Potential of using green adsorbent of heavy metal removal from aqueous solutions: Adsorption kinetics, isotherm, thermodynamic, mechanism and economic analysis

Heavy metals are discharged into water from various industries. They can be toxic or carcinogenic in nature and can cause severe problems for humans and aquatic ecosystems. Thus, the removal of heavy metals from wastewater is a serious problem. The adsorption process is widely used for the removal of heavy metals from wastewater because of its low cost, availability and eco-friendly nature. Both commercial adsorbents and bioadsorbents are used for the removal of heavy metals from wastewater, with high removal capacity. This review article aims to compile scattered information on the different adsorbents that are used for heavy metal removal and to provide information on the commercially available and natural bioadsorbents used for removal of chromium, cadmium and copper, in particular.

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Heavy metal removal from wastewater using various adsorbents: a review

An initiative has been taken to develop different solid, liquid, and gaseous biofuels as the alternative energy resources. The current research and technology based on the third generation biofuels derived from algal biomass have been considered as the best alternative bioresource that avoids the disadvantages of first and second generation biofuels. Algal biomass has been investigated for the implementation of economic conversion processes producing different biofuels such as biodiesel, bioethanol, biogas, biohydrogen, and other valuable co-products. In the present review, the recent findings and advance developments in algal biomass for improved biofuel production have been explored. This review discusses about the importance of the algal cell contents, various strategies for product formation through various conversion technologies, and its future scope as an energy security.

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Scope of algae as third generation biofuels

Recent advances in biorefinery of astaxanthin from Haematococcus pluvialis.

Many authorities have reached the conclusion that using fossil fuels, as the main source of energy to satisfy the increasing global energy demand, is ultimately unsustainable. This is because of depleting resources, and also because, if this approach is followed, emissions of carbon dioxide would continue to build up. Consequently, research on biofuel, that is fuel made from biomass, derived from materials that were recently living, has attracted attention. In this context, the generation of biofuels from algae shows promise for the following reasons. The algae can be grown quickly, all the materials produced are non-toxic and biodegradable, and during this growth there is an opportunity to cause greenhouse gas fixation. Also, since growing algae does not need arable land, it can be grown without competing with food or feed crops, the fuel derived from it being a “third generation” biofuel.

This paper describes different types of algae (microalgae and seaweeds), and presents different technologies employed in making biofuels (biogas and biodiesel) from them.

Technologies and developments of third generation biofuel production

Algae are a filamentous waste plant growing in any type of water such as fresh, sea water etc. Normally algae are regarded as a menace in water bodies. Algae oil is an interesting sustainable feedstock for biodiesel manufacturing. There are various methods for extracting the oil from algae, such as mechanical pressing, hexane solvent extraction etc. The paper discusses experimental method developed for the extraction of oil from algae which is obtained from open pond system. It is observed that the solvent extraction method recovers almost all the oil and leaves behind only 0.5% to 0.7% residual oil in the raw material. Because of the high percentage of recovered oil, solvent extraction is found to be an effective method for extraction of oils and fats, but is having disadvantage of being costly as compared to expeller method. An experimental investigation shows that expeller pressing method can recover 75% of the oil from algae. Even though expeller pressing method is an economical method than the hexane solvent extraction method, further to make this method more effective, some modifications in the design of expeller are required which will increase the recovery of oil.

Extraction of Oil from Algae by Solvent Extraction and Oil Expeller Method

The adsorption process is being widely used by various researchers for the removal of heavy metals from waste streams and activated carbon has been frequently used as an adsorbent. Despite its extensive use in the water and wastewater treatment industries, activated carbon remains an expensive material. In recent years, the need for safe and economical methods for the elimination of heavy metals from contaminated waters has necessitated research interest towards the production of low cost alternatives to commercially available activated carbon. Therefore there is an urgent need that all possible sources of agro-based inexpensive adsorbents should be explored and their feasibility for the removal of heavy metals should be studied in detail. The objective of this study is to contribute in the search for less expensive adsorbents and their utilization possibilities for various agricultural waste by-products such as seaweed, algae, chitosan, egg shell and saw dust etc. for the elimination of heavy metals from wastewater.

Removal of heavy metals from wastewater using low cost adsorbents : a review

The quantum of plastic waste in municipal solid waste (MSW) is increasing due to increase in population, urbanization, development activities and changes in life style, which leading widespread littering on the landscape. Thus disposal of waste plastic is a menace and become a serious problem globally due to their non-biodegradability and unaesthetic view. Since these are not disposed scientifically & possibility to create ground and water pollution. This waste plastic partially replaced the conventional material to improve desired mechanical characteristics for particular road mix. In the present paper developed techniques to use plastic waste for construction purpose of roads and flexible pavements has reviewed. In conventional road making process bitumen is used as binder. Such bitumen can be modified with waste plastic pieces and bitumen mix is made, which can be used as a top layer coat of flexible pavement. This waste plastic modified bitumen mix show better binding property, stability, density and more resistant to water.

Utilization of Waste Plastic in Asphalting of Roads

Enzymes are proteins, which act as catalysts. Enzymes lower the energy required for a reaction to occur, without being used up in the reaction. Many types of industries, to aid in the generation of their products, utilize enzymes. Examples of these products are; cheese, alcohol and bread. Fermentation is a method of generating enzymes for industrial purposes. Fermentation involves the use of microorganisms, like bacteria and yeast to produce the enzymes. There are two methods of fermentation used to produce enzymes. These are submerged fermentation and solid-state fermentation. Submerged fermentation involves the production of enzymes by microorganisms in a liquid nutrient media. Solid-state fermentation is the cultivation of microorganisms, and hence enzymes on a solid substrate. Carbon containing compounds in or on the substrate are broken down by the microorganisms, which produce the enzymes either intracellular or extracellular. The enzymes are recovered by methods such as centrifugation, for extracellularly produced enzymes and lysing of cells for intracellular enzymes. Many industries are dependent on enzymes for the production of their goods. Industries that use enzymes generated by fermentation are the brewing, wine making, baking and cheese making.

V. C. Renge

Papers

Extraction of Oil from Algae by Solvent Extraction and Oil Expeller Method

Removal of heavy metals from wastewater using low cost adsorbents : a review

Utilization of Waste Plastic in Asphalting of Roads

Enzyme synthesis by fermentation method : a review

A review utilization of waste plastic in asphalting of roads