Microalgae Chlorella vulgaris and Scenedesmus dimorphus co-cultivation with landfill leachate for pollutant removal and lipid production

Enhancing mixed-species microalgal biofilms for wastewater treatment: Design, construction, evaluation and optimisation

Biofilm-based cultivation of microalgae is a powerful method for wastewater treatment with low harvesting costs, water and energy consumption. This article provides a detailed summary of the design, construction, evaluation, and optimisation (DCEO) of mixed-species biofilms including algal and bacteria, and discusses their relevant applications in the treatment of industrial and agricultural wastewater and new pollutants. Finally, it presents the problems faced by mixed-species microalgal biofilms, along with solutions. DCEO is a typical synthetic biology concept, in which design and construction are bottom-up, and evaluation and optimisation are top-down approaches. Detailed knowledge of the metabolic pathways and the regulation of microalgae and other microorganisms is helpful for designing mixed-species biofilms. Three dimensional bioprinting is a powerful tool for constructing structured biofilms. Further analysis after evaluation is beneficial to optimise such biofilms. This review provides a new insight into using DCEO to enhance mixed-species biofilms for wastewater treatment.

Comparison of single and mixed microalgae in microalgae-bacteria MB-MBR:From efficiency of wastewater treatment, bioactivity and membrane fouling

In this study, two microalgae-bacterial moving bed membrane bioreactors (MB-MBRs) were constructed for co-culture of L1 (Scenedesmus obliquus) and L2 (Chlorella pyrenoidosa and Scenedesmus obliquus) with activated sludge. Nutrient removal efficiency, biological activity and membrane fouling of two microalgae-bacterial MB-MBRs were evaluated. Both reactors demonstrated robust performance, with L2 exhibiting superior functionality. near-complete ammonia nitrogen removal (99.33 ± 1.11 %), total organic carbon (TOC) removal of 73.72 ± 4.83 %, chemical oxygen demand (COD) removal of 92.93 ± 3.23 %, and dehydrogenase activity (DHA) peaked at 10 μg TF/(mL·h). L2 sludge flocs displayed a more compact circular morphology compared to those of L1. It was found that proteins in the extracellular polymeric substance (EPS) were the key to initial biofilm attachment, while polysaccharides facilitated biofilm maturation. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy demonstrated that tryptophan and aromatic proteins played critical roles in biofilm formation and membrane fouling. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, ΔGAB was the main factor influencing membrane fouling. These results demonstrate that hybrid microalgae-bacterial systems with biofilm carriers synergistically enhance wastewater treatment efficiency, increase biological activity, and alleviate membrane fouling, offering a sustainable strategy for wastewater treatment.

Ozone oxidation of actual waste leachate coupled with culture of microalgae for efficient lipid production under different temperatures

The production of waste leachate (WL) has been increasing annually with the growth of population and the improvement of living standards, but it has become a difficult task to treat and resource it. Furthermore, the shortage of energy is becoming more serious, so the development of renewable energy instead of expensive fossil fuels is especially essential for productive life. This study constructed a system to oxidize WL by ozone at different temperatures and used it as a culture substrate for microalgae to produce biodiesel. It was shown that the biomass and lipid content of microalgae reached 420 ± 43.59 mg/L and 41 ± 2.2 % at a low temperature of 15 °C, respectively. Compared with the reaction system at 5 °C, the oxidation of WL by ozone at 25-45 °C was more effective in removing ammonia nitrogen, total phosphorus, and chromaticity. Three-dimension excitation emission matrix (3D-EEM) fluorescence spectroscopy results showed that the fluorescence intensity of dissolved organic matter in WL was reduced by 59.4 %-67.7 % after the ozone oxidation, which improved the bioavailability of WL and laid a nutrient foundation for the growth of microalgae. At 45 °C, 72.7 % of the chromaticity of WL was removed by ozone oxidation alone, and the ozone-coupled microalgae treatment system reduced ammonia nitrogen from 416.25 ± 1.05 to 214.6 ± 7.99 mg/L in WL. In addition, microalgae regulated the antioxidant system to mitigate oxidative damage induced by high concentrations of reactive oxygen species (ROS) caused by extreme temperatures by adjusting the levels of superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH). The lipids of microalgae cultured in WL were dominated by saturated and unsaturated fatty acids, and the saturated fatty acids content of lipids reached 60.8 % at 15 °C, which was favorable for the production of biodiesel with better lubricating and combustion properties. This study provides a valuable theoretical basis for the resource utilization of WL and the practical production of microalgae biodiesel in cold regions.

Efficient wastewater treatment and biomass co-production using energy microalgae to fix C, N, and P

Distillery wastewater (DWW), characterized by high organic and nutrient loads, represents a significant environmental challenge, requiring effective and sustainable treatment solutions. This study investigates an innovative approach that integrates microalgae cultivation with DWW treatment for simultaneous bioremediation and biomass production, while also exploring carbon sequestration. We analyzed the growth characteristics, nutrient removal efficiency, protein accumulation, and ultrastructural changes of Chlamydomonas reinhardtii and Scenedesmus dimorphus under varying nitrogen-to-phosphorus (N/P) ratios in diluted DWW. Optimal nutrient removal and biomass accumulation were achieved at N/P concentrations of 46/11.5 mg L-1. C. reinhardtii showed particularly high nutrient removal rates, with significantly high removal rates for total nitrogen, total phosphorus, and chemical oxygen demand. S. dimorphus, under the same conditions, demonstrated exceptional protein accumulation and also effectively removed pollutants. Both species showed enhanced performance under these conditions, with microalgal cell organelles remaining structurally intact, and chloroplasts and thylakoid layers well-developed. The study also explored carbon sequestration potential using varying CO2 concentrations, where C. reinhardtii exhibited enhanced biomass accumulation at 3000 ppm CO2. This integrated approach offers an effective and economically feasible solution for distillery wastewater treatment, simultaneously enabling biomass production and carbon capture. The dual benefits of bioremediation and bioenergy generation position this technology as a promising pathway for sustainable resource management and environmental protection.

Advancements and hurdles in symbiotic microalgal co-cultivation strategies for wastewater treatment

Microalgae offer significant potential in various industrial applications, such as biofuel production and wastewater treatment, but the economic barriers to their cultivation and harvesting have been a major obstacle. However, a promising strategy involving co-cultivating microalgae in wastewater treatment could overcome the limitations of monocultivation and open the possibility for increased integration of microalgae into various industrial processes. This symbiotic relationship between microalgae and other microbes can enhance nutrient removal efficiency, increase value-added bioproduct production, promote carbon capture, and decrease energy consumption. However, unresolved challenges, such as the competition between microalgae and other microbes within the wastewater treatment system, may result in imbalances and reduced efficiency. The complexity of managing multiple microbes in a co-cultivation system poses difficulties in achieving stability and consistency in bioproduct production. In response to these challenges, strategies such as optimizing nutrient ratios, manipulating environmental conditions, understanding the dynamics of microbial relationships, and employing genetic modification to enhance the metabolic capabilities of microalgae and improve their competitiveness are critical in transitioning to a more sustainable path. Hence, this review will provide an in-depth analysis of recent advancements in symbiotic microalgal co-cultivation for applications in wastewater treatment and CO2 utilization, as well as discuss approaches for improving microalgal strains through genetic modification. Furthermore, the review will explore the use of efficient bioreactors, advanced control systems, and advancements in biorefinery processes.

Enhancement of microalgae co-cultivation self-settling performance and water purificationcapacity of microalgae biofilm

Cultivating microalgae for the remediation of aquaculture wastewater provides a promising solution for pollution control. However, the economic viability of this approach faces challenges due to the high costs associated with microalgal biomass harvesting. This study aims to address this issue by immobilizing microalgae onto coral velvet carriers, enhancing the efficiency of biomass recovery. Four types of microalgae were screened: Chlorella sp., Isochrysis galbana, Chaetoceros sp., and Nannochloropsis sp. Among them, Isochrysis galbana exhibited the best self sedimentation rate, achieving a self sedimentation rate of 94.36%. Chlorella sp. demonstrated the best denitrification rate, with a nitrate removal rate of 100% and an inorganic nitrogen removal rate of 79.13%. In addition, this study found that extracellular polymeric substances(EPS) affects the self-settling performance of microalgae, and the results emphasize the key role of tightly-bound EPS(TB-EPS) content in determining self settling efficiency. Furthermore,the assessments of the purification of simulated aquaculture wastewater were conducted, comparing the outcomes of co-cultivation with mono-culture. The co-cultivation strategy showed exceptional efficacy, achieving a 100% removal rate for NO3--N by the 5th day. In contrast, mono-cultures of Chlorella sp. and Isochrysis galbana showed removal rates of 77.76% and 45.72%, respectively, at the same interval. Applying of the co-cultivation microalgal biofilm to treat the actual aquaculture wastewater showed remarkable denitrification performance, attaining a 100% removal rate for NO3--N by the 7th day. The study proposes the co-cultivation of Chlorella sp. and Isochrysis galbana for treating aquaculture wastewater and explores the potential application of immobilization technology to remove nitrogen-containing pollutants.

Silicate Derived from Phaeodactylum tricornutum for Removal of Polystyrene: Interfacial Effects of Living Organism and Its Derivatives with Nanoplastics

The deposition of nanoplastics in the environment poses a direct threat to human health through the food chain. There is an urgent need to investigate how they can be effectively removed from water. In this work, the toxic effects of nanopolystyrene (PS) at different concentrations on Phaeodactylum tricornutum (PT) were investigated. The results show that PS affects the cell activity of PT through cell wall adhesion and shading effect and hinders the transmission of light energy, thus inhibiting the growth of PT. Considering that living PT is not suitable for the removal of heterogeneous aggregation of PS, magnesium silicate (MS) was obtained by calcination of PT biomass based on retaining salt. The maximum adsorption capacity of PS by MS was 40.85 mg g-1, which was 10 times higher than that of conventional adsorbents. The presence of competitive anions significantly affects the removal of PS. The application in real water bodies and the reusability of the adsorbents were also verified. By characterizing the materials before and after adsorption, it is found that the adsorption mechanism mainly includes electrostatic attraction, hydrogen bonding, π-π interaction, and complexation between Si-O bond and PS. This study explains the toxic effect of nano-PS on PT and innovatively develops a biomass derivative from diatoms, which provides a novel and feasible strategy for environmental remediation.

Impact of butylparaben on growth dynamics and microcystin-LR production in Microcystis aeruginosa

The presence of butylparaben (BP), a prevalent pharmaceutical and personal care product, in surface waters has raised concerns regarding its impact on aquatic ecosystems. Despite its frequent detection, the toxicity of BP to the cyanobacterium Microcystis aeruginosa remains poorly understood. This study investigates the influence of BP on the growth and physiological responses of M. aeruginosa. Results indicate that low concentrations of BP (below 2.5 mg/L) have negligible effects on M. aeruginosa growth, whereas higher concentrations (5 mg/L and 10 mg/L) lead to significant growth inhibition. This inhibition is attributed to the severe disruption of photosynthesis, evidenced by decreased Fv/Fm values and chlorophyll a content. BP exposure also triggers the production of reactive oxygen species (ROS), resulting in elevated activity of antioxidant enzymes. Excessive ROS generation stimulates the production of microcystin-LR (MC-LR). Furthermore, lipid peroxidation and cell membrane damage indicate that high BP concentrations cause cell membrane rupture, facilitating the release of MC-LR into the environment. Transcriptome analysis reveals that BP disrupts energy metabolic processes, particularly affecting genes associated with photosynthesis, carbon fixation, electron transport, glycolysis, and the tricarboxylic acid cycle. These findings underscore the profound physiological impact of BP on M. aeruginosa and highlight its role in stimulating the production and release of MC-LR, thereby amplifying environmental risks in aquatic systems.

Performance evaluation of typical flocculants for efficient harvesting of Chlorella sorokiniana under different carbon application modes

In this study, the growth characteristics of microalgae cultured with different carbon sources were analyzed, and the flocculation characteristics under the influence of carbon sources were evaluated using three typical flocculants. The results showed that the organic carbon sources could significantly increase the content of extracellular proteins in microalgae. Specifically, the extracellular protein concentrations of microalgae cultured with pure BG-11, ethanol, sodium acetate and glucose were 18.2 29.2, 97.3, and 34.7 mg/g, respectively. During the flocculation process, microalgae cultured with sodium acetate exhibited a weak response to the flocculant because of excessive extracellular proteins inhibited flocculation. In addition, the flocculation efficiency was also less than 50.0% cultured with sodium acetate in all pH test ranges when alum and chitosan were used as flocculants. It could be inferred that the flocculant initially happened to charge neutralization with the negatively charged proteins in the solution and then bridged the charges with the microalgae. These findings provide insights into the effects of different carbon sources on microalgal flocculation, promising organic integration of microalgae wastewater treatment and harvesting.

A whole process study of dual microalgae cultivation coupled to domestic wastewater treatment and wheat growth

The multiple microalgal collaborative treatment of domestic wastewater has been extensively investigated, but its whole life cycle tracking and consequent potential have not been fully explored. Herein, a dual microalgal system was employed for domestic wastewater treatment, tracking the variation in microalgal growth and pollutants removal from shake flask scale to 18 L photobioreactors scales. The results showed that Chlorella sp. HL and Scenedesmus sp. LX1 combination had superior growth and water purification performance, and the interspecies soluble algal products promoted their growth. Through microalgae mixing ratio and inoculum size optimized, the highest biomass yield (0.42 ± 0.03 g/L) and over 91 % N, P removal rates were achieved in 18 L photobioreactor. Harvested microalgae treated in different forms all promoted wheat growth and suppressed yellow leaf rate. This study provided data support for the whole process tracking of dual microalgal system in treating domestic wastewater and improving wheat growth.

A new microalgal negative carbon technology for landfill leachate treatment: Simultaneous removal of nitrogen and phosphorus

Replete with ammonia nitrogen and organic pollutants, landfill leachate typically undergoes treatment employing expensive and carbon-intensive integrated techniques. We propose a novel microalgae technology for efficient, low-carbon simultaneous treatment of carbon, nitrogen, and phosphorus in landfill leachate (LL). The microbial composition comprises a mixed microalgae culture with Chlorella accounting for 82.58%. After seven days, the process with an N/P ratio of approximately 14:1 removed 98.81% of NH4+-N, 88.62 % of TN, and 99.55% of TP. Notably, the concentrations of NH4+-N and TP met the discharge standards, while the removal rate of NH4+-N was nearly three times higher than previously reported in relevant studies. The microalgae achieved a removal efficiency of 64.27% for Total Organic Carbon (TOC) and 99.26% for Inorganic Carbon (IC) under mixotrophic cultivation, yielding a biomass of 1.18 g/L. The treatment process employed in this study results in a carbon emissions equivalent of -8.25 kgCO2/kgNremoved, representing a reduction of 33.56 kgCO2 compared to the 2AO + MBR process. In addition, shake flask experiments were conducted to evaluate the biodegradability of leachate after microalgae treatment. After microalgae treatment, the TOCB (Biodegradable Total Organic Carbon)/TOC ratio decreased from 56.54% to 27.71%, with no significant improvement in biodegradability. It establishes a fundamental foundation for further applied research in microalgae treatment of leachate.

Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m-2) than Scenedesmus sp. biofilm (9.39 g m-2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L-1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L-1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L-1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L-1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L-1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68-81 % of removed nitrogen in biomass, while in suspension, only 55-71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

Purple acid phosphatase promoted hydrolysis of organophosphate pesticides in microalgae

When organophosphate pesticides (OPs) are not used and handled in accordance with the current rules and standards, it results in serious threats to the aquatic environment and human health. Phaeodactylum tricornutum is a prospective microalgae-based system for pollutant removal and carbon sequestration. Genetically engineered P. tricornutum, designated as the OE line (endogenously expressing purple acid phosphatase 1 [PAP1]), can utilize organic phosphorus for cellular metabolism. However, the competencies and mechanisms of the microalgae-based system (namely the OE line of P. tricornutum) for metabolizing OPs remain to be addressed. In this study, the OE line exhibited the effective biodegradation competencies of 72.12% and 68.2% for 30 mg L-1 of dichlorvos and 50 mg L-1 of glyphosate, accompanied by synergistic accumulations of biomass (0.91 and 0.95 g L-1) and lipids (32.71% and 32.08%), respectively. Furthermore, the biodiesel properties of the lipids from the OE line manifested a high potential as an alternative feedstock for microalgae-based biofuel production. A plausible mechanism of OPs biodegraded by overexpressed PAP1 is that sufficient inorganic P for adenosine triphosphate and concurrent carbon flux for the reduced form of nicotinamide adenine dinucleotide phosphate biosynthesis, which improved the OP tolerance and biodegradation competencies by regulating the antioxidant system, delaying programmed cell death and accumulating lipids via the upregulation of related genes. To sum up, this study demonstrates a potential strategy using a genetically engineered strain of P. tricornutum to remove high concentrations of OPs with the simultaneous production of biomass and biofuels, which might provide novel insights for microalgae-based pollutant biodegradation.

Environmental pitfalls and associated human health risks and ecological impacts from landfill leachate contaminants: Current evidence, recommended interventions and future directions

The improper management of solid waste, particularly the dumping of untreated municipal solid waste, poses a growing global challenge in both developed and developing nations. The generation of leachate is one of the significant issues that arise from this practice, and it can have harmful impacts on both the environment and public health. This paper presents an overview of the primary waste types that generate landfill leachate and their characteristics. This includes examining the distribution of waste types in landfills globally and how they have changed over time, which can provide valuable insights into potential pollutants in a given area and their trends. With a lack of specific regulations and growing concerns regarding environmental and health impacts, the paper also focuses on emerging contaminants. Furthermore, the environmental and ecological impacts of leachate, along with associated health risks, are analyzed. The potential applications of landfill leachate, suggested interventions and future directions are also discussed in the manuscript. Finally, this work addresses future research directions in landfill leachate studies, with attention, for the first time to the potentialities that artificial intelligence can offer for landfill leachate management, studies, and applications.

Proteomics reveals toxin tolerance and polysaccharide accumulation in Chlorococcum humicola under high CO2 concentration

Algae have great application prospects in excess sludge reclamation and recovery of high-value biomass. Chlorococcum humicola was cultivated in this research, using sludge extract (mixed with SE medium) with additions of 10%, 20%, and 30% CO2 (v/v). Results showed that under 20% CO2, the dry weight and polysaccharide yield reached 1.389 ± 0.070 g/L and 313.49 ± 10.77 mg/L, respectively. 10% and 20% CO2 promoted the production of cellular antioxidant molecules to resist the toxic stress and the toxicity of 20% CO2 group decreased from 62.16 ± 3.11% to 33.02 ± 3.76%. 10% and 20% CO2 accelerated the electron transfer, enhanced carbon assimilation, and promoted the photosynthetic efficiency, while 30% CO2 led to photosystem damage and disorder of antioxidant system. Proteomic analysis showed that 20% CO2 mainly affected energy metabolism and the oxidative stress level on the early stage (10 d), while affected photosynthesis and organic substance metabolism on the stable stage (30 d). The up-regulation of PSII photosynthetic protein subunit 8 (PsbA, PsbO), A0A383W1S5 and A0A383VRI4 promoted the efficiency of PSII and chlorophyll synthesis, and the up-regulation of A0A383WH74 and A0A2Z4THB7 led to the accumulation of polysaccharides. The up-regulation of A0A383VDH1, A0A383VX37 and A0A383VA86 promoted respiration. Collectively, this work discloses the regulatory mechanism of high-concentration CO2 on Chlorococcum humicola to overcome toxicity and accumulate polysaccharides.

Taxonomic reinvestigation of the genus Tetradesmus (Scenedesmaceae; Sphaeropleales) based on morphological characteristics and chloroplast genomes

The genus Tetradesmus (Scenedesmaceae; Sphaeropleales) comprises one of the most abundant green algae in freshwater environments. It includes morphologically diverse species that exhibit bundle-like, plane-arranged coenobia, and unicells, because several different Scenedesmus-like groups were integrated into this genus based on phylogenetic analysis. Nevertheless, there is no clear information regarding the phylogenetic relationship of Tetradesmus species, determined using several marker genes, because of low phylogenetic support and insufficient molecular data. Currently, genome information is available from diverse taxa, which could provide high-resolution evolutionary relationships. In particular, phylogenetic studies using chloroplast genomes demonstrated the potential to establish high-resolution phylogenetic relationships. However, only three chloroplast genomes are available from the genus Tetradesmus. In this study, we newly generated 9 chloroplast genomes from Tetradesmus and constructed a high-resolution phylogeny using a concatenated alignment of 69 chloroplast protein sequences. We also report one novel species (T. lancea), one novel variety (T. obliquus var. spiraformis), and two novel formae (T. dissociatus f. oviformis, T. obliquus f. rectilineare) within the genus Tetradesmus based on morphological characteristics (e.g., cellular arrangements and coenobial types) and genomic features (e.g., different exon-intron structures in chloroplast genomes). Moreover, we taxonomically reinvestigated the genus Tetradesmus based on these results. Altogether, our study can provide a comprehensive understanding of the taxonomic approaches for investigating this genus.

Eco-friendly cultivation of microalgae using a horizontal twin layer system for treatment of real solid waste leachate

Solid waste leachate (SWL) requires dilution with water to offset the negative effects of high nutrient concentration and organic compounds for its microalgae-based treatment. Among attached cultivation systems, twin layer is a technology in which limited information is available on treatment of high strength wastewater using microalgae. Moreover, widespread application of twin layer technology is limited due to cost of substrate and source layer used. In the present study, potential of Scenedesmus sp. for the treatment of SWL was assessed on horizontal twin layer system (HTLS). Novel and cost-effective substrate layers were tested as attachment material. Wetland treated municipal wastewater (WMW) was used to prepare SWL dilutions viz, 5%, 10%, 15%, 20% and 25% SWL. Recycled printing paper showed maximum biomass productivity of 5.19 g m-2 d-1. Among all the SWL dilutions, Scenedesmus sp. achieved maximum growth of 103.05 g m-2 in 5% SWL which was 16% higher than WMW alone. The maximum removal rate of NH4+ -N, TKN, and PO43- P was obtained in 20% SWL which was 1371, 1588 and 153 mg m-2 d-1 respectively. Varying concentrations of nutrients in different SWL dilutions significantly affected lipid biosynthesis, with enhanced productivity of 2.28 g m-2 d-1 achieved in 5% SWL compared to 0.97 g m-2 d-1 in 20% SWL. Hence, it can be concluded that 5% SWL dilution was good for biomass and lipid production, while the highest nutrient removal rates were obtained at 20% SWL mainly attributed to biotic and abiotic processes. Based on these results HTLS can be a promising technology for pilot scale to explore industrialized application of wastewater treatment and algal production.

Improving biomass yields of microalgae biofilm by coculturing two microalgae species via forming biofilms with uniform microstructures and small cell-clusters

Microalgae coculture has the potential to promote microalgae biofilm growth. Herein, three two-species cocultured biofilms were studied by determining biomass yields and detailed microstructure parameters, including porosity, average pore length, average cluster length, etc. It was found that biomass yields could reduce by 21-53 % when biofilm porosities decreased from about 35 % to 20 %; while at similar porosities (∼20 %), biomass yields of cocultured biofilms increased by 37 % when they possessed uniform microstructure and small cell-clusters (pores and clusters of 1 ∼ 10 μm accounted for 96 % and 68 %, respectively). By analyzing morphologies and surface properties of cells, it was found that cells with small size, spherical shape, and reduced surface polymers could hinder the cell-clusters formation, thereby promoting biomass yields. The study provides new insights into choosing cocultured microalgae species for improving the biomass yield of biofilm via manipulating biofilm microstructures.

Harnessing the potential of microalgae-bacteria interaction for eco-friendly wastewater treatment: A review on new strategies involving machine learning and artificial intelligence

In the pursuit of effective wastewater treatment and biomass generation, the symbiotic relationship between microalgae and bacteria emerges as a promising avenue. This analysis delves into recent advancements concerning the utilization of microalgae-bacteria consortia for wastewater treatment and biomass production. It examines multiple facets of this symbiosis, encompassing the judicious selection of suitable strains, optimal culture conditions, appropriate media, and operational parameters. Moreover, the exploration extends to contrasting closed and open bioreactor systems for fostering microalgae-bacteria consortia, elucidating the inherent merits and constraints of each methodology. Notably, the untapped potential of co-cultivation with diverse microorganisms, including yeast, fungi, and various microalgae species, to augment biomass output. In this context, artificial intelligence (AI) and machine learning (ML) stand out as transformative catalysts. By addressing intricate challenges in wastewater treatment and microalgae-bacteria symbiosis, AI and ML foster innovative technological solutions. These cutting-edge technologies play a pivotal role in optimizing wastewater treatment processes, enhancing biomass yield, and facilitating real-time monitoring. The synergistic integration of AI and ML instills a novel dimension, propelling the fields towards sustainable solutions. As AI and ML become integral tools in wastewater treatment and symbiotic microorganism cultivation, novel strategies emerge that harness their potential to overcome intricate challenges and revolutionize the domain.

Microalgae and co-culture for polishing pollutants of anaerobically treated agro-processing industry wastewater: the case of slaughterhouse

Anaerobically treated slaughterhouse effluent is rich in nutrients, organic matter, and cause eutrophication if discharged to the environment without proper further treatment. Moreover, phosphorus and nitrogen in agro-processing industry wastewaters are mainly removed in the tertiary treatment phase. The objective of this study is to evaluate the pollutant removal efficiency of Chlorella and Scenedesmus species as well as their co-culture treating two-phase anaerobic digester effluent through microalgae biomass production. The dimensions of the rectangular photobioreactor used to conduct the experiment are 15 cm in height, 20 cm in width, and 30 cm in length. Removal efficiencies between 86.74-93.11%, 96.74-97.47%, 91.49-92.91%, 97.94-99.46%, 89.22-94.28%, and 91.08-95.31% were attained for chemical oxygen demand, total nitrogen, nitrate, ammonium, total phosphorous, and orthophosphate by Chlorella species, Scenedesmus species, and their co-culture, respectively. The average biomass productivity and biomass yield of Chlorella species, Scenedesmus species, and their co-culture were 1.4 ± 0.1, 1.17 ± 0.12, 1.5 ± 0.13 g/L, and 0.18, 0.21, and 0.23 g/L*day, respectively. The final effluent quality in terms of chemical oxygen demand, total nitrogen, and total phosphorous attained by Chlorella species and the co-culture were below the permissible discharge limit for slaughterhouse effluent standards in the country (Ethiopia). The results of the study showed that the use of microalgae as well as their co-culture for polishing the nutrients and residual organic matter in the anaerobically treated agro-processing industry effluent offers a promising result for wastewater remediation and biomass production. In general, Chlorella and Scenedesmus species microalgae and their co-culture can be applied as an alternative for nutrient removal from anaerobically treated slaughterhouse wastewater as well as biomass production that can be used for bioenergy.

Nutrient recovery from municipal solid waste leachate in the scope of circular economy: Recent developments and future perspectives

Holistically considering the current situation of the commercial synthetic fertilizer (CSF) market, recent global developments, and future projection studies, dependency on CSFs in agricultural production born significant risks, especially to the food security of foreign-dependent countries. The foreign dependency of countries in terms of CSFs can be reduced by the concepts such as the circular economy and resource recovery. Recently, waste streams are considered as a source in order to produce recovery-based fertilizers (RBF). RBFs produced from different waste streams can be substituted with CSFs as input for agricultural applications. Municipal solid waste leachate (MSWL) is one of the waste streams that have a high potential for RBF production. Distribution of the published papers over the years shows that this potential was noticed by more researchers in the millennium. MSWL contains a remarkable amount of nitrogen and phosphorus which are the main nutrients required for agricultural production. These nutrients can be recovered with many different methods such as microalgae cultivation, chemical precipitation, ammonia stripping, membrane separation, etc. MSWL can be generated within the different phases of municipal solid waste (MSW) management. Although it is mainly composed of landfill leachate (LL), composting plant leachate (CPL), incineration plant leachate (IPL), and transfer station leachate (TSL) should be considered as potential sources to produce RBF. This study compiles studies conducted on MSWL from the perspective of nitrogen and phosphorus recovery. Moreover, recent developments and limitations of the subject were extensively discussed and future perspectives were introduced by considering the entire MSW management. Investigated studies in this review showed that the potential of MSWL to produce RBF is significant. The outcomes of this paper will serve the countries for ensuring their food security by implementing the resource recovery concept to produce RBF. Thus, the risks born with the recent global developments could be overcome in this way besides the positive environmental outcomes of resource recovery.

Combination of non-sterilized wastewater purification and high-level CO2 bio-capture with substantial biomass yield of an indigenous Chlorella strain

The indigenous microalga Chlorella sorokiniana NBU-3 grown under air, 5 %, 15 %, and 25 % CO₂ supply was evaluated to determine its potential for flue gas bio-capture, nutrient removal capacity and biomass yield using non-sterilized wastewater as growth medium. The results indicated that C. sorokiniana NBU-3 exhibited high nutrient removal efficiency (>95 % for NH₄⁺-N, TN and TP) with either air or CO₂ aeration. 5 %-15 % CO₂ supplies promote biomass yield, nutrient utilization and CO₂ biofixation of C. sorokiniana NBU-3. In particular, 15 % CO₂ promotes C. sorokiniana NBU-3 growth in non-sterilized MW, but inhibits its growth in BG11 medium, indicating the importance of non-sterilized MW and high CO₂ aeration concurrence for C. sorokiniana NBU-3 economically practical cultivation. Moreover, the highest values of lipid (27.84 ± 2.12 %) and protein (32.65 ± 4.11 %) contents were obtained in MW with 15 % CO₂ aeration. Conceivably, microalgal-bacterial symbiosis may help C. sorokiniana NBU-3 tolerate high concentration of CO₂ and promote microalga growth. The succession of the community diversity toward the specific functional bacterial species such as Methylobacillus and Methylophilus (Proteobacteria) which were predicted to possess the function of methylotroph, methanol oxidation and ureolysis would help facilitate the microalgal-bacterial symbiosis and promote the microalgae biomass accumulation with high dosage of CO₂ aeration. Overall, these findings clearly highlight the potential of this indigenous microalga C. sorokiniana NBU-3 for industrial-emission level CO₂ mitigation and commercial microalga biomass production in MW.

Mechanisms for the increase in lipid production in cyanobacteria during the degradation of antibiotics

This study evaluated the responses of cell density, photosynthesis activity, dry cell weight, lipid productivity, proteome and metabolome in two non-toxic cyanobacterial species (Synechococcus sp. and Chroococcus sp.) exposed to two frequently detected antibiotics (sulfamethoxazole and ofloxacin) at test concentrations of 0.2-20.0 μg L^-1 in a 4-day culture period. Upregulated antioxidant enzymes and oxidoreductases contributed to antibiotic biodegradation in Synechococcus sp.; whereas, upregulated carotenoid protein contributed to antibiotic biodegradation in Chroococcus sp. The 4-day removal efficiencies of sulfamethoxazole and ofloxacin by cyanobacteria were 35.98-66.23% and 33.01-61.92%, respectively. In cyanobacteria, each antibiotic induced hormetic responses, such as increase in cell density, dry cell weight, and photosynthetic activity; upregulation of photosynthesis-related proteins; and elevation of lipid expression by up to 2.05-fold. Under antibiotic stress, the two cyanobacterial species preferred to store energy in the form of lipids rather than ATP, with fructose-bisphosphate aldolase playing an essential role in lipid synthesis. The downregulation of lipid transporters also facilitated lipid accumulation in Synechococcus sp. In general, the two non-toxic cyanobacterial species achieved a good combination of lipid deposition and antibiotic treatment performance, especially in Chroococcus sp. exposed to sulfamethoxazole.

Enhanced energy recovery from landfill leachate by linking light and dark bio-reactions: Underlying synergistic effects of dual microalgal interaction

Bioconversion of nutrients and energy from landfill leachate (LL) to biohydrogen and volatile fatty acids (VFAs) using dark fermentation (DF) is a promising technique for developing a sustainable ecosystem. However, poor performance of DF caused by vulnerable fermentative bacteria vitality and strong LL toxicity significantly hinder its commercialization. Herein, an integrated technique linking microalgae photosynthesis and DF was proposed, in which mixed microalgae were applied to robustly reclaim nutrients and chemical oxygen demand (COD) from LL. Then, microalgae biomass was fermented into biohydrogen and VFAs using the DF process. Underlying synergistic mechanisms of the interaction of Scenedesmus obliquus and Chlorella vulgaris resulting from the functioning of extracellular polymeric substances (EPS) were discussed in detail. For better absorption of nutrients from LL, the mixed microalgae secreted obviously more EPS than pure microalgae, which played vital roles in the assimilation of cellular nutrients by forming more negative zeta potential and secreting more tyrosine-/tryptophan-family proteins in EPS. Besides, mixed microalgae produced more intracellular proteins and carbohydrates than the pure microalgae, thereby providing more feedstock for DF and achieving higher energy yield of 10.80 kJ/L than 6.64 kJ/L that was obtained when pure microalgae were used. Moreover, the energy conversion efficiency of 7.75% was higher for mixed microalgae than 4.77% that was obtained for pure microalgae. This work may inspire efficient disposal of LL and production of bioenergy, together with filling the knowledge gaps of synergistic mechanisms of dual microalgal interactions.

Nutrient removal and lipid production by the co-cultivation of Chlorella vulgaris and Scenedesmus dimorphus in landfill leachate diluted with recycled harvesting water

Applying microalgae for landfill leachate (LL) treatment is promising. However, LL usually needs to be diluted with much fresh water, aggravating water shortage. In this study, mono- and co-culturing microalgae (Chlorella vulgaris and Scenedesmus dimorphus) were used to treat LL diluted with recycled harvesting water, to investigate nutrient removal and lipid production. The results showed that microalgae in co-culture treatment had more biomass and stronger superoxide dismutase activity, which might be related to humic acids contained in recycled harvesting water, according to dissolved organic matters (DOMs) analysis. In addition, the lipid content and yield of co-cultured microalgae reached 27.60 % and 66.87 mg·L^-1, respectively, higher than those of mono-culture, proving the potential of co-culture for the improvement of lipid production. This study provided a freshwater-saving dilution method for LL treatment with recycled harvesting water as well as a strategy for the increase of biomass and lipid accumulation by microalgae co-cultivation.

Interaction of Scenedesmus quadricauda and native bacteria in marine biopharmaceutical wastewater for desirable lipid production and wastewater treatment

Improving knowledge of the alga-bacterium interaction can promote the wastewater treatment. The untreated marine biopharmaceutical wastewater (containing native bacteria) was used directly for culturing microalgae. Unlike previous studies on specific bacteria in algal-bacterial co-culture systems, the effect of native bacteria in wastewater on microalgae growth was investigated in this study. The results showed that the coexistence of native bacteria greatly promoted the microalgae growth, ultimately producing biomass of 0.64 g/L and biomass productivity of 56.18 mg/L·d. Moreover, the lipid accumulation in the algae + bacteria group was 1.31 and 1.13 times higher than those of BG11 and pure algae, respectively, mainly attributed to the fact that bacteria provided a good environment for microalgae growth by using extracellular substances released from microalgae for their own growth, and providing micromolecules of organic matter and other required elements to microalgae. This study would lay the theoretical foundation for improving biopharmaceutical wastewater treatment.

Toxic responses of freshwater microalgae Chlorella sorokiniana due to exposure of flame retardants

Flame retardants, such as Tetrabromobisphenol A (TBBPA), Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tributyl phosphate (TBP), are frequently detected in surface water. However, the effects of FRs exposure on aquatic organisms especially freshwater microalgae are still unclear. In this study, the toxicities of TBBPA, TDCPP and TBP to microalgae Chlorella sorokiniana, in terms of growth inhibition, photosynthetic activity inhibition and oxidative damage, were investigated, and according ecological risks were assessed. The results showed that TBBPA, TDCPP and TBP had inhibitory effects on C. sorokiniana, with 96 h EC₅₀ (concentration for 50% of maximal effect) values of 7.606, 41.794 and 49.996 mg/L, respectively. Fv/Fm decreased as the increase of exposure time under 15 mg/L TBBPA. Under 50 mg/L TDCPP and 80 mg/L TBP exposure, Fv/Fm decreased significantly after 24 h. However, Fv/Fm rose after 96 h, indicating that the damaged photosynthetic activity was reversible. The content of chlorophyll a decreased, as the increase of TBBPA concentration from 3 to 15 mg/L. However, chlorophyll a increased first and then decreased, as the increase of TDCPP and TBP concentrations from 0 to 50 mg/L and 0-80 mg/L, respectively. Results indicated that C. sorokiniana could use the phosphorus of TDCPP and TBP to ensure the production of chlorophyll a. The risen content of reactive oxygen species, malondialdehyde as well as superoxide dismutase activity indicated that exposure to FRs induced oxidative stress. Additionally, the risk quotients showed that tested FRs had ecological risks in natural waters or wastewaters. This study provides insights into the toxicological mechanisms of different FRs toward freshwater microalgae for better understanding of according environmental risks.

Biotechnological Approaches for Biomass and Lipid Production Using Microalgae Chlorella and Its Future Perspectives

Heavy reliance on fossil fuels has been associated with increased climate disasters. As an alternative, microalgae have been proposed as an effective agent for biomass production. Several advantages of microalgae include faster growth, usage of non-arable land, recovery of nutrients from wastewater, efficient CO₂ capture, and high amount of biomolecules that are valuable for humans. Microalgae Chlorella spp. are a large group of eukaryotic, photosynthetic, unicellular microorganisms with high adaptability to environmental variations. Over the past decades, Chlorella has been used for the large-scale production of biomass. In addition, Chlorella has been actively used in various food industries for improving human health because of its antioxidant, antidiabetic, and immunomodulatory functions. However, the major restrictions in microalgal biofuel technology are the cost-consuming cultivation, processing, and lipid extraction processes. Therefore, various trials have been performed to enhance the biomass productivity and the lipid contents of Chlorella cells. This study provides a comprehensive review of lipid enhancement strategies mainly published in the last five years and aimed at regulating carbon sources, nutrients, stresses, and expression of exogenous genes to improve biomass production and lipid synthesis.

Microalgal cultivation for the upgraded biogas by removing CO2, coupled with the treatment of slurry from anaerobic digestion: A review

Biogas is the gaseous by product generated from anaerobic digestion (AD), which is mainly composed of methane and CO2. Numerous independent studies have suggested that microalgae cultivation could achieve high efficiency for nutrient uptake or CO2 capture from AD, respectively. However, there is no comprehensive review on the purifying slurry from AD and simultaneously upgrading biogas via microalgal cultivation technology. This paper aims to fill this gap by presenting and discussing an information integration system based on microalgal technology. Furthermore, the review elaborates the mechanisms, configurations, and influencing factors of integrated system and analyzes the possible challenges for practical engineering applications and provides some feasibility suggestions eventually. There is hope that this review will offer a worthwhile and practical guideline to researchers, authorities and potential stakeholders, to promote this industry for sustainable development.

The Influence of Forward Osmosis Module Configuration on Nutrients Removal and Microalgae Harvesting in Osmotic Photobioreactor

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.

Micro-algae assisted green bioremediation of water pollutants rich leachate and source products recovery

Water management and treatment are high concern fields with several challenges due to increasing pollutants produced by human activity. It is imperative to find integral solutions and strategic measures with robust remediation. Landfill leachate production is a high concern emerging problem. Especially in low middle-income countries due to no proper local waste disposition regulation and non-engineered implemented methods to dispose of urban waste. These landfills can accumulate electronic waste and release heavy metals during the degradation process. Similar phenomena include expired pharmaceuticals like antibiotics. All these pollutants accumulated in leachate made it hard to dispose of or treat. Leachate produced in non-engineered landfills can permeate soils and reach groundwater, dragging different contaminants, including antibiotics and heavy metals, which eventually can affect the environment, changing soil properties and affecting wildlife. The presence of antibiotics in the environment is a problem with particular interest to solve, mainly to avoid the development of antibiotic-resistant microorganisms, which represent a future risk for human health with possible epidemic implications. It has been reported that the use of contaminated water with heavy metals to produce and grow vegetables is a risk for consumers, heavy metals effects in humans can include carcinogenic induction. This work explores the opportunities to use leachate as a source of nutrients to grow microalgae. Microalgae stand out as an alternative to bioremediate leachate, at the same time, microalgae produce high-value compounds that can be used in bioplastic, biofuels, and other industrial applications.