Copper (Cu) is a high-profile ubiquitous contaminant found in numerous point and non-point source effluents, including those generated by activities from the Department of Defense (DoD). Because copper is highly toxic to larval organisms, the U.S. Environmental Protection Agency (U.S. EPA) considers this heavy metal a priority pollutant, and its discharge is under regulatory control. Water quality criteria (WQC) for dissolved copper in receiving bodies of water includes a freshwater criterion maximum concentration (CMC), also known as acute value, of 13 µg/L-1 (micrograms per liter or parts per billion, ppb), and a freshwater criterion continuous concentration (CCC), also referred to as chronic value, of 9 µg/L-1. For saltwater those criteria are a CMC of 4.8 µg/L-1 and a CCC of 3.1 µg/L-1. While concentrations in ambient waters are regulated as the dissolved fraction (i.e., filtered through 0.45 µm pore-size), regulation of effluents is done on the total recoverable fraction (i.e., unfiltered, acidified to pH 2 and digested).
A rapid, in-place, characterization of total recoverable copper in effluents can be accomplished by the Total Copper Analyzer (TCA). This in-place characterization will allow for the rapid separation of the effluent between that in compliance and that in need of treatment, thus reducing the costs of operation since the volume of water sent for treatment can be minimized. This characterization also will provide important information for the management of sources of copper within the installation.
There is no other known instrument capable of measuring total recoverable copper, either in situ or at near real-time (i.e., within 5 minutes). Conventional characterization of effluents is performed off-site with laboratory tests, with the associated costs and turnaround time often taking weeks for processing. As the TCA will provide a means to verify that the discharge is within permit requirements for copper, in near real-time and at the place of discharge, it will be a great asset for any regulated discharger, both private and public, including the DoD.
The main objective of the demonstration was to validate the use of the TCA for continuous measurement of total recoverable copper in industrial situations at full-scale. The TCA was deployed in three industrial settings and was allowed to operate continuously for more than a month in each case. Parameters determined were the precision, accuracy and dynamic range of the total recoverable copper measurements, working-life expectancy, and required maintenance schedule.
Total recoverable copper measured in effluents by the TCA agrees to that measured with more traditional methods. This was demonstrated by the similitude in total copper concentrations measured by the TCA to those measured by both Graphite Furnace Atomic Absorption (GFAA) and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) in grab samples taken from Puget Sound Naval Shipyard (PSNS) and Pearl Harbor Naval Shipyard (PHNS) at the time of the demonstration.
The range of total recoverable copper concentrations and its output rate make the TCA a significant discharge management tool. The dynamic range of the TCA measured under laboratory conditions is from 0.5 to 400 µg/L-1 in deionized (DI) water and from 2 to 400 µg/L-1 in artificial seawater with salinity 32 psu (practical salinity units). The lower limits in these ranges are considered the limits of detection. These ranges and limits of detection are considered relevant for industrial and regulatory purposes. The TCA has an accuracy of 99% with a precision better than ±3 µg/L-1 (±6.8%) at the 30 µg/L-1 level. The TCA measurements are considered as near real-time as there is a lag of 5 minutes from intake to measurement of total copper in the sample. But, as the TCA is a flow-through system, the continuous output of data can be adjusted down to a few seconds, providing a stream of information for management of the discharge. However, there is a need for daily verification of the working status of the TCA.
Use of the TCA under extreme conditions of organic matter and in the presence of oxidizers is not warranted. In controlled laboratory conditions, the TCA had a decrease in sensitivity of 16% in the presence of 5 µg/mL-1 humic acid. The effect of organic matter was observed in the demonstration at Schofield Barracks Waste Water Treatment Plant (SBWWTP). There the TCA measured copper concentrations up to 29 µg/L-1 larger than those measured by GFAA and ICP-MS. Experience shows that copper measurements by the copper ion selective electrode (Cu-ISE) are affected by the presence of strong oxidants, such as hypochlorite (bleach).
The Total Copper Analyzer is the first instrument capable of measuring total recoverable copper in effluents, in situ, in near real-time, and at environmentally relevant concentrations. This demonstration and validation of the TCA under industrial situations supports its use as a management tool in most situations. Agreement with copper concentrations measured with the accepted GFAA and ICP-MS technologies support the performance of the TCA in cases of saline waters with low organic matter content (i.e., discharges from dry docks). However, as the performance of the TCA did not meet the expectations under conditions of high organic matter (i.e., outfall of a wastewater treatment plant), application of the TCA for regulatory purposes is not warranted.