Feedstock biogas production

For anaerobic systems, methane gas is an important product. Depending on the type and nature of the biological components, different yields can be obtained for different biodegradable wastes. For pure cellulose, for example, the biogas product is 50% methane and 50% carbon dioxide. Mixed waste feedstocks yield biogas with methane concentrations of 40-60% (by volume). Fats and oils can yield biogas with 70% methane content. 

Most often, the rates for feedstock destruction in anaerobic digestion systems are based upon biogas production or reduction of total solids (TS) or volatile solids (VS) added to the system. Available data for analyses conducted on the specific polymers in the anaerobic digester feed are summarized in Table II. The information indicates a rapid rate of hydrolysis for hemicellulose and lipids. The rates and extent of cellulose degradation vary dramatically and are different with respect to the MSW feedstock based on the source and processing of the paper and cardboard products (42). Rates for protein hydrolysis are particularly difficult to accurately determine due the biotransformation of feed protein into microbial biomass, which is representative of protein in the effluent of the anaerobic digestion system. 

Yadvika S., Seekrishnan, T.R., Kohli, S. and Rana, V. (2004). Enhancement of Biogas Production From Solid Substrates Using Different Techniques - A Review. Bioresour. Technol., 95, 1-10. Yaman, S. (2004). Pyrolysis of Biomass to Produce Fuels and Chemicals Feedstocks. Energy Conversion Manag., 45, 651-671. 

Core feedstock is blackwater. Anticipated advantages of blackwater utilization compared to traditional methods of wastewater treatment (Chapter 7, Section 3.2.2) are energy savings, if conventional treatment via nitrification and denitrification is avoided, energy gain from the biogas, products for fertilization from wastewater ingredients etc. 

All types of biomass can be used as substrates for biogas production as long as they contain carbohydrates, proteins, fats, cellulose, and hemiceUuloses as main components. The composition of biogas and the methane yield depends on the feedstock type, the digestion system, and the retention time [82]. The theoretical gas yield varies with the content of carbohydrates, proteins, and fats (Table 1.1). 

Feedstocks used for biogas production and the corresponding composition and type of contaminants are reported in Table 4.1. 

In continuous and semi continuous-flow systems waste go into reactor continuously or at certain intervals. The introduction of a new portion of feedstock is accompanied by a simultaneous discharge of an equivalent quantity of the batch of reactor. Part of the material leaves the reactor without being completely decomposed. Parameters determined in these systems are called biogas/methane yield. Some results of laboratory estimation of biogas production from waste are presented in Table 2.5. 

In Australia, electricity generation from biogas has been increased from 1605 GWh to 3234 GWh from 2000 to 2007 (UN-Statistics-Division, 2010). Wastes from food processing plants, livestock manure, and human sewage are the primary feedstocks for biogas production. Most of the installed capacity is at sewage treatment plants, which are considered highly cost-effective. 

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