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Impact of varying nitrate (NO3-N) and phosphate (PO4-P) concentrations and sewage water (SW) on the growth, nutrient removal, lipid accumulation, enzymatic antioxidant activity and phytochemical contents of the microalgae Scenedesmus dimorphus, Coelastrella tenuitheca, Chroococcus turgidus and Parachlorella kessleri under monoculture and their consortia have been investigated. High growth rates were observed for all the four algae in both mono and mixed culture conditions at enhanced concentrations of N (1500 mg/L NO3-N) and P (40 mg/L PO4-P). The species Scenedesmus dimorphus outperformed other microalgae growing in SW in efficiently removing nitrogen. The algal consortia of mixed species was found to be more effective in phosphorus removal. The carbohydrate and protein contents were highest in Parachlorella kessleri, about 37% and 44%, respectively, in SW cultivation. The algal consortia demonstrated highest starch content (4%) in nitrogen deprived growth medium. Highest lipid production (43%) was observed in the SW culture. The species Coelastrella tenuitheca, Chroococcus turgidus and Scenedesmus dimorphus irrespective of the growth media indicated significant accumulation of phenol, flavonoid and tannin. The DPPH, catalase and ascorbic peroxidase assay showed pronounced antioxidant activity. Nutrient (N and P) enrichment exhibited enhanced antioxidant enzymatic activity and accumulation of cell storage products. NOVELTY STATEMENT: This study explores the response mechanisms and nutrient removal capabilities of various microalgal species and their consortia in sewage water treated media. The results provide valuable insights into the potential role of algae in wastewater treatment processes, revealing high tolerance and considerable NO3-N and PO4-P removal capabilities of Scenedesmus dimorphus and algal consortia toward different wastewaters. The results of the study are relevant for the development of sustainable solutions for water pollution management. The algae and their consortia grown in wastewater showed high levels of carbohydrates, proteins, lipids, bioactive compounds accumulation and antioxidant activity rendering them a sustainable and renewable resource for various industrial applications. [ABSTRACT FROM AUTHOR]

Rising concerns over water scarcity, driven by industrialization and urbanization, necessitate the need for innovative solutions for wastewater treatment. This study focuses on developing an eco‐friendly and cost‐effective biochar‐zeolite composite (BZC) adsorbent using waste materials—spent coffee ground biochar (CGB) and steel slag zeolite (SSZ). Initially, the biochar was prepared from spent coffee ground, and zeolite was prepared from steel slag; their co‐pyrolysis resulted in novel adsorbent material. Later, the physicochemical characteristics of the BZC were examined, which showed irregular structure and well‐defined pores. Dye removal studies were conducted, which indicate that BZC adsorption reach equilibrium in 2 h, exhibiting 95% removal efficiency compared to biochar (43.33%) and zeolite (74.58%). Moreover, the removal efficiencies of the novel BZC composite toward dyes methyl orange (MO) and crystal violet (CV) were found to be 97% and 99.53%, respectively. The kinetic studies performed with the dyes and phosphate with an adsorbent dosage of 0.5 g L−1 suggest a pseudo‐second‐order model. Additionally, the reusability study of BZC proves to be effective through multiple adsorption and regeneration cycles. Initially, the phosphate removal remains high but eventually decreases from 92% to 70% in the third regeneration cycle, highlighting the robustness of the BZC. In conclusion, this study introduces a promising, cost‐effective novel BZC adsorbent derived from waste materials as a sustainable solution for wastewater treatment. Emphasizing efficiency, reusability, and potential contributions to environmentally conscious water treatment, the findings highlight the composite's significance in addressing key challenges for the removal of toxic pollutants from the aqueous solutions. Practitioner Points: A novel biochar‐zeolite composite (BZC) material has been synthesized.Excellent removal of dyes by BZC (~95%) was achieved as compared to their counterpartsThe kinetic studies performed suggest a pseudo‐second‐order model.BZC proves to be highly effective for multiple adsorption studies.Excellent reusability showed potential as a robust adsorbent [ABSTRACT FROM AUTHOR]

Refinery wastewater treatment was performed using a novel submerged tubular ceramic membrane bioreactor (STMBR) with the oleaginous hydrocarbonoclastic bacterium Rhodococcus opacus. A membrane‐based flux study with the STMBR was carried out to assess the performance of the tubular ceramic membrane. Continuous experiments with the STMBR achieved a maximum chemical oxygen demand (COD) removal of 84 %, with an average flux of 0.4 × 10−3 m3m−2s−1. To further enhance the COD removal efficiency, two STMBR were operated under the optimum conditions. Complete COD removal along with 2.98 g L−1 biomass growth was achieved during two‐stage STMBR operation. Furthermore, a toxicity assessment of the permeate water established its reuse potential. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Different bioreactors evaluated for refinery wastewater treatment by R. opacus. • Continuous operation mode with membrane cell recycle proved for better efficiency. • Low cost ceramic based tubular membrane was used for cell separation. • Hydrothermal liquefaction of biomass for suitable bio-fuel applications. Abstract Rapid consumption of fossil fuels has led to the search for alternative energy sources. Bio-fuels as an alternative energy source require cheap and abundantly available substrates to keep the economics of the production process low. The present study was therefore focused on utilizing raw refinery wastewater by the oleaginous bacterium Rhodococcus opacus for converting it into bio-oil via hydrothermal liquefaction of the lipid rich biomass produced during the treatment process. For treating the wastewater, different operating modes using a bioreactor were evaluated including batch, fed-batch, sequential batch, continuous and continuous with cell recycle using low cost tubular ceramic membrane. Among the different strategies, the continuous cell recycle system proved efficient in terms of complete removal of chemical oxygen demand (COD) (99%) and high lipid production (86%, w/w) at a hydraulic retention time (HRT) of 16 h (dilution rate of 0.06 h−1). Furthermore, the residual bacterial biomass from the bioreactor was treated by HTL to produce bio-oil which showed excellent bio-fuel properties. This study demonstrated the application of R. opacus for simultaneous wastewater treatment and production of bio-oil for energy application. [ABSTRACT FROM AUTHOR]

This study investigated utilization of refinery wastewater containing complex hydrocarbons as the sole substrate for lipid-rich biomass production by Rhodococcus opacus in batch system followed by its kinetic modeling. The effect of different initial chemical oxygen demand (COD) concentrations of the wastewater in the range 2.5–4.5 g L−1 was examined on biomass growth, COD utilization and lipid production by R. opacus. Almost complete utilization (96.8%) of COD present in the wastewater was achieved for an initial COD concentration of 2.5 g L−1 and the value decreased to 90% and 75% for 3.5 g L−1and 4.5 g L−1COD concentrations, respectively. Moreover, a maximum lipid production of 1.3 g L−1 was obtained for an initial COD concentration of 3.5 g L−1. The results of COD utilization by the bacterium were further fitted to substrate utilization kinetic models reported in the literature, which matched well with the Logistic model. Modified Gompertz model best fitted the kinetic data on biomass growth and lipid production by the bacterium. Whereas R. opacus biomass specific growth was found to be inhibited at a high COD concentration of the wastewater, Haldane model predicted the experimental specific growth rate values with a very high determination of coefficient (R2) value of more than 0.99. All these results suggest that refinery wastewater can serve as the sole substrate for lipid-rich biomass production by R. opacus , thereby adding value to the wastewater treatment process. Image 1 • Kinetics of refinery wastewater utilization and lipid-rich biomass production by Rhodococcus opacus are reported. • High concentration of organics inhibited biomass growth and lipid production. • Modified Gompertz model accurately described the biomass growth. • Experimental specific COD utilization rates are close to the Haldane model predicted values. • Estimated values of bio-kinetic model parameters indicate scale up potential of the process. [ABSTRACT FROM AUTHOR]