Sludge drying reed beds stand as a suitable technology for sludge management in certain situations. This work examines two full-scale sludge drying reed beds systems located in a Mediterranean region. Samples of influent sludge and sludge accumulated in the reed beds were analysed for total solids (TS), volatile solids (VS), chemical oxygen demand, nutrients, heavy metals and faecal bacteria indicators. The results show a high dewatering degree (from 1–3 to 20–22%TS), progressive organic matter removal (10–30% VS/TS) and sludge mineralization during sludge storage. The concentration of nutrients, heavy metals and faecal bacteria indicators suggest a good quality of the sludge for land application.
The objective of this work was to investigate the effect of a low temperature pre-treatment (70°C) on the thermophilic anaerobic digestion of sewage sludge. Experimental results were used for the calculation of theoretical energy balances of full-scale digesters with and without pre-treatment step. The 70°C sludge pre-treatment increased sludge solubilization by 10 times and enhanced volatile fatty acids generation. Biogas production increased up to 30–40% and methane content in biogas from 64 to 68–70%. Theoretical calculations showed that additional surplus energy production would be expected by incorporating a 70°C pre-treatment step to a thermophilic reactor.