Green synthesis of Microalgal biomass-silver nanoparticles composite showing antimicrobial activity and heterogenous catalysis of nitrophenol reduction

In this study we have demonstrated an integrated approach for utilization of microalga Scenedesmus sp, generated during CO2 sequestration, in fabrication of catalytic and antimicrobial silver nanoparticles composite. The algal biomass was grown in open raceway pond of 30,000 L scale for CO2 sequestration, after which it was harvested and dried. The dried biomass served as a reducing and immobilizing agent for silver nanoparticles. The biomass-silver nanoparticles composite was used for the first time, as a heterogenous catalyst for reduction of a prominent industrial pollutant, p-Nitrophenol, in aqueous medium under ambient condition. Series of experiments were conducted to evaluate the effect of calcination temperature, load and reuse of the material on its catalytic efficiency. The calcined composite material was found to be an excellent catalyst for reduction of p-Nitrophenol. As low as 5 mg mL− 1 calcined material could catalyse the reduction of more than 95% p-Nitrophenol at the rate of 0.60 mg L− 1 min − 1 in aqueous solution at 10 ppm concentration. The efficiency of catalysis was evaluated for ten cycles of reuse. The material was found to be a potential candidate as a reusable heterogenous catalyst for designing continuous flow system for remediation of industrial effluents rich in p-Nitrophenol. Furthermore the material served as a good antimicrobial agent against pathogenic bacteria and fungi. Two strains each of gram + ve and gram –ve bacteria and three strains of fungi were used in the antimicrobial studies using well diffusion method.

Growth Kinetic Model for Microalgae Cultivation in Open Raceway Ponds: A System Dynamics Tool

Microalgae culture has the potential to play an essential role in the application of circular economy principles. Microalgae cultivation allows utilizing industrial side-waste streams while ensuring biomass for a wide range of applications in the industrial sector. Specifically, cultivation in outdoor open raceway ponds are a preferred solution due to low costs, ease of operation and large-scale application. However, the economic viability of the cultivation system largely depends on the amount of biomass produced, the technology implemented and the microalgae species and strains. For this purpose, screening of numerous physical, chemical, and environmental factors affecting microalgae growth must be performed before implementing large-scale microalgae cultivation systems. Furthermore, to obtain the highest biomass yield, the design and operating parameters for open raceway pond cultivation must be investigated in depth. Therefore, this study proposes a kinetic growth model for microalgae cultivation in open raceway ponds based on System Dynamics modelling approach. The proposed model aims at overcoming the major problems of existing growth evaluation tools such as separate assessment of different parameters, high complexity, time consumption and other challenges. The proposed system dynamics model proves to be a simple yet powerful tool for modelling the behaviour of algae biomass in an open raceway pond.

Production of Phycocyanin from Marine Cyanobacteria in Open Raceway Pond

Phycocyanin is one of the major light harvesting accessory pigment present in microalgae and cyanobacteria. This water-soluble pigment protein exhibits antioxidant, anti-inflammatory, and neuroprotective effects. Application of this pigment has also been used in dietary nutritional supplements in many food, nutraceutical, cosmetic, and biotechnology industries. In the present study phycocyanin was extracted from locally isolated marine cyanobacteria Geitlerinema sp. Geitlerinema sp. showed a higher growth during the summer perioed of 0.75 g/L and 0.54 g/L. Similarly, the maximum Phycocyanin obtained was up to 7.1% during summer period.

Pretreatment of Cyanobacterial Chroococcidiopsis: Biomass prior to Hydrothermal Liquefaction for Enhanced Hydrocarbon Yield and Energy Recovery

Chroococcidiopsis sp. was grown in 200 L open raceway pond. Biomass density and average biomass productivity were 0.41 g/L and 16.1 g/m2/d. Chroococcidiopsis biomass was harvested by self-settling. Self settled biomass was further subjected to centrifugation to obtain a biomass paste with 25-30% solid content. Centrifuged biomass was dried at 80 °C overnight and used as a feedstock for pretreatment step. Biomass was pretreated in water at 105 °C for 15 minutes. A slurry containing 15 wt% pretreated and untreated biomass (control) in deionized water was prepared and subjected to hydrothermal liquefaction for biocrude oil production. Hydrothermal liquefaction for both pretreated and untreated biomass was conducted at temperatures ranging from (275, 300, 325, 350 °C) in a 500 mL high-pressure PARR reactor for 30-minute reaction holding time. Maximum biocrude yields for pretreated and untreated biomass was 42.4 % and 26.4 % based on ash free dry weight basis. Biocrude oil was characterized for hydrocarbons using GC-MS technique. Biocrude oil obtained from pretreated and untreated biomass contained 58.9% and 41.01% (C8-C19) hydrocarbons. Higher heating values for biomass and biocrude oil were 16.93 and 31.28 MJ/kg, with an energy recovery value of 41.1%.

The Strategies for the Production of Biodiesel through Eco-Friendly Microalgal Systems

The fast depleting energy sources and other environmental concerns, like carbon emissions, have led the scientific community on a race against time to find an ecofriendly, sustainable and renewable source of energy. Biofuels obtained from domestic used materials cannot practically satisfy the existing demand for an industrial fuel. Biodiesel is mono-alkyl esters of vegetable oils or animal fats. The major advantage of biodiesel is that it can be used directly into existing engines without any modifications. One of the potential sources for renewable biodiesel production which can effectively supply biodiesel for international and industrial demand is microalgae. Besides production of biofuels microalgae have been seen as a potential source for a number of areas including pharmaceuticals, nutrition and aquaculture. This review discusses on the different aspects, challenges and current scenario in the biodiesel production from microalgae. Cultivation of a high yielding marine microalgal strain in a very economical and well scrutinised open raceway pond could prove to be the key to future of energy sector. Various lipid enhancement methods and proposed culture methods are also discussed. On an industrial perspective, a well-engineered and continuously monitored open raceway pond for cultivation of marine micro algae seems to be a promising economically viable method for production of biofuel.