Phycoremediation potential ofTetradesmus sp.SVMIICT4in treating dairy wastewaterusingFlat-Panel photobioreactor

Biotreatment of Industrial Wastewater using Microalgae: A Tool for a Sustainable Bioeconomy

Fresh water is one of the essential sources of life, and its requirement has increased in the past years due to population growth and industrialization. Industries use huge quantities of fresh water for their processes, and generate high quantities of wastewater rich in organic matter, nitrates, and phosphates. These effluents have contaminated the freshwater sources and there is a need to recycle this wastewater in an ecologically harmless manner. Microalgae use the nutrients in the wastewater as a medium for growth and the biomass produced are rich in nutrition that can cater growing food and energy needs. The primary and secondary metabolites of microalgae are utilized as biofuel and as active ingredients in cosmetics, animal feed, therapeutics, and pharmaceutical products. In this review, we explore food processing industries like dairy, meat, aquaculture, breweries, and their wastewater for the microalgal growth. Current treatment methods are expensive and energy demanding, which indirectly leads to higher greenhouse gas emissions. Microalgae acts as a potential biotreatment tool and mitigates carbon dioxide due to their high photosynthetic efficiency. This review aims to address the need to recycle wastewater generated from such industries and potentiality to use microalgae for biotreatment. This will help to build a circular bioeconomy by using wastewater as a valuable resource to produce valuable products.

An investigation on removal of ciprofloxacin and norfloxacin by phycoremediation with an emphasis on acute toxicity and biochemical composition

Ciprofloxacin (CIP) and norfloxacin (NOR) belong to the class of emerging contaminants that are frequently detected in the aquatic environment as a binary mixture, responsible for the development of antibiotic-resistant genes and antibiotic-resistant bacteria. This study aims to investigate five different algal species Chlorella vulgaris (Cv), Chlorella pyrenoidosa (Cp), Scenedesmus obliquus (So), Tetradesmus sp (T) and Monoraphidium sp (M) for their tolerance and removal of binary mixture. The effects on biochemical composition in the algal species concerning the binary mixture and its removal efficiency are first reported in this study. The acute toxicity (96 h EC50) values are in the order of So > Cp > T > M > Cv, Chlorella vulgaris is the most sensitive algal species with 17.73 ± 0.24 mg/L and Scenedesmus obliquus is the least sensitive algal species with 39.19 ± 0.79 mg/L. The removal efficiency of the binary mixture was found to be in the order of So > Cp > T > M > Cv, Scenedesmus obliquus removed CIP (52.4%) and NOR (87.5%) with biodegradation as the major contributing removal mechanism. Furthermore, less toxic biotransformed products were detected in Scenedesmus obliquus and the biochemical characterization revealed that the growth-stimulating effect is higher with lipid (35%), carbohydrate (18%), and protein (33%) providing an advantage in the production of valuable biomass.

Dairy wastewater treatment using Monoraphidium sp. KMC4 and its potential as hydrothermal liquefaction feedstock

Monoraphidium sp. KMC4 was cultivated mixotrophically for simultaneous treatment of dairy wastewater and biomass production. The KMC4 was cultivated with varying chemical oxygen demand concentrations of simulated synthetic dairy wastewater. Monoraphidium sp. KMC4 outperformed in 50% strength with biomass concentration of 1.47 g L^-1. A significant change in biomass of 3.69 g L^-1 was achieved after maintaining the pH of algal culture. The nutrient consumption promoted microalgal growth in the form of biomass productivity (122 mg L^-1 day^-1), accumulation of carbohydrate (28.73±1.6 wt%), protein (48.50±1.3 wt%), and lipid (20.29±2.3 wt%). This strain showed efficacious performance in treating simulated synthetic dairy wastewater obtaining biomass for various applications. The algal biomass derived from wastewater reported a significant volatile matter content and higher heating value. The biomass demonstrates satisfactory thermal degradation behavior which reveals its feasibility as feedstock for thermochemical conversion to biocrude. The integration of biomass production in high-scale raceway pond along with biocrude production is a promising pathway toward the generation of green energy for replacing traditional fossil fuels..

Comparative appraisal of nutrient recovery, bio-crude, and bio-hydrogen production using Coelestrella sp. in a closed-loop biorefinery

A closed loop algal-biorefinery was designed based on a three-stage integration of dairy wastewater (DWW) treatment, hydrothermal liquefaction (HTL) of defatted algal biomass, and acidogenic process in a semi-synthetic framework. Initially, Coelestrella sp SVMIICT5 was grown in a 5 L photo-bioreactor and scaled up to a 50 L flat-panel photo-bioreactor using DWW. The microalgal growth showed higher photosynthetic efficiency, resulting in a biomass growth of 3.2 g/L of DCW with 87% treatment efficiency. The biomolecular composition showed 26% lipids with a good fatty acid profile (C12-C21) as well as carbohydrate (24.9%) and protein (31.8%) content. In the second stage, the de-oiled algal biomass was valorized via HTL at various temperatures (150°C, 200°, and 250°C) and reaction atmospheres (N2 and H2). Among these, the 250°C (H2) condition showed a 52% bio-crude fraction and an HHV of ∼29.47 MJ/kg (bio-oil) with a saturated hydrocarbon content of 64.3% that could be further upgraded to jet fuels. The energy recovery (73.01%) and elemental enrichment (carbon; 65.67%) were relatively greater in H2 compared to N2 conditions. Finally, dark fermentation of the complex-structured HTL-AF stream resulted in a total bio-H2 production of 231 ml/g of TOC with a 63% treatment efficiency. Life cycle analysis (LCA) was also performed for the mid-point and damage categories to assess the sustainability of the integrated process. Thus, the results of this study demonstrated comprehensive wastewater treatment and valorization of de-oiled algal biomass for chemical/fuel intermediates in the biorefinery context by low-carbon processes.

Biomass production and phycoremediation of microalgae cultivated in polluted river water

The present study evaluated polluted river water as a medium for the growth of oleaginous microalgae under mixotrophic conditions. Microalgae grow in the medium and produce biomass, pigments, and lipids with the removal of pollution loads from wastewater. Selenastrum sp. SL7 produced maximum biomass and lipids of 660 mg L^-1 and 194.5 mg L^-1, respectively. Fatty acid profiling data showed that elevated saturated fatty acid production and major fatty acids found in lipid from these algae were palmitic acids, oleic acid, stearic acid, linolenic acid, and linoleic acid. The low percentage of polyunsaturated fatty acids of EPA was also detected. Water quality in terms of pH, DO, TDS, COD, and BOD was significantly improved. The use of this medium for microalgae cultivation not only improves the biomass and lipid yields but also serves as an excellent means of phycoremediation of pollutants in waste streams with value addition and environmental benefits.

Mixotrophic cultivation of Monoraphidium sp. In dairy wastewater using Flat-Panel photobioreactor and photosynthetic performance

Monoraphidium sp. SVMIICT6 was isolated and mixotrophically cultivated in a flat-panel photobioreactor (8 days) to treat synthetic dairy wastewater. COD, nitrates, and phosphates removal efficiencies were 75%, 85%, and 60% respectively. The nutrient removal supported the growth of microalgae in terms of biomass productivity (50 mg L^-1d^-1), and accumulation of carbohydrate (228.8 mg g^-1), protein (88.8 mg g^-1), and lipid content (25%). Elemental analysis of microalgal biomass revealed carbon (50.6%) as a major fraction. Quantum yield and electron transport rate (ETR) from PSII to PSI increased with time correlating well with chlorophyll pigments (89.53 mg g^-1). The lipid profile resulted in a major fraction of Heptadecanoic acid (C17:0; 51.5%), followed by Myristoleic acid (C14:1; 24.3%) with potent nutraceutical properties. The isolated strain showed efficient treatment of dairy wastewater yielding biomass for diverse applications.