This paper describes the results of two pilot studies in which continuous chloramination
was 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 aerated
groundwater contaminated with trichloroethylene (TCE) for the removal of total dissolved
solids (TDS), nitrate and arsenic. A major concern
in the application of RO to this groundwater was the potential for biological fouling due to
the elevated dissolved oxygen content (from air stripping of the groundwater to remove the
TCE) 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 biofouling
would occur and to assess the ability of continuous chloramination to control biofouling
without causing any membrane degradation. The paper provides
a 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 lakes
located along the St. Johns River, which drains the watershed located in the northeastern
portion of Florida. The paper provides the mean, maximum and minimum values for key water
quality parameters of the lake water as measured during the sampling period January 2000
to August 2002. RO treatment was evaluated to remove color, reduce dissolved organic
carbon (DOC) levels (to ensure compliance with disinfection byproduct regulations
following free chlorine disinfection) and to reduce TDS to <400 mg/L to match the
minerality of existing groundwater supplies. To comply with the Surface Water Treatment
Rule (SWTR) and to minimize RO membrane fouling, the lake water was first pretreated
using ferric sulfate coagulation, high rate clarification (SuperPulsator) and granular media
filtration. Ferric sulfate was dosed prior to rapid mix along with either sulfuric acid or
caustic to attain a pH of 4.3 to optimize DOC removal. A cationic polymer was also added to
improve 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 achieve
a target combined chlorine residual of 1.0 mg/L as measured in the filter effluent. From 900
hours to the end of testing, the point of chloramination was re-located to filter influent
based on changes in RO performance. The paper includes the overall process schematic for the
Study B treatment system.
Includes 7 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 870 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 16 |
| Published : | 03/01/2005 |
