Some Bolivian industries use solid soybean oil residues as raw material in their soap manufacturing processes because of their high fat content (30-60%). Nevertheless, in the saponification step, a considerable amount of bad smell odours (mainly ammonia) is produced and expelled to the surrounding neighbourhoods, generating an important negative environmental impact.

Addressing this problem, a laboratory-scale study that deals with the development of a hybrid system for odour treatment generated in the saponification process of soybean oily solid residues is presented. The system consists in a gas scrubber for ammonia and soluble organic gases with water and a fog scrubbing contactor in which remnant non soluble organic compounds are removed by means of a nebulized emulsion of essential oils.

Soybean solid residues and gases produced in their saponification were characterized both physically and chemically. Numerous experimental runs were carried out for the assessment of efficiency of three treatment systems that were designed and constructed in our laboratory: A closed system which was used for characterization of vapours and for establishing relations between essential oil doses and odour concentrations; a contact system for nebulized essential oils and odorous gases and the mentioned hybrid system.

The untreated gases mainly contain water soluble/non soluble volatile organic gases (VOC’s), ammonia and carbon dioxide. Solid residues with higher protein content generate higher amounts of free ammonia. Good fit relations of VOC concentrations and Minimum Detectable Threshold Odour Concentration (MDTOC) with essential oil doses were obtained. Distillate product of eucalyptus oil was shown to be the most efficient and economic option for treatment of the three types of soybean oil residues proved. Offensive perception of bad smells was completely eliminated by use of the hybrid system which proved to be the most efficient. Experimental methods and apparatus used in this study may be useful to carry out similar investigations on odour problems that presently occur in several and diverse local and national industries.

Investigación & Desarrollo, No 5, pág. 33-52, (2005)