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ePaper created 2014-05-07, 13:23:14 | version 1.30.01
122 BIOGAS PRODUCTION USING BY-PRODUCTS FROM CRAB SHELL REUTILIZATION Barbara E. Waelkens M.Sc. Initial situation Chitin is one of the main components of the exoskeleton of arthropods such as crabs, lobsters and shrimps, and is therefore one of the most commonly occurring biopolymers in the world. Chitin and its derivatives have a large applica- tion potential, however this has not yet been implemented in practice. Together with an international team of researchers, the EU-funded ChiBio project is working to further develop the sustainable utilization of crab and shrimp shells. New pro- cesses based on the biorefinery concept are being developed to use chitin as the base material for specialty chemicals. Energetic use of protein-rich waste streams Besides chitin, the main components of crab shells are mineral substances, such as calcium salts, and proteins [1]. The first step in processing chitin is to extract it. This process can be carried out chemically (acid-base extraction) or enzymatically. The chemical process results in a protein-rich alkaline and a calcium-rich acid solution. Within the biorefinery concept that is virtually wastefree, the protein-rich waste stream can be employed for energy production through an anaerobic digestion. The advantages of anaerobic digestion of organic substances were identified by McCarty [2] as early as 1964: a high degree of stabilization of the organic material, low nutri- ent requirements, no need for oxygen and the production of biogas, which can serve as a renewable source of energy. Challenges for biogas production In principle, almost any type of organic substance can be con- verted into biogas. In Europe, the production and use of bio- gas are now widespread in the wastewater treatment as well as in the agriculturural sector. In over 65 countries anaerobic systems are also used in industry and so far more than 1400 plants have been installed by 16 main plant construction companies [3]. One of the challenges in the ChiBio project is the technical implementation of reutilizing the resulting by- products in a sustainable way. For this purpose, the biogas production potential was determined for the by-products obtained from the chemical extraction of chitin of shrimp and crab shells (Fig. 1). Compared with other substrates, these by-products are char- acterized by low total volatile solids content, extreme pH val- ues and high salt concentrations. Whereas typical substrates such as sludge from wastewater treatment or liquid manure have a ratio of total volatile solids to total solids (TVS / TS ratio) of 60 percent and 80 percent respectively, the TVS / TS ratio for the byproducts obtained by chitin extraction from crab and shrimp shells is approx. 15 percent and 30 percent respec- tively. Potential for biogas production To determine the biogas production potential, 1-liter labora- tory-scale bioreactors (Fig. 2) were feeded with the protein- rich by-product of the chitin extraction of shrimp shells and of two different batches of crab shells (May and July). The experiments were carried out as fed-batches with two feed- ing cycles. The specific biogas production of the shrimp shell sidestream (Fig. 3) corresponded to 1125 mlN / gTVS in the first and 830 mlN / gTVS in the second feeding cycle. The biogas production was higher than the specific biogas yield of the crab shell sidestreams (Fig. 4), for which we measured 305 or 319 mlN / gTVS in the first and 283 or 391 mlN / gTVS in the second feeding cycle. 21 ENERGY