Relative performance of duckweed ponds and rock filtration as advanced in-pond wastewater treatment processes for upgrading waste stabilisation pond effluent: a pilot study. 
An experimental pilot plant was operated over a five month period to assess the relative treatment performances of: a duckweed (DW) pond; a rock filter (RF); and an open pond (OP); for the upgrading of final WSP effluent prior to reuse applications.  Each pilot treatment system consisted of three identical ponds arranged in three parallel series, each fed a continuous flow of wastewater from the local Bolivar treatment plant.  Light penetration profiling for the DW and OP systems revealed some 55% greater light attenuation capacity for DW ponds compared to the OP system.  Results showed a significantly elevated performance capacity for the RF treatment with respect to BOD5, SS, turbidity and NH4-N removal, but equal treatment performances for algal (chlorophyll) removal.  No significant performance differences were evident between the DW and OP treatments for any of the monitored parameters.  Soluble reactive phosphorus, faecal coliform and E. coli removals were similar for all pilot treatment systems.  Rock filters not only demonstrated an enhanced performance capacity in terms of removal of loaded parameters, but also showed greater reliability of performance and produced a consistently higher quality final effluent.  Rock filters demonstrated greater potential over both DW and OP systems for the upgrading of WSP effluent prior to reuse application.