Decomposition behavior of five selected amino acids in high-temperature and high-pressure water was studied using a continuous-flow tubular reactor. The reaction was carried out in the temperature range of 200−340 °C at a pressure of 20 MPa. Alanine and its derivatives leucine, phenylalanine, serine, and aspartic acid were used as model amino acids. The effect of temperature on reaction products, pathway, and rate was determined as a function of reaction time. Alanine decomposed into lactic acid and pyruvic acid, then finally mineralized to carbon dioxide with an activation energy of 154 [kJ/mol] at 20 MPa. The degradation rate decreased in the following order:  aspartic acid, serine, phenylalanine, leucine, and alanine. The general reaction network of amino acids under hydrothermal conditions takes two main paths:  deamination to produce ammonia and organic acids, and decarboxylation to produce carbonic acid and amines. Deamination was the predominant reaction in the decomposition of aspartic acid, an acidic amino acid. Production of glycine and alanine from serine, an oxy amino acid, was also observed.

lbyohashi 441 -8580, Japan nvironmental pollution resulting from daily human and industrial solid waste discharges, including those from the seafood processing E industry, is becoming a serious social problem nowadays. In Japan, for example, about half of 9.8 million tons of fish processed in the industry per year is being put into waste. In this regard, technologies that would treat these waste or even better recover some useful organic materials before disposal are of significant importance. Martin (1 999) suggested a low-energy process of converting fish wastes by composting with peat. Dapkevicius et al. (1998) studied ensilage processes of upgrading protein residues in fish wastes by acid (using formaldehyde) and biological silages (using molasses or dehydrated whey). Other than the aforementioned processes, more efficient methods are strongly desired since large amount of fish wastes are being discharged from industries every day. One possible method for the treatment of fish wastes is the use of sub-or supercritical water.Sub-and supercritical water has attracted many scientists because of its fascinating properties as a reaction medium (Shaw et al., 1991;Savage et al., 1995). Supercritical water is completely different from water at ordinary pressure and temperature. For example, at room temperature and atmospheric pressure, water has a dielectric constant of 80 and ion product (K, ) of 1 O-14. The dielectric constant expresses the affinity of water, as a reaction medium, to reaction materials. These values can be controlled by changing temperature and pressure, and could greatly affect the reactivity of various compounds in water. In addition, ion product of water can also be adjusted by changing temperature and pressure to control the ability of hydrolysis. High ion product is good for hydrolysis. Under saturated vapour pressure, water has a maximum ion product at around 250°C. The use of sub-and supercritical water has been widely applied to various reactions such as reduction, pyrolytic, decomposition and dehydration (Savage et al., 1995). Examples are oxidation of phenols (Martino and Savage, 1999), pyridine (Aki and Abraham, 1999a, b) and methanol (Anitescu et al., 1999), and hydrolysis of esters (Krammer and Vogel, 1999) and thiodiglycol (Lachance et al., 1999), among others. The technique was also applied to chemical recycling processes such as hydrolysis of polyethylene terephthalate (PET) into ethylene glycol and terepthak acid (Arai and Adschiri, 1999). The most significant applications A resource recovery technique using sub-and supercritical water hydrolysis was applied to convert waste fish entrails into amino acids. The effect of reaction parameters such as temperature and time necessary for the control of reaction towards optimum yield of amino acids was investigated. Results showed a maximum yield of total amino acids (1 37 mg/g dry fish) from waste fish entrails a t T = 523 K (P = 4 MPa) and reaction time of 60 min in a batch reactor. Under supercritical conditions (e.g., T = 653 K, P = 4...

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