The use of artificial aeration in horizontal sub-surface flow constructed wetlands for tertiary nitrification

Increased treatment capability is required on small sewage treatment works to meet ammonium consents that are tightening to effluent concentrations of below 5 mg[Ammonical nitrogen (mg/L)] and in some cases as low as 0.5mg[Ammonical nitrogen (mg/L)] Optimisation of existing assets is preferential over the addition or expansion of the works to minimise associated costs and energy usage. Many small works in the UK currently employ horizontal sub-surface flow constructed wetlands (HSSF CWs) that have restricted capability to nitrify due to limited oxygen transfer and as such artificial aeration has been proposed as a potential upgrade technology. To assess the performance of the technology, full- scale sites were monitored in terms of ammonium and solids removal and hydraulic characterisation over 3 years. Supporting pilot studies were carried out to assess the effect of aeration on the planted vegetation and to determine optimum transfer efficiencies. Cont/d.