ELSEVIER Bioresource Technology 48 (1994) 65-70 Printed in Great Britain. All rights reserved 0960-8524/94/$7.00 BIOLOGICAL CONVERSION OF POULTRY PROCESSING WASTE TO SINGLE CELL PROTEIN G. D. Najafpour, K. T. Klasson, M. D. Ackerson, E. C. Clausen & J. L. Gaddy Department of Chemical Engineering, Universityof Arkansas, 3202 Bell Engineering Center, Fayetteville,Arkansas 72701-1201, USA (Received 3 May 1993; revised version received 5 November 1993; accepted 8 November 1993) Abstract In the processing of poultry for the production of pre- pared foods such as soups and frozen dinners, waste- water is generated containing significant quantities of fats, protein and starchy materials. These materials must be removed from the wastewater before it is discharged. Typical recovery consists of removing the solids through a combination of dissolved air flotation and filtration. The solids can then be rendered and utilized as poultry feed. This paper investigates an alternative to traditional processing in biologically producing valuable single cell protein from poultry processing waste. The results of fermentation experiments to produce single cell protein by both direct and indirect routes are presented. Key words: Poultry processing waste, single cell protein, enzymatic hydrolysis. INTRODUCTION Increased public concern for the environment has created pressure on industry to minimize waste dis- charge into the environment. In many instances, even when particular waste treatment practices seem com- patible with the local environment, industry is forced to change those practices due to the public's growing concern about future harmful effects of certain long- term waste treatment techniques. While public pressure poses short-term problems for industry, the modifications are likely to prove bene- ficial in the long run. The processing of waste streams is usually not economically driven, but instead, is driven by state and federal regulations as well as public pressure. As regulations tighten, the cost of processing wastes increases sharply. This forces industry to examine the entire process, not just waste processing, and often leads to process changes which result in a more efficient and economical process. It may be possible to convert waste streams into valuable product streams by simple separation and recovery, or by biological conversion. Many products can be produced biologically from process waste. However, often the biological process route cannot 65 compete economically with the conventional industrial practice. One advantage of biological processes is the flexibility of the microorganisms to adapt to different feedstocks. Therefore, when combined with the treat- ment of process waste streams, the biological conver- sion of these wastes to products can be both environmentally and economically favorable. The various steps involved in poultry processing generate unique types of waste streams. The industry has developed methods for the recovery of most of these wastes by recycling them into feed for the raising of poultry. In the further processing of poultry (produc- tion of prepared foods, soups, frozen dinners, etc.), waste streams are generated which offer the opportun- ity for biological conversion to products other than animal feed. These aqueous waste streams often con- tain significant quantities of protein, fats, and carbohy- drates from cooking oils and breading materials used in the process. Waste streams such as these, with a rela- tively high percentage of carbohydrates, may be good candidates for biological conversion of the carbohydr- ate to more valuable products. The Northwest Arkansas area is home to several poultry processing companies and dozens of 'further- processing' plants. The aqueous effluent from these plants may contain several hundred parts per million suspended solids which must be removed before dis- charging the aqueous effluent to the sewer. Figure 1 shows a process for recovering suspended solids. The solids are first concentrated by flotation and settling, and then further concentrated by filtration. The con- centrated solids may now be removed and disposed of, processed into poultry feed or converted in a biological process to various products. The purpose of this paper is to present preliminary results on the biological conversion of the carbohy- drate fraction of the suspended solids from the ~further-processing' of poultry. Presently this waste stream is being rendered to produce a feed for poultry. However, the high moisture content, 80%, makes ren- dering uneconomical. An alternative to rendering, this particular material could make the entire rendering operation more economical, in addition to converting