POTENTIAL BIOGAS PRODUCTION FROM FISH WASTE AND ...

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Chen Shi TRITA LWR Degree Project 12:37Fig. 5 The time line for incubating of inoculums used in this project.respectively. All the inoculums were incubated by fish waste, by-catchand sludge under mesophilic condition for 20 days.Inoculums in this projectThe inoculums in the Test I were derived from Tomczak-Wandzel’sexperiment by mixing its three types of incubated inoculums as equalproportion. It had been stored for 7 days before they were used. After13 days digestion of Test I, the inoculums had been stored for 3 daysbefore they were used in the Test II.3.1.2. SubstratesSubstrates are used to provide organic matter to produce biogas. In thisproject, co-digested substrates are fish wastes, by-catch and sludge whichare introduced in this section.Fish wasteThe cod intestine was mainly studied in this project which was the mostcaught and treated in the fisheries of Simrishamn. Under the analysis ofBechtel (2003) on the properties of pollock, cod and salmon, the proteinand fat content of cod viscera without the cod roe and milt were around13 % and 8.1 % separately. But, they varied based on the fish size, timeof harvest, gender and other environmental factors. In addition, in thisproject, the roes were contained in the cod intestine which had richerprotein (Intarasirisawat et al, 2011). So the protein content of cod viscerashould be higher than it in the analysis of Bechtel (2003). Moreover, thecod intestine as one of the feedstocks also provided an enormous benefitfrom high content of enzymes contained (Shahidi & Jana-Kamil, 2001),which could promote the speed of hydrolysis process.By-catchIn this project, the cod meat from Simrishamn would be used to be thesubstitute of by-catch to simulate the real condition. According toBechtel (2003), a cod contained around 18.2 % protein content and0.5 % fat content, which were also affected by some environmentalfactors and cod itself such as size and gender. Such high protein content12
Potential Biogas Production from Fish Waste and SludgeFig. 6 The digestion system in Hammarby Sjöstadverk.should be taken into consideration in the AD process due to high risk ofammonia inhibition to the methanogenesis process.Secondary sludge in Simrishamn municipal WWTPThe secondary sludge from the Simrishamn municipal WWTP wasselected as the supplementary substrate mixed with fish intestine and bycatchto reduce the total concentration of ammonia (Almkvist, 2012). Inaddition, the use of sludge was similar to the reality. In Simrishamnmunicipal WWTP, the activated sludge was used in the biologicaldenitrification and nitrification processes for removing nitrogen andorganics (County Administrative Board of Skåne, 2010) (Fig. 8).Therefore, the secondary sludge after thickening from Simrishamntreatment plant contained less complex organic matter and more aerobicbacteria which were better for decomposition of long-chain organiccomponents only in oxygen-rich condition.3.1.3. NaOH solutionThe 3 mol/L NaOH solution was needed to be prepared before theexperiment start. It was used for fixing the CO 2 and H 2S to obtain the13
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