Pollutants Removal Efficiency of two Mangroves Species (<i>Avicennia marina</i> and <i>Rhizophora mucronata</i>) in Treating Domestic Sewage

Abstract

Bucket experiments were conducted to evaluate the effect of domestic sewage loading and inundation time on pollutants removal efficiency for cells planted with Avicennia marina and Rhizophora mucronata mangroves species. Domestic sewage from the University of Dar es Salaam primary facultative waste stabilization pond was loaded onto buckets planted with the two mangroves species and unplanted buckets (bare sediment) used as control units. Sea water was used to dilute the sewage to make desired sewage strength of 0, 25%, 50%, 75% and 100%. Inundation times of 1 week, 24 hours and 12 hours were used in these experiments. Based on the obtained results, units planted with mangroves showed optimal removal of phosphates, total phosphorous and ammonium-nitrogen at sewage loading of 100% when inundated for 1 week. There was a significant reduction in concentration of phosphorous, total phosphorous and ammonium-nitrogen observed in planted units. However, there was insignificant difference in nutrients removal between the two mangrove species. While Avicennia marina units removed phosphorous, total  phosphorous and ammonium-nitrogen by 94.49%, 93.25% and 94.76% respectively, removal efficiency of the same pollutants by Rhizophora mucronata units were 94.00%, 92.82% and 94.05%, respectively.  Generally, the removal percentage of phosphorous, total phosphorous and ammonium-nitrogen were significantly higher in 1 week inundation time than in both 24 hours and 12 hours inundation time. Based on the  performance of mangrove on nutrient removal, it was concluded that the two mangrove species could be used as phytoremediators of domestic wastewater in mangroves constructed wetlands in coastal areas.

Key words: Avicennia marina, Rhizophora mucronata, domestic sewage, inundation.