Welcome to Nakuru Defluoridation Company Ltd

COMBINED FILTERS (BACTERIA AND FLUORIDE)

 

At the beginning of 2005, the first combined filters were field tested. The combined filter is a recent development, arising from the need to remove fluoride and microbiological contaminants from the water. The combined filter consists of 2 filter processes within the same system. The upper bucket for raw water storage is transparent hence the water level is visible without opening the lid. The raw water passes through a ceramic candle filter containing silver nitrate and activated carbon. Two different processes lead to a removal of microorganisms: Filtration through the ceramic candle and toxic silver nitrate that kills microorganisms that passed through the filter. Additionally activated carbon adsorbs chemical impurities, such as dissolved organic material or/and heavy metals. The ceramic filter (Kshs 800) is imported from Brazil as this filter candle is more effective than locally manufactured ones. Then the water first flows top-down through a PVC pipe filled with bone char then bottom-up through an inner bucket also containing bone char (7 L). The treated water spills over to the 20 L water bucket where it is stored and ready for withdrawal. Apart from removing bacteria, organic impurities and heavy metals from the water, the first filtration step with the candle filter also controls the flow rate to the defluoridation part of the system. Studies showed that the flow rate strongly depends on the turbidity of the raw water (the higher the turbidity, the stronger the clogging) and the raw water level (decreasing flow rate with decreasing amount of water). Tests with 10 L of raw water filled to the bucket containing the candle filter showed that the flow rate is constant for the first few liters of water passed through the ceramic filter. At the beginning the flow rates of raw water with 1 NTU were more than twice as big as for raw water with 5 NTU (25 mL/min and 10 mL/min, respectively). After 4 hours, 5.5 L and 2.4 L of treated water can be withdrawn for raw water with 1 NTU and 5 NTU, respectively. The contact time in the defluoridation filter at the beginning of the filtration process amounts to ~30 min for the raw water with 1 NTU and increases with time and turbidity of the raw water. Further experiments are ongoing to determine the maximum turbidity that still allows the use of the combined filter system. The special design of the defluoridation part of the unit leads to an increased filter distance and therefore optimizes the removal ability of bone char. combined filter —   for more information contact us on info@cdnwaterquality.co.ke