Removal of Fluoride and Hardness in Dietary Intake (water) in Chronic Kidney Disease of unknown Etiology (CKDu) Prevalent Areas by Domestic Reverse Osmosis Units

Abstract

The origin of Chronic Kidney Disease of unknown etiology (CKDu) that is rapidly invading
the dry zone of Sri Lanka has not yet been identified. However, occurrence of the disease is
thought to be linked with excess levels of fluoride and hardness in drinking water. Hence, the
study herein focuses to evaluate the suitability of domestic Reverse Osmosis (RO) units;
which introduced in CKDu affected areas to remove excess fluoride and hardness.
Accordingly, the drinking water quality in CKDu prevalent areas in terms of fluoride and
hardness was simulated in the laboratory and the removal of aforesaid constituents using
domestic ROs was investigated.
According to water quality analyses, domestic RO units effectively removed hardness even at
extremely high initial concentrations, such as 1,730 mg/L (as CaCO3). Excessive removal of
Calcium and Magnesium by the RO units was observed, thus remineralization of the
permeate up to 80-100 mg/L as CaCO3 is required to ensure health benefits. Meanwhile,
fluoride removal was observed to be highly dependent upon initial fluoride and hardness
concentrations. It was not possible to suggest an „optimum removal level‟ for fluoride, where
permeate fluoride concentration exceeded the maximum permissible WHO Drinking Water
Guideline value of 1.5 mg/L. However, it may arise at a point where fluoride and hardness
concentrations in raw water fall within 1.7-3.5 mg/L and 570-1,130 mg/L as CaCO3,
respectively.
Plausible reasons for ineffective removal of fluoride could be the relatively small size and
low ionic charge of fluoride. Additionally, high concentration of heavy ions may interfere
with fluoride adsorption of activated carbon filter in the domestic RO unit. Effective fluoride
removal could be achieved by adopting appropriate pre-treatment methods for hardness
removal. Separate threshold levels for fluoride and hardness levels in drinking water should
be defined, especially for CKDu patients.
Keywords: Chronic Kidney Disease, Domestic reverse osmosis units, Fluoride, Hardness