Removal of faecal coliforms in a wastewater stabilisation pond system in Mindelo, Cape Verde

Abstract

In Mindelo, Cape Verde, domestic wastewater is treated in a waste water stabilisation pond system with the aim of reusing the water for agricultural purposes. The conductivity in influent wastewater is high and in order to minimise an increase in the conductivity the plant is operated with as low retention time as possible. An investigation was performed over two and a half months in 1995 with the aim of finding factors that affect the removal of faecal coliform bacteria. COD, conductivity, flow, pH and faecal coliforms were then followed through the system. The results show that the die-off rate, K, is high when the pH is high. The results also indicate that the retention time seems to be the most important factor, which means that the plant has to be operated with at least 3-4 maturation ponds in series and the inlets and outlets have to be constructed in a way that avoids short-circuiting. It was also found that not only the evapuation but also chemical and/or biological reactions affect the conductivity. This phenomenon will be investigated further.