Preliminary investigation of the potential of four tropical emergent macrophytes for treatment of pre-treated pulp and papermill wastewater in Kenya

The potential of four aquatic macrophytes for treatment of wastewater in constructed wetlands was investigated in bucket mesocosms at Pan African Paper Mills (E.A) Limited. The buckets were operated as semi-continuous batch reactors with reversed vertical flow for a period of 3 months. Four treatments were applied involving two hydraulic retention times (HRT) and two wastewater concentrations. Plants appeared healthier and greener in treatments at HRT5 than at HRT10. Cyperus immensus and Typha domingensis had higher biomass gain compared to the other two species. Plant nitrogen and phosphorus content, based on dry weight, was lower at the end of the experiment than at the beginning in all treatments for all species. The removal efficiency achieved for COD ranged from 10 to 55% for planted buckets at HRT5 and 15 to 65% at HRT10 for similar buckets. The mean percentage COD removal in unplanted buckets was significantly lower than in planted ones. TSS removal efficiency ranged from 44-86%. Buckets planted with Typha exhibited the highest removal efficiency in all treatments. Those at HRT5 showed significantly higher removal efficiencies than those at HRT10 for all species. The results indicate that the plants are suitable for use in constructed wetlands for treatment of the wastewater provided the appropriate treatment is applied.