## 1 Introduction  
A significant increase in worldwide poultry and poultry product consumption has been observed. This has led to intensification of livestock production and increasing amounts of waste, mainly poultry manure, which can affect human health and the quality of animal life due to the generation of volatile odorous compounds. There are many ways to reduce odour from poultry farms, inter alia, biological, chemical and physical methods. Among biological methods, biopreparations are of great interest. They are the only methods that do not require specialized use of installations and equipment. Biopreparations: (1) are safe and easy in practical use; (2) do not corrode metals or destroy ceramics and plastics; (3) prevent excessive microorganism development, (4) contribute to the restoration/ reconstruction of natural microflora; (5) bind some heavy metals; and (6) contribute to manure hygiisation. In our previous research, we selected six bacterial strains for deodorization of poultry manure: Pseudomonas fluorescens, Enterococcus faecium, Bacillus subtilis, Bacillus megaterium, Leuconostoc mesenteroides and Lactobacillus plantarum, on the basis of their ability to reduce the content of volatile odorous compounds from poultry manure and the antagonistic interactions between the strains [1; 2]. These strains were then applied to produce a novel biopreparation which consisted of two parts: a perlite-bentonite mixture (20:80 by weight) used as a mineral sorbent, and a 20% addition (by weight) of active microorganisms in the form of spray-dried microcapsules. The preparation showed great effectiveness in the removal of volatile odorous compounds, especially ammonia, for which concentration was reduced in the exhaust air by more than 90% during 2 days of deodorization. The other nitrogenous odorants--indole and pyridine--were removed by 78% and 59%, respectively. The average reduction rate of hydrogen sulphide by the biopreparation was 60%, whereas dimethyl sulphide and dimethyl disulfide were removed with around 70% efficiency. The preparation also revealed high activity against hydrocarbons, aldehydes and phenols. It is worth mentioning that the biopreparation was stable, as no decrease of its microbial stability was reported with at least 5 months of storage at both cool (4 \({}^{\circ}\)C) and room (22 \({}^{\circ}\)C) temperatures [3]. The efficiency of biotechnological processes involving microorganism cultivation depends on many factors, among which the composition of culture medium is of great importance. Microorganisms, depending on their nutritional requirements, need access to different sources of carbon and nitrogen, as well as vitamins. Both a shortage and excess of even one component may inhibit the growth and activity of the cells, and consequently decrease the process efficiency. Moreover, large-scale production forces the use of cheap waste materials. Due to the number of variables, optimization of media composition is a great challenge. Conventional methods, such as one-factor-at-time (OFAT), rely on matching the concentration of each substrate individually while maintaining a constant concentration of the remaining components. Such a solution, although still very popular, is time-consuming and generates significant costs. Synergistic and antagonistic effects that appear only in a certain range of concentrations of selected components, resulting in an increase or decrease of the process efficiency, respectively, are skipped. Consequently, attempts are being made to intuitively modify the parameters of the culture, however, this does not lead to achievement of the given goals [4; 5]. A solution to the described problem may lie in the statistical methods of experimental design, which quickly and efficiently allow for determination of the appropriate values of all operating variables [6].