3.1 Thermal Treatment of Wastes
Thermal treatment of waste and its advanced form, plasma technology, constitutes an excellent option for the management of waste according to the recent directives of the European Commission, due to the fact that it leads to maximum reduction of waste’s volume as well as maximum energy recovery. After a general description of thermal waste treatment technologies, the environmental and energetic performance of the plasma technology is introduced. Next the sewage sludge treatment is presented as a case study, for which the application of a simulation model results in net electrical energy production of 2.4 MW for the treatment of 250 ton/day of waste material.

3.2 Water Purification and Recycling
3.2.1. Application of Supercritical Extraction in Industrial Waste Treatment (removal of phenol from aqueous solutions)

The removal of phenol from water, a common priority pollutant, using the Supercritical Fluid Extraction (SFE) is examined in this study. The thermodynamic modelling, the experimental measurements and the design of a process have been done. The thermodynamic modelling was succeeded through an EoS/GE model, the LCVM model, with very satisfactory results. The process was tested in a bench-scale pilot plant unit. The operating parameters of pressure, solvent flow rates, and cosolvent were studied. Using the developed thermodynamic model, the overall mass transfer coefficients for this process were also determined. Finally, a industrial scale process was designed and the operating parameters for this unit were optimised in terms of minimum cost.

More information and detailed results can be found in:

- Boukouvalas, Ch. J., Magoulas, K.G., and Tassios, D.P., "Application of Supercritical Fluid Extraction in Industrial Waste Treatment: thermodynamic modeling and Design", Separ. Sci. Technol., 33(3) (1998) 387-410.
- Boukouvalas, Ch., Louli, V., Magoulas, K., "Bench-scale application of Supercritical Fluid Extraction for the removal of phenol from aqueous solution", Separation Science & Technology, 36(10) (2001) 2279-2292.

3.2.2 Membrane Technology Applications
1. Purification of Water from the Diary Industry with an Ultrafiltration/Reverse Osmosis pilot unit.
The equipment of milk stations is cleaned using potable water. The produced wastes are biological treated and rejected. Water reuse could be accomplished by tertiary treatment of the rejected water. When membrane separation techniques are selected, three stages of separation are involved, in serial mode of operation:
  • (MF) Macro Filtration for suspended solids removal
  • (UF) Ultra Filtration for removal of bacteria and colloids
  • (RO) Reverse Osmosis for ion rejection

The pure water obtained, is recycled, and the wastes are returned to biological water treatment unit.

The following two engineering problems are related with the above flowsheet:
  • The Design Problem: Given the required water flowrate and quality characteristics, calculate the size of the equipment and the appropriate operating conditions, in order to reuse a portion of the water wastes, using membrane separation techniques.
  • The Rating Problem: Given the required water flowrate and quality characteristics, and the existing equipment characteristics, calculate the appropriate operating conditions, in order to reuse a portion of the water wastes.
Both problems can be formulated and solved effectively using the simulator developed in this work.

More information and detailed results can be found in:

- Voros, N.G., Fountoukidis, E., Magoulas, K.G., Maroulis, Z.B., Papadimitriou, L., "A combined UF/RO Waste water cleaning system: design, operation and Economic Assessment", Internat. Desal. Water Reuse, 9(3) (1999) 26-31.

2. Application of Integrated Treatment Processes on Tannery Wastewater for Water Reuse

Tanneries generate annually thousands of tons of heavy polluted liquid wastes in Greece (25-80 m3/ton of raw hides) containing contaminants, such as organic load as BOD and COD, salinity, suspended solids, sulphide, chloride, heavy metals. The objective of present study is the development of an integrated pilot unit for the treatment of tannery wastewater resulted from beam house operations focusing on the recovery and reuse of water. This pilot unit includes the stages of pre-treatment and primary, and the stage of final treatment, which introduces the use of integrated membrane processes, like microfiltration, ultrafiltration, nanofiltration and reverse osmosis. The operation of this unit aims to:

  • The production of water flow streams of different quality which:

    1. comply to the permissible limits for the wastewater disposal
    2. substitute the potable water in a variety of uses (i.e. tannery operations, washing of facilities, irrigation of corps etc.).

  • The minimization of the final waste volume and the reduction of its polluting load.

Laboratory-scale tests have been carried out using samples of tannery waste. The results of these tests have been used to design and operate a pilot treatment unit.

3.3 Polymer Recycling
3.3.1 Application of the Selective Dissolution/Precipitation Technique for the Recovery of Pure Polymers from Polymer Mixtures
A new method - the Selective Dissolution/Precipitation method - is being applied for the recycling of polymers/separation of polymer mixtures in a pilot plant unit. The method involves dissolution of each polymer of a mixture using properly selected solvent and dissolution temperature. The undissolved polymers are filtered out while the dissolved one is precipitated in grains by adding a properly selected anti-solvent. The procedure is repeated for the all polymers of the mixture. The precipitated polymers, after filtration, are dried while solvent and anti-solvent are separated with distillation and recycled. Solvent/anti-solvent screening was carried out using predictive thermodynamic models while the final selection was based on laboratory experiments.

The mixture to be separated consists of poly(vinylchloride) (PVC), polystyrene (PS), polyprolylene (PP), high density polyethylene (HDPE) and low density polyethylene (LDPE), which are the most often met polymers (more than 80%) in municipal solid waste. The polyolefins are separated from the rest of the polymers with floatation.

The two mixtures obtained are further separated either by using a common solvent and changing only temperature or by using different solvent for each polymer.The experiments carried out so far indicate that this method is a promising one and can be successfully applied for the recycling of polymers in the municipal solid waste. Its financial feasibility seems to depend on the environmental protection policy of EU, which will become more strict in the next years.

More information and detailed results can be found in:

- Pappa, G.D., Boukouvalas, Ch., Giannaris, K., Ntaras, N., Zographos, V., Magoulas, K., Lygeros, A., Tassios, D., "The Selective Dissolution/Precipitation technique for polymer recycling: A Pilot Unit Application", Conservation, Resources & Recycling, 34(1) (2001) 33-44.

3.4 Separation Processes
3.4.1 Recovery of Near-Anhydrous Ethanol as Gasoline Additive from Fermentation Products

The use of near-anhydrous ethanol, obtained from fermentation products through low pressure distillation, as a gasoline additive is examined. To this purpose, a reliable model for prediction of the azeotropic composition of ethanol-water mixture as function of the pressure is presented. It is developed by considering the available thermodynamic consistent experimental data and using the Wilson and the Virial equations for the liquid and vapor phase nonideality respectively.

It is concluded that, for an area with no extremely cold winters - minimum ambient temperature 20oC - alcohol with 96.5% (wt) purity can be used in a 90/10 (vol.) gasohol mixture. Such alcohol can be produced with a single distillation column operating at 140 mm Hg pressure with an energy consumption of 5150 MJ/kg of product; or, with a system of two columns with lower energy consumption but higher capital cost. These energy consumptions are very sensitive to the accuracy of the predicted azeotropic composition at the operating pressures.

These results have also been confirmed in a pilot unit application.

More information and detailed results can be found in:

- Boukouvalas, Ch., Markoulaki, E., Magoulas, K. and Tassios, D.P., "Recovery of Near-Anhydrous Ethanol as Gasoline Additive from Fermentation Products", Separ. Sci. Technol., 30(11) (1995) 2315-2335

3.4.2 Recovery of Fructose Laurate Produced through Enzymatic Esterification
Though laboratory scale recovery methods for sugar–fatty acid (FA) esters have been developed (column and preparative chromatography), larger scale methods involving unit operations (distillation, extraction, evaporation etc.) have not been presented. In this work a process based on the successive application of unit operations is presented for the industrial scale recovery of sugar–FA esters. The crucial step for the recovery, the sugar–FA monoester/FA separation, is accomplished through liquid–liquid extraction. The feasibility and efficiency of the suggested key separation are demonstrated by the experimental equilibrium partition coefficients of lauric acid (LA) and fructose (mono- and di-) laurate in mixtures of hexane/alcohol (methanol or ethanol)/water, measured in this work, and the consequent calculations for a counter-current LLE column.

More information and detailed results can be found in:

- Spiliotis, N., Voutsas, E., Magoulas, K., Tassios, D., "Recovery of Fructose Laurate produced through Enzymatic Esterification", Separation & Purification Technology, 19 (2000) 229.

3.5 Supercritical Extraction: Recovery of High Valued Components from Natural Products
The objective of this project is the recovery of high valued components from natural products using supercritical CO2. The following cases have been studied in the SFE-500 pilot apparatus
  • Recovery of celery and parsley seed oil
  • Recovery of antioxidants from red grape marc
  • Supercritical extraction and fractionation of mastic gum oil

The effect of various process parameters- pressure, temperature, solvent flow rate, particle size- in the extraction rate has been examined.

More information and detailed results can be found in:

- Papamichail, I., Louli, V., Magoulas, K., "Supercritical fluid extraction of celery seed oil", Journal of Supercritical Fluids, 18(3) (2000) 213-226.
- Louli, V., Folas, G., Voutsas, E., Magoulas, K., "Extraction of Parsley Seed Oil by Supercritical CO2", J. Supercritical Fluids, 30 (2004) 163.