Technologies and Costs for Removal of Arsenic From Drinking Water

Domestic sewage means untreated sanitary wastes that pass through a sewage system. Dischargesmeeting the above criteria are excluded from regulation as hazardous waste.Although the brine stream may be deemed a hazardous waste, such characterization would not,in itself, prevent disposal to a POTW since wastes that passes through a sewer system to a POTW areexempt from RCRA regulation. Discharge to the sanitary sewer may be limited by TBLLs for arsenicor TDS. The TDS is the more likely limiting factor since the arsenic TBLL would need to berecalculated since the background arsenic will change. The only net increase in arsenic is related tothe water loss from the drinking water treatment plant to the POTW. TDS is different. TDS is beingadded to the waste stream. Due to the potential for an increase in total dissolved solids, anionexchange would be favored in areas other than the southwest where the volume of brine is very smallrelative to the total volume of wastewater being treated at the POTW.Although one small system was reported to have disposed of its waste brine to the facility’sseptic tank (EPA October 2000), such disposal is likely to be regulated by local and State regulationsand therefore was not considered in the cost analysis for the final rule.4.4.8 Activated AluminaActivated alumina (AA) can be operated with or without pH optimization and regeneration.Systems optimizing pH and regenerating will produce a regenerant waste solution with a pH ofapproximately 12 and high in dissolved solids, aluminum, and arsenic (AWWARF, 1998).Regeneration of AA is accomplished using 15 to 25 bed volumes (BV) of 2N NaOH, 7 BV of rinse,and 15 BV of 2N H 2 SO 4 for neutralization (approximately 42 BV per regeneration cycle). Arsenicis strongly adsorbed to the media, so only about 50 - 70% of the adsorbed arsenic is removed evenusing a strong base.. The brine stream produced by the regeneration process then requires disposal.The November 1999 Technology and Cost Document listed discharge to a sanitary sewer as thedisposal mechanism for the brines. It was noted that TBLLs for arsenic might restrict discharge ofbrine streams to the sanitary sewer. Since activated alumina run lengths are much longer than anionexchange, the arsenic concentrations in the brine stream would likely be much higher even withincomplete regeneration. Regeneration of activated alumina media is not recommended even forlarger systems because disposal of the brine may be difficult, the regeneration process is incompletewhich reduces subsequent run lengths, and for most systems it will be cheaper to replace the mediarather than regenerate it. As a result, regeneration of AA was not considered for the final rule.4-19