The bioaccumulation of chromium from retan chrome liquor by Spirulina fusiformis was investigated under laboratory as well as field conditions. At the optimal conditions, metal ion uptake increased with initial metal ion concentration up to 300mg/l. The effect on various physico-chemical parameters like total solids (TS), total dissolved solids (TDS), total suspended solids (TSS), chlorides, sulphates, phenols, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) and biochemical studies related to biomass, chlorophyll-a and protein were also carried out. The present study indicates that S. fusiformis is very effective in removal of chromium (93-99%) besides removing other toxicants from retan chrome liquor. The sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and FTIR studies indicate the interaction/complexation between Cr and alga. The mechanism involved in bioaccumulation of chromium is also discussed. The process when upgraded can be applied for detoxification of tannery effluents.

Increasing concentrations of carbon dioxide (CO2), one of the important greenhouse gases, due to combustion of fossil fuels, particularly burning coal, have become the major cause for global warming. As a consequence, many research programs on CO2 management (capture, storage, and sequestration) are being highlighted. Biological sequestration of CO2 by algae is gaining importance, as it makes use of the photosynthetic capability of these aquatic species to efficiently capture CO2 emitted from various industries and converting it into algal biomass as well as a wide range of metabolites such as polysaccharides, amino acids, fatty acids, pigments, and vitamins. In addition, their ability to thrive in rugged conditions such as seawater, contaminated lakes, and even in certain industrial wastewaters containing high organic and inorganic nutrients loads, has attracted the attention of researchers to integrate carbon capture and wastewater treatment. Algae offer a simple solution to tertiary treatments due to their nutrient removal efficiency, particularly inorganic nitrogen and phosphorus uptake. The algal–bacterial energy nexus is an important strategy capable of removing pollutants from wastewater in a synergistic manner. This review article highlights the mechanism involved in biological fixation of CO2 by microalgae, their cultivation systems, factors influencing algal cultivation in wastewater and CO2 uptake, the effect of co-cultivation of algae and bacteria in wastewater treatment systems, and challenges and opportunities.

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Trivalent chromium in the form of basic chromium sulfate (BCS) is used for tanning hides/skins and is a strong pollutant of the soil and water bodies. Significant quantities of unutilized chemicals, such as sulfates, chlorides, are also discharged, contributing to high levels of total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), etc. Though many treatment techniques are being practiced, biotechnological methods are gaining importance. Biosorption is recognized as a costeffective technology worldwide; one potential sorbent being blue-green algae (BGA), for treating metal-bearing effluents. This work studies the feasibility of using a species each of Spirulina, Oscillatoria, and Synechocystis, individually and as a consortium, as sorbents to remove Cr 3þ from a segregated stream, viz. exhaust chrome liquor (ECL) and synthetic BCS solution. The species studied were found to be effective in removing Cr 3þ considerably at varying concentrations, besides reducing sulfates, BOD, COD, etc. The results of ECL experiments were more encouraging than those for BCS solution. The kinetic data on Cr 3þ sorption onto algal biomass fit well into the pseudo-second order model. The equilibrium data were analyzed using the classic Langmuir and Freundlich isotherm models, yielding good fits. The results of the experiments indicate that algal consortia could be good alternatives to the conventional treatment methods for leather and other industrial wastewaters containing chromium.