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As shown in Table 1, food waste, in general, has good potential forenergy production through anaerobic degradation due to itscharacteristics such as moisture content (72e85.2%), high substrateconcentration (COD: 19.3e346 g/L; Carbohydrate: 25.5e143 g/L) andhigh carbon to nitrogen (C/N) ratio (9e21) (Hwang et al., 2011;Elbeshbishy et al., 2011a; Jayalakshmi et al., 2009). The physicochemicalcharacteristics of food waste are very important indesigning and operation of an anaerobic digestion system for biohydrogenproduction. Pre-treatment of food waste, temperature, pHand low hydrogen partial pressure etc. are regarded as importantparameters in influencing biohydrogen production and yield (Kimet al., 2009). In addition, other characteristics such as moisture content,volatile solid composition, nutrient content, particle size andbiodegradability of food waste are also important to achieve highbiohydrogen yield (Zhang et al., 2007). Table 1 shows the characteristicsof food waste being used in biohydrogen production studies.Different characteristicswere observed for each study indicating thatthe composition of this feedstock differed depending on the type ofwaste generated in different countries and cafeterias and also on thetype of actual food waste being used by different researchers.In order to have optimum concentration of food components,water is usually added to homogenize food waste thereby stimulatingthe degradation rate for biohydrogen production (Chu et al.,2008; Shin et al., 2004). Ismail et al. (2009) found the optimumbiohydrogen production to be at controlled COD concentration of200 g/L food waste while Han and Shin (2004) controlled thedilution rate of food waste to achieve high biohydrogen yield. Highcarbon to nitrogen (C/N) ratios resulted in better biohydrogenproduction even though nitrogen is also an important source ofnutrient to be added in anaerobic fermentation (Mohan et al.,2009). Kim et al. (2010) found that C/N ratios of over 20 resultedin the decline of biohydrogen production. Therefore, based on ourliterature search, C/N ratios of food waste should fall between 20and 21 for optimum yield.Biohydrogen production from food waste has been carried outwidely by many researchers using mixed cultures from anaerobicsludge, manure and compost in batch, repeated batch, semicontinuousand continuous modes (Table 2). This implied that thepresence of indigenous microorganisms and high carbon content infood waste made it suitable as a feedstock for biohydrogen productionunder non-sterile conditions. So far, pure culture inoculumhas not been employed by any researcher for the production ofbiohydrogen from food waste. However, Jo et al. (2007) managed toTable 1Characteristics of food waste used in biohydrogen production studies.References ParameterspH MoisturecontentTotalsolidVolatilesolidTotal KjeldalnitrogenTotal COD TotalcarbohydrateC/N TotalVFAKim et al. (2008b) 11.80 nd 4.6b 4.4b 1.1c 44.2c nd nd 3.6cKim and Shin (2008) 4.60 nd 16.8b 16.1b 4.0c 162.2c 99.0c nd 13.5cLi et al. (2008) nd 85.3b 14.7b 88.8b 2.0b nd nd 21.0 ndZhu et al. (2008) 4.70 nd 11.4c 10.5c 0.5c nd nd 9.0 1.1cLee et al. (2010) 4.35a nd 10b 9.5b 4.0c 150.0c 34.9c nd 5.5cJayalakshmi et al. (2009) 5.51 83.8b 16.2b 86.1b 2.3b nd nd 21.0 ndWang and Zhao (2009) 4.68 nd 17.6b nd 2.3b 211.8e nd nd ndChu et al. (2008) 4.90 nd 117.0c 108.0c 3.8d 142.0c 66.0c nd 5.4cShin et al. (2004) 5.80 nd 67.8c 63.7c 2.8d nd 25.5 18.3 ndIsmail et al. (2009) 6.25 72.0b 255.5c nd 0.2c nd nd nd ndWang et al. (2010) 4.50 nd 266.0c 256.0c 5.5c 346.0c 143.0c nd ndZhu et al. (2009) 4.70 nd 11.4c 10.5c 0.5c 19.3c nd nd ndTawfik et al. (2011) 6.50 nd 61c 56c nd 64c nd nd 2.7cValdez-Vazquez and Poggi-Varaldo (2009a, b) 7.20 nd nd 10.1c nd 110c 64c nd ndnd not determined.a Average in range series.b % (w/w).c g/L.d % TS.e g O2/kg.
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