultivation strategy. In the strategy, Chlorella sacchrarophila was grown in bioreactor while a xylanolytic bacterium Cellvibrio pealriver grown in an inner bag that embedded in the bioreactor; after the first-step co-cultivation, the inner bag is removed which then start the second-step cultivation of C. sacchrarophila. Based on the strategy, the lipid production was determined as 825.34-929.79 mg·L^-1, which were 1.7-1.9 times higher than that of cultivation in canonical two-step strategy using glucose as feedstock. During the CTS strategy, the co-cultivation using xylan as feedstock promotes the microalgal growth and the removal of inner bag produces nutrient-depleted condition for enhancing microalgal lipid production.

Novel sequential flow baffled microalgal-bacterial photobioreactor for enhancing nitrogen assimilation into microalgal biomass whilst bioremediating nutrient-rich wastewater simultaneously

A novel sequential flow baffled microalgal-bacterial (SFB-AlgalBac) photobioreactor was designed to cater for the synergistic interactions between microalgal and bacterial consortia to enhance nitrogen assimilation into microalgal biomass from nutrient-rich wastewater medium. The performance of the SFB-AlgalBac photobioreactor was found to be optimum at the influent flow rate of 5.0 L/d, equivalent to 20 days of hydraulic retention time (HRT). The highest microalgal nitrogen assimilation rate (0.0271 /d) and biomass productivity (1350 mg/d) were recorded amidst this flow rate. Further increase to the 10.0 L/d flow rate reduced the photobioreactor performance, as evidenced by a reduction in microalgal biomass productivity (>10%). The microalgal biomass per unit of nitrogen assimilated values were attained at 16.69 mg/mg for the 5.0 L/d flow rate as opposed to 7.73 mg/mg for the 10.0 L/d flow rate, despite both having comparable specific growth rates. Also, the prior influent treatment by activated sludge was found to exude extracellular polymeric substances which significantly improved the microalgal biomass settleability up to 37%. The employment of SFB-AlgalBac photobioreactor is anticipated could exploit the low-cost nitrogen sources from nutrient-rich wastewaters via bioconversion into valuable microalgal biomass while fulfilling the requirements of sustainable wastewater treatment technologies.

Tolerance of Tetraselmis tetrathele to High Ammonium Nitrogen and Its Effect on Growth Rate, Carotenoid, and Fatty Acids Productivity

Microalgae can use either ammonium or nitrate for its growth and vitality. However, at a certain level of concentration, ammonium nitrogen exhibits toxicity which consequently can inhibit microalgae productivity. Therefore, this study is aimed to investigate the tolerance of Tetraselmis tetrathele to high ammonium nitrogen concentrations and its effects on growth rate, photosynthetic efficiency (F_v/F_m), pigment contents (chlorophyll a, lutein, neoxanthin, and β-carotene), and fatty acids production. Experiments were performed at different ammonium nitrogen concentrations (0.31–0.87 gL⁻¹) for 6 days under a light source with an intensity of 300 μmol photons m⁻² s⁻¹ and nitrate-nitrogen source as the experimental control. The findings indicated no apparent enhancement of photosynthetic efficiency (F_v/F_m) at high levels of ammonium nitrogen (NH4+-N) for T. tetrathele within 24 h. However, after 24 h, the photosynthetic efficiency of T. tetrathele increased significantly (p < 0.05) in high concentration of NH4+-N. Chlorophyll a content in T. tetrathele grown in all of the different NH4+-N levels increased significantly compared to nitrate-nitrogen (NO₃-N) treatment (p < 0.05); which supported that this microalgal could grow even in high level of NH4+-N concentrations. The findings also indicated that T. tetrathele is highly resistant to high ammonium nitrogen which suggests T. tetrathele to be used in the aquaculture industry for bioremediation purpose to remove ammonium nitrogen, thus reducing the production cost while improving the water quality.

Comparative Performances of Microalgal-Bacterial Co-Cultivation to Bioremediate Synthetic and Municipal Wastewaters Whilst Producing Biodiesel Sustainably

The potentiality of a microalgal-bacterial culture system was explored in bioremediating wastewater while generating biomass for biodiesel production. A pre-determined optimal activated sludge and microalgal ratio was adopted and cultivation performance was evaluated in both synthetic and municipal wastewater media for nitrogen removal along with biomass and lipid generation for biodiesel production. The microalgal-bacterial consortium grown in the municipal wastewater medium produced higher biomass and lipid yields than those in the synthetic wastewater medium. The presence of trace elements in the municipal wastewater medium, e.g., iron and copper, contributed to the upsurge of biomass, thereby leading to higher lipid productivity. Both the microbial cultures in the synthetic and municipal wastewater media demonstrated similar total nitrogen removal efficiencies above 97%. However, the nitrification and assimilation rates were relatively higher for the microbial culture in the municipal wastewater medium, corresponding to the higher microbial biomass growth. Accordingly, the feasibility of the microalgal-bacterial consortium for bioremediating real municipal wastewaters was attested in this study by virtue of higher biomass and lipid production. The assessment of fatty acid methyl esters (FAME) composition showed the mixed microbial biomasses comprised 80–93% C16 to C18 FAME species, signifying efficient fuel combustion properties for quality biodiesel requirements.

Development of Digital Image Processing as an Innovative Method for Activated Sludge Biomass Quantification

Activated sludge process is the most common method for biological treatment of industrial and municipal wastewater. One of the most important parameters in performance of activated sludge systems is quantitative monitoring of biomass to keep the cell concentration in an optimum range. In this study, a novel method for activated sludge quantification based on image processing and RGB analysis is proposed. According to the results, the intensity of blue color in the macroscopic image of activated sludge culture can be a very accurate index for cell concentration measurement and R² coefficient, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), and Mean Absolute Percentage Error (MAPE) which are 0.990, 2.000, 0.323, and 13.848, respectively, prove this claim. Besides, in order to avoid the difficulties of working in the three-parameter space of RGB, converting to grayscale space has been applied which can estimate cell concentration with R ² = 0.99. Ultimately, an exponential correlation between RGB values and cell concentrations in lower amounts of biomass has been proposed based on Beer-Lambert law which can estimate activated sludge biomass concentration with R ² = 0.97 based on B index.

Co-culture of microalgae-activated sludge for wastewater treatment and biomass production: Exploring their role under different inoculation ratios

In this study, mixed culture (microalgae:activated sludge) of a photobioreactor (PBR) were investigated at different inoculation ratios (1:0, 9:1, 3:1, 1:1, 0:1 wt/wt). This work was not only to determine the optimal ratio for pollutant remediation and biomass production but also to explore the role of microorganisms in the co-culture system. The results showed high total biomass concentrations were obtained from 1:0 and 3:1 ratio being values of 1.06, 1.12 g L^-1, respectively. Microalgae played a dominant role in nitrogen removal via biological assimilation while activated sludge was responsible for improving COD removal. Compared with the single culture of microalgae, the symbiosis between microalgae and bacteria occurred at 3:1 and 1:1 ratio facilitated a higher COD removal by 37.5-45.7 %. In general, combined assessment based on treatment performance and biomass productivity facilitated to select an optimal ratio of 3:1 for the operation of the co-culture PBR.

Recent advances in production and extraction of bacterial lipids for biofuel production

Lipid-based biofuel is a clean and renewable energy that has been recognized as a promising replacement for petroleum-based fuels. Lipid-based biofuel can be made from three different types of intracellular biolipids; triacylglycerols (TAGs), wax esters (WEs), and polyhydroxybutyrate (PHB). Among many lipid-producing prokaryotes and eukaryotes, biolipids from prokaryotes have been recently highlighted due to simple cultivation of lipid-producing prokaryotes and their ability to accumulate high biolipid contents. However, the cost of lipid-based biofuel production remains high, in part, because of high cost of lipid extraction processes. This review summarizes the production mechanisms of these different types of biolipids from prokaryotes and extraction methods for these biolipids. Traditional and improved physical/chemical approaches for biolipid extraction remain costly, and these methods are summarized and compared in this review. Recent advances in biological lipid extraction including phage-based cell lysis or secretion of biolipids are also discussed. These new techniques are promising for bacterial biolipids extraction. Challenges and future research needs for cost-effective lipid extraction are identified in this review.

Exploration of microalgal species for simultaneous wastewater treatment and biofuel production

Microalgal isolates obtained from stream water and wastewater treatment plant were examined to select a suitable microalgal species capable of simultaneously removing nutrient and producing biofuel. Ten isolates were identified using internal transcribed spacer (ITS) region sequencing analysis and were determined to be green microalgae, belonging to phylum Chlorophyta. The highest nutrient removal rates of 8.1 mg-T-N/L-d and 1.6 mg-T-P/L-d were achieved by Chlorella sorokiniana UTEX 1810 under photo-autotrophic cultivation conditions. Fatty acid methyl ester (FAME) composition analysis was conducted to estimate biofuel quality using gas chromatography with mass spectrometry on the basis of the lipid content extracted from microalgal cell. The composition of FAME is mainly composed of palmitic acid (C16:0), stearic acid (C18:0), linoleic acid (C18:2), and heneicosanoic acid (C21:0). These results suggest that C. sorokiniana UTEX 1810 is a promising candidate for simultaneous removal of nutrient and biofuel production from wastewater.

How suspended solids concentration affects nitrification rate in microalgal-bacterial photobioreactors without external aeration

The use of microalgae for the treatment of municipal wastewater makes possible to supply oxygen and save energy, but must be coupled with bacterial nitrification to obtain nitrogen removal efficiency above 90%. This paper explores how the concentration of Total Suspended Solids (TSS, from 0.2 to 3.9 g TSS/L) affects the nitrification kinetic in three microalgal-bacterial consortia treating real municipal wastewater. Two different behaviors were observed: (1) solid-limited kinetic at low TSS concentrations, (2) light-limited kinetic at higher concentrations. For each consortium, an optimal TSS concentration that produced the maximum volumetric ammonium removal rate (around 1.8–2.0 mg N L⁻¹ h⁻¹), was found. The relationship between ammonium removal rate and TSS concentration was then modelled considering bacteria growth, microalgae growth and limitation by dissolved oxygen and light intensity. Assessment of the optimal TSS concentrations makes possible to concentrate the microbial biomass in a photobioreactor while ensuring high kinetics and a low footprint.

Synergy of biofuel production with waste remediation along with value-added co-products recovery through microalgae cultivation: A review of membrane-integrated green approach

Development of advanced biofuels such as bioethanol and biodiesel from renewable resources is critical for the earth's sustainable management and to slow down the global climate change by partial replacement of gasoline and diesel in the transport sector. Being a diverse group of aquatic micro-organisms, algae are the most prominent resources on the planet, distributed in an aquatic system, a potential source of bioenergy, biomass and secondary metabolites. Microalgae-based biofuel production is widely accepted as non-food fuel sources and better choice for achieving goals of incorporation of a clean fuel source into the transportation sector. The present review article provides a comprehensive literature survey as well as a novel approach on the application of microalgae for their simultaneous cultivation and bioremediation of high nutrient containing wastewater. In addition to that, merits and demerits of different existing conventional techniques for microalgae culture reactors, harvesting of algal biomass, oil recovery, use of different catalysts for transesterification reactions and other by-products recovery have been discussed and compared with the membrane-based system to find out the best optimal conditions for higher biomass as well as lipid yield. This article also deals with the use of a tailor-made membrane in an appropriate module that can be used in upstream and downstream processes during algal-based biofuels production. Such membrane-integrated system has the potential of low-cost and eco-friendly separation, purification and concentration enrichment of biodiesel as well as other valuable algal by-products which can bring the high degree of process intensification for scale-up at the industrial stage.

Impact of various microalgal-bacterial populations on municipal wastewater bioremediation and its energy feasibility for lipid-based biofuel production

The microalgal-bacterial co-cultivation was adopted as an alternative in making microbial-based biofuel production to be more feasible in considering the economic and environmental prospects. Accordingly, the microalgal-bacterial symbiotic relationship was exploited to enhance the microbial biomass yield, while bioremediating the nitrogen-rich municipal wastewater. An optimized inoculation ratio of microalgae and activated sludge (AS:MA) was predetermined and further optimization was performed in terms of different increment ratios to enhance the bioremediation process. The nitrogen removal was found accelerating with the increase of the increment ratios of inoculated AS:MA, though all the increment ratios had recorded a near complete total nitrogen removal (94-95%). In light of treatment efficiency and lipid production, the increment ratio of 0.5 was hailed as the best microbial population size in accounting the total nitrogen removal efficiency of 94.45%, while not compromising the lipid production of 0.241 g/L. Moreover, the cultures in municipal wastewater had attained higher biomass and lipid productions of 1.42 g/L and 0.242 g/L, respectively, as compared with the synthetic wastewater which were only 1.12 g/L (biomass yield) and 0.175 g/L (lipid yield). This was possibly due to the presence of trace elements which had contributed to the increase of biomass yield; thus, higher lipid attainability from the microalgal-bacterial culture. This synergistic microalgal-bacterial approach had been proven to be effective in treating wastewater, while also producing useful biomass for eventual lipid production with comparable net energy ratio (NER) value of 0.27, obtained from the life-cycle analysis (LCA) studies. Thereby, contributing towards long-term sustainability and possible commercialization of microbial-based biofuel production.