Lalit Goswami

Eutrophication is a nutrient-driven shift in trophic status characterized by the appearance of green or blue green algae and declining water quality. Non-point source (NPS) pollutants are diffuse pollutants originating from multiple sources like agriculture runoff, urban waste, animal or human activities, etc. are major drivers of trophic transitions and algal proliferation. However, their seasonal influences on nutrient balance and trophic state remain understudied. This study provides an integrated framework combining water quality parameters, Carlson trophic state index (CTSI), Redfield ratio, and normalized differentiated chlorophyll index (NDCI) to understand the effect of NPS on nutrient loading and trophic transition across three major wetlands in Guwahati city, Deepor Beel, Dighalipukhuri, and Jorpukhuri during the post-monsoon season. Water quality parameters including temperature, pH, EC, TDS, DO, chlorophyll-a, NO ₃ ⁻ , TKN, TN, TP, PO ₄ ³⁻ , and COD were analyzed from sampling points vulnerable towards NPS pollution across the wetlands. Results showed severe eutrophication intensity with CTSI values ranging from 113 to 115 in Deepor Beel, 110 to 114 in Dighalipukhuri, and 108 to 114 in Jorpukhuri. Redfield ratio of all the three wetlands indicated strong nitrogen dominance (TN/TP >16), with Deepor Beel showing highest spatial heterogeneity, while Dighalipukhuri and Jorpukhuri remain consistently phosphorus-limited across all points. Overall eutrophication intensity is highest in November across sites, with multiple hotspots exceeding TN/TP >50. NDCI mapping validated these findings, showing elevated chl-a concentrations along the pollution-prone margins of Deepor Beel. Across all wetlands, lower DO coincided with elevated chlorophyll-a, phytoplankton driven turbidity (T _chl-a > T _sd ) and warmer post-monsoon temperatures are consistent markers of high eutrophication.

Conversion of waste biomass into nanobiochar-based photocatalyst offers a sustainable route for addressing wastewater pollution caused by persistent organic dye. In this study, a green-synthesized Fe2O3/NB/CeO2 (FNBC) photocatalyst was developed using tea-waste biomass-derived nanobiochar as support for the fabrication of Fe2O3 and CeO2 nanoparticles, aimed at the efficient photocatalytic degradation of Rhodamine B (RhB) under visible light. The synthesized nanocomposite was comprehensively characterized using advanced analytical techniques including FTIR, XRD, DSC, SEM-EDS, XPS, VSM, DLS-Zeta, BET, and band gap analysis, confirming the successful formation of photocatalyst. The composite had bigger surface area (112.6 m² g-1) and mesopores (7.8 nm), with optical band gap of 5.60 eV. XPS analysis showed the co-existence of Fe3+/Fe2+ and Ce4+/Ce3+ oxidation states. Photocatalytic studies were systematically conducted to optimize the reaction parameters, under which the FNBC showed outstanding performance by achieving 96.4 % degradation of RhB at pH 7 using 20 mg/L within 120 min by following first-order kinetics model (k = 0.031 min-1). Moreover, the catalyst shows excellent stability and reusability, retaining high photocatalytic efficiency even after the fifth reuse cycle following magnetic recovery. Reactive oxygen species (ROS) scavenging studies further confirmed that the •OH played a dominant role in the degradation mechanism of RhB. Further, GC-MS analysis of the degraded products confirmed effective dye mineralization without the formation of harmful intermediate compounds, highlighting the environmental safety of the process. Overall, this study demonstrates an effective waste-to-wastewater treatment strategy, where tea waste is valorised into a highly efficient, stable, and eco-friendly photocatalyst for sustainable wastewater remediation.

Wastewater contaminated with hexavalent chromium (Cr(VI)) is a potential health and environmental hazard and hence the need for sustainable and cost-effective adsorbents. Cellulose nanocrystals (CNCs) were isolated from sugarcane bagasse by mild acid hydrolysis (10 % v/v H2SO4) and then used to prepare two different membranes, Membrane 1 (Chitosan-CNC, NaOH-crosslinked) and Membrane 2 (PVA-CNC, crosslinker-free) for comparative Cr(VI) removal from synthetic wastewater. DLS and XRD indicated the CNCs were colloidally stable (zeta potential: −25.7 mV) and were crystalline (cellulose Iβ) and had an average particle size of 90–126 nm. Successful composite formation and superior hydrophilicity of Membrane 2 (37.4°) compared to Membrane 1 (74.2°) was confirmed by FESEM, FTIR and contact angle measurements. The maximum adsorption capacities for Cr(VI) were 67.0 and 80.0 mg g ⁻¹ for the Membrane 1 and Membrane 2, respectively, which were obtained in batch adsorption studies at pH 4 and pH 3, respectively. The adsorption behavior of both membranes was well described by the Langmuir and Freundlich isotherm models, indicating monolayer adsorption on homogeneous sites alongside adsorption on heterogeneous surfaces. The pseudo-second-order kinetic model, together with positive values of Δ H ° and Δ S °, and negative for Δ G ° suggested that the adsorption process was predominantly chemisorption-driven, endothermic, and spontaneous. Moreover, after 5 regeneration cycles, both membranes still showed a good Cr(VI) removal percentage (Membrane 1: 86–70 %, Membrane 2: 94–72 %), proving their reusability. The results indicate that the agro-waste produced nanocellulose composites, with very little use of chemicals, can be useful, mechanically strong, and environmentally friendly heavy-metal adsorbents.

Globally, the ever‐rising energy demand has altered the techniques for producing oil, especially in the upstream processing, such as horizontal hydraulic fracturing and targeted drilling. Drilling deep oil and gas wells necessitates specialized drilling fluid formulations to ensure safe and efficient operations, as the conventional drilling fluids, such as the water‐based drilling fluids (WBDF), can cause shale swelling, and the oil‐based drilling fluids (OBDF) can cause other environmental concerns because of the presence of aromatic compounds. Synthetic‐based drilling fluids (SBDF) address these issues by combining superior performance with reduced environmental impact. Esters have shown the highest biodegradability and good performance as compared to other synthetic bases in drilling fluids. The present review article highlights the potential advantages of ester‐based drilling fluid (EBDF) under high‐pressure and high‐temperature (HPHT) environments. Moreover, the review articles show the advancement in the ester synthesis by using different carboxylic acids and oil feedstocks and provide beneficial insights on the recent advances in EBDF formulations. Furthermore, the review demonstrates EBDF cost efficiency over OBDF by comparison of formulation and disposal cost. This review also comprehends the studies that examined the utilization of various nanoparticles as a Pickering emulsion stabilizer in OBDF and SBDF formulations to enhance their properties and emulsion stabilities. Lastly, the review has proposed a futuristic formulation of drilling fluids via incorporating the nanoparticles that can improve the thermal stability of EBDF.

In this study, pigment-producing yeast (Rhodotorula alborubescens) was isolated from the soil sample, demonstrating the potential for carotenoid biosynthesis. Physiological, morphological, biochemical, and molecular characterization confirmed the identity of the isolate. Optimization of the physical parameters for carotenoid production was achieved through batch shake flask experiments. The optimal conditions were determined to be 84 h of incubation at pH 6.0 and 28 °C under white light irradiation, utilizing the Yeast Peptone Dextrose (YPD) medium composed of 10 g/L yeast extract, 5 g/L of peptone, and 5 g/L dextrose, resulting in maximum carotenoid content. Further, the presence of β-carotene was confirmed using High-Performance Liquid Chromatography and Fourier Transform Infrared Spectroscopy. These findings highlight the potential of the isolated soil yeast (R. alborubescens) as a potential source of carotenoids, offering natural alternatives for various industrial applications.