Many industries, such as those belonging to the textile, wine, and paper industry, consume huge volumes of water and, as a result, generate a large amount of contaminated water containing persistent colour pollutant compounds. These compounds represent an environmental and health threat due to their well-known associated problems, such as carcinogenicity, toxicity and mutagenicity. Furthermore, they entail a great environmental impact when discharged in aquatic environments, perceptible at very low concentrations, creating an undesirable visual impact, which, in many cases, does not meet the degree of conformity under the current directives on the wastewater treatment for industrial effluents (Directive 91/271 / EEC).
The solution proposed by the research group Chemical Engineering at the University of Vigo, is the use as adsorbent of peat, or a similar lignocellulosic material, immobilized in calcium alginate beads. This process is efficient, cheap and environmentally friendly, unlike other processes and technologies. In fact, the utilization of peat instead of activated carbon as industrial adsorbent has the advantage that peat requires no activation, unlike activated carbon, reducing operating costs. In addition, the low cost of the adsorbent would be translated into significant economic benefits. Moreover, depending on the contaminant removed from the waste effluent, the exhausted adsorbent may be used as soil fertilizer at its end of life.
New and innovative aspects
The bioadsorbent proposed by this research group consists in peat encapsulated in hydrogel beads, enhancing its competitiveness in contrast to usual adsorbents. The advantages of this adsorbent compared to other bioadsorbents and technologies are summarized below: • Efficient wastewater treatment: high colour reductions and micronutrients removal from industrial water effluents. • Environmentally respectful process: from the utilization of a sustainable and cheap adsorbent as peat. • Significant reduction of the operating costs: the immobilization process in calcium alginate beads reduces significantly the operating costs at industrial scale. • Possibility of using the exhausted bioadsorbent, depending on the substances extracted from the water stream, as a new generation of fertilizers for the slow delivery of micronutrients and organic matter contained in the polymeric matrix to soil, opening new possibilities for the recycling of bioadsorbents with agronomic interest. • Entrapped peat not only could be used to remove dyes from water ex situ, but it also may be used in in situ treatments.
Main advantages of its use
Activated carbon is the oldest adsorbent known and it is regarded as one of the most effective methodologies for treatment in both liquid and gaseous phases. This material is widely used due to its exceptional properties, such as its extended surface area, its microporous structure, its high adsorption capacity and high degree of surface reactivity. However, commercial activated carbons are expensive and not ecofriendly. Basically, agroindustrial wastes can undergo two different kinds of processes to get activated: physical or chemical. Physical activation involves the transformation of the residue into char and is usually carried out in two steps. In the first stage, carbonization, a normally non-porous char is obtained by pyrolysis of the precursor at temperatures between 600-900°C in an inert atmosphere (usually nitrogen). The second part of the process implies the proper activation of the char by putting it in contact with an oxidising gas (CO2 or steam) at 600-1200ºC in order to remove the more disorganised carbon and to develop an appropriate microporous structure. Chemical activation, on the other hand, implies the utilization of chemicals like H3PO4, KOH or NaOH, to impregnate the precursor before heating it at high temperatures (between 450 and 900ºC, depending on the chemical) and under nitrogen flow. Contrarily to activated carbon, the Chemical Engineering research group proposes the utilization of greener adsorbents obtained by the spontaneous biodegradation of peat as well as the other materials, like lignocellulosic residues, and entrapped in calcium alginate beads. The entrapping of these adsorbents will reduce the problems derived from the separation of adsorbents and the water streams.
Raw peat contains lignin, cellulose, fulvic and humic acid as major constituents. These components, especially lignin and humic acid, contain polar functional groups, such as alcohols, aldehydes, ketones, carboxylic acids, phenolic hydroxides and ethers, that can be involved in chemical bonding. It was observed that peat tends to have a high cation exchange capacity and is an effective sorbent for the removal of dyes. However, when peat is used directly as an adsorbent, many limitations exist: natural peat has a low mechanical strength, high affinity for water, poor chemical stability, tendency to shrink and/or swell, and to leach fulvic acid. Therefore, the Chemical Engineering research group proposes the immobilization of peat in calcium alginate beads. For example, decolouration of vinasses from winery industry can be achieved using this bioadsorbent formulated with 2% of peat, 3% of sodium alginate and 0.05 M of calcium chloride.
This technology has potential application in industries that generate large amount of dye compounds wastewater, such as textile, food, pharmaceutical or paper industries, among others. Besides, this new technology is also interesting for companies that develop wastewater treatment equipment or industrial adsorbent suppliers.
Intellectual property status
Current development status
Testing results available.
Desired business relationship