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50-18 Impact of Effluent from Reverse Osmosis (RO) Water Treatment Plant (WTP) on Water Quality in Albemarle Sound, Nor PowerPoint Presentation
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50-18 Impact of Effluent from Reverse Osmosis (RO) Water Treatment Plant (WTP) on Water Quality in Albemarle Sound, North Carolina. Background of Study. Temporal Variation in Water Chemistry (excluding pH and alkalinity). RO Impact Assessment

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50-18 Impact of Effluent from Reverse Osmosis (RO) Water Treatment Plant (WTP) on Water Quality in Albemarle Sound, North Carolina

Background of Study

Temporal Variation in Water Chemistry (excluding pH and alkalinity)

RO Impact Assessment

•At the present time there are no state or federal criteria for assessing the environmental impacts of discharge waters.

•The oligohaline estuaries of northern North Carolina have received little study to document ambient water chemistry, or abundance of benthic macroinvertebrates.

•Each site is unique in salinity, sediments, and water currents

•Influence of swamps and blackwaters must be considered

•Impacts are considered on a site-by-site basis – no cumulative impacts have been assessed.

Online (MLPD) –

Production = 49.9

Discharge = 13.2

Several counties in northeastern North Carolina are rapidly increasing in population but may soon be under a building moratorium due to inadequate water supply. Two of these counties have proposed 5-million gallon per day (mgd) RO-WTP to process groundwater, which will result in a discharge concentrate of 1.67 mgd of concentrate into Albemarle Sound, classified as fish-spawning habitat. State agencies have expressed the need for a one-year pre-operation study, followed by a two-year post-startup study to evaluate the potential effects on the water quality and thus the pelagic and benthic biota.

Proposed (MLPD) –

Production = 37.9

Discharge = 12.6

Change in US Population

Study Objectives

(1) document existing environmental conditions at the proposed discharge sites;

(2) determine existing environmental conditions at a working RO-WTP at Camden, NC, which currently discharges 0.2 mgd of concentrate into the Pasquotank river;

(3) determine existing food chains at proposed discharge sites, and at the Camden discharge site, and document seasonal patterns of change; and

(4) use the results of the Camden study to predict possible environmental changes at the proposed RO-WTP discharge sites

Concerns about Whole Effluent Toxicity led us to analyze all major elements instead of relying on TDS or conductivity to indicate water quality.

Sources of Water in the Study Area

  • High in silts and clays
  • Blackwater swamps and streams
  • Tannins and lignins difficult to remove
  • Groundwater very plentiful but saltier close to the ocean

Temporal Variation in alkalinity

RO Treatment Plants in North Carolina

Study Area


• Water samples from the surface and bottom were collected bimonthly from July, 2005 – June, 2006 with an Alpha sampler. The 18 sites included a grid around the producing plant, a control site 0.3km

from the discharge pipe, and two locations at each of the proposed sites on Albemarle Sound. Other samples were taken as needed to assess ambient conditions and determine extent of the concentrate plume.

• Major cations were analyzed by ICP, Cl- and SO4- by chromatograph, pH and alkalinity by titration. Nutrients were analyzed by spectrophotometry and autoanalyzer.

•At each of the 18 sites the upper 5 cm of the sediment were collected monthly from July, 2005 through December, 2006. Grain size and organic content were determined by sieving, pipette analysis and LOI.

Whole Effluent Toxicity

Effluent toxicity to aquatic organisms can come from inorganic ion imbalance present in the permitted discharge [Goodfellow et al. (2000)]. Aquatic organisms may be adversely affected by effluents containing abnormal ratios of major ions and high concentrations of the major ions. This so-called “ion imbalance toxicity” is caused by some of the common chemical constituents found in freshwater, groundwater and seawater (American Petroleum Institute, 1998). For freshwater organisms the relative toxicity of these common constituents is: K+ > HCO3- > Mg 2+ > Cl- > SO42- > Br-. However, for certain species high Ca2+ levels can be responsible for the toxicity. In particular wastewater having a Ca2+ to Na+ ratio of 15:1 has caused high mortality rates among test organisms (API study). In some cases the TDS alone causes the toxicity. In one documented case, salinities near 50% that of seawater were believed to be responsible for toxicity due to osmotic stress. Marine data are less common than those for freshwater species.

Terri Woods1, Jennifer R. Smith1, Roger Rulifson2, and Katharine Kleber2

1 Dept. of Geological Sciences,East Carolina University, Greenville, NC (

2Dept. of Biology,East Carolina University, Greenville, NC


Piper Diagram depicting water chemistry in study area and North Carolina estuaries.

Geographic Variation-Major Elements

Temporal Variation in pH



Component Matrix for PCA Analysis of Castle Hayne Wells in Southern Coastal Plain

Component Matrix for PCA Analysis of Castle Hayne Wells in Southern Coastal Plain

Potential for Mineral Precipitation

Ratios of Major Ions

November II Bottom

July II Bottom

December Bottom

September I Bottom

June I Bottom


November I Bottom

Movement of concentrate plume based

on alkalinity in bottom samples


•Physical and chemical conditions around the Camden RO-WTP site and the two proposed discharge sites appeared normal for similar habitats in this portion of North Carolina.

•Dock samples collected in October, 2005 were 2-20 times saltier than samples collected near Elizabeth City by the USGS in October from 1958-1971 (Site: USGS at EC).

•For all river and estuary sites sampled, [Na+] was about 10 times greater than that of other major cations & [Cl-] was about 10 times higher than other anions.

•Except around the Camden RO-WTP site the water column at all sampling sites was relatively well-mixed.

•Sediment at all study sites was primarily sand-sized and generally contains ~ 2% organic matter.

•In all of the surface waters analyzed, including areas immediately surrounding the diffuser pipe at the Camden RO-WTP, Ca2+ to Na+ ratios ranged from 0.026-0.08. These ratios are much less than the value of 15:1 observed to cause high mortality rates among test organisms. Of the major-element ratios, only HCO3-/Cl- was significantly higher than ambient ratios and this was only for a fewbottom samples nearest the diffuser.

•Of the waters analyzed during this study, only one sample, an in-plant discharge (44% of seawater salinity), was close to being half the salinity of seawater – a value that was shown by laboratory study, either directly or indirectly, to be responsible for toxicity due to osmotic stress.

•Significantly higher ammonium concentrations within 15 meters of the diffuser at the Camden RO-WTP suggest the possibility of increased photosynthetic activity and perhaps algal blooms. No such effect was observed during the study period, however, the naturally dark color of the river water results in visibilities of less than 0.5 meters suggesting that minimal light penetration may limit photosynthesis. High ammonium levels could be a more significant problem in the well-lit estuarine waters at the proposed discharge sites.

•The plume emanating from the Camden RO-WTP diffuser was easily detectable by major-element analysis, but not readily apparent to common hand-held equipment (YSI water quality meter) or to stationary monitoring equipment (i.e., Hydrolab). The plume shifts its position frequently, presumably with prevailing wind and current conditions.

•For all ions at the Camden RO-WTP, concentrations were much more variable at the bottom sites around the diffuser than at surface sites, and generally showed decreasing concentrations away from the diffuser in all directions. Surface waters are not noticeably affected and show less variable chemistry than bottom waters.

•The discharge was not detectable at the Control site, nor in a linear transect away from the diffuser (“P” sites) into the Pasquotank River. The discharge signal was not detectable more than about 50 meters from the diffuser.

•Aragonite is the only mineral likely to achieve saturation in any receiving water influenced by discharged concentrate, but precipitated phases should quickly redissolve in shifting water masses.

•There was no evidence that the embayment containing the Camden diffuser is accumulating the discharge stream; waters were similar in composition to the Pasquotank River.

•Relative abundances and distribution of the benthos at the Camden RO-WTP did not indicate that there was influence from the discharge plume, with the possible exception of the 10m X 10m sampling grid containing the diffuser.


American Petroleum Institute. 1998. The toxicity of common ions to freshwater and marine organisms. Document 0300-029. Washington, DC.

Goodfellow, W.L., L.W. Ausley, D.T. Burton, D.L. Denton, P.B. Dorn, D.R.Grothe, M.A. Heber, T.J. Norberg-King, and J.H. Rodgers, Jr.2000. Major ion toxicity in effluents; a review with permitting recommendations. Environmental Toxicity and Chemistry 19(1). 175-182.


This project was funded by the State of North Carolina and the Counties of Pasquotank and Currituck. The work could not have been completed without the help of students Amanda Martin, Brad Panneton, Jeremy Brandsen, Robert Howard, David Parks, Annie Gerry, Mike Guzman, Tripp Amos, and Becca Pruitt. As with virtually every field project in Geology-ECU, the help of Jim Watson, “lab mechanic extraordinaire”, was essential.

Distribution of Biota and Response to Discharge Plume

Number of species caught with all gear over the course of the study.

Seasonal variations in the species observed.

Typical assemblages…larval fish and eggs seen

in late spring 2006 only. DAY SAMPLES ONLY!

Reflects some seasonality of the species assemblage at the different locations.

Typical for oligohaline taxa in these areas. Number of species

may be higher @ diffuser site because of increased effort.

Average density of Macroplankton (density/m3) by location. Some seasonality may be implied.

Typical assemblages…larval fish and eggs seen in late spring 2006 only. No obvious effect by the diffuser…DAY SAMPLES!

Average density of macrobenthos (m-3) including all locations. The average of the Chantilly Bay-Diffuser includes all 13 sites within the 50 m2 plot around the diffuser.

Some seasonality. Diffuser and control seem to be following each other. (Even though there were more species, the density did not show the increase)

Reflects some seasonality of the species assemblage at the different locations.

P-sites transect from N3

into the Pasquotank

River to P4