Analys av system för rening av avloppsvatten i en anaerob membranbioreaktor

Sammanfattning: The most common way to treat wastewater in Sweden today is by a combination of an activated sludge process and a chemical treatment. These processes are not very energy efficient and may not be the most environmentally friendly. That is why it is interesting to evaluate new alternative methods to see if they can be less harmful to the environment and help to a lower resource consumption. New techniques are tested in a pilot installation at Hammarby Sjöstad, Sjöstadsverket. To be able to evaluate these techniques in a wide perspective system analyses are conducted where different impacts can be considered, advantages and disadvantages in the systems. Five system structures for water treatment have been constructed in Matlab/Simulink in this study. The URWARE (URbanWAter REsearch) model was used to conduct a system analysis, which made a comparison of the different systems possible. Four of the systems contained a new technique for water treatment, consisting of an anaerobic membrane bioreactor (MBR) combined with a VSEP (Vibratory Shear Enhanced Process) unit. This is one of the techniques that now are tested in Sjöstadsverket. The fifth system was a reference system designed as a conventional treatment plant. The wastewater treated in the different systems was in some cases mixed wastewater, in other source sorted, with or without food waste from kitchen waste disposers. Results from the system analysis shows that the MBR technique gives some advantages compared to the conventional water treatment. A large part of the nutrients in incoming materials are recycled. The highest recycling percent is reached when the MBR technique is combined with compost that handles the food waste. The total impact on the environment by greenhouse gases and eutrophic substances is lower in all the alternative systems compared to the reference system. The system with the source sorted urine has the most favourable exergy turnover. When reversed osmosis is used in the treatment a lot of energy is needed which leads to a poor exergy turnover and the conventional technique is more advantageous in these cases. All the alternative systems give a larger acidification which is a disadvantage with the MBR technique.