Removal of arsenic (V) from drinking water using chitosan-modified natural diatomaceous earth

Addressing the unique challenges faced by resource-constrained small public utilities will require the development of more diverse, cost-effective, low-technology, and sustainable alternatives for removing arsenic and other contaminant clusters to provide safe drinking water. A hybrid bio-sorbent (CNDE) was prepared by coating natural diatomaceous earth (NDE) with chitosan at an 85% degree of deacetylation. The newly developed adsorbent was characterized to evaluate the various physical and chemical characteristics, and its effectiveness for removing arsenic(V) (As(V)) from water was evaluated. The chitosan to DE percent mass ratios were varied between 0 and 50% to assess the effect of chitosan content on the effectiveness of the resulting adsorbent. Batch bottle point equilibrium adsorption experiments were conducted to study the uptake of As(V) by CNDE and the effect of pH. Kinetic experiments were conducted to study the CNDE's rate of uptake of As(V). The residual As(V) in the solution was measured by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The results indicated that the amount of As(V) adsorbed increased with the chitosan to DE mass ratio, even if the filterability of treated water diminished. A ratio of 0.3 (30% chitosan or CNDE30) was optimal and highly effective for removing As(V) from drinking water. As(V) uptake decreased with increasing pH, with an optimal pH range between 5 and 6. The isotherm data fits both the Langmuir and Freundlich models. In a comparative study, CNDE30 showed great potential for small system applications as a sustainable alternative to Bayer’s Bayoxide E33®due to its added benefit of permitting multiple regenerations, despite having 3 to 4 times less capacity than E33®, because of its effectiveness, ease of preparation, affordability, and potential for sustainability.