A study of pilot Sludge Treatment Reed Beds for the dewatering of surplus activated sludge from a winery wastewater treatment plant

The technology of Sludge Treatment Reed Beds (STRB) is widely applied for dewatering of domestic and municipal sludge, but the applications of these systems for industrial sludge dewatering are so far extremely limited. This study presents the first test of STRB for dewatering of sludge produced during winery wastewater biological treatment. Two groups of four pilot STRB units were constructed and operated for 19 months testing low and high sludge loading rates (SLR). The results showed a remarkable dewatering efficiency with the sludge volume reduction exceeding 99% in all beds and final TS content exceeding 60%. The stressing of the beds with high SLR up to 60 kg TS/m 2 /yr showed that more conservative SLR such as 20 kg TS/m 2 /yr should be selected during the start-up phase to allow for proper plant establishment, before an increase to 40 kg TS/m 2 /yr once the STRB are matured. Feeding cycles consisting of 3 days of feeding followed by 1–2 weeks of resting appear appropriate for sufficient sludge drying. The quality of the final biosolids was found to be below the national and European limits for biosolids reuse in agriculture; metals content (Cu, Cr, Hg, Ni, Pb, Zn) was always below 250 mg/kg, well below the respective legislative limits. The overall results of this study provide the first insight into the feasibility of STRB application for industrial/agro-industrial wastewater sludges and demonstrate the potential to adopt this sustainable technology in the industrial sector.