Graduation Year

2004

Document Type

Thesis

Degree

M.S.E.V.

Degree Granting Department

Environmental Engineering

Major Professor

Daniel P. Smith.

Keywords

TOC, disinfection by-products, Microcystin-LR, Geosmin, 2-Methylisoborneol

Abstract

Nanofiltration (NF) membrane technology is effective for removal of natural organic matter (NOM) and Disinfection By-Product (DBP) precursors from treated surface water (Allgeier et al., 1995, Chellam et al., 2000, Smith et al., 2002). However, there is a need to control other micropollutants, such as compounds released from algal blooms. In this research, the feasibility of using NF for removal of cyanobacterial exudates was evaluated as a polishing process for conventionally treated surface water. Screening tests were conducted to compare the performance of four NF membranes, Filmtec's NF90 and NF270, and Hydranautics's LFC1 and NTR7450, for removal of NOM and cyanobacterial exudates. The source water for the experiments was derived from Lake Manatee (FL) following full scale treatment by enhanced coagulation and dual media filtration. Water samples were amended with low levels of three cyanobacterial exudates: microcystin-LR, geosmin and 2-Methylisoborneol (MIB).

The rapid bench scale membrane test (RBSMT) protocol was used to test NF at four recoveries of 50%, 70%, 85% and 95%. Bulk organics (TOC and UV₂54) and inorganics (conductivity, total and calcium hardness) were monitored along with other operating parameters during the setting and recovery tests. Spike tests were performed by spiking microcystin-LR (9.5 to 12.0 micro g/L), geosmin (45 to 220 ng/L) and MIB (45 to 225 ng/L). Three NF membranes (NF90, NF270 and LFC1) were effective for over 90% rejection of TOC and associated disinfection by-product formation potential (DBPFP). Due to NF treatment, the bromide:TOC ratio increased resulting in a shift towards higher levels of brominated DBPFPs. Similarly, these three NF membranes (NF90, NF270 and LFC1) were effective for removal of microcystin-LR to below the World Health Organization (WHO) guideline of 1 micro g/L.

Only two of the NF membranes tested (NF90 and LFC1), were capable of removing geosmin and MIB to levels below the taste and odor threshold. These membranes removed greater than 92% of the geosmin and MIB. Based on these bench scale tests, further testing of NF on a pilot scale is warranted.

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