Influence of water hyacinth on the presence of pathogens in wastewater ponds.

Water hyacinth (Eichhornia crassipes) is a free floating macrophyte that has been used for water treatment in many parts of the world. Water hyacinth biomass was planted in a wastewater pond and its influence on pathogens and heterotrophic bacteria were studied. The plants provide the water body with oxygen produced from leaf photosynthesis, it is then used by heterotrophic bacteria (both suspended and attached microorganisms for organic matter degradation. The water hyacinth- bacterial relationship is symbiotic. The root swabs of the water hyacinth played a role of massive attachment reservoirs for the bacteria. The bacteria survived longer on the root zone than the wastewater since nutrient and oxygen are available at the root zone. The bacterial root attachment to bulk wastewater ratios for various bacterial species were: total coliforms, 105; faecal coliforms, 104; faecal streptococci, 103; and heterotrophic bacteria 108. This implied that root swabs contained more bacteria than wastewater. A model that used the plug flow philosophy, to predict faecal coliform mortality rate was developed. It incorporated; physical parameters (solar intensity, pH and dissolved oxygen), sedimentation and biofilm terms. These three terms covered the mortality of both the suspended and biofilm-attached faecal coliform bacteria. The model was found to be quite satisfactory and logical in predicting faecal coliform mortality. The sedimentation term was later omitted as it contributed only 3.2 % to the entire model.