Future trends

Research is needed to examine whether CGAs can be used to separate proteins from complex mixtures (Jauregi and Varley, 1998). Assessing the use of CGAs for recovery of valuable products from cheese whey and vegetable-oil-containing wastewater should be carried out. Continuous operation of this technology should also be evaluated. Further research is needed to optimize the yield of gases and ethanol from different kinds of food processing wastes using reactive-separation technology. Further research is also required to examine the effectiveness of AC/EC to remove organic contaminants from diluted wastewaters. Optimization of many of the aforementioned separation processes has not yet been accomplished. Finally, detailed studies need to be made of the elemental composition of the byproducts recovered from different food processing wastes using the different separation technologies.

298 Handbook of waste management and co-product recovery 12.5 Conclusions

Many separation technologies are being used to treat wastes and wastewaters from the food processing industry. This chapter reviews the theories behind, and the applications of, many of the different technologies. The most important design parameters for each are presented.

The major purpose of using the various separation technologies is to reduce environmental pollution by the waste or wastewater discharge. The recovery of valuable products for human, animal or industrial uses is, in many cases, a secondary purpose. In some cases, the product recovery is necessary in order to make the treatment process an economically viable option. The separation technologies use one or more of the physical, thermal, chemical or electrical processes or a combination of them. The choice among different technologies depends mainly on the characteristics of the waste stream, the technical and financial considerations, and the final use of the recovered products. Increasing the number of separation steps increases the purity of the final product, but sometimes at an unacceptably high cost.

Some physico-chemical processes do not usually provide the selectivity necessary for producing valuable products for reuse. Screening and sedimentation are applied as a primary treatment of wastewater. Crystallization can be applied for protein recovery from milk processors. Chemical coagulation is applied for removal of insoluble colloidal particles. Many inorganic or organic coagulants of different origin (natural or synthetic) are currently used. The most preferred ones are those produced from biological origins, such as chitosan, because the recovered product can be safely used as animal/human feed additives. Another physico-chemical process uses CGAs; it can be a cost-effective technology for the recovery of protein and oil products from wastewaters. Some other technologies, such as reactive separation and EC, can also be used for treatment of food processing wastewater. Reactive separation could be a promising technology for the recovery of hydrogen, methane, ethanol and volatile fatty acids from food processing wastes. EC was found to be effective for the removal of oil and grease from food processing and olive mill wastewaters.

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