Assessment of biogas potential for aerobic granular sludge and activated sludge at Gryaab

Sammanfattning

The population of the Gothenburg region is expected to increase in the coming years, which will lead to increasing flows into the Rya Wastewater Treatment Plant (WWTP). Therefore, the treatment capacity will be increased by building a parallel WWTP on new land. One of the wastewater treatmenttechnologies considered to be implemented is aerobic granular sludge (AGS). AGS is a promising biotechnology that has demonstrated several advantages when compared to the conventional activated sludge (CAS) process such as lower energy usage and area requirements. A broader understanding of the biochemical methane potential (BMP) of the two different types of sludge produced by the AGS process, waste aerobic granular sludge (WAGS) and mixed aerobic granular sludge (Mixed AGS), is necessary as there are few previous studies available. The BMPs of these two AGS-sludge fractions were compared to primary sludge (PS) and waste activated sludge (WAS). Additionally, the effect of primary clarification on the BMP of the AGS-sludges was elucidated by sampling the AGS-sludge when the pilot plant was fed with incoming or pre-clarified wastewater. The results indicated that PS had the highest BMP (365 ± 7 ml CH4/gVS) of all the sludge fractions. From all the AGS-sludge fractions the highest BMP (223 ± 19 ml CH4/gVS) was obtained from the WAGS-sludge when the pilot plant was fed with incoming wastewater without primary clarification. This value was 1.64 times lower than the BMP of the PS. The BMP of the WAGS-sludge was affected by primary clarification as a higher BMP result (223 ± 19 ml CH4/gVS) was observed when the pilot was fed with incomingwastewater when compared to its BMP when the pilot was fed with pre-clarified water (185 ± 10 ml CH4/gVS). The BMPs of the mixed AGS-sludge were not affected by primary clarification (213 ± 19 ml CH4/gVS with pre-settled wastewater and 208 ± 15 ml CH4/gVS with incoming wastewater). Mixed AGS-sludge was the substrate that took the most time in being digested, taking 21 days to reach a daily production of <1% of the accumulated volume of CH4. The results showed that AGS-sludges are biodegradable, however their biodegradability was lower in comparison to WAS and PS.