“…This increase in organic matter content when CA was used to treat sludge can be attributed to a change in the structure of the sludge (Jakobsen et al, 2004;Hahladakis et al, 2014;Suèr et al, 2003;Wang et al, 2015). In previous studies, Wang et al (2015) also observed increases after CA extraction; specifically, the organic matter content in the sludge from that study increased from 256.2 to 376.7 g/kg because of the residual citric acid, which may act as a nutrient source for fertilizers.…”