Water is crucial not only for sustaining life but also for socio-economic development of a country. However, its availability in the right quality remains a great challenge. Groundwater is presently one of the major sources of water supply in Kiambu town and its environs. The town is surrounded by hilly Kikuyu farmland although it is under urbanization as Nairobi is growing fast and more people are settling in neighbouring towns. Kiambu Water and Sewerage Company is a Water Service Provider operating within Kiambu Town, under a Service Provision Agreement with Athi Water Services. In its mandate to ensure efficient and economical provision of water services in Kiambu Town it has drilled 11 boreholes within the Town. The water from some of the boreholes contains iron concentrations in excess of the WHO recommendations, which gives the water a sour metal taste, stains laundry and food cooked in the water receives an unappetizing colour. As a result, people use unprotected surface water instead hence the need for removal of the iron. Also in an attempt to remove the iron from water, various methods are used which may not be effective hence the need for evaluation of the treatment methods. The purpose of this study is to therefore evaluate the use of chlorine as a treatment method for removal of iron in the borehole water.
Thuku BH was identified for sampling since it contains iron in excess of the WHO recommendations of 0.3 mg/l. Two samples were collected and tested at the University of Nairobi Public Health Engineering Laboratory in order to establish the concentration of iron. The efficiency of chlorine in removal of iron was determined by comparing the difference in the iron concentration before and after treatment. A bench test was carried out to determine chlorine dosage. Different retention times were tested to assess the effect on iron concentration.
The iron concentration in Thuku BH was found to be 0.6 mg/l. Therefore, the water required treatment. The result from the performance evaluation of the chlorination method showed 66.7 percent efficiency in iron removal. From the laboratory test, it was determined that the chlorine dosage for Thuku BH was 2 mg/l. The amount of chlorine required to treat Thuku BH water was calculated to be 2.42 kg Cl2/day. The results showed remarkable iron removal with increased retention time with 83.3% percent iron removal with a retention time of one hour. Therefore, it was concluded that chlorination method is an effective method in removal of iron but it requires a higher retention time than the 20 minutes for full oxidation of iron to take place.