Butyric acid is a short-chain fatty acid (C3H7COOH). Its esters occur naturally in animal fat and some vegetable oils [18]. Butyric acid can be used as an ingredient in paints, perfumes, pharmaceuticals, disinfectants and used for the production of plastics, plasticizers, surfactants and textile auxiliaries [18]. It can be applied in animal feed and used as a flavoring agent in food products in the form of esters and salts [18]. It can also serve as a substrate to produce butanol [1, 2]. Butyric acid can be produced by petrochemical or biological methods [18,76]. Although butyric acid is mainly produced from petroleum feedstocks nowadays, its production from renewable feedstocks via microbial fermentation attracts more attention due to limited resources and application as food additives or cosmetic products [18,22]. In microbial fermentation, a number of gram-positive, obligate anaerobic microorganisms have the ability to produce butyric acid in significant quantities such as Clostridium sp. and Butyrivibrio fibrisolnes [18]. Among these, Clostridium tyrobutyricum, a gram-positive and obligate anaerobic bacterium, is the most promising due to its ability to produce butyric acid with high selectivity, tolerance to high concentrations of products [22] and relatively high and stable productions [3, 4, 5, 6]. The metabolic pathway of Clostridium tyrobutyricum is shown in Figure. 1. The final products are butyrate and butanol while acetate and acetone are by-products. Lactate and ethanol are produced but only in small quantities [77]. Solvents include butanol, ethanol and acetone which are produced when pH <5 during the solventogenesis phase. Acids are produced during the acidogenesis phase when the pH is higher [77]. Acetyl-CoA is the intermediate branch point… at the center of the paper… after pretreatment with dilute acid and enzymatic hydrolysis, respectively [26]. Furthermore, some research has chosen 1 g/l [27, 28] or 2 g/l [21, 29] as the maximum concentration of furfural. Furfural concentrations in this research were divided into four levels to study: 0.6 g/l, 1.2 g/l, 1.8 g/l, and 2.4 g/l. As for syringaldehyde and vanillin, similar to furfural, concentrations of 0.06 g/l and 0.04 g/l respectively were found in corn solution after hydrolysis of sulfuric acid and the author also tested them both at 2 g/l [24]. S.cerevisiae and Z. mobilis cells are mostly killed by 2 g/l vanillin or 1.5 g/l syringaldehyde [23]. So, even though the concentrations in the hydrolysis solution were not high, this research still chose a maximum of 2.8 g/l for both for the study. They had the same concentration levels: 0.7 g/l, 1.4 g/l, 2.1 g/l and 2.8 g/l.