Technologies and Costs for Removal of Arsenic From Drinking Water

The most significant weakness of this technology appears to be its cost. Currently, GFH mediacosts approximately $4,000 per ton. However, if a GFH bed can be used several times longer thanan alumina bed, for example, it may prove to be the more cost effective technology. Indeed, the systemprofiled in the field study presented above tested AA as well as GFH and found that GFH wassufficiently more efficient that smaller adsorption vessels and less media could be used to achieve thesame level of arsenic removal (reducing costs). In addition, unlike AA, GFH does not require preoxidation.A treatment for leaching arsenic from the media to enable regeneration of GFH seems feasible,but it results in the generation of an alkaline solution with high levels of arsenate which requiresfurther treatment to obtain a solid waste. Thus, direct disposal of spent GFH should be favored.2.6.4 Iron FilingsIron filings and sand may be used to reduce inorganic arsenic species to iron co-precipitates,mixed precipitates and, in conjunction with sulfates, to arsenopyrites. This type of process isessentially a filter technology, much like greensand filtration, wherein the source water is filteredthrough a bed of sand and iron filings. Unlike some technologies, ion exchange for example, sulfateis actually introduced in this process to encourage arsenopyrite precipitation.This arsenic removal method was originally developed as a batch arsenic remediationtechnology. It appears to be quite effective in this use. Bench-scale tests indicate an average removalefficiency of 81% with much higher removals at lower influent concentrations. This method wastested to arsenic levels of 20,000 ppb, and at 2000 ppb consistently reduced arsenic levels to less than50 ppb (the current MCL). While it is quite effective in this capacity, its use as a drinking watertreatment technology appears to be limited. In batch tests a residence time of approximately sevendays was required to reach the desired arsenic removal. In flowing conditions, even though removalsaveraged 81% and reached greater than 95% at 2000 ppb arsenic, there is no indication that thistechnology can reduce arsenic levels below approximately 25 ppb, and there are no data to indicatehow the technology performs at normal source water arsenic levels. This technology needs to befurther evaluated before it can be recommended as an approved arsenic removal technology fordrinking water.2-47