Faithin Omaha eBook Collection

Download or read book Thermal Pretreatment of Dairy Cow Manure for Solid-state Anaerobic Digestion written by Wilton McVoitte and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "This study investigates the effects of thermal pretreatment on the biogas yield and methane concentration from the solid-state anaerobic digestion of dairy cow manure. Anaerobic digestion is the biological degradation of organic biomass in the absence of oxygen, yielding a biogas containing methane - a gas that can be harnessed for energy. Anaerobic digestion is mediated by microbes that cannot efficiently break down lignocellulose. The process is normally conducted with liquid substrates having a total solid content less than 15%. However, research has been emerging into solid-state digestion (> 15% total solid content) for its ability to better degrade lignocellulose. Dairy cow manure is a substrate used for anaerobic digestion that has a high fiber content and recalcitrant lignocellulose resulting in low methane concentration. Thermal pretreatment improves digestion by breaking down the lignin and cellulose in the cell wall of the plant residues of manure. Therefore, the thermal pretreatment of dairy cow manure should facilitate the hydrolysis and microbial decomposition of lignocellulose, disintegrate the cell wall and increase the methane concentration in the biogas.Currently, limited knowledge is available about the effects that the temperature and duration of thermal pretreatment have on the biogas yield and methane concentration of solid-state digested cow manure. A response surface methodology called the central composite rotatable design was used to estimate the optimal pretreatment temperature and duration under the conditions of this experiment. This method is beneficial, allowing for fewer tests and less time when compared to a full-factorial design. A laboratory experiment was conducted to determine the effect that temperature and duration had on the biogas yield and methane concentration and the change in volatile solid and pH due to digestion. Under the conditions of this experiment, the treatment factors (temperature and duration) had no significant effect on the biogas yield and methane concentration. The treatments that yielded the highest biogas volumes and methane concentrations were for the control (untreated samples) and those treated at the center temperature and duration of the statistical model (125°C, 37.5 min). It cannot be concluded that thermal pretreatment increases the biogas yield and methane concentration from the solid-state digestion of dairy cow manure. Therefore, it is important to further study the effect of thermal pretreatment prior to implementation in industry as the added cost to supply heat may not offer any benefit.To better characterize the pretreatment temperature and duration, a single variable was devised that summarizes the heat distribution throughout the manure for each treatment. Initially, the oven temperature was reported as the pretreatment temperature. However, the temperature of the substrate was not the same temperature of the oven, especially with the dairy cow manure in its solid state. Most research thus far has been conducted on dairy manure in the liquid state and even so, heating is a transient process, resulting in uneven heat distribution throughout the manure sample. A single variable, called the volumetric heating factor (H), was therefore devised. This variable quantifies the effect of the transient temperature regime on the solid-state digestion of dairy cow manure, specifically the biogas yield and methane concentration. The volumetric heating factor had similar statistical significance as did temperature and duration in the conventional statistical model, i.e. no statistically significant effects on the biogas yield or methane concentration. However, H does allow researchers to use one variable instead of two to give an indication of the severity of the heat treatment. The volumetric heating factor is also a better descriptor in theory of the transient temperature regime within the sample material." --