APPLICATION OF IMMERSED ULTRAFILTRATION MEMBRANES FOR TREATMENT OF GROUND WATERS CONTAINING HYDROGEN SULFIDE

摘要

A nuisance compound commonly encountered in groundwater supplies is hydrogen sulfide (H_2S), which causes an unpleasant rotten-egg smell in water at concentrations as low as 0.05 ppm. Treatment strategies for H_2S removal often consist of air stripping and oxidation. Since hydrogen sulfide is a reactive gas, the aeration process will only remove that portion of the H_2S that is in the gaseous state. One method of removing the remaining fraction of sulfide is by the conversion of sulfide to insoluble elemental sulfur by oxidation. Once oxidized, the colloidal sulfur causes high levels of turbidity (>20 NTU), which must be removed by a subsequent solid-liquid separation step.rnThe use of microfiltration (MF) and ultrafiltration (UF) membranes for municipal water treatment has traditionally been limited to high quality surface water sources. Despite the recent, significant increase in the acceptance and application of both MF and UF membrane systems in North America, UF and MF membranes have typically not been applied on waters having an average turbidity level greater than 20 NTU without extensive pretreatment. The application of membranes at water treatment plants with moderate to poor quality raw water has generally been limited to either settled or filtered water for polishing treatment. The application of membranes for groundwater treatment has also been limited due to the relatively high water quality of groundwater with respect to turbidity and microbiological parameters. The promulgation of increasingly stringent regulations for groundwater under the direct influence of surface water (GWUDI) has resulted in increased interest in membrane filtration for the treatment of groundwater sources.rnRecent advances in the configuration and application of immersed membrane systems offers an opportunity to economically apply UF membranes to treat groundwater containing high turbidity caused by elemental sulfur on a large scale without conventional pretreatment. This can be accomplished using a combined treatment process in which vacuum driven, hollow fiber membranes are directly immersed in coagulated and flocculated raw water. The membranes provide a positive barrier to parasites such as Giardia and Cryptosporidium, as well as high concentrations of both organic and inorganic solids, which are either suspended in the raw water or developed by coagulation and co-precipitation. This integrated coagulation/membrane process eliminates the need for sedimentation and rapid gravity sand filtration and is not negatively impacted by high turbidity levels. In addition to turbidity and pathogen reduction, the process can also be optimized for iron, manganese, color and TOC reduction.