Microalgae-based Wastewater Treatment Research Articles

Impact of light spectrum on outdoors tubular photobioreactors used for microalgae-based wastewater treatment

Microalgae-based wastewater treatment involves various factors, including algal ecosystems and environmental conditions. Light spectral composition, particularly wavelength and intensity, is a key but underexplored under out-of-laboratory conditions. Therefore, this study investigates the effects of different light wavelengths on microalgae in wastewater treatment systems using filtered sunlight. It examines critical physiological and biochemical processes in microalgae, including pigment synthesis, carbon fixation, and nutrient uptake. A tubular photobioreactor (PBR) setup with two diameters, 4-inch (10.16 cm) and 6-inch (15.24 cm), was tested outdoors for three months using blue, green, and red filters. These filters transmitted radiation and were transparent to infrared light, ranging from 750 nm to blue-green-infrared light (peaking at 450 nm), green-infrared light (peaking at 520 nm), and red-infrared light (peaking at 600 nm). The study analyzed 56 absorption curves, finding that light color influences microalgae physiology even under the same radiation levels. Pigment production was enhanced with only 10 % of total solar radiation, avoiding photoinhibition. Chlorophyll production was highest in the 4-inch PBR with a green filter, while blue light filters promoted pigment accumulation in 6-inch PBRs. However, the 6-inch reactors exhibited a lower growth rate compared to the 4-inch reactors, with significant effects of light color seen only at extreme irradiance levels. Larger diameter PBRs also increased the nitrification process, regardless of the filter used. These results have important implications for biofuel production, wastewater treatment, and bioremediation, underscoring the role of filtered light in enhancing microalgae performance in environments requiring deeper sunlight penetration.

Development of an efficient pretreatment process and multi-functional acetate co-metabolism strategy for the treatment of high strength biogas slurry using a newly isolated Chlorella sorokiniana

The efficient treatment of biogas slurry (BS) to meet the government’s discharge standards is a major challenge for most livestock and poultry enterprises. Although microalgae-based wastewater treatment has many significant benefits over traditional technologies, the poor ammonium tolerance of regular algal species, the pH imbalance during microalgae cultivation, and the complex and expensive BS pretreatment process greatly limit its application in BS treatment. Aimed at these issues, this study firstly isolated a robust Chlorella sp. with strong ammonium and acidic tolerance, as well as heterotrophy ability. To facilitate optimal pH stability and growth enhancement, a co-metabolism cultivation strategy based on the addition of 0.1 g·L-1 acetate in the form of fed-batch was developed. In addition, an efficient pretreatment process integrating ammonia reduction by air stripping with turbidity and chromaticity reduction by acidic precipitation was developed for the elimination of inhibitory factors of microalgal growth in BS. The isolated Chlorella sp. was capable of growing in the pretreated real BS and no growth inhibition was observed even in the undiluted BS. The acetate co-metabolism cultivation strategy obviously enhanced cell growth and pollutant removal and both NH4+ and total phosphorus were reduced to meet the discharge standards of China via 2.5-fold dilutions of BS. The accumulation of high-value biomass could not only fully cover the cost of wastewater treatment, but also bring significant returns. The net profit from treating 1 m3 of BS reached $ 116.2. This study provides a simple and efficient packaged process for the treatment of high strength BS and is expected to greatly reduce the process cost of BS.

Phycoremediation of Potato Industry Wastewater for Nutrient Recovery, Pollution Reduction, and Biofertilizer Production for Greenhouse Cultivation of Lettuce and Celery in Sandy Soils

Microalgae-based wastewater treatment offers an eco-friendly opportunity for simultaneous nutrient recovery and biomass generation, aligning with the circular bioeconomy concept. This approach aims to utilize the nutrients of potato industry wastewater (PIW) for algal growth while mitigating the environmental impact of this industrial byproduct. This study focused on cultivating three cyanobacterial strains, Anabaena oryzae, Nostoc muscorum, and Spirulina platensis, in PIW and synthetic media for 30 days to assess feasibility. Growth performance was monitored by measuring chlorophyll content, dry weight (DW), optical density (OD), and pH at 3-day intervals. The high-performing cyanobacterial biomass from the laboratory findings was formulated into a biofertilizer, which was then evaluated in a controlled greenhouse experiment on celery and lettuce plants. The biofertilizer replaced conventional NPK mineral fertilizers at different levels (25%, 50%, and 75%), while a control group received 100% chemical fertilizer. The results showed favourable growth of all three cyanobacteria strains and their mixture in PIW throughout the experiment. The mixed cyanobacteria followed by Spirulina platensis exhibited the highest growth rates, achieving chlorophyll contents of 3.75 and 2.30 µg·mL−1, DWs of 1.79 g·L−1 and 1.63 g·L−1, and ODs of 0.41 and 0.38, respectively, surpassing the other treatments. The formulated biofertilizers, Spi-PIW (Spirulina platensis + potato industry wastewater) and Cyano-PIW (mixed culture+ potato industry wastewater), significantly enhanced plant height, root and stem lengths, and the number of leaves per plant in celery and lettuce compared to the control group. These biofertilizer treatments also improved chlorophyll contents, as well as macro- and micronutrient levels, in the two crops. Additionally, the application of these biofertilizers improved certain sandy soil properties, i.e., pH, total organic matter, total nitrogen, phosphorus, and potassium. In conclusion, utilizing PIW as a substrate for cultivating cyanobacteria strains and producing high-quality liquid bio-organic fertilizers holds potential for reducing recommended NPK fertilizer doses by 25–50% in celery and lettuce growth, providing an environmentally friendly approach.

A comprehensive review of the challenges and opportunities in microalgae-based wastewater treatment for eliminating organic, inorganic, and emerging pollutants

This review addresses the critical issue of illegal discharge of partially or untreated wastewater effluents, resulting in the accumulation of various inorganic and organic contaminants in the environment. Numerous industries release these toxins into the atmosphere, posing significant threats to wildlife and human health. Consequently, there is an increasing need to mitigate these harmful pollutants through innovative research initiatives. Traditional physicochemical methods for pollutant management are often energy-intensive and can lead to secondary pollution. In contrast, microalgae bioremediation has emerged as an effective and environmentally friendly method for reducing the impact of both organic and inorganic pollutants. Microalgae can decompose complex organic compounds into simpler, less harmful substances without producing additional secondary pollutants. Moreover, certain organic pollutants can serve as carbon sources for the growth of mixotrophic microalgae. The bioremediation potential of microalgae can be further enhanced through advanced modification techniques. This review employs descriptive analysis to explore the application of bioremediation technologies for the removal of organic and inorganic contaminants, assessing their viability and applicability for emerging organic pollutants. It underscores the potential of microalgae to provide cost-effective and ecological solutions for the remediation of various contaminants and outlines successful bioremediation methods. This review effectively elucidates the nature of harmful contaminants, current challenges in industrial-scale water purification, and potential future solutions.

Knowing with Microalgae: On the Maintenance of a Wastewater Treatment Prototype in an Ecovillage

In this article, we present a case study of an experimental set up of a microalgae-based wastewater treatment prototype in an ecovillage requiring many maintenance operations to function. Taking our cue from maintenance and repair studies, we focus on the embodied engagements by which caring for wastewater unfolds. We examine how aquatic ecologists, environmental engineers and villagers use their senses as instruments of inquiry when handling wastewater, as they observe its colour and smell its occupants, and manually check the connections between tubes and pumps. A multispecies body of microbial wastewater figures prominently, as the metabolism of three species of microalgae dwelling in the wastewater is key to the functioning of the prototype. Turning to insights from multispecies ethnographies of laboratory studies, we expand our focus on embodied engagements across the species barrier while maintenance unfolds. We show how ecologists, engineers and villagers engage in ‘knowing with microalgae’ as the algal community invokes and adapts its metabolism in surprising ways to the interferences stirred by their human caretakers. By juxtaposing three ethnographic stories about knowing (1) with hungry, (2) with stressed, and (3) with dying microalgae, we show how algal bodies are both object and instrument of inquiry. Unexpectedly, they also become, tools of repair, liaising with their human caretakers, with other microorganisms and with added chemicals in the wastewater, as well as natural forces such as heat, sunshine, and frost. Considering the maintenance of and by living matter such as microalgae, we raise questions about life and death as the object of maintenance shifts. In so doing, we urge for a multispecies perspective on maintenance that acknowledges that ‘the inclusion of nonhuman others from the animal/organic world produces a different set of ethical concerns than the engagement with technological entities’ (Puig de la Bellacasa 210, 159). This is needed as societies advance towards ecologically sustainable modes of living in which humans will progressively cohabitate with a wide variety of species as well as the technologies that house and facilitate them.

Exploring effects of carbon, nitrogen, and phosphorus on greywater treatment by polyculture microalgae using response surface methodology and machine learning

The microalgae-based wastewater treatment is a promising technique that contribute to achieving sustainable development goals (SDGs), such as SDG-6, “Clean Water and Sanitation”. However, it is strongly influenced by the initial composition of wastewater. In this study, the impact of initial organics and nutrient concentration on the removal of total organic carbon (TOC), total carbon (TC), ammonium (NH4+), total nitrogen (TN), and phosphate (PO43−) from greywater using native polyculture microalgae was explored. Response surface methodology was employed along with two machine learning approaches, AdaBoost and XGBoost, to evaluate the interactions among three main factors: TOC, NH4+, and PO43−, and their effects on treatment efficiency. The C/N ratios for achieving maximum TOC and TC removal efficiency of 99.2% and 97.7% were determined to be 10.3, and 65.4–73.6, respectively. Notably, the N/P ratio did not significantly affect their removal. The highest NH4+ removal efficiency, reaching 96.2%, was attained at C/N ratios of 4.3, 24.0, 38.2, and 212.9, coupled with N/P ratios of 0.3, 2.6, and 23.4. Highest TN removal efficiency of 77.2% was achieved at C/N and N/P ratios of 12.2 and 2.0, respectively. Highest PO43− removal of 78.8% was obtained at N/P ratio 12.8. However, C/N ratio did not affect the removal efficiency. Maintaining these specified C/N and N/P ratios in the influent greywater would ensure that the treated greywater meets the required standards for various reuse applications, including flushing, groundwater recharge, and surface water discharge. The integration of RSM with AdaBoost and XGBoost provided accurate predictions of removal efficiencies. For all the models, XGBoost had the highest R2, and lowest MAE and MSE values. The cross validation of RSM models with AdaBoost and XGBoost further reinforced the reliability of these models in predicting treatment outcomes.

Life cycle assessment on environmental feasibility of microalgae-based wastewater treatment for shrimp recirculating aquaculture systems

This life cycle assessment (LCA) study analyzed the environmental consequences of integrating microalgae-based wastewater treatment into a shrimp farm with recirculating aquaculture systems (RAS). Microalgae treatment produced <10 % of the system’s freshwater eutrophication potential (FEP), marine eutrophication potential (MEP) and global warming potential, which was dominantly contributed by electricity use. Microalgae treatment performed comparably to activated sludge treatment for FEP reduction, and was more effective in remediating marine eutrophication. Replacing coal in electricity mix, particularly with renewables, reduced the system’s impacts by up to 90–99 %. Performing the LCA based on system expansion generally obtained higher impacts compared to allocation. Utilizing algal biomass for biogas production reduced the MEP; however, production of feed ingredient and biodiesel were not environmentally beneficial. This study proved the use of microalgae for aquaculture wastewater treatment to be environmentally feasible, the results can guide more sustainable RAS operations and design of full-scale microalgae treatment.

The enhanced performance of Chlorococcum sphacosum in rich carbon wastewater treatment under the influence of calcium ion

The performance of microalgae-based wastewater treatment process is probably affected by high concentrations of organic carbon in wastewater, and calcium ions may influence this process. Nevertheless, the phenomena and mechanism involved have not been well explored. Here the performance of Chlorococcum sphacosum in treating wastewater with high concentrations of organic carbon was studied by coupling calcium ion concentration regulation (adding CaCl2 and free Ca2+ chelator EGTA) via physicochemical and transcriptomic analysis. It was found that photosynthesis and nutrients removal were suppressed and lipid accumulation was enhanced as the microalga was used to treat wastewater with high concentrations of organic carbon (more than 1500 mg/L). Simultaneously, antioxidant enzymes (SOD, CAT and POD) activity and calcium signaling-related protein (CaM, CDPK, and Ca2+-ATPase) content rose implying that the microalga was in a state of stress and calcium was involved in stress response. It was found that EGTA treatment further weakened the performance of microalgal photosynthesis and nutrients removal. However, the supplementation of Ca2+ had the opposite effect. Transcriptomic analysis revealed that Ca2+ strengthened the heterotrophic decomposition process of carbon (up-regulating the gene expression related to glycolysis and tricarboxylic acid cycle) and inhibited lipid accumulation (down-regulating lipid synthesis) via Ca2+ signalings transduction. Briefly, Ca2+ alleviated the stress of high concentration of organic carbon and strengthened the performance treating the corresponding wastewater.

Assessing sustainability of microalgae-based wastewater treatment: Environmental considerations and impacts on human health

An integrated life cycle assessment (LCA) and quantitative microbial risk assessment (QMRA) were conducted to assess microalgae-mediated wastewater disinfection (M-WWD). M-WWD was achieved by replacing ultraviolet disinfection with a microalgal open raceway pond in an existing sewage treatment plant (STP) in India. Regarding impacts on human health, both M-WWD and STP yielded comparable life cycle impacts, around 0.01 disability-adjusted life years (DALYs) per person per year. However, QMRA impacts for M-WWD (0.053 DALYs per person per year) were slightly lower than that for STP while considering exposure to E. coli O157:H7 and adenovirus. Additionally, a comparative LCA resolved the dilemma about the appropriate utilization of microalgal biomass. Among biodiesel, biocrude, and biogas production, the lowest impacts of 0.015 DALYs per person per year were obtained for biocrude for 1 m3 water treated by M-WWD. Electricity consumption in microalgae cultivation was a major environmental hotspot. Overall, M-WWD, followed by production of microalgal biocrude, emerged as a sustainable alternative from environmental and public health perspectives. These findings set the foundation for pilot-scale M-WWD system development, testing, and economic evaluation. Such comprehensive investigations, encompassing LCA, QMRA, and resource recovery scenarios, offer crucial insights for stakeholders and decision-makers in wastewater treatment and environmental management.

Integrating microalgae-based wastewater treatment, biostimulant production, and hydroponic cultivation: a sustainable approach to water management and crop production.

A natural appearing microalgae-bacteria consortium was used to process urban wastewater. The process was done in an 80m2 raceway reactor and the results were compared to an identical reactor operated using freshwater supplemented with commercial fertilisers. The biomass harvesting was done using commercial ultrafiltration membranes to reduce the volume of culture centrifuged. The membrane allowed achieving a biomass concentration of ∼9-10gL-1. The process proposed avoids the use of centrifuges and the drying of the biomass, two of the most energy consuming steps of conventional processes. The specific growth rate in freshwater and the wastewater-based media was estimated as 0.30 ± 0.05 and 0.24 ± 0.02 days-1, respectively (p < 0.05). The maximum concentration reached at the end of the batch phase was 0.96 ± 0.03 and 0.83 ± 0.07gL-1 when the biomass was produced using freshwater and wastewater, respectively (p < 0.05). The total nitrogen removal capacity of the system was on average 1.35gm-2·day-1; nitrogen assimilation into biomass represented 60%-95% of this value. Furthermore, the P-PO4 3- removal capacity of the system varied from 0.15 to 0.68gm-2·day-1. The outlet effluent of the reactor was used as a nutrient source in the hydroponic production of zucchini seedlings, leading to an increase in the root dry weight and the stem diameter compared to the water alone. The produced biomass showed potential for use as feedstock to produce plant biostimulants with positive effects on root development and chlorophyll retention.

Assessing the effect of Fe2O3 nanoparticle addition on microalgae wastewater treatment and biomass composition

The addition of Fe2O3 nanoparticles to microalgae cultures has gained popularity since it has been demonstrated to enhance microalgae growth and metabolite accumulation. However, most of the literature has been focused on small batch laboratory-scale studies under controlled conditions and the need of continuous studies under real environmental conditions is needed to demonstrate the feasibility of this process. In this study, the effect of Fe2O3 nanoparticles on the metabolism and nutrient uptake of a microalgae-cyanobacteria consortium cultivated in wastewater was elucidated. Different concentrations of Fe2O3 nanoparticles (10, 20, 30 and 70 mg L−1) were assessed at least for 21 days in outdoor cylindrical PBRs at 7 days of hydraulic retention time. No significant difference in microalgae growth, microalgae biomass composition and nutrient uptake was observed at concentrations <30 mg L−1. Moreover, when 30 mg L−1 were added to the culture, the carbohydrate content increased up to 38 % but a decrement in biomass concentration of 18 % was observed by the deposition of nanoparticles on the cyanobacteria cell wall. The addition of 70 mg Fe2O3 L−1 reduced the content of carbohydrate and biomass concentration but did not influence the nutrient uptake from wastewater. In brief, Fe2O3 NP supplementation at 30 mg L−1 can be added as a strategy to stimulate carbohydrate content during microalgae-based wastewater treatment.

Semi-continuous cultivation for enhanced protein production using indigenous green microalgae and synthetic municipal wastewater

Cultivation of microalgae has gained significant interest as an alternative protein source, potentially becoming a target commodity recovered from microalgae-based wastewater treatment. This study examined a semi-continuous cultivation strategy to optimize protein accumulation of the indigenous freshwater chlorophytes, Lobochlamys segnis and Klebsormidium flaccidum, and simultaneously remove nutrients from wastewater efficiently. A strain-specific regime was made based on a fixed biomass concentration at the start of 24-h cultivation cycle, i.e., a constant initial cell density, which regulated harvesting and fresh medium supply volume according to the dilution rate. Six cultivation cycles were conducted in lab-scale 1L reactors with a synthetic municipal wastewater. Lobochlamys segnis and K. flaccidum grew exponentially in all cycles. The biomass productivity was 573 and 580 mg L–1 day–1, in which the total protein consisted of 62 and 45% of dry cell weight (dw), respectively. When a culture medium deficient in nitrogen and phosphorus was used, protein level was significantly reduced. L. segnis consumed all NH4+ and PO43– supplied by the medium replacement, giving the removal rate of 9.2 and 5.2 mg L–1 day–1. Whereas K. flaccidum removed 13.8 mg L–1 day–1 NH4+ without completing PO43– removal. The amino acid profile of both strains was characterized by glutamic acids content (4–5% dw). We concluded that the designed cultivation regime would support a constant biomass production with stable and high protein content, along with an efficient removal of nutrient from the wastewater.

Physiological responses and removal mechanisms of ciprofloxacin in freshwater microalgae

Antibiotics, such as ciprofloxacin (CIP), are frequently detected in various environmental compartments, posing significant risks to ecosystems and human health. In this study, the physiological responses and elimination mechanisms of CIP in Chlorella sorokiniana and Scenedesmus dimorphus were determined. The exposure CIP had a minimal impact on the growth of microalgae, with maximum inhibit efficiency (IR) of 5.14% and 22.74 for C. sorokiniana and S. dimorphus, respectively. Notably, the photorespiration in S. dimorphus were enhanced. Both microalgae exhibited efficient CIP removal, predominantly through bioaccumulation and biodegradation processes. Intermediates involved in photolysis and biodegradation were analyzed through Liquid Chromatography High Resolution Mass Spectrometer (HPLC-MS/MS), providing insights into degradation pathways of CIP. Upregulation of key enzymes, such as dioxygenase, oxygenase and cytochrome P450, indicated their involvement in the biodegradation of CIP. These findings enhance our understanding of the physiological responses, removal mechanisms, and pathways of CIP in microalgae, facilitating the advancement of microalgae-based wastewater treatment approaches, particularly in antibiotic-contaminated environments.

Effect of ammonium/nitrate ratio on microalgae continuous cultures: Species-specificity of nutrient uptake and modelling perspectives

Microalgae-based wastewater treatment is promising in view of circularity as they can uptake most of the nitrogen sources usually present in waste streams: ammonium, nitrite and nitrate as well as some organic species. However, regulation pathways are not fully understood yet. This complexity is a challenge for accurate modelling of these processes, necessary for the design and optimization of wastewater treatment systems. It is generally observed in microalgae that the presence of ammonium inhibits the assimilation of other nitrogen compounds. This was confirmed in this work for Synechocystis sp. PCC6803, even in acclimated continuous cultures. A different uptake regulation was instead observed for the species Auxenochlorella protothecoides, able to uptake nitrate even when high concentrations of ammonium are present. From a modelling perspective, the Droop model was implemented to account for the exploitation of both ammonium and nitrate: a switch function was used to describe the ammonium inhibition, but this was applicable for Synechocystis only. For A. protothecoides, a changing nutrient uptake rate is needed, which was found to be function of the dissolved nitrogen concentration. A bioinformatic analysis was performed to infer putative players involved in nitrogen uptake, accounting for the different behavior of the two taxonomic groups.

Effects of staged multiple phytohormones application on capillary-driven attached Chlorella sp. biofilm

Comparing with single phytohormone application, applying multiple phytohormones to microalgae-based wastewater treatment systems can offer more extensive growth-promoting and stress-protecting effects for microalgae, yet the advantage of stress-relieving salicylic acid (SA) under combined phytohormones application scenario has not been exploited. Employing the improved capillary-driven attached microalgae culturing device (CD-PBR) previously used for single phytohormone application, this study compared the effects of mixed and single phytohormone(s) addition under as low as 10−7 M dosage. In order to make the best of SA for its stress-relieving property, postponed SA addition combined with applying other phytohormone(s) at the beginning of microalgae cultivation was also investigated. Combination of 10−6 M 6-benzylaminopurine (6-BA) with 10−7 M SA was sufficient for enhancing growth-promoting effects and anti-oxidative responses for attached Chlorella sp., while indole-3-acetic acid (IAA) addition was unnecessary. Combination of 6-BA addition at the beginning while postponed SA addition on Day 4 could further sustain such beneficial effects, while removing up to 99.7% total nitrogen (TN) and 97.9% total phosphorus (TP) from the bulk liquid. These results provided innovative strategies on mixed phytohormones addition for microalgae.

Circular bioeconomy approach for pig farming systems using microalgae-based wastewater treatment processes

The circular bioeconomy (CBE) presents a sustainable solution for the pig farming system, delivering economic and environmental benefits. This shift from a linear to a CBE model is anticipated to result in substantial economic, environmental, and social transformations. In this study, the CBE outcomes are evaluated with Scenarios (1 to 3): (1) pig farming and anaerobic digestion (AD) only, (2) pig farming, AD, and microalgae system (MS) with partial microalgae-based biomass (MB) recycle, and (3) pig farming, AD, and MS without MB recycle. Through economic and life cycle analyses, the internal rate of return for Scenarios (1 to 3) are 13.3%, 15.0%, and 12.3%, respectively, but the corresponding endpoint indicators are 483pt, 363pt, and 398pt. To address the best CBE, Scenario 2 by using MB product as a pig feed supplement could achieve higher revenue as well as lower environmental impact.

Using correlation of variables to compare different configurations of microalgae-based wastewater treatment systems

Using correlation of variables to compare different configurations of microalgae-based wastewater treatment systems

Partitioning and inactivation of enveloped and nonenveloped viruses in activated sludge, anaerobic and microalgae-based wastewater treatment systems

Anaerobic and microalgae-based technologies for municipal wastewater treatment have emerged as sustainable alternatives to activated sludge systems. However, viruses are a major sanitary concern for reuse applications of liquid and solid byproducts from these technologies. To assess their capacity to reduce viruses during secondary wastewater treatment, enveloped Phi6 and nonenveloped MS2 bacteriophages, typically used as surrogates of several types of wastewater viruses, were spiked into batch bioreactors treating synthetic municipal wastewater (SMWW). The decay of Phi6 and MS2 in anaerobic and microalgae-based reactors was compared with the decay in activated sludge batch reactors for 96 h (Phi6) and 144 h (MS2). In each reactor, bacteriophages in the soluble and solids fractions were titered, allowing the assessment of virus partitioning to biomass over time. Moreover, the influence of abiotic conditions such as agitation, oxygen absence and light excess in activated sludge, anaerobic and microalgae reactors, respectively, was assessed using dedicated SMWW control reactors. All technologies showed Phi6 and MS2 reductions. Phi6 was reduced in at least 4.7 to 6.5 log10 units, with 0 h concentrations ranging from 5.0 to 6.5 log10 PFU mL−1. Similarly, reductions achieved for MS2 were of at least 3.9 to 7.2 log10 units, from starting concentrations of 8.0 to 8.6 log10 PFU mL−1. Log-logistic models adjusted to bacteriophages’ decay indicated T90 values in activated sludge and microalgae reactors of 2.2 and 7.9 h for Phi6 and of 1.0 and 11.5 h for MS2, respectively, all within typical hydraulic retention times (HRT) of full-scale operation. In the case of the microalgae technology, T99 values for Phi6 and MS2 of 12.7 h and 13.6 h were also lower than typical operating HRTs (2–10 d), while activated sludge and anaerobic treatment achieved less than 99 % of Phi6 and 50 % of MS2 inactivation within 12 h of typical HRT, respectively. Thus, the microalgae-based treatment exhibited a higher potential to reduce the disinfection requirements of treated wastewater.

Machine learning-based optimisation of microalgae biomass production by using wastewater

Microalgae biomass a valuable resource for energy source and fertilisers. Among all available media sources, wastewater serves as cost-efficient media for microalgae biomass production. However, improvements are still needed to increase microalgae biomass productivity in wastewater, particularly optimising cultivation parameters, including light intensity, CO2 content, and initial inoculum level. Machine learning algorithms can easily optimise the cultivation parameters by analysing the microalgae-based wastewater treatment dataset without experimental runs. In the present work, a machine learning algorithm, Decision Tree, was used to analyse microalgae-based datasets and predict different optimised combinations of descriptor variables leading to high growth rate and microalgae biomass production. The decision tree model presented 18 combinations of descriptor variables leading to increased biomass production with a general accuracy of 81.25%. Seven of them were experimentally verified by using two newly isolated strains that predicted a 10% error after experimental verification. Models also revealed that the medium's initial inoculum level and nitrogen/phosphorus ratio highly influence microalgae growth as compared to other parameters. Results obtained in the analysis can be easily implemented at pilot and industrial scales without any laboratory experiments.

Current Insights into Growing Microalgae for Municipal Wastewater Treatment and Biomass Generation

Municipal wastewater (MWW) provides a promising platform for microalgae cultivation due to its rich content of essential nutrients. Recent research has showcased the multifaceted benefits of microalgae-based wastewater treatment, from the potent depollution capabilities of these organisms to their biomass potential for ecofriendly applications. A significant advantage lies in the ability of these systems to promote environmental sustainability without producing secondary pollutants, aligning with the circular economy model. This approach encompasses various stages, from cultivating microalgae to biomass separation and subsequent valorization. However, challenges arise when scaling these systems to industrial levels. A predominant barrier is the difficulty in maintaining consistent control over all the factors influencing wastewater phytoremediation. This can compromise both biomass survival and the efficiency of pollution removal and valorization. Notably, using native microalgal consortiums from the effluent appears to be a promising strategy. These autochthonous communities often demonstrate superior adaptability and treatment capacity, emphasizing the importance of further exploring their potential to provide effective and economically viable solutions for wastewater treatment.