Ashiwin Vadiveloo

The valorization of food and agro-industrial wastes into platform chemicals offers a sustainable solution to waste management and resource utilization, addressing both environmental and economic challenges. This review explores the latest advancements in bioconversion technologies for producing platform chemicals, such as bioethanol, lactic acid, succinic acid, and levulinic acid. It highlights the potential of utilizing agro-industrial residues, including crop residues, fruit and vegetable processing waste, and dairy by-products, as valuable feedstocks for chemical production. These residues, often discarded as waste, contain organic compounds that can be converted into essential platform chemicals, which are vital for biofuels, bioplastics, and specialty chemicals. The review examines both thermochemical and biochemical processes, such as pyrolysis, gasification, enzymatic hydrolysis, and fermentation, for converting food and agro-industrial wastes into valuable products. Case studies, including the enzymatic production of lactic acid from spoiled grains and anaerobic digestion of fruit wastes to produce volatile fatty acids, demonstrate the effectiveness of these technologies in waste valorization. Furthermore, the review discusses the environmental and economic benefits of waste-to-value processes, incorporating life cycle assessments and circular economy principles. Despite challenges such as feedstock variability, process scaling, and the need for regulatory standards, ongoing innovations in genetic engineering and integrated biorefineries present promising solutions for overcoming these barriers. The successful commercialization of these technologies requires collaboration among researchers, industries, and policymakers to foster sustainable production practices and reduce dependence on fossil-based resources, ultimately contributing to a circular bioeconomy.

Fluoride ion contamination in drinking water poses a considerable environmental and health risk. Thus, novel sustainable and economic removal techniques are needed. This study examined the biosorption of fluoride ions from aqueous solutions utilizing the dead biomass of the green alga
Chara vulgaris
as an adsorbent. First, the biomass was studied for its structural and functional characteristics using Fourier transform infrared spectroscopy (
FTIR
), scanning electron microscopy (
SEM
), transmission electron microscopy (
TEM
), X-ray diffraction (
XRD
), and Brunauer–Emmett–Teller (
BET
) techniques. The optimal conditions for the biosorption were studied experimentally. Dead
Chara vulgaris
biomass achieved fluoride removal efficiency of 91% under optimal conditions (pH 2, 35 °C, 0.4 g adsorbent dose, and 300 min contact time). The surface characteristics and functional groups of the algal biomass were assessed to enable effective fluoride adsorption via a spontaneous, exothermic mechanism. The examination of fluoride biosorption indicated that the process was best explained by a Langmuir model with a high fit (
R
2
 = 0.99). It shows that fluoride adheres to the surface in a monolayer. The kinetics of the process followed the pseudo-second-order model (
R
2
 = 0.98), with the internal movement of particles being of lesser significance. The findings indicate that dead
Chara vulgaris
biomass can be used as an efficient material for fluoride removal, making it highly beneficial for purifying natural water and treating industrial effluent.

Biocrusts are essential for soil stabilization and nutrient cycling in arid ecosystems, yet their formation is often limited by coarse texture, low fertility, and extremely low cyanobacterial biomass in shifting sands. To address these constraints, this study conducted a field experiment in the Gurbantunggut Desert using four treatments that combined two inocula, crushed natural cyanobacteria dominated biocrust fragments and laboratory-cultured cyanobacteria, with or without the addition of sepiolite. The results showed that sepiolite addition significantly enhanced biocrust development by promoting exopolysaccharides accumulation, biocrust thickness and structural integrity. It also improved soil organic carbon, microbial biomass carbon, and some enzymes activities involved in carbon and nitrogen cycling, especially β-glucosidase. Furthermore, a general C limitation was observed across all biocrust groups, and the addition of sepiolite effectively alleviate N limitation. Microbial α-diversity remained unchanged, but β-diversity and community composition were distinctly shaped by both sepiolite and inoculum type. Notably, although sepiolite facilitated biocrust formation in both inoculation strategies, crushed natural biocrusts outperform cyanobacterial monoculture in enhancing recovery efficiency, indicated by achieving much higher microbial biomass, stability, enzyme activities and nutrient levels. Overall, sepiolite addition plays multiple key roles in promoting the biocrust restoration in arid sandy soils by improving soil microhabitats and supporting microbial assembly and nutrient cycling, thereby enhancing biocrust development. These results provide new field-based evidence that integrating functional clay minerals with microbial inoculation can effectively overcome abiotic barriers to biocrust formation.

The large-scale application of algae-bacteria systems in wastewater treatment faces two key challenges: inefficient post-cultivation separation and insufficient understanding of their cross-kingdom interactions. To address these limitations, we developed a dialysis membrane photobioreactor (DMP) that simultaneously enables effective microalgae-bacteria separation and mechanistic investigation of their interactions. The DMP system, integrating microalgae-activated sludge consortia, achieved significantly higher removal efficiencies for nitrogen (95.8 %), phosphorus (68.1 %), and chemical oxygen demand (96.1 %) compared to conventional activated sludge, while also enhancing microalgal biomass production. Mechanistic studies revealed that microalgae promoted the synthesis of cross-kingdom signaling molecules (C6-HSL and IAA), establishing a molecular dialogue between algae and bacteria. Multi-omics analyses uncovered bidirectional regulation: microalgae reshaped bacterial community structure and upregulated bacterial IAA synthesis genes, while bacteria reciprocally activated microalgal IAA-related genes. This mutual feedback mechanism amplified cross-kingdom signaling and synergistically upregulated functional genes involved in nitrogen/phosphorus metabolism, driving enhanced pollutant removal. Our findings demonstrate that the DMP system fosters a syntrophic partnership where AHLs and IAA mediate bidirectional metabolic regulation-simultaneously optimizing pollutant degradation and biomass conversion. This work provides both fundamental insights into algae-bacteria communication and a practical framework for advancing wastewater bioremediation technologies.
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Microalgae-based wastewater treatment offers dual advantages of carbon sequestration and resource recovery, yet its efficacy in removing pharmaceutical contaminants (PCs) remains limited. Phytohormone augmentation presents a promising strategy to enhance PCs removal and bioresource production, but the mechanisms and scalability of this approach are poorly understood. This study systematically evaluated the dual effects of seven phytohormones including indole-3-acetic acid (IAA), abscisic Acid (ABA), salicylic acid (SA), gibberellin A3 (GA3), jasmonic acid (JA), brassinolide (BR), and zeatin (ZT) on the degradation of triclocarban (TCC) and the production of bioresources in Chlorella pyrenoidosa. All phytohormones significantly improved microalgal growth, TCC removal, and biomolecule yields. SA exhibited the most balanced performance, achieving near-peak biomass yield (0.52 g L
, vs. ZT's 0.53 g L
) and TCC removal (86.2 %, vs. GA's 87.4 %), and the highest lipid productivity (4.27 mg L
d
). Mechanistic analyses revealed that phytohormones acted via dual pathways: enhancing degradation metabolism to reduce oxidative stress and modulating calcium ion (Ca
)/nitric oxide (NO) signaling to maintain reactive oxygen species (ROS) balance. Scaling up to 50-L photobioreactors treating real domestic wastewater, SA boosted removal of 16 PCs by 74.7 % (2.60-fold of the algae-only control) while elevating lipid, starch, protein, and pigment productivities by 2.86-, 4.71-, 8.91-, and 6.96-fold, respectively. Notably, 99.997 % of supplemented SA was utilized by microalgae, ensuring no secondary pollution. This work demonstrates phytohormone-augmented microalgae as a sustainable, scalable biotechnology for simultaneous wastewater purification and circular bioeconomy applications.

Recent studies have revealed that N-acyl-homoserine lactones (AHLs), common quorum-sensing (QS) signal molecules in Gram-negative bacteria, can also influence microalgal cells. However, their role in regulating the metabolism of pollutants, such as antibiotics, within microalgae remains poorly understood. This study investigated the effects of N-hexanoyl-L-homoserine lactone (C6-HSL) on the degradation of sulfamethoxazole (SMX) in aquaculture wastewater by Chlorella vulgaris. The addition of 0.5 μM C6-HSL resulted in the highest biomass accumulation and the maximum SMX removal efficiency (95.6 %). At optimal concentrations, C6-HSL effectively modulated key secondary messenger signaling pathways including reactive oxygen species (ROS), nitric oxide (NO), and calcium ions (Ca2+) in microalgal cells. Additionally, it upregulated the activity of detoxification enzymes such as glutathione S-transferase (GST) and cytochrome P450 (CYP450), thereby altering SMX degradation pathways and significantly enhancing its removal. Transcriptomic analysis further demonstrated that exogenous C6-HSL upregulated critical genes associated with ROS, Ca2+, and NO signaling, along with genes encoding antioxidant enzymes and those involved in SMX metabolism. These findings indicated that C6-HSL, as a bacterial QS signal, could enhance microalgal tolerance and antibiotic degradation, offering a novel strategy to improve microalgae-based antibiotic removal in wastewater treatment.

Conventional methods of nanoparticle production suffer from various limitations, including the toxicity of precursor materials, the imperative for stringent temperature regulation, and exorbitant synthesis costs, thereby limiting their applicability. Therefore, the green synthesis of nanoparticles has emerged as a clean, non-toxic, and eco-friendly technique, which offers great potential due to both environmental and economic prospects. This review comprehensively explores the green synthesis of metallic nanoparticles, with focus on microalgae-mediated processes, and provides comparative insights of biogenic synthesis contrasted to traditional synthesis while critically discussing the major unresolved issues in using microalgae for nanoparticle synthesis. Furthermore, this work critically examines the factors influencing nanoparticle synthesis, and addresses the challenges and strategies pertaining to stability, separation, yield, agglomeration, morphology, crystal growth, and toxicity. This work also explores new opportunities and directions to improve toxicity mitigation strategies and enhance the biosynthesis efficiency through genetic engineering and metabolic pathway.

Municipal wastewater is rich in essential nutrients required for microalgae growth, making it a promising alternative for cultivating microalgae biomass and producing valuable metabolic compounds. This study investigated the simultaneous biomass production and nutrient removals from municipal wastewater using two locally isolated microalgae strains, Desmodesmus armatus MO1 and Tetradesmus obliquus MO2. After eight days of cultivation, nitrogen and phosphorus removal reached 96% and 60%, respectively. Biomass production was recorded at 1.375 g/L which exceeded the productivity obtained in the positive control using AF-6 media. Metabolic compound analysis revealed increased production of carbohydrates and lipids when wastewater was used as the cultivation medium, The highest carbohydrate content, 49%, was observed in Tetradesmus obliquus MO2, while Desmodesmus armatus MO1 produced the highest lipid yield at 0.214 g/L in wastewater. The study also highlighted increased production of omega fatty acids (omega-3, omega-6, and omega-9) in both species by cultivation in wastewater samples. These included the production of oleic acid (C18:1), linoleic acid (C18:2), arachidonic acid (C20:4) and docosahexanoic acid (C22:6). Major fatty acid was found to be oleic acid (C18:1), noted at 20% in Desmodesmus armatus MO1 and 51% in Tetradesmus obliquus MO2. These findings suggest that biomass from locally isolated microalgae strains cultivated in municipal wastewater holds significant potential for various applications.

Background
The ubiquity of ammonical nitrogen (NH3-N) in aquatic habitats is a contradictory phenomenon since it serves a crucial function in maintaining these ecosystems, yet when levels are too high, they can have adverse effects on ecological balance and human welfare. An extensive set of batch tests were used in this study to see how well the bacterial species Klebsiella sp. broke down ammonical nitrogen (NH3-N).

Results
The research results established that Klebsiella sp. has a remarkable capacity to adapt to ammonical nitrogen concentrations of up to 125 mg/l over a long period of time. The adaptation process depends on several factors such as biomass abundance, ammonical nitrogen concentration, pH, and temperature. This study identified the optimal method for the absorption of ammonical nitrogen (NH3-N) from a solution at a concentration of 100 parts per million (ppm), achieving an efficiency of 89 ± 1.5% mg/g under specified conditions. At a pH of 6.5, the adsorbent dosage was 0.3 g in 50 milliliters of NH3-N at a temperature of 26 degrees C. We used an extensive range of analytical techniques, such as Scanning Electron Microscopy, Xray diffraction, Brunauer-Emmett-Teller analysis, Transmission Electron Microscopy, and Fourier-Transform Infrared Spectroscopy, to confirm the accuracy of our results. The study also showed that the biosorption process closely followed pseudo-second-order kinetics and the Langmuir model, which propose that both physical and chemical processes were involved. The thermodynamic studies also showed that this process can happen on its own and can be used in industry.

Conclusion
This study emphasizes the great ability of Klebsiella sp. to reduce NH3-N, providing important knowledge for water quality management and aquatic ecosystem preservation.

The lack of cost-effective nutrient sources and harvesting methods is currently a major obstacle to the production of sustainable biofuels from microalgae. In this study, Chlorella pyrenoidosa was cultured with saline wastewater in a stirred photobioreactor, and lipid-rich flocculent microalgae particles were successfully constructed. As the influent salinity of the photobioreactor increased from 0% to 3%, the particle size and sedimentation rate of flocculent microalgae particles gradually increased, and the lipid accumulation of microalgae also increased gradually. Transcriptome analysis showed that the number of differentially expressed genes (DEGs) in microalgae increased as the salinity of wastewater increased from 1% to 3%, and the number of up-expressed genes was greater than that of down-expressed genes in microalgae at different salinity levels. The enrichment analysis of DEGs showed that the up-expressed genes under salt stress mainly involved in fatty acid biosynthesis and other metabolic processes, which initially revealed the mechanism of the lipid accumulation of microalgal particles in saline wastewater. In addition, the expression and functions of genes involved in lipid and EPS synthesis pathway in microalgae were analyzed, and the key genes involved in salinity affecting lipid and EPS synthesis in microalgae were preliminarily identified. The results could provide novel insight for genetic engineering to regulate the construction of lipid-rich flocculent microalgae particles.