A comparative study of worm-sludge treatment reed bed planted with Phragmites australis and Arundo donax in the Mediterranean region

Abstract

AbstractSludge treatment reed bed planted (STRB) with Phragmites australis (P.australis) and Arundo donax (A.donax) was assessed in the presence of Eisenia fetida under control condition during the dry season. Worm-planted units were fed with mixed sewage sludge (dry and volatile solids of 29.44 g DS.L−1 and 24.23 g VS.L−1). Sludge loading rates (SLR) of 50, 60, and 70 kg DS m−2 year−1 were examined to assess dewatering efficiency. Surface layers in units with P.australis and A.donax achieved DS of 80 and 81% at a loading rate of 50 kg DS m−2 year−1, while their subsurface DS were 41 and 25%, respectively. Units with A.donax experienced plant loss when subjected to SLR exceeding 60 kg DS m−2 year−1. More than 10 cm of residual sludge accumulated on the top of units after a 2-month final rest. Evapotranspiration was greater in the unit with P.australis (5.23 mm day−1) compared to the unit with A.donax (4.24 mm day−1) while both were fed with 70 kg DS m−2 year−1. Water loss contributions from residual sludge layer, drained water, and evapotranspiration were 3, 46, and 51%, respectively. Units with P.australis indicated 20% higher water loss compared to units with A.donax. Although the drained water quality improved over time, it did not meet standard limits. The residual sludge layer contained macro and micronutrients, and heavy metals with a significant elemental order of N > Ca > P > S > mg > K (N:P:K = 31:8:1), Fe > Na > B > Mn > Mo and Zn > Cr > Cu > Pb > Ni > Cd. Overall, STRB could be a sustainable alternative technology to conventional sewage sludge management techniques. Graphical Abstract