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Käppala wastewater treatment plant situated on the island of Lidingö northeast of Stockholm is running a project during 2004 and 2005 with the purpose to map out the capacity of anaerobic digestion in the digesters that treat primary and excess sludge. The purpose of this thesis work, which is part of that project, was to characterize the present anaerobic digestion process and to investigate its capacity to treat other organic wastes such as restaurant waste and waste from water works. To decide the potential of both methane and biogas production from different substrates batch laboratory tests were carried out. To imitate the anaerobic digestion process at Käppala continuous tests with small scale reactors were carried out. These reactors were later fed with restaurant waste. The batch laboratory tests showed that primary sludge had a potential biogas and methane production of 0,62 and 0,35 Ndm3/g VS respectively after 40 days of digestion. After 15 to 20 days of digestion (average retention time in the digester at Käppala wastewater treayment plant that treats primary sludge) the biogas production was between 0,55 and 0,60 Ndm3/g VS, which is within the range of the production at the digester that treats the primary sludge. This leads to the conclusion that the digestion of primary sludge is well functioning at the plant. Batch laboratory tests showed that excess sludge had a potential biogas and methane production of 0,31 and 0,16 Ndm3/g VS respectively after 40 days of digestion. Batch laboratory tests with restaurant waste showed a potential biogas and methane production of 0,81 and 0,38 Ndm3/g VS respectively after 47 days of digestion. This means that the total production of methane gas can increase with 7-8 per cent with an annual load of 3500 tonnes of restaurant waste (estimated amount of available restaurant waste). Tests to imitate transport of restaurant waste with influent wastewater showed that 35-60 per cent of the increase of gas production would be “washed out” if the waste was tranported this way to the plant. Batch laboratory tests with waste from water works showed that no gas was produced from this substrate. The continuous tests with small scale reactors which were fed with restaurant waste resulted in an increase of biogas production with 12 per cent (corresponding to an annual load of 3500 tonnes of restaurant waste) compared to the present process. Avloppsreningsverket Käppalaverket på Lidingö driver under år 2004-2005 ett projekt med syftet att kartlägga rötningskapaciteten i den befintliga anläggningen där primär- och överskottsslam behandlas i två rötkammare. Syftet med examensarbetet, som är en del av kartläggningsprojektet, var att karakterisera Käppalaverkets nuvarande rötningsprocess och undersöka processens kapacitet att behandla organiskt avfall i form av restaurangavfall och vatttenverksslam. För att bestämma potentialen hos olika substrat har satsvisa utrötningar genomförts. För att efterlikna processen på Käppalaverket har kontinuerliga försök med små reaktorer bedrivits. Till dessa reaktorer har sedan restaurangavfall tillsats. De satsvisa utrötningarna av primärslam visade en potentiell bio- respektive metangasproduktion om 0,62 respektive 0,35 Ndm3/g VS efter 40 dagars utrötning. Efter 15-20 dagars utrötning (som är den genomsnittliga uppehållstiden i Käppalaverkets rötkammare där primärslammet behandlas) var biogasproduktionen mellan 0,55 och 0,60 Ndm3/g VS, vilket är inom samma intervall som vid den verkliga driften av rötkamrarna vid Käppalaverket. Detta betyder att utrötningen av primärslammet fungerar bra vid Käppalaverket. De satsvisa utrötningarna av överskottsslammet visade en potentiell bio- respektive metangasproduktion om 0,31 respektive 0,16 Ndm3/g VS efter 40 dagars utrötning. För restaurangavfallet visade de satsvisa utrötningarna på en potentiell bio- respektive metangasproduktion om 0,81 respektive 0,38 Ndm3/g VS efter 47 dagars utrötning. Detta innebär att den totala metangasproduktionen vid Käppalaverket skulle kunna ökas med 7-8 procent om 3500 ton restaurangavfall skulle tas emot årligen (uppskattad mängd restaurangavfall som finns att tillgå). Försök att efterlikna transport av restaurangavfallet via avloppsledningsnätet visade dock att 35-60 procent av den ökade metangasproduktionen skulle ”tvättas ur” om avfallet fördes till verket via avloppsledningsnätet. Försöken med satsvis utrötning av vattenverksslam visade att detta substrat inte bidrar med någon produktion av biogas eller metangas. De kontinuerliga försöken med tillsats av restaurangavfall (motsvarande en årlig belastning med 3500 ton) resulterade i en ökning av biogasproduktionen med 12 procent.

Hammarby Sjöstad is a new district of southern Stockholm built with focus on reduced environmental impact by recirculation of materials and sustainability. The environmental goals aim to cut the water consumption by half and a separate storm water treatment. Thus, the wastewater will be more concentrated and will originate from the households only. The Sjöstad project includes the idea of a local treatment plant for the household wastewater. To evaluate this possibility, Sjöstadsverket, an experimental treatment plant was constructed. New wastewater treatment processes are tested and evaluated and compared to conventional methods including both aerobic and anaerobic treatment processes. One of the aerobic treatment processes includes enhanced biological phosphorus removal (EBPR or Bio-P) as the method for the removal of phosphorus. In biological phosphorus removal the wastewater is alternately being exposed to anaerobic and aerobic conditions, which favours a certain bacteria, which can accumulate more phosphorus than is required for their growth. For this phosphorus accumulation the bacteria need volatile fatty acids (VFA) to cover their energy demand, but normally there is a shortage in VFA in the incoming wastewater. The main purpose of this master thesis work has been to create the best possible conditions in order to produce VFA by hydrolysis and fermentation of primary sludge. In this way the organic material in the incoming wastewater can be used in biological phosphorus removal. The sludge temperature, total solids (TS) and retention time are regarded as important parameters for a successful biological phosphorus removal and a laboratory study was set up to investigate these conditions for the wastewater at the Hammarby Sjöstad experimental plant. These laboratory-scale hydrolysis experiments showed that high temperature and high TS favours VFA-production. The results have also shown that four to five days retention time is suitable at a process temperature higher than 23°C, but also that the retention time likely should be extended at lower temperatures. In a full-scale process experiment, primary sludge was pumped from a primary clarifier to a hydrolysis tank and then back to the primary clarifier. The hydrolysis gave rise to increased VFA-production when TS was increased. A temperature difference between the primary sludge and the hydrolysis sludge of 3°C was observed. The reason behind the difference has not been determined, but is considered important, since the temperature affects the VFA-production. Further on, analyses with gas chromatograph (GC) have shown that acetate has been the most frequently occurring VFA, although significant levels of other VFA, such as propionate, has also been detected. Phosphorus release tests in laboratory-scale, where phosphorus was released during an anaerobic phase and taken up during an aerobic phase, proved that biological phosphorus removal occurred at the full-scale experimental train. The full-scale hydrolysis experiment has shown that the VFA contribution by the hydrolysis tank to the biological phosphorus removal was low. The main reason is that the sludge-flow through the hydrolysis tank has been insignificant compared to the incoming wastewater flow. The problem is most likely connected to the incoming wastewater characteristics, since the low share of suspended solids (SS) entailed that not enough organic material in the primary clarifier settled. I figur 57 på sidan 76 stämmer inte trendlinjernas ekvationer i den tryckta versionen. Dessa är nu korrigerade i den elektroniska versionen, så att rätt ekvationer finns i den aktuella figuren.