Arsenic Removal from Water VSN-33
A convenient and cost-effective solution for removing arsenic from drinking water
VSN-33, an iron hydroxide-based media, was designed to assist help in reaching the newest World Health Organization (WHO) requirement for arsenic: 10 parts per billion. VSN-33 has improved capabilities compared to all other commercially available media. Advantages include:
- Highest capacity over a wide range of water conditions
- High capacity results in smaller diameter vessels and a smaller system footprint
- Removal of both As(III) and As(V) across a wide pH range without use of pretreatment
- Stable performance during pH fluctuations without pretreatment
- Granular product that is easily installed and maintained
- Spent media can be disposed as a nonhazardous material
- NSF/ANSI Standard 61 certified without limitations
- DIN/EN 1509 certified for potable water production
VSN-33 media’s high capacity makes it an ideal non-regenerable, single-use product. It offers an affordable, easy-to-operate approach, especially for small or mid-sized systems. Eliminating regeneration means avoiding the hassles and cost of chemical storage and usage, while eliminating waste stream disposal issues. VSN-33’s strong affinity for arsenic allows it to maintain a strong bond to the removed arsenic, allowing easier and safer disposal. VSN-33 also features a longer useful life than traditional adsorbent media, for more productive, cost-advantaged operation.
The operation cost varies between 6 and 12 cents (USD) per cubic meter of treated water for typical well waters, but its capacity and cost vary depending on raw water quality (pH, silica concentration, redox potential).
Variation in the pH level of feed water, which is common with all kinds of water, affects the adsorption capacity of filter media. Although VSN-33’s capacity can be slightly reduced with pH variation, the level of arsenic in the effluent remains below 10 ppb.
All media experience reduced capacity when handling water with a high silica content (above 40 ppm). This reduction is less noticeable in arsenic removal with VSN-33, which translates into a longer life for the media.
Different configurations — series or parallel — allow for efficient operation. Required limits are met even when water has a very high concentration of arsenic. On systems with standby units, when the filter is not operating arsenic can travel from the surface to deeper within the filter, maximizing final capacity.
Applications where VSN-33 excels over other media include:
- Mineral water production when addition of chemicals is not allowed (other media require pH regulation or dosage with oxidants to obtain consistent and efficient arsenic removal).
- Reverse osmosis installations that successfully complied with the previous arsenic limit of 50 ppb, but require a polishing unit to comply with the new WHO limit of 10 ppb. In these cases, low pH and low silica concentration increase media capacity, reducing operating costs more than 20 times.
VSN-33 removes not only arsenic, but the following contaminants:
Pressure drop across the bed determines the frequency of backwashing, which is usually performed every month or so, but can be increased depending on the turbidity and amount of suspended solids present in raw water. Prefiltration with a multimedia filter is recommended. As a final polish, a 5-micron filter is needed. The diagram shows the pressure drop across the bed as a function of filtration velocity:
An average filtration rate of 10 m/h is recommended, never exceeding 20 m/h.
This diagram shows the expansion percentage of the bed, depending on backwash flux. A 26-28 m/h backwash rate should be guaranteed.