Integrating micro-algae into wastewater treatment: A review

Review of biological algal fertilizer technology: Alleviating salinization, sequestering carbon, and improving crop productivity

Periphyton-based biofertilizer have a high potential for soil remediation, particularly for controlling soil salinization. This global environmental problem leads to low soil utilization and insufficient crop yields. Efficient and sustainable methods of managing saline soils are needed to reduce salinization and improve soil fertility and crop quality. Traditional methods such as physical mulching and chemical amendments, while improving soil conditions, exhibit limited effectiveness and may damage soil structure. This study aims to evaluate the feasibility of algae-based fertilizers in remediating saline-alkali soils and improving crop performance. The review delves into the and application prospects of algae-based fertilizers, highlighting their potential from both sustainable development and economic perspectives. It further advocates integrating other emerging technologies with the production and application of algae-based fertilizers to address the increasingly severe challenges posed by degraded soil resources and environmental instability. The review found that algal fertilizers are more environmentally friendly than traditional chemical fertilizers but are not inferior in function. This approach offers more efficient and sustainable solutions for managing saline-alkaline soils and effectively achieves sustainable agricultural production. Furthermore, it is necessary to conduct experimental research and monitoring evaluations of algal fertilizers to formulate scientific and rational fertilization plans to meet the increasingly serious challenges facing soil resources and unstable environments. The findings of this study will provide theoretical and technical support for using algae biofertilizers for soil remediation, improving crop quality and sequestering carbon.

Research progress and application of carbon sequestration in industrial flue gas by microalgae: A review

Global warming caused by the emission of CO2 in industrial flue gas has attracted more and more attention. Therefore, to fix CO2 with high efficiency and environmentally friendly had become the hot research field. Compared with the traditional coal-fired power plant flue gas emission reduction technology, carbon fixation and emission reduction by microalgae is considered as a promising technology due to the advantages of simple process equipment, convenient operation and environmental protection. When the flue gas is treated by microalgae carbon fixation and emission reduction technology, microalgae cells can fix CO2 in the flue gas through photosynthesis, and simultaneously absorb NOx and SOx as nitrogen and sulfur sources required for growth. Meanwhile, they can also absorb mercury, selenium, arsenic, cadmium, lead and other heavy metal ions in the flue gas to obtain microalgae biomass. The obtained microalgae biomass can be further transformed into high value-added products, which has broad development prospects. This paper reviews the mechanisms and pathways of CO2 sequestration, the mechanism and impacts of microalgal emission reduction of flue gas pollutants, and the applications of carbon sequestration in industrial flue gas by microalgae. Finally, this paper provides some guidelines and prospects for the research and application of green emission reduction technology for industrial flue gas.

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.

Decontamination of Sewage Wastewater by an Aeration Method Utilizing Water Hardness-Reducing Spirulina platensis

This study investigates the potential of Spirulina platensis, a blue-green algae species, for the remediation of sewage wastewater, providing a sustainable approach to wastewater management. Over a 20-day period, with aeration at 3 L/min, Spirulina effectively reduced key pollutants, including chemical oxygen demand (COD), phosphate, nitrate, magnesium, and other impurities. Advanced analyses using FTIR, SEM, and EDX revealed that the primary mechanism of remediation was the adsorption of contaminants onto Spirulina. In addition, rapid photosynthetic growth under sunlight (200-400 μmol photons/m2/s) facilitated nutrient absorption while producing high-value biomass rich in proteins and essential nutrients. This dual-purpose approach not only purifies wastewater but also enables resource recovery, reducing the need for chemical fertilizers and promoting circular economy practices. Furthermore, the process contributes to carbon sequestration, offering a viable method to lower greenhouse gas emissions. The findings highlight Spirulina platensis as an eco-friendly, innovative solution with significant environmental and socio-economic benefits.

Biodegradation of Xenoestrogens by the Green Tide Forming Seaweed Ulva: A Model System for Bioremediation

Anthropogenic xenoestrogens pose serious threats to humans and the environment. Ulva (Chlorophyta), a green macroalga that can propagate in environments of various salinities, is a potential candidate for efficient wastewater treatment and bioremediation. In this study, we tested the class of bisphenols and ethinylestradiol and investigated the underlying removal mechanisms of these xenoestrogens. The model organism Ulva mutabilis demonstrated over 99% removal efficiency for bisphenols A, B, E, F, P, and Z, and partial removal of bisphenol S. Ulva showed complete removal capabilities even under axenic conditions, while its associated bacteria were not involved. Complete removal of 6.6 mg L-1 of bisphenol A was achieved within 2 days and a half-time of 1.85 h. Biodegradation was the leading cause of removal, whereas bioaccumulation was minimal. The model substance bisphenol A underwent various reactions, and 20 transformation products were detected using stable isotope labeling. While most of the bisphenol A was completely biodegraded, the primary transformation products were monobromobisphenol A, bisphenol A bisulfate, and 4-hydroxypropanylphenol. This study highlights the potential of the green seaweed Ulva to provide a pathway for more effective and sustainable bioremediation strategies to tackle the environmental pollution caused by xenoestrogens.

New insights into chicken processing wastewater treatment: the role of the microalgae Parachlorella kessleri on nitrogen removal

Microalgal Technologies have recently been employed as an alternative treatment for high nitrogen content wastewater. Nitrogen is an essential nutrient for microalgae growth, and its presence in wastewater may be an alternative source to synthetic medium, contributing to a circular economy. This study aimed to investigate the effect of using Parachlorella kessleri cultivated in wastewater from the thermal processing of chicken meat. Experiments were performed to obtain the ideal sampling site, inoculum dosage, and contact time. P. kessleri had better growth in the sample from the settling basin. Nitrogen removal was 95% (0,15 mg TNK/107 cells) in 9 days, and the final nitrogen concentration was lower than 20 mg/L, and the nitrate concentration was lower than 1 mg/L. However, during the third cycle in the kinetic assay, there was a decline in the microalgae growth, occasioned by the accumulation of nitrite (38,4 mg/L) in the inside of the cell. The study demonstrated that nitrogen concentration is directly related to the cell growth of the algae. Parachlorella kessleri efficiently removed nitrogen from chicken meat thermal processing wastewater and is a potential option for tertiary treatment and valorisation of such effluent as a nitrogen source.

Microalgae and biogas: a boon to energy sector

The global energy generation market immensely depends on fossil fuels which balances our survival on this planet. Energy can be called as the "master element" for our daily needs, starting from household power supply, agricultural purpose, automobile and transportation, industrial workload to economic and research domains. Fuel switching initiatives are being adapted by environmentalist and scientists to bring a novel sustainable source of energy. An environment and renewable alternative to fossil fuels are a must. Over the years, the world has shifted toward generating green fuels immensely. One such potential alternative to fossil fuels are biogases. Being versatile and renewable in nature, it has drawn immense attention globally. Despite having such potentials there exist some major drawbacks which mainly deal with the starting material. One such source for biogases can be microalgae. Microalgae based biogas production can produce huge amount of energy and that has been implemented by many foreign countries and their companies. Despite being in use in many countries, there are issues which needs to be addressed which will overall improve the biogas potential from microalgae even more. This review mainly focuses on generation of biogas from microalgae as a feedstock which are very economical and sustainable in its nature, presenting improvement strategies which can be impended to boost the over biogas sector globally.

Effects of nitrogen phosphorus ratio and light on phosphorus removal by microalgae in high-phosphorus wastewater

The removal of phosphorus from wastewater has consistently posed a major focus in the field of wastewater treatment. Microalgae-based phosphorus removal is widely acknowledged as an effective biological approach. However, ensuring the microalgae-mediated high phosphorus concentration removal remains a persistent challenge. In this study, a kind of multicellular microalgae, Klebsormidium sp., was used to explore its ability to remove phosphorus in high-phosphorus wastewater. The phosphorus removal rate by Klebsormidium sp. in highly concentrated (>20 mgP/L) wastewater can exceed 90%. To investigate the phosphorus absorption process, various nitrogen and phosphorus concentrations along with light conditions were employed. The results showed that 50% to 80% of the total phosphorus absorbed by microalgae entered the intracellular polymer. The phosphorus concentration and light intensity did not exert any significant effects on the absorption of phosphorus by microalgae. However, the nitrogen concentration and the light-to-dark ratio significantly influenced the storage of phosphorus by microalgae. At a nitrogen concentration over 300 mgN/L, phosphorus absorption by microalgae was inhibited. A higher light-to-dark ratio increased phosphorus transfer by microalgae, while the light duration exceeds 16 h inhibited it. Microalgae have emerged as promising materials for phosphorus removal in high-phosphorus sewage, the study offering potential solutions for a cleaner and more sustainable future.

Reduction of biogenic CO2 emissions, COD and nutrients in municipal wastewater via mixotrophic co-cultivation of Chlorella vulgaris - aerobic-activated sludge consortium

In this study, biogenic CO2 emissions, COD and other nutrients (i.e. TP, TN and N H 4 + - N ) from aerobic treatment in municipal Wastewater Treatment Plants (WWTP) were quantified and reduced by phycoremediation using a mixotrophic co-cultivation of Chlorella vulgaris and activated sludge. It has been shown that the microalgae sludge consortium (A-ASR, R1) outperformed the normal-activated sludge system (ASR, R2). In fact, estimated biogenic CO2 emissions with algae mark 1.20-fold higher removal, COD marks 1.40-fold higher removal, TP marks 1.70-fold higher removal, and N H 4 + - N marks 1.40-fold higher removal, compared to normal activated sludge (ASR, R2). Meanwhile, due to aeration, N O 3 - - N concentration increased in both reactors because some Ns were oxidized through nitrification. Furthermore, COD increased again during C. vulgaris stationary growth; thus, activated sludge addition every 4 days (optimal time) was implemented to maintain algae-bacteria balance. The results suggest that integrating the treatment of GHG emissions and water pollutants in a single, concurrent process can significantly enhance the sustainability and efficiency of wastewater treatment plants, which has not been explored comprehensively. Finally, by leveraging C. vulgaris capabilities for carbon and nutrients sequestration, this study can provide practical guidance for achieving carbon neutrality in a WWTP.

Self-cleaning micro/nano graded porous groove structure fiber membranes by coaxial spinning for purification of dye wastewater

Adjusting the structure of the membrane and improving its performance proved to be an effective technique for accomplishing efficient dye wastewater purification. Water erosion of polyvinylpyrrolidone (PVP) core in polyacrylonitrile (PAN) nanofiber membrane modified with UiO-66-NH2 was successfully achieved, in this study, using coaxial electrospinning, and ZIF-8 with excellent performance was further epitaxy-grown in situ. Two differently shaped and positively charged MOFs confer strong adsorption capacity (adsorption capacity >2042 mg/g) on cationic dyes. In addition, the multi-dimensional separation pores brought by the micro/nano graded porous groove structure and MOFs not only make the membrane have excellent static adsorption performance, but also have excellent dynamic separation performance under the influence of toxic heavy ions (separation efficiency >99 %; Flux >1666 L m-2 h-1 bar-1). More importantly, this special structure of the membrane has an excellent photocatalytic activity for the dye, so the membrane can be used for a long time in a green and environmentally friendly way. Together, membranes show a significant deal of potential for the treatment of wastewater containing dyes due to the combination of these outstanding characteristics.

Comparing continuous and perfusion cultivation of microalgae on recirculating aquaculture system effluent water

Effluent water from recirculating aquaculture systems (RAS) contains nutrients from fish excrements and leftover feed. This study investigated the nutrient remediation potential from RAS effluent water through microalgae cultivation in 25 L tubular reactors. We compared nutrient uptake and biomass productivity in continuous and perfusion cultivation modes for freshwater, brackish water and saltwater. Stable high biomass densities were achieved with additional nitrate during continuous cultivation (up to 3.88 g L-1) or by membrane filtration during perfusion cultivation (up to 3.59 g L-1). A life cycle assessment (LCA) compared the two different cultivation modes in terms of environmental sustainability on a 1 ha scale. The LCA and preliminary economic assessment showed that perfusion cultivation appears to have a lower environmental impact for relatively low nutrient concentrations, but additional equipment and higher energy demands are leading to increased operational (+6 %) and capital expenses (up to +60 %).

Applicability of plant-clay mineral composite for rapid algae removal from eutrophic freshwaters at the laboratory and field scales

The global issue of water source eutrophication is exacerbated by increasing industrialization and urbanization, posing significant challenges for clean water management. Although strategies such as nutrient management and biomanipulation are employed, these methods often take longer to demonstrate effectiveness and indirectly work on algal blooms. This has led to the evaluation of eco-friendly technologies such as plant-mineral composites (PMCs) for faster and targeted control of algal proliferation and organic pollution. This study assessed the suitability of PMCs for rapid improvement of eutrophic water quality (focusing on algal control) and optimized their application methods at laboratory and field scales. Laboratory experiments were conducted to identify the critical factors influencing removal activity (RA), considering variables such as water temperature and light intensity. Field trials in reservoirs and a water treatment plant (WTP) explored the controlling factors influencing the RAs for various pollutants. Optimal conditions for maximizing PMC efficacy were determined using response surface methodology (RSM) and generalized linear models. RSM highlighted water temperature as a key factor influencing chlorophyll a RA in a unimodal manner, while demonstrating PMC's effectiveness across varying concentrations, depths, and pH levels. Results from the WTP emphasized the high PMC efficacy in humic matter-rich environments, and those from reservoirs consistently demonstrated PMC's effectiveness regardless of ambient water quality factors such as nutrient and conductivity levels. Comparative analyses indicated distinct PMC impact on algae-associated parameters, emphasizing its potential as an innovative solution for utilizing plant allelopathy and mineral adsorption for efficient algal bloom control and water quality enhancement.

An indigenous microalgal pool containing Klebsormidium sp. K39 as a stable and efficacious biotechnological strategy for Escherichia coli removal in urban wastewater treatment

BACKGROUND

In recent decades the demand for freshwater has drastically increased as a consequence of population growth, economic development, climate change and pollution. Therefore, any strategy for wastewater treatment can play a role in alleviating the pressure on freshwater sources.

RESULTS

In the present study an autochthonous microalgal pool (MP), isolated from a constructed wetland, was proposed as an alternative to the secondary treatment of an urban wastewater treatment system. The MP removal efficacy was compared to those obtained using Chlorella vulgaris and Scenedesmus quadricauda, against E. coli. Results exhibited a comparable removal efficacy and after 2 days, in samples inoculated with E. coli at lower density, S. quadricauda and C. vulgaris induced a decrease of 2.0 units Log and the autochthonous MP of 1.8 units Log, whereas in samples with E. coli at higher density the bacteria were reduced 2.8, 3.4 and 2.0 units Log by S. quadricauda, C. vulgaris and the autochthonous MP, respectively. Moreover, the identification of microalgal strains isolated from the MP revealed the presence of Klebsormidium sp. K39, C. vulgaris, Tetradesmus obliquus and S. quadricauda. Although the MP composition remained quite constant, at the end of the treatment, a different distribution among the microalgal species was observed with Klebsormidium sp. K39 found as dominant.

CONCLUSION

The microalgal-based wastewater treatment appears as a valuable alternative, although further investigations, based on 'omics' approaches, could be applied to better explore any fluctuation within the MP species composition in an in situ trial. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Upcycling of Enzymatically Recovered Amino Acids from Textile Waste Blends: Approaches for Production of Valuable Second-Generation Bioproducts

Tremendous quantities of textile waste generated and primarily landfilled annually represent a huge risk of contaminating the environment, together with loss of valuable resources. Especially, blended fabrics further pose a challenge for recycling and valorization strategies, while enzymatic hydrolysis offers a highly specific and environmentally friendly solution. In this study, we demonstrate that proteases specifically hydrolyze the wool components in blends with polyester, allowing recovery of pure polyester fibers as well as amino acids and peptides as platform molecules for further valorization. Recovered amino acids and peptides were successfully used as a nitrogen source for cultivation of Chlorella vulgaris and Rhodotorula mucilaginosa for the production of valuable biomolecules including pigments and lipids. Here, 11.3 mg/gCDW chlorophyll and 47% lipid content were obtained from algal biomass, while 1.1 mg/gCDW carotenoids and 35% lipids content were reached from the yeast grown on wool hydrolysate as the sole nitrogen source. These could be applied as natural dyes for textile applications or as biofuels to replace toxic synthetic compounds and fossil resources, respectively. The presented concept demonstrates feasibility of enzymatic recovery and microbial valorization of components of blended textile waste to support the development toward a circular bioeconomy.

Effect of salinity on nitrogen removal performance, enzymatic activity and metabolic pathway of Chlorella pyrenoidosa treating aquaculture wastewater

The nitrogen removal performance, enzymatic activity, antioxidant response and metabolic pathway of Chlorella pyrenoidosa (C. pyrenoidosa) under different salinities have been investigated during the treatment of aquaculture wastewater. The growth, chlorophyll content and photosynthetic activity of C. pyrenoidosa were negatively correlated with the salinity from 1% to 3%. The removal performance of chemical oxygen demand (COD) and nitrogen compounds for C. pyrenoidosa decreased with the increase of salinity from 1% to 3%, which was due to the decrease of their corresponding metabolism enzymatic activities. The equilibrium between the reactive oxygen species production and antioxidant defensive system in C. pyrenoidosa was destroyed under high salinity stress and then caused an irreversible damage, which decreased the nitrogen assimilation of C. pyrenoidosa. The metabolic pathway of C. pyrenoidosa under 3% salinity had some obvious variation by comparison with 1% salinity, which led to the discrepancy in the microalgae activity and nitrogen transformation performance. Additionally, high salinity could inhibit the expression of gene associated with the chlorophyll synthesis and damaged the photosystem II reaction center. This study can provide an insight into the effect of salinity on the nitrogen removal from aquaculture wastewater by microalgae.

Microalgae-based bioremediation of refractory pollutants: an approach towards environmental sustainability

Extensive anthropogenic activity has led to the accumulation of organic and inorganic contaminants in diverse ecosystems, which presents significant challenges for the environment and its inhabitants. Utilizing microalgae as a bioremediation tool can present a potential solution to these challenges. Microalgae have gained significant attention as a promising biotechnological solution for detoxifying environmental pollutants. This is due to their advantages, such as rapid growth rate, cost-effectiveness, high oil-rich biomass production, and ease of implementation. Moreover, microalgae-based remediation is more environmentally sustainable for not generating additional waste sludge, capturing atmospheric CO2, and being efficient for nutrient recycling and sustainable algal biomass production for biofuels and high-value-added products generation. Hence, microalgae can achieve sustainability's three main pillars (environmental, economic, and social). Microalgal biomass can mediate contaminated wastewater effectively through accumulation, adsorption, and metabolism. These mechanisms enable the microalgae to reduce the concentration of heavy metals and organic contaminants to levels that are considered non-toxic. However, several factors, such as microalgal strain, cultivation technique, and the type of pollutants, limit the understanding of the microalgal removal mechanism and efficiency. Furthermore, adopting novel technological advancements (e.g., nanotechnology) may serve as a viable approach to address the challenge of refractory pollutants and bioremediation process sustainability. Therefore, this review discusses the mechanism and the ability of different microalgal species to mitigate persistent refractory pollutants, such as industrial effluents, dyes, pesticides, and pharmaceuticals. Also, this review paper provided insight into the production of nanomaterials, nanoparticles, and nanoparticle-based biosensors from microalgae and the immobilization of microalgae on nanomaterials to enhance bioremediation process efficiency. This review may open a new avenue for future advancing research regarding a sustainable biodegradation process of refractory pollutants.

A critical review on the symbiotic effect of bacteria and microalgae on treatment of sewage with biofertilizer production

Wastes like sewage, kitchen and industrial are the major sources of environmental pollution and health hazards. Sewage contains 99.9% water and 0.1% solid waste including urinal waste and faecal matter alongwith large amounts of nitrate, nitrite, ammonium and phosphate ions. Sewage may also contain a variety of harmful contaminants like analgesics, antihypertensive drugs, antibiotics, dioxin, furans, polychlorinated biphenyls, chlorinated hydrocarbon pesticides, chlorine derivatives and plasticizers etc. making it more harmfull to environment and public health. Hence, sewage must be adequately treated by an effective process before its final discharge into the environment. Biological treatment of sewage is an emerging idea in recent years, which has diverse economic and environmental advantages. Sewage treatment by bacteria and microalgae has numerous advantages as it removes various excessive nutrients from waste with large biomass production and also prevents the utilization of toxic chemicals in conventional treatment process. Microalgae-bacterial biomass have potential to be used as biofertilizers, bio-stimulants and bio-seed primers in agricultural field as these contain various biologically active substances like polysaccharides, carotenoids, free fatty acids, phenols, and terpenoids. This review paper mainly discussing the sewage characteristics and different kinds of organic and inorganic pollutants it contained alongwith its harmfull impacts on environment and public health. It also deals the different conventional as well as emerging treatment technologies and different factors affecting the treatment efficiency. In addition, the utilization of developed microalgal and bacterial biomass as biofertilizer and its effects on crop plant alongwith future prospects has been also discussed in detail.

Microalgae for bioremediation: advances, challenges, and public perception on genetic engineering

The increase in the global population and industrial activities has led to an extensive use of water, the release of wastewater, and overall contamination of the environment. To address these issues, efficient treatment methods have been developed to decrease wastewater nutrient content and contaminants. Microalgae are a promising tool as a sustainable alternative to traditional wastewater treatment. Furthermore, the biomass obtained from the wastewater treatment can be used in different applications, having a positive economic impact. This review describes the potential of microalgae as a biological wastewater remediation tool, including the use of genetically engineered strains. Their current industrial utilization and their untapped commercial potential in terms of bioremediation are also examined. Finally, this work discusses how microalgal biotechnology is perceived by the public and governments, analyses the potential risks of microalgae to the environment, and examines standard procedures that can be implemented for the safe biocontainment of large-scale microalgae cultures.

Effect of temperature and CO2 concentration on biological nutrient removal from tertiary municipal wastewater using microalgae Chlorella prototheocoides

This study investigates the potential of phototrophic microalgae, specifically Chlorella protothecoides, for biological wastewater treatment, with a focus on the effects of air temperature and CO2 concentration on nutrient removal from tertiary municipal wastewater. Utilizing both the Monod and Arrhenius kinetic models, the research examines how temperature and nutrient availability influence microalgal growth and nutrient removal. The study finds that optimal biomass productivity occurs at 25 °C, with growth slowing at higher temperatures (30 °C, 40 °C, and 45 °C). The Monod and Arrhenius models, which showed strong agreement with experimental data, revealed that temperature significantly impacted growth kinetics, with the Arrhenius model accurately predicting growth rates at lower temperatures. Activation energies for growth and cell death were determined as 5.4 kJ mol⁻1 and 88.4 kJ mol⁻1, respectively. The study also demonstrated that optimal nitrogen and phosphorus removal occurred at 25°C-30 °C, with 100 % total nitrogen (TN) removal and 85 % total phosphorus (TP) removal achieved at 30 °C. Additionally, CO2 concentration influenced biomass productivity, with peak productivity and nutrient removal at 6 % CO2, highlighting the importance of CO2 levels in optimizing growth and nutrient elimination. These findings provide valuable insights into optimizing conditions for microalgae-based wastewater treatment, particularly in seasonal cultivation strategies, and contribute to improving biodiesel production and nutrient removal efficiency.

An efficient co-culture of Halomonas mongoliensis and Dunaliella salina for phenol degradation under high salt conditions

Phenol is one of the major organic pollutants in high salt industrial wastewater. The biological treatment method is considered to be a cost-effective and eco-friendly method, in which the co-culture of microalgae and bacteria shows a number of advantages. In the previous study, a co-culture system featuring Dunaliella salina (D. salina) and Halomonas mongoliensis (H. mongoliensis) was established and could degrade 400 mg L-1 phenol at 3% NaCl concentration. In order to enhance the performance of this system, D. salina strain was subjected to adaptive laboratory evolution (ALE) by gradually increasing the phenol concentration from 200 mg L-1 to 500 mg L-1 at 3% NaCl concentration. At a phenol concentration of 500 mg L-1, the phenol removal rate of the resulting D. salina was 78.4% within 7 days, while that of the original strain was only 49.2%. The SOD, POD, and MDA contents of the resulting strain were lower than those of the original strain, indicating that the high concentration of phenol was less harmful to the resulting strain. A co-culture system was established with the resulting D. salina and H. mongoliensis, which could complete degrade 500 mg L-1 of phenol within 8 days, outperforming the original D. salina co-culture system. This study proved that ALE could improve the phenol tolerance and phenol degradation capability of D. salina, and then effectively improve the phenol degradation capability of D. salina and H. mongoliensis co-culture system.

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 light intensity on Chlorella sp. biofilm growth on anaerobically digested food effluents (ADFE)

Optimizing light conditions in any culture design for effluent treatment is crucial for maximizing microalgae growth and nutrient uptake. We investigated the impact of low (53 ± 1 μmol m-2 s-1), medium (208 ± 12 μmol m-2 s-1), and high (518 ± 22 μmol m-2 s-1) light intensities on the diffused biofilm-based growth of Chlorella sp. for treating anaerobically digested food effluent (ADFE). The alga grew well across all treatments, irrespective of light intensity. However, biomass yields, and productivity positively correlated with light intensity, with the highest biomass yield (120 g m-2) and productivity (11.6 g m-2 d-1) occurring at high light intensity. Notably, specific growth rates peaked uniformly on day 2 across all treatments, indicating an initial surge in growth. A relatively stable photosynthetic performance occurred under medium light treatment, while stress evidence was noticed particularly after day 4 at high and low light treatments, with higher magnitude seen under low light treatments. Total ammonia nitrogen (TAN) and phosphate removal efficiencies increased with light intensities, reaching 100 % removal at high light after 10 days. Intriguingly, there was a notable enhancement in chemical oxygen demand (COD) removal under low light conditions, being 2.9- and 1.64-fold higher compared to medium and high light intensities, respectively. Despite the superior performance of Chlorella sp. biofilm under high-light conditions in biomass yield and uptake of nutrients, the low-light treatment also achieved remarkable results, indicating that this biofilm design offers enhanced exposure to light. Therefore, this biofilm configuration presents an enticing opportunity for treating ADFE at lower light intensities, potentially minimizing energy consumption while maximizing profitability.

Bioremediation of azo dye: A review on strategies, toxicity assessment, mechanisms, bottlenecks and prospects

The synthetic azo dyes are widely used in the textile industries for their excellent dyeing properties. They may be classified into many classes based on their structure and application, including direct, reactive, dispersive, acidic, basic, and others. The continuous discharge of wastewater from a large number of textile industries without prior treatment poses detrimental effects on the environment and human health. Azo dyes and their degradation products are extremely poisonous for their carcinogenic, teratogenic and mutagenic nature. Moreover, exposure to synthetic azo dyes can cause genetic changes, skin inflammation, hypersensitivity responses, and skin irritations in persons, which may ultimately result in other profound issues including the deterioration of water quality. This review discusses these dyes in details along with their detrimental effects on aquatic and terrestrial flora and fauna including human beings. Azo dyes degrade the water bodies by increasing biochemical and chemical oxygen demand. Therefore, dye-containing wastewater should be effectively treated using eco-friendly and cost-effective technologies to avoid negative impact on the environment. This article extensively reviews on physical, chemical and biological treatment with their benefits and challenges. Biological-based treatment with higher hydraulic retention time (HRT) is economical, consumes less energy, produces less sludge and environmentally friendly. Whereas the physical and chemical methods with less hydraulic retention time is costly, produces large sludge, requires high dissolved oxygen and ecologically inefficient. Since, biological treatment is more advantageous over physical and chemical methods, researchers are concentrating on bioremediation for eliminating harmful azo dye pollutants from nature. This article provides a thorough analysis of the state-of-the-art biological treatment technologies with their developments and effectiveness in the removal of azo dyes. The mechanism by which genes encoding azoreductase enzymes (azoG, and azoK) enable the natural degradation of azo dyes by bacteria and convert them into less harmful compounds is also extensively examined. Therefore, this review also focuses on the use of genetically modified microorganisms and nano-technological approaches for bioremediation of azo dyes.

Effect of hydraulic retention time and treated urban wastewater ratio on progressive adaptation of an inoculated microalgae in membrane photobioreactors

Currently, there is a growing concern about water scarcity. The rising demand for wastewater treatment systems that facilitate the reuse of wastewater has resulted in a focus on the use of microalgae in sustainable treatments. These methods not only eliminate nutrients from the wastewater but also produce biomass that can be used to obtain high-value products. This study aimed to observe the effect of different hydraulic retention times (HRTs) and treated urban wastewater (TUWW) percentages on the growth of microalgae biomass and nutrient consumption in membrane photobioreactors. Microalgae biomass growth increases with HRT regardless of the percentage of TUWW. Biomass concentration stabilises at between 40% and 60% TUWW but significantly increases when 100% TUWW is used, resulting in the highest biomass concentrations. As HRT increases, ammonium and total nitrogen consumption also rise. A positive trend in ammonium consumption was observed with increasing TUWW, reaching its peak with 100% TUWW. The optimal conditions for biomass growth and nutrient removal are achieved with a 7-day HRT and 100% TUWW as influent, which was confirmed as optimal with the response surface methodology.

Bio-Food Quality, Environmental Pollution, and the Role of Algae in Promoting Human Health and Sustainability

Healthcare resources have changed fundamentally compared to decades ago. Modern bio-food products and sustainable solutions for their production have increased the attention of researchers, taking into account the current level of pollution of the earth and atmosphere along with modern technologies applied to processed foods. Therefore, this review aims to highlight: (1) the impact and relationship between the physiological parameters of the atmosphere, solar radiation and soil, (in terms of their composition and stages of formation and organization) along with the evolution to modern life; (2) the environmental impacts on algae, living organisms, food, and human health and sustainability. In addition, we address the significant impact of algae as a sustainable resource in reducing environmental pollution contributing to a healthier life.

Light-dependent switching between two flagellar beating states selects versatile phototaxis strategies in microswimmers

Microorganisms have evolved sophisticated sensor-actuator circuits to perform taxis in response to various environmental stimuli. How any given circuit can select between different taxis responses in noisy vs. saturated stimuli conditions is unclear. Here, we investigate how Euglena gracilis can select between positive vs. negative phototaxis under low vs. high light intensities, respectively. We propose three general selection mechanisms for phototactic microswimmers, and biophysical modeling demonstrates their effectiveness. Perturbation and high-speed imaging experiments show that of these three mechanisms, the "photoresponse inversion mechanism" is implemented in E. gracilis: a fast, light-intensity-dependent switching between two flagellar beat states responsible for swimming and turning causes positive vs. negative phototaxis at low vs. high light intensity via run-and-tumble vs. helical klinotaxis strategies, respectively. This coordinated beat-switching mechanism then also accounts for a larger set of previously reported E. gracilis behaviors; furthermore, it suggests key design principles for other natural as well as synthetic microswimmers.

Pharmaceutical Removal with Photocatalytically Active Nanocomposite Membranes

The advancement of pharmaceutical science has resulted in the development of numerous tailor-made compounds, i.e., pharmaceuticals, tuned for specific drug targets. These compounds are often characterized by their low biodegradability and are commonly excreted to a certain extent unchanged from the human body. Due to their low biodegradability, these compounds represent a significant challenge to wastewater treatment plants. Often, these compounds end up in effluents in the environment. With the advancement of membrane technologies and advanced oxidation processes, photocatalysis in particular, a synergistic approach between the two was recognized and embraced. These hybrid advanced water treatment processes are the focus of this review, specifically the removal of pharmaceuticals from water using a combination of a photocatalyst and pressure membrane process, such as reverse osmosis or nanofiltration employing photocatalytic nanocomposite membranes.

Modern-Day Green Strategies for the Removal of Chromium from Wastewater

Chromium is an essential element in various industrial processes, including stainless steel production, electroplating, metal finishing, leather tanning, photography, and textile manufacturing. However, it is also a well-documented contaminant of aquatic systems and agricultural land, posing significant economic and health challenges. The hexavalent form of chromium [Cr(VI)] is particularly toxic and carcinogenic, linked to severe health issues such as cancer, kidney disorders, liver failure, and environmental biomagnification. Due to the high risks associated with chromium contamination in potable water, researchers have focused on developing effective removal strategies. Among these strategies, biosorption has emerged as a promising, cost-effective, and energy-efficient method for eliminating toxic metals, especially chromium. This process utilizes agricultural waste, plants, algae, bacteria, fungi, and other biomass as adsorbents, demonstrating substantial potential for the remediation of heavy metals from contaminated environments at minimal cost. This review paper provides a comprehensive analysis of various strategies, materials, and mechanisms involved in the bioremediation of chromium, along with their commercial viability. It also highlights the advantages of biosorption over traditional chemical and physical methods, offering a thorough understanding of its applications and effectiveness.

Beyond Earth: Harnessing Marine Resources for Sustainable Space Colonization

The quest for sustainable space exploration and colonization is a challenge in its infancy, which faces scarcity of resources and an inhospitable environment. In recent years, advancements in space biotechnology have emerged as potential solutions to the hurdles of prolonged space habitation. Taking cues from the oceans, this review focuses on the sundry types of marine organisms and marine-derived chemicals that have the potential of sustaining life beyond planet Earth. It addresses how marine life, including algae, invertebrates, and microorganisms, may be useful in bioregenerative life support systems, food production, pharmaceuticals, radiation shielding, energy sources, materials, and other applications in space habitats. With the considerable and still unexplored potential of Earth's oceans that can be employed in developing space colonization, we allow ourselves to dream of the future where people can expand to other planets, not only surviving but prospering. Implementing the blend of marine and space sciences is a giant leap toward fulfilling man's age-long desire of conquering and colonizing space, making it the final frontier.

Wastewater treatment optimization utilizing polyvinyl alcohol cryogel immobilized microalgae for nutrient removal

This study investigated the use of polyvinyl alcohol (PVA) cryogels to immobilize microalgae for wastewater treatment. Chlorella sorokiniana was successfully entrapped in PVA cryogels via repeated freeze/thaw cycles. The nutrient removal efficiency of these cryogels was tested in a continuously stirred photobioreactor under varying conditions, both with and without the addition of an organic carbon source (sodium acetate). The presence of organic carbon significantly enhanced nutrient removal. Specifically, PVA cryogels with immobilized C. sorokiniana achieved 100% nitrogen removal and 97.2% phosphorus removal under mixotrophic conditions. Furthermore, the maximum nutrient removal capacities of the PVA cryogels were found to be 0.033 mg-N/cube·day for nitrogen and 0.0047 mg-P/cube·day for phosphorus. As the inorganic carbon (bicarbonate) concentration increased from 5 to 100 mg/L, the N/P ratio rose from 6 to 8, with a higher N/P ratio of 10 observed when nitrate nitrogen was used as the nitrogen source, compared to ammonia nitrogen, at 100 mg/L bicarbonate. This study offers an effective method for using microalgae immobilized in PVA cryogels for wastewater treatment. The findings highlight the potential for PVA cryogels to significantly improve nutrient removal efficiency, particularly in the presence of organic carbon sources, thereby enhancing bioreactor performance. High nitrogen and phosphorus removal efficiencies can help reduce eutrophication in water bodies, protect aquatic ecosystems, and enable nutrient recovery and reuse, supporting a circular economy in wastewater treatment practices.

Acclimated green microalgae consortium to treat sewage in an alternative urban WWTP in a coastal area of Central Italy

This study exposed a microalgal consortium formed by Auxenochlorella protothecoides, Tetradesmus obliquus, and Chlamydomonas reinhardtii to six mixed wastewater media containing different proportions of primary (P) or secondary (S) effluents diluted in centrate (C). Algae could grow at centrate concentrations up to 50 %, showing no significant differences between effluents. After acclimation, microalgae cultivated in 50%P-50%C and 50%S-50%C grew at a rate similar to that of control cultures (0.59-0.66 d-1). These results suggest that the consortium acclimated to both sewage streams by modulating the proportion of the species and their metabolism. Acclimation also altered the photosynthetic activity of wastewater-grown samples compared to the control, probably due to partial photoinhibition, changes in consortium composition, and changes in metabolic activity. No major differences were observed between the two streams with respect to biochemical composition, biomass yield, or bioremediation capacity of the cultivated algae but algae grown in the secondary effluent showed qualitatively higher exopolysaccharides (EPS) production than algae grown in primary. Regarding wastewater remediation, microalgae grown in both WW media showed proficient nutrient removal efficiencies (close to 100 %); however, the final pH value (close to 11) would be controversial if the system were upscaled as it is over the legal limit and would cause phosphorus precipitation, so that CO2 addition would be required. The theoretical scale-up of the microalgae system could achieve water treatment costs of 0.109 €·m-3, which was significantly lower than the costs of typical activated sludge systems.

Sustainable aquaculture and seafood production using microalgal technology - A circular bioeconomy perspective

The aquaculture industry is under the framework of the food-water-energy nexus due to the extensive use of water and energy. Sustainable practices are required to support the tremendous growth of this sector. Currently, the aquaculture industry is challenged by its reliance on capture fisheries for feed, increased use of pharmaceuticals, infectious outbreaks, and solid/liquid waste management. This review posits microalgal technology as a comprehensive solution for the current predicaments in aquaculture in a sustainable way. Microalgae are microscopic, freshwater and marine photosynthetic organisms, capable of carbon mitigation and bioremediation. They are indispensable in aquaculture due to their key role in marine productivity and their position in the marine food chain. Microalgae are nutritious and are currently used as feed in specific sectors of aquaculture. Due to their bioremediation potential, direct application of microalgae in shellfish ponds and in recirculating systems have been adopted to improve water quality and aquatic animal health. The potential of microalgae for integration into various aspects of aquaculture processes, namely hatcheries, feed, and waste management has been critically analyzed. Seamless integration of microalgal technology in aquaculture is feasible, and this review will provide new insights into using microalgal technology for sustainable aquaculture.

Use of microalgal-fungal pellets for hydroponics effluent recycling and high-value biomass production

Hydroponic effluent (HE), enriched with inorganic nutrients, presents a viable, low-cost cultivation medium for microalgal biomass production and subsequent resource recovery. However, downstream processing, particularly biomass harvesting, remains a critical challenge for microalgal biorefineries. Therefore, the present study explored the potential of microalgal-fungal pellets (MAFP) in HE recycling for the production of biochemical-rich biomass. The optimized fungi-to-microalgae ratio (F:A) of 1:3 resulted in 100 % microalgal pelletization within 6 h. Surface characteristics suggested that metabolically active fungi with opposite charges facilitate microalgal pelletization. Further, MAFP exhibited a packed porous structure that was resilient to shear forces and had a high capacity for nutrient uptake. MAFP cultivation in HE demonstrated complete removal of ammonia-nitrogen (NH₃-N), phosphate (PO₄³⁻), and nitrate-nitrogen (NO₃⁻-N) within 7-9 days. The produced biomass was rich in biomolecules, including lipids (18.36 ± 0.12 % TS), protein (52.06 ± 2.1 % TS), and carbohydrates (28.95 ± 0.05 % TS). Besides, the high methane potential of MAFP (SMP ≈ 502.74 ± 19.1 mL CH4 g-1 VS, and TMP ≈ 817.68 ± 12.5 mL CH4 g-1 VS) indicated its suitability for biogas production. In essence, MAFP offers efficient HE recycling and biochemically rich biomass production, advancing towards a green and circular bioeconomy.

Photosynthesizing carbonate/nitrate into Chlorococcum humicola biomass for biodiesel and Bacillus coagulans-based biohydrogen production

Biofuel can be generated by different organisms using various substrates. The green alga Chlorococcum humicola OQ934050 exhibited the capability to photosynthesize carbonate carbon, maybe via the activity of carbonic anhydrase enzymes. The optimum treatment is C:N ratio of 1:1 (0.2 mmoles sodium carbonate and 0.2 mmoles sodium nitrate) as it induced the highest dry mass (more than 0.5 mg.mL-1). At this combination, biomass were about 0.2 mg/mL-1 carbohydrates, 0.085 mg/mL-1 proteins, and 0.16 mg/mL-1 oil of this dry weight. The C/N ratios of 1:1 or 10:1 induced up to 30% of the Chlorococcum humicola dry mass as oils. Growth and dry matter content were hindered at 50:1 C/N and oil content was reduced as a result. The fatty acid profile was strongly altered by the applied C.N ratios. The defatted leftovers of the grown alga, after oil extraction, were fermented by a newly isolated heterotrophic bacterium, identified as Bacillus coagulans OQ053202, to evolve hydrogen content as gas. The highest cumulative hydrogen production and reducing sugar (70 ml H2/g biomass and 0.128 mg/ml; respectively) were found at the C/N ratio of 10:1 with the highest hydrogen evolution efficiency (HEE) of 22.8 ml H2/ mg reducing sugar. The optimum treatment applied to the Chlorococcum humicola is C:N ratio of 1:1 for the highest dry mass, up to 30% dry mass as oils. Some fatty acids were induced while others disappeared, depending on the C/N ratios. The highest cumulative hydrogen production and reducing sugar were found at the C/N ratio of 10:1.

Utilizing Mixed Cultures of Microalgae to Up-Cycle and Remove Nutrients from Dairy Wastewater

This study explores the novel use of mixed cultures of microalgae-Spirulina platensis, Micractinium, and Chlorella-for nutrient removal from dairy wastewater (DW). Microalgae were isolated from a local wastewater treatment plant and cultivated under various light conditions. The results showed significant biomass production, with mixed cultures achieving the highest biomass (2.51 g/L), followed by Spirulina (1.98 g/L) and Chlorella (1.92 g/L). Supplementing DW (75%) with BG medium (25%) significantly enhanced biomass and pH levels, improving pathogenic bacteria removal. Spirulina and mixed cultures exhibited high nitrogen removal efficiencies of 92.56% and 93.34%, respectively, while Chlorella achieved 86.85% nitrogen and 83.45% phosphorus removal. Although growth rates were lower under phosphorus-limited conditions, the microalgae adapted well to real DW, which is essential for effective algal harvesting. Phosphorus removal efficiencies ranged from 69.56% to 86.67%, with mixed cultures achieving the highest removal. Microbial and coliform removal efficiencies reached 97.81%, with elevated pH levels contributing to significant reductions in fecal E. coli and coliform levels. These findings suggest that integrating microalgae cultivation into DW treatment systems can significantly enhance nutrient and pathogen removal, providing a sustainable solution for wastewater management.

Comprehensive assessment of microalgal-based treatment processes for dairy wastewater

The dairy industry is becoming one of the biggest sectors within the global food industry, and these industries use almost 34% of the water. The amount of water used is governed by the production process and the technologies employed in the plants. Consequently, the dairy industries generate almost 0.2-10 L of wastewater per liter of processed milk, which must be treated before being discharged into water bodies. The cultivation of microalgae in a mixotrophic regime using dairy wastewater enhances biomass growth, productivity, and the accumulation of value-added product. The generated biomass can be converted into biofuels, thus limiting the dependence on petroleum-based crude oil. To fulfill the algal biorefinery model, it is important to utilize every waste stream in a cascade loop. Additionally, the harvested water generated from algal biomass production can be recycled for further microalgal growth. Economic and sustainable wastewater management, along with proper reclamation of nutrients from dairy wastewater, is a promising approach to mitigate the problem of water scarcity. A bibliometric study revealing limited work on dairy wastewater treatment using microalgae for biofuel production. And, limited work is reported on the pretreatment of dairy wastewater via physicochemical methods before microalgal-based treatment. There are still significant gaps remains in large-scale cultivation processes. It is also crucial to discover robust strains that are highly compatible with the specific concentration of contaminants, as this will lead to increased yields and productivity for the targeted bio-product. Finally, research on reutilization of culture media in photobioreactor is necessary to augument the productivity of the entire process. Therefore, the incorporation of the microalgal biorefinery with the wastewater treatment concept has great potential for promoting ecological sustainability.

Sustainable treatment scheme for in-situ remediation of contaminated drains using engineered natural systems

Ensuring water security in resource-constrained, densely populated regions is a significant challenge globally. Due to insufficient treatment infrastructure, untreated sewage discharge into drainage channels is prevalent, especially in developing countries. This leads to the pollution of already dwindling water bodies and threatens future water availability. In this context, in-situ treatment within drains using nature-based systems is an attractive option. This study evaluates microbial bioremediation and phytoremediation as engineered natural solutions for in-stream treatment of municipal wastewater. A three-stage treatment system consisting of anoxic biofilm, aerobic biofilm, and hydroponic floating wetlands was adopted. Each stage was optimized for operational parameters through batch and continuous flow studies. The anoxic biofilm system using autoclaved aerated concrete (AAC) as the attachment media, at an optimized hydraulic retention time (HRT) of 2 h, showed the best performance with respect to COD removal. Comparable COD removal was observed in both externally aerated and non-aerated aerobic biofilm systems with coir fibre at 6 h HRT. However, aerated system outperformed non-aerated system at low HRTs. The hydroponic system with Canna indica effectively removed residual ammonia-N with an HRT of 2 h. The sequential continuous flow studies employing the optimized conditions showed significant removals of COD (86%) and ammonia-N (97.6%). The results highlight that locally available materials having a high specific surface area can be used as biofilm supports for COD removal, and floating wetlands employing indigenous macrophytes can be an ideal choice for in-situ nutrient removal. The Life Cycle Assessment (LCA) showed that the developed system did not have direct significant impacts on freshwater eco-toxicity and eutrophication. The proposed hybrid treatment system can be implemented as modular units without major drainage modifications or energy-intensive operations. The study, therefore, finds potential application in densely populated settlements in low-income countries where systematic sewage treatment options remain inadequate.

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.

Progress in the Sustainable Development of Biobased (Nano)materials for Application in Water Treatment Technologies

Water pollution remains a widespread problem, affecting the health and wellbeing of people around the globe. While current advancements in wastewater treatment and desalination show promise, there are still challenges that need to be overcome to make these technologies commercially viable. Nanotechnology plays a pivotal role in water purification and desalination processes today. However, the release of nanoparticles (NPs) into the environment without proper safeguards can lead to both physical and chemical toxicity. Moreover, many methods of NP synthesis are expensive and not environmentally sustainable. The utilization of biomass as a source for the production of NPs has the potential to mitigate issues pertaining to cost, sustainability, and pollution. The utilization of biobased nanomaterials (bio-NMs) sourced from biomass has garnered attention in the field of water purification due to their cost-effectiveness, biocompatibility, and biodegradability. Several research studies have been conducted to efficiently produce NPs (both inorganic and organic) from biomass for applications in wastewater treatment. Biosynthesized materials such as zinc oxide NPs, phytogenic magnetic NPs, biopolymer-coated metal NPs, cellulose nanocrystals, and silver NPs, among others, have demonstrated efficacy in enhancing the process of water purification. The utilization of environmentally friendly NPs presents a viable option for enhancing the efficiency and sustainability of water pollution eradication. The present review delves into the topic of biomass, its origins, and the methods by which it can be transformed into NPs utilizing an environmentally sustainable approach. The present study will examine the utilization of greener NPs in contemporary wastewater and desalination technologies.

Microalgae-mediated bioremediation: current trends and opportunities-a review

Environmental pollution poses a critical global challenge, and traditional wastewater treatment methods often prove inadequate in addressing the complexity and scale of this issue. On the other hand, microalgae exhibit diverse metabolic capabilities that enable them to remediate a wide range of pollutants, including heavy metals, organic contaminants, and excess nutrients. By leveraging the unique metabolic pathways of microalgae, innovative strategies can be developed to effectively remediate polluted environments. Therefore, this review paper highlights the potential of microalgae-mediated bioremediation as a sustainable and cost-effective alternative to conventional methods. It also highlights the advantages of utilizing microalgae and algae-bacteria co-cultures for large-scale bioremediation applications, demonstrating impressive biomass production rates and enhanced pollutant removal efficiency. The promising potential of microalgae-mediated bioremediation is emphasized, presenting a viable and innovative alternative to traditional treatment methods in addressing the global challenge of environmental pollution. This review identifies the opportunities and challenges for microalgae-based technology and proposed suggestions for future studies to tackle challenges. The findings of this review advance our understanding of the potential of microalgae-based technology wastewater treatment.

Sustainable media feedstocks for cellular agriculture

The global food system is shifting towards cellular agriculture, a second domestication marked by cultivating microorganisms and tissues for sustainable food production. This involves tissue engineering, precision fermentation, and microbial biomass fermentation to establish food value chains independent of traditional agriculture. However, these techniques rely on growth media sourced from agricultural, chemical (fossil fuels), and mining supply chains, raising concerns about land use competition, emissions, and resource depletion. Fermentable sugars, nitrogen, and phosphates are key ingredients derived from starch crops, energy-intensive fossil fuel based processes, and finite phosphorus resources, respectively. This review explores sustainable alternatives to reduce land use and emissions associated with cellular agriculture media ingredients. Sustainable alternatives to first generation sugars (lignocellulosic substrates, sidestreams, and gaseous feedstocks), sustainable nitrogen sources (sidestreams, green ammonia, biological nitrogen fixation), and efficient use of phosphates are reviewed. Especially cellulosic sugars, gaseous chemoautotrophic feedstocks, green ammonia, and phosphate recycling are the most promising technologies but economic constraints hinder large-scale adoption, necessitating more efficient processes and cost reduction. Collaborative efforts are vital for a biotechnological future grounded in sustainable feedstocks, mitigating competition with agricultural land and emissions.

Pilot-scale microalgae cultivation and wastewater treatment using high-rate ponds: a meta-analysis

Microalgae cultivation in wastewater has been widely researched under laboratory conditions as per its potential to couple treatment with biomass production. Currently, only a limited number of published articles consider outdoor and long-term microalgae-bacteria cultivations in real wastewater environmental systems. The scope of this work is to describe microalgal cultivation steps towards high-rate algal pond (HRAP) scalability and identify key parameters that play a major role for biomass productivity under outdoor conditions and long-term cultivations. Reviewed pilot-scale HRAP literature is analysed using multivariate analysis to highlight key productivity parameters within environmental and operational factors. Wastewater treatment analysis indicated that HRAP can effectively remove 90% of NH4+, 70% of COD, and 50% of PO43-. Mean reference values of 210 W m-2 for irradiation, 18 °C for temperature, pH of 8.2, and HRT of 7.7 are derived from pilot-scale cultivations. Microalgae biomass productivity at a large scale is governed by solar radiation and NH4+ concentration, which are more important than retention time variations within investigated studies. Hence, selecting the correct type of location and a minimum of 70 mg L-1 of NH4+ in wastewater will have the greatest effect in microalgae productivity. A high nutrient wastewater content increases final biomass concentrations but not necessarily biomass productivity. Pilot-scale growth rates (~ 0.54 day-1) are half those observed in lab experiments, indicating a scaling-up bottleneck. Microalgae cultivation in wastewater enables a circular bioeconomy framework by unlocking microalgal biomass for the delivery of an array of products.

Treatment of agricultural wastewater using microalgae: A review

The rapid development of agriculture has led to a large amount of wastewater, which poses a great threat to environmental safety. Microalgae, with diverse species, nutritional modes and cellular status, can adapt well in agricultural wastewater and absorb nutrients and remove pollutants effectively. Besides, after treatment of agricultural wastewater, the accumulated biomass of microalgae has broad applications, such as fertilizer and animal feed. This paper reviewed the current progresses and further perspectives of microalgae-based agricultural wastewater treatment. The characteristics of agricultural wastewater have been firstly introduced; Then the microalgal strains, cultivation modes, cellular status, contaminant metabolism, cultivation systems and biomass applications of microalgae for wastewater treatment have been summarized; At last, the bottlenecks in the development of the microalgae treatment methods, as well as recommendations for optimizing the adaptability of microalgae to wastewater in terms of wastewater pretreatment, microalgae breeding, and microalgae-bacterial symbiosis systems were discussed. This review would provide references for the future developments of microalgae-based agricultural wastewater treatment.

Novel technique for the ultra-sensitive detection of hazardous contaminants using an innovative sensor integrated with a bioreactor

This study introduces an evaluation methodology tailored for bioreactors, with the aim of assessing the stress experienced by algae due to harmful contaminants released from antifouling (AF) paints. We present an online monitoring system equipped with an ultra-sensitive sensor that conducts non-invasive measurements of algal culture's optical density and physiological stage through chlorophyll fluorescence signals. By coupling the ultra-sensitive sensor with flash-induced chlorophyll fluorescence, we examined the dynamic fluorescence changes in the green microalga Chlamydomonas reinhardtii when exposed to biocides. Over a 24-h observation period, increasing concentrations of biocides led to a decrease in photosynthetic activity. Notably, a substantial reduction in the maximum quantum yield of primary photochemistry (FV/FM) was observed within the first hour of exposure. Subsequently, we detected a partial recovery in FV/FM; however, this recovery remained 50% lower than that of the controls. Integrating the advanced submersible sensor with fluorescence decay kinetics offered a comprehensive perspective on the dynamic alterations in algal cells under the exposure to biocides released from antifouling coatings. The analysis of fluorescence relaxation kinetics revealed a significant shortening of the fast and middle phases,  along with an increase in the duration of the slow phase, for the coating with the highest levels of biocides. Combining automated culturing and measuring methods, this approach has demonstrated its effectiveness as an ultrasensitive and non-invasive tool for monitoring the physiology of photosynthetic cultures. This is particularly valuable in the context of studying microalgae and their early responses to various environmental conditions, as well as the potential to develop an AF system with minimal harm to the environment.

Conventional activated sludge vs. photo-sequencing batch reactor for enhanced nitrogen removal in municipal wastewater: Microalgal-bacterial consortium and pathogenic load insights

Municipal wastewater treatment plants are mostly based on traditional activated sludge (AS) processes. These systems are characterised by major drawbacks: high energy consumption, large amount of excess sludge and high greenhouse gases emissions. Treatment through microalgal-bacterial consortia (MBC) is an alternative and promising solution thanks to lower energy consumption and emissions, biomass production and water sanitation. Here, microbial difference between a traditional anaerobic sludge (AS) and a consortium-based system (photo-sequencing batch reactor (PSBR)) with the same wastewater inlet were characterised through shotgun metagenomics. Stable nitrification was achieved in the PSBR ensuring ammonium removal > 95 % and significant total nitrogen removal thanks to larger flocs enhancing denitrification. The new system showed enhanced pathogen removal, a higher abundance of photosynthetic and denitrifying microorganisms with a reduced emissions potential identifying this novel PSBR as an effective alternative to AS.

Sludge degradation, nutrient removal and reduction of greenhouse gas emission by a Chironomus-Azolla wastewater treatment cascade

Wastewater treatment plants (WWTPs) are a point source of nutrients, emit greenhouse gases (GHGs), and produce large volumes of excess sludge. The use of aquatic organisms may be an alternative to the technical post-treatment of WWTP effluent, as they play an important role in nutrient dynamics and carbon balance in natural ecosystems. The aim of this study was therefore to assess the performance of an experimental wastewater-treatment cascade of bioturbating macroinvertebrates and floating plants in terms of sludge degradation, nutrient removal and lowering GHG emission. To this end, a full-factorial experiment was designed, using a recirculating cascade with a WWTP sludge compartment with or without bioturbating Chironomus riparius larvae, and an effluent container with or without the floating plant Azolla filiculoides, resulting in four treatments. To calculate the nitrogen (N), phosphorus (P) and carbon (C) mass balance of this system, the N, P and C concentrations in the effluent, biomass production, and sludge degradation, as well as the N, P and C content of all compartments in the cascade were measured during the 26-day experiment. The presence of Chironomus led to an increased sludge degradation of 44% compared to 25% in the control, a 1.4 times decreased transport of P from the sludge and a 2.4 times increased transport of N out of the sludge, either into Chironomus biomass or into the water column. Furthermore, Chironomus activity decreased methane emissions by 92%. The presence of Azolla resulted in a 15% lower P concentration in the effluent than in the control treatment, and a CO2 uptake of 1.13 kg ha-1 day-1. These additive effects of Chironomus and Azolla resulted in an almost two times higher sludge degradation, and an almost two times lower P concentration in the effluent. This is the first study that shows that a bio-based cascade can strongly reduce GHG and P emissions simultaneously during the combined polishing of wastewater sludge and effluent, benefitting from the additive effects of the presence of both macrophytes and invertebrates. In addition to the microbial based treatment steps already employed on WWTPs, the integration of higher organisms in the treatment process expands the WWTP based ecosystem and allows for the inclusion of macroinvertebrate and macrophyte mediated processes. Applying macroinvertebrate-plant cascades may therefore be a promising tool to tackle the present and future challenges of WWTPs.

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Microalgal-bacterial treatment of ice-cream wastewater to remove organic waste and harvest oil-rich biomass

The diversity of microalgae and bacteria allows them to form beneficial consortia for efficient wastewater treatment and nutrient recovery. This study aimed to evaluate the feasibility of a new microalgal-bacterial combination in the treatment of ice cream wastewater for biomass harvest. The bacterium Novosphingobium sp. ICW1 was natively isolated from ice cream wastewater and the microalga Vischeria sp. WL1 was a terrestrial oil-producing strain of Eustigmatophyceae. The ice cream wastewater was diluted 4 folds for co-cultivation, which was relatively less inhibitory for the growth of Vischeria sp. WL1. Four initial algal-bacterial combinations (v:v) of 150:0 (single algal cultivation), 150:1, 150:2, and 150:4 were assessed. During 24 days of co-cultivation, algal pigmentation was dynamically changed, particularly at the algal-bacterial combination of 150:4. Algal growth (in terms of cell number) was slightly promoted during the late phase of co-cultivation at the combinations of 150:2 and 150:4, while in the former the cellular oil yield was obviously elevated. Treated by these algal-bacterial combinations, total carbon was reduced by 67.5 ~ 74.5% and chemical oxygen demand was reduced by 55.0 ~ 60.4%. Although single bacterial treatment was still effective for removing organic nutrients, the removal efficiency was obviously enhanced at the algal-bacterial combination of 150:4. In addition, the harvested oils contained 87.1 ~ 88.3% monounsaturated fatty acids. In general, this study enriches the biotechnological solutions for the sustainable treatment of organic matter-rich food wastewater.

Research advances on production and application of algal biochar in environmental remediation

Algae, comprising microalgae and macroalgae, have emerged as a promising feedstock for the production of functional biochar. Recently, the application of algal biochar in environmental remediation gains increasing attention. This review summarizes research advancements in the synthesis and application of algal biochar, a versatile and sustainable material for environmental remediation ranging from wastewater treatment to soil improvement. Algal biochar can be prepared by pyrolysis, microwave-assisted pyrolysis, and hydrothermal carbonization. Physical and chemical modifications have proven to be effective for improving biochar properties. Algal biochar is promising for removing diverse pollutants including heavy metals, organic pollutants, and microplastics. The role in soil improvement signifies a sustainable approach to enhancing soil structure, nutrient retention, and microbial activity. Research gaps are identified based on current understanding, necessitating further exploration into variations in biochar characteristics, the performance improvement, large-scale applications, and the long-term evaluation for environmental application. This review provides a better understanding of algal biochar as a sustainable and effective tool in environmental remediation.

Harnessing spin and orbital angular momentum light for optimal algae growth

The present study investigated the difference in transmittance of light carrying opposite spin angular momentum (SAM) and orbital angular momentum (OAM) through chlorella algal fluid with varying concentrations and thicknesses. Our results indicate that, under specific conditions, right-handed light sources exhibit higher transmittance in the algal fluid compared to left-handed light sources. Furthermore, we observed that light with OAM also demonstrated higher transmittance than other types of light sources, leading to faster cell density growth of Chlorella. Interestingly, we also discovered that light with OAM stimulates Chlorella to synthesize more proteins. These findings provide different insights for selecting appropriate light sources for large-scale algae cultivation, and may facilitate the realization of carbon peaking and carbon neutrality in the future.