AWWA WQTC64106

The Membrane Concentrate Pilot Wetland Project was conducted by the City of Oxnard, California between2003-2005 to investigate use of membrane concentrate as a water source to brackish or salt marshwetlands. Twelve 1 m³ tanks were constructed of six wetland types, including five flow-throughmesocosms (surface flow [SF] high marsh, SF low marsh, horizontal subsurface flow [SSF], peatbasedvertical upflow [VF], and submerged aquatic vegetation [SAV]), and a saltgrass evaporationsystem. The water source was RO membrane concentrate trucked weekly from the Port HuenemeWater Authority's Brackish Water Research Desalination Facility. This paper presents previouslyunpublished results of supplemental testing of bins re-plumbed as two sequential treatment trains ofthree cells each to test the hypothesis that a sequence of varied types of wetland treatment cells willprovide higher mass removal rates of trace metals than individual cells. Train 1 consisted of VF, SSF,and SAV cells in series, designed as a pretreatment system with the least potential exposure of theconcentrate to sensitive ecological receptors. Train 2 consisted of VF, SFHM, and SFLM cells inseries, designed to approximate a natural salt marsh gradient of high to low marsh types. Averageinflow rates averaged 51.1 gpd (16.3 cm/d HLR) to Train 1 and 56.5 gpd (18.1 cm/d HLR) to Train 2.Train 1 showed varying concentration changes in TDS, SO4, alkalinity, and Cl through the system,from a 16% alkalinity reduction to a 19% Cl increase. Through water loss by evapotranspiration, allfour salts showed a net mass removal through the series. Train 2 showed salt concentration increasesof 37% for Cl, but mass removals for all salts ranged from 33% for Cl to 59% for alkalinity. Metals(Hg, Cu, Mn, Be, As, Zn) were near or below reporting limits in the concentrate influent and showedlittle change through the wetland cells. Al typically increased slightly through the wetland. Fe and Sedecreased measurably. NO₃ decreased measurably in all systems. TP decreased and COD increased inall systems. Tests on mysid shrimp demonstrated that effluent from both treatment trains was lesstoxic than raw concentrate water. Chronic toxicity testing results indicated that only raw membraneconcentrate samples affected survival of both mysid shrimp and topsmelt. These data suggest that apretreatment train of wetland systems could be constructed for treatment of concentrate to safelydischarge to a natural system. Includes 11 references, tables, figure.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

16

File Size:

1 file , 400 KB