AWWA MTC61143

This paper describes the results of two pilot studies in which continuous chloraminationwas evaluated for control of biofouling during reverse osmosis (RO) treatment of a brackish groundwater(Study A), and a surface water (Study B).Study A comprised the testing of RO treatment for demineralization of an aeratedgroundwater contaminated with trichloroethylene (TCE) for the removal of total dissolvedsolids (TDS), nitrate and arsenic. A major concernin the application of RO to this groundwater was the potential for biological fouling due tothe elevated dissolved oxygen content (from air stripping of the groundwater to remove theTCE) and presence of trace levels of assimilable organic matter from groundwater pollution.To address this concern, a pilot study was conducted to determine to what extent biofoulingwould occur and to assess the ability of continuous chloramination to control biofoulingwithout causing any membrane degradation. The paper providesa schematic for the pilot-scale treatment process used. The surface water used in Study B pilot testing was taken from Lake Monroe, one of many lakeslocated along the St. Johns River, which drains the watershed located in the northeasternportion of Florida. The paper provides the mean, maximum and minimum values for key waterquality parameters of the lake water as measured during the sampling period January 2000to August 2002. RO treatment was evaluated to remove color, reduce dissolved organiccarbon (DOC) levels (to ensure compliance with disinfection byproduct regulationsfollowing free chlorine disinfection) and to reduce TDS to <400 mg/L to match theminerality of existing groundwater supplies. To comply with the Surface Water TreatmentRule (SWTR) and to minimize RO membrane fouling, the lake water was first pretreatedusing ferric sulfate coagulation, high rate clarification (SuperPulsator) and granular mediafiltration. Ferric sulfate was dosed prior to rapid mix along with either sulfuric acid orcaustic to attain a pH of 4.3 to optimize DOC removal. A cationic polymer was also added toimprove floc settleability. During the first portion of testing (0 to 900 hours), ammonia,followed by chlorine, were dosed to the raw water prior to ferric sulfate addition to achievea target combined chlorine residual of 1.0 mg/L as measured in the filter effluent. From 900hours to the end of testing, the point of chloramination was re-located to filter influentbased on changes in RO performance. The paper includes the overall process schematic for theStudy B treatment system. Includes 7 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

03/01/2005

Number of Pages:

16

File Size:

1 file , 870 KB