SSF pilot design, test and optimization.

Solid State fermentation refers to cultivation of filamenteous microorganisms on bed of moist solids. The SSF target may be protein enrichement of solids, improvement of digestability, production of enzymes and a wide range of metabolites from organic acids to antibiotics and bioligical pestiside agents, and even decontamination. This broad area of aplications along with the fact that most of agricultural residues and wastes are soild, implicates vast potential of SSF in agriculture. Despite this fact some bottlenecks prevented SSF commertialisation. A major one is lack of knowledge of design and constraction of appropriate bioreactors. The aim of present research was to develop the mentioned knowledge. For this, a pilot consisting of a bioreactor and its aeration, steaming and control systems was designed, constructed and tested. The aeration system includes blower, saturation colomn, filters, relative humidity adjusting heaters , and heaters for warming of drying air. Bioreactor case dimentions were 1*0.8*0.5 m3 and had a 5cm thickness. A stack of two trays were mounted in the case, the air stream was evenly disributed in the lower one and followed into the bed of solids filled in the 0.765*0.43*0.1 m3upper tray . mixing and wetting of the bed was provided by an special moving mixer. The control system included both hardwares and a software which was produced during the project. The software makes online estimations of the bed moisture variations and controls mixing and wetting operations and also the relative humidity of the air stream. An small boiler was constracted to supply steam required for pastorisation of the bed and bioreactor. Several experimnets were conducted atto check the pilot plant plant performance. In each experiment, Aspergillus niger was cultivated on 4000g of wet brans and trend of activity of some hydrolytic enzymes, namely glucoamylase, protease, pectinase, protease, xylanase, and cellulase were measured during the 60 hour fermentation period. The attained activities were compared with flask culture ones and the effects of operational parameters namely volumetric air flow rate, inlet air temperature, avarage bed moisture and bed moisture variation range were investigated. The expriments revealed the pilot technical deffects and bottlenecks some of which were removed and remediation procedures were suggested for the others. The attained knowledge could be used to design and constract larger SSF units.