Effect of hydraulic loading frequency on performance of planted drying beds for the treatment of faecal sludge El hadji Mamadou Sonko, Mbaye Mbéguéré, Cheikh Diop, Seydou Niang and Linda Strande ABSTRACT This study was conducted to evaluate the effect of loading frequency on treatment performance of faecal sludge (FS) with drying beds planted with Echinochloa pyramidalis. Beds were loaded at a constant total solids (TS) loading rate of 200 kg TS/m 2 *year, at a frequency of 1X, 2X or 3X per week. The FS was highly variable, with a range of 2,600–21,492 mg/L TS, which resulted in variable hydraulic loadings. Weekly monitoring was conducted 23 times over a period of nine months. Increased loading frequency resulted in increased plant growth with 211, 265 and 268 plants/m 2 , respectively, for the 1X, 2X and 3X, and the 2X and 3X loadings had 12–13% more liquid lost due to evapotranspiration versus percolation. Even with high removals that were resistant to variable hydraulic loadings, leachate had 883–5,228 mg/L TS, 49–727 mg/L total suspended solids and 92–1,853 mg/L chemical oxygen demand due to the high initial concentrations. Increased loading frequency resulted in greater nitrification, with 7–28, 18–43 and 28–51 mg/L NO 3 À for 1X, 2X and 3X, respectively. FS requires a longer storage time than three months for stabilization and pathogen reduction. These results provide valuable information for FS planted drying bed operation. El hadji Mamadou Sonko Linda Strande (corresponding author) Eawag: Swiss Federal Institute of Aquatic Science and Technology, Sandec: Department of Water and Sanitation in Developing Countries, Ueberlandstrasse 133, 8600 Duebendorf, Switzerland E-mail: linda.strande@eawag.ch Mbaye Mbéguéré Senegalese National Sanitation Utility, Cité TP SOM, No. 4, Hann, BP 13428, Dakar, Senegal El hadji Mamadou Sonko Cheikh Diop Institute of Environmental Sciences (ISE), Faculty Sciences and Technics, Cheikh Anta Diop University of Dakar, B.P 5005, Dakar-Fann, Senegal Seydou Niang Laboratory of Wastewater Treatment, Fundamental Institute of North Africa (IFAN), Cheikh Anta Diop University of Dakar, B.P 5005, Dakar-Fann, Sénégal Key words | biosolids, Echinochloa pyramidalis, fodder, leachate, low- and middle-income countries, wastewater INTRODUCTION Faecal sludge (FS) is the sludge that accumulates in onsite sanitation technologies (e.g., septic tanks, pit latrines). There are few technological options for the reliable treat- ment of FS, and this represents an important research need as globally 2.7 billion people are served by onsite sanitation technologies (Boston Consulting Group ). The need is especially urgent in low-income countries, where the vast majority of people in urban areas are served by onsite tech- nologies, but for the most part a FS management infrastructure is not in place. Planted drying beds have had limited but increasing use in Europe for the dewatering and stabilization of wastewater sludge over the last 30 years (Uggetti et al. ), and there have been a few attempts to transfer this technology to the treatment of FS in low- income countries (Koottatep et al. ; Kengne et al. ). However, this limited information is not adequate to transfer the technology from treatment of wastewater in tem- perate climates to FS in southern climates, as FS is more concentrated and less stabilized than wastewater sludge. Planted drying beds appear to be a very promising tech- nology for FS treatment in low-income countries. They can be loaded directly with untreated sludge (Molle et al. ) and produce treatment end products that can be sold to offset operation costs, including animal fodder and organic Journal of Water, Sanitation and Hygiene for Development | 04.4 | 2014 doi: 10.2166/washdev.2014.024 Final Manuscript Submitted to: Journal of Water Sanitation and Hygiene for Development, Volume 4, Issue 4, 2014, Pages 633-641