“…Contrary to WWTPs with pipeline networks for sludge in large cities (Gyobu et al, 2015), sewage sludge with high solid content (less sludge volume) is helpful for trucking sewage sludge from other WWTPs, because it requires less energy and cost. Anaerobic digestion with high solid content is popular for anaerobic digestion of the organic fraction of municipal solid waste, food processing waste and manure with over 18% total solids (TS) (Hegde and Pullammanappallil, 2007;Yamashiro et al, 2013;Sensai et al, 2014). It has several further advantages, including smaller space requirements and lower energy consumption for heating, although some disadvantages, including a higher ammonia concentration and higher viscosity, need to be considered (Guendouz et al, 2008;Aymerich et al, 2013).…”