14 Dec 2015
Arsenic filter units using sustainable biopolymers
In many rural areas, substitution of arsenic contaminated drinking water by a safe source may not be possible and arsenic removal may be a more appropriate water supply option in these situations. Removal methods like coagulation, suffers from the drawback of sludge disposal and have difficulty consistently meeting a low-level MCL of 10 µg/l. Reverse osmosis and electrodialysis requires power input, results in 20 -25% water wastage, expensive and thus not suitable for rural areas, especially in regions of water scarcity. Methods like ion exchange resins remove only arsenate. The main drawback of AA adsorption technology –is the cost of the material, decreasing uptake at pH 8, requirement of regeneration and lack of selectivity for arsenic. The biggest challenges ahead lie in applying the technologies described in poor, rural settings, and in enabling those communities to choose safe sources of water for drinking and cooking.
Chitosan, has been reported to be an efficient heavy metal scavenger due to the presence of hydroxyl and amino group. Peninsular India with a large coastline contains numerous seafood processing industries, which generate chitosan as a waste product. Due to the versatility of chitosan towards heavy metal adsorption and efficiency of iron oxide hydroxide towards arsenic removal the iron oxide coated chitosan proved to be a novel adsorbent for the removal of both As (III) and As (V) from real life arsenic contaminated ground water (1). A domestic filter unit has been developed and design of the same is shown in Fig.1. An orifice was made (1.5 mm) using the brass and nut assembly. Flow rate was found to be 7 l/h and nylon filter bag was used in the upper chamber to hold the adsorbent. Around 500g of iron coated chitosan flakes was used as the adsorbent. The results obtained are shown in Fig. 2. It should be noted that with 10 ppb as the cut off, 500 l of water could be treated and with 50 ppb as cutoff 950 l of water could be treated. Further the used chitosan flakes could be easily regenerated with 0.1 N NaOH and exhausted adsorbent was found to be non-hazardous as per EPA’s TCLP leaching test. Additional advantage of using chitosan is that it has antibacterial property and hence fouling of the sorbent bed will not occur. Thus this chitosan-based adsorbent is cost effective and environment friendly and could be applied to treat both As (III) and As (V) contaminated ground water streams.
Reference
1. Anjali Gupta and Nalini Sankararamakrishnan, Preparation and Evaluation of iron – chitosan composites for removal of As (III) and As (V) from arsenic contaminated real life groundwater, Water Research, 43, 2009, 3862 – 3870.
Fig. 1. Schematic Representation of Arsenic domestic filter unit
Fig. 2 Validation of Arsenic filter unit using Arsenic contaminated water
Total Arsenic concentration 192 ppb, pH of the water 7.82, flow rate 7 l, adsorbent dose 500 g of Iron Chitosan Flakes
About the Author:
Nalini Sankararamakrishnan is a Scientist at Centre for Environmental Science and Engineering, Indian institute of Technology, Kanpur
For more information, contact: nalini@iitk.ac.in