Influence of sand layer depth and percolate impounding regime on nitrogen transformation in vertical-flow constructed wetlands treating faecal sludge.
Four laboratory-scale units of vertical-flow constructed wetlands (VFCW) were fed once a week with faecal sludge (FS) at a constant solids loading rate (SLR) of 250 kg TS/(m2.year) (equivalent to 260-300 gN/(m2.week)) for a period of 12 weeks to study: i) the nitrification and denitrification potential of the sand layer of VFCWs and ii) the effect of percolate impounding regime (permanent or batch-impounding) on nitrogen transformation. The TN content of raw FS was characterised by 65% org-N, 34% NH4-N and 1% NOx-N. After FS application and a six-day impounding period, 8-13% TN were recovered in the percolate exhibiting the following composition: 70-80% NH4-N, 25-30% org-N and <1% NOx-N. A large fraction of the influent organic N (55%) was filtered in the bed and 24-29% of initial NH4-N were lost due to nitrification and volatilisation. In permanent impounding systems, 8-11% TN were recovered in the percolate versus 13% in batch-operated beds. N loss was increased with sand layer depth (20-40 cm) under permanent impounding regimes.
School of Environment, Resources and Development (SERD), Asian Institute of Technology (AIT), P.O. Box 4, Pathumtani 12120, Thailand. atitya.panuvatvanich@ait.ac.th
Atitaya
A
Panuvatvanich
Thammarat
T
Koottatep
Doulaye
D
Kone
D005243:Feces; D009584:Nitrogen / Q000737:chemistry*; D012722:Sewage; D053833:Wetlands
D012722:Sewage; D009584:Nitrogen