Exploitation of indigenous bamboo macrophyte species and bamboo biochar for faecal sludge treatment with constructed wetland technology in the Sudano-Sahelian ecological zone

Abstract

Treatment of faecal sludge (FS) has been a major challenge in most developing countries of Sub-Saharan Africa due to the difficulties in finding appropriate technology. Previous studies have however highlighted the potentials of the vertical flow constructed wetland for FS treatment, yet efforts in the identification of potential indigenous plant species as macrophyte for the Sudano-Sahelian ecological zone have been unsuccessful due to toxic levels of FS quality. This research studied the macrophyte potentials of indigenous bamboo species and bamboo biochar as a conditioner for FS treatment in a vertical flow constructed wetland (VFCW). Typical yard scale experiment consisting of filter media of sand supported at the base with gravels and planted with Bamboo shoots was used. Treatments were Bamboo Constructed Wetland (CW) and Faecal Sludge (FS) load only (CW-FS), Bamboo CW with a mixture of FS and Bamboo biochar (CW–BCH), unplanted drying bed with a mixture of FS and bamboo biochar (UDB-BCH) and an unplanted drying bed with FS (UDB-FS), and in triplicates. Control setup (CTR) consisted of Bamboo CW irrigated with wastewater. Morphological development (plant height, number of plants, number of leaves and culm diameter) of indigenous Bamboo species and reduction of faecal contaminants were monitored. Loading of FS was carried out in a single batch twice per week with a hydraulic loading rate of 56.47/mm/d with an annual Total Solid loading rate of 155.6 and 233.2 kg TS/m2/year for CW-FS and CW-BCH respectively. The bamboo species adapted to the complex wetland conditions, observed by a progressive increase in morphological development for all the treatments. Removal efficiencies of effluent quality parameters generally ranged from 70 to 99%, except for PO43−, TOC and TDS and indicator micro-organisms which were found below 50%. A strong positive linear relationship was determined among species growth parameter with coefficient (r) ranging between 0.83 – 0.99. Except for pH and TSS, all the effluent quality parameters exceeded the national allowable limits for safe discharge. Nonetheless, the study demonstrated positive potentials for adopting indigenous bamboo species as emergent macrophytes for FS treatment using VFCW. Further treatment to reduce contaminant levels in a second to a third series of a connected constructed is recommended wetland prior to reuse for agriculture.