CICEET Progress Report for the period 9/15/04 though 3/15/05

Project Title: Electrochemical Remediation and Stabilization of Contaminated Sediments
Principal Investigator(s): Kevin H.Gardner, Jeffrey Melton

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Figure 9a

Figure 9b

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• Hire an employee to conduct laboratory experiments unfinished by the initial graduate student and previous visiting scholar, essentially, to complete the project planned in the 2002 proposal to CICEET
• Conduct bench scale experiments using direct electrical current to remove polycyclic aromatic hydrocarbons (PAHs) and heavy metals from Cocheco River sediments
• Characterize the sediment pre- and post-remediation, including water content, pH, chloride, organic carbon, and black (soot) carbon
• Compare leaching methods for metals digestion/total metals availability, including the Dutch Nordtest NT Envir 003 Availability test (in-house) and USEPA Method 3051 Microwave Digestion (contracted laboratory)

Progress on Tasks
Research engineer, former BS (’01) and MS (’03) graduate of UNH, Deana Aulisio, was hired in January 2005 to complete the electrochemical experiments proposed in the CICEET-funded project. In the past three months, two bench-scale experiments were conducted with Cocheco sediments under a direct current of 40 mA for 15 and 33 days. Voltage was measured using the Dr. DAQ data collection system employed in previous experiments.

Sediment samples were or will be measured pre- and post-remediation for several constituents, including water content, pH, chloride, organic carbon, and black (soot) carbon. Nine metals of concern and the suite of 16 PAH compounds are the contaminants of concern in the sediment; they will be investigated to determine removal efficiency of electroremediation.

Two methods of metals digestion were compared to determine the effectiveness of in-house experimental procedures. Ms. Aulisio prepared sediment samples for metals analysis using the Nordtest Dutch Availability Method adapted by several past research scholars visiting UNH from Netherlands, including Anne Pedersen and Gunvor Nystrom. Inductively Coupled Plasma ­ Atomic Emission Spectroscopy (ICP-AES) is used to analyze metals concentrations in the extracts. Two duplicate samples (one pre- and one post-remediation) were sent to Eastern Analytical, Inc. (EAI) of Concord, NH for a more rigorous digestion procedure, USEPA Method 3051 ­ Microwave Digestion. ICP-AES was also the means of chemical analysis at the laboratory.

Anticipated Success in Meeting Project Objectives
Although project goals were not met in the anticipated 2-year timeframe, adhering to an extension on the proposal issued by CICEET, the project will expectantly reach a conclusion by the summer of 2005.

Preliminary Data
Two reactors (30 x 11.5 x 7.5 cm) were arranged in series, each containing approximately 1400g of sediment and 500mL of additional overlying water (Figure 1). A graphite steel electrode was inserted 5cm from each end and connected with alligator clips to the outside power source. The clips are also connected, in series, to the Dr. Daq data collector (Figure 2). The Dr. Daq measured voltage for the experiments. The two reactors remained at ambient conditions for 15 and 33 days, respectively.

Past research indicates that at the electrodes, a water splitting phenomenon occurs in which hydrogen gas is produced at the anode and oxygen gas is produced at the cathode. This reaction causes the sediments to be dewatered during electroremediation. During the experiment, adequate water content was maintained to permit migration of the contaminants until the final days when dewatering was permitted to gain shear strength of the sediment. When the reactors began to dry up (indicated by an increase in voltage readouts), additional water was added to continue remediation. In the 15-day experiment, 550mL of total additional water was added and in the 33-day experiment, 1,350mL of total additional water was added. At the end of the 33-day experiment, the reactor was allowed to dry out until the voltage reached a maximum of 5,000mV and current decreased to 0mV (Figure 3).

Figure 4 shows the solids content of the sediment before remediation, after 15 days (dewatering not allowed), and after 33 days (dewatering allowed). Note that 5 samples (slices) and one duplicate were collected from each reactor. The theory of electroosmotic flow and electromigration of solutes are responsible for the migration of contaminants from one electrode to another. Electroosmotic flow moves from the anode to the cathode, so that the sediment near the anode is notably drier (Figure 5).

The pH front within the reactor is also responsible for migration of contaminants. At low pHs (near the anode), metals will dissolve and transport with the electroosmotic flow of water. pH of the sediment was monitored in each section after stirring for 24 hours at a L/S ratio of 20. Figure 6 shows the results, which span from a pH of 3 at the anode to above 10 at the cathode.

Because organic contaminants tend to sorb to organic carbon found in sediments, organic carbon percentage was the next parameter measured. Samples were weighed before and after baking in a muffle furnace at 350°C for 2 hours to determine the percentage of organic carbon in the sediment. Figure 7 displays the results. Organic carbon tends to increase closer to the anode. PAH concentrations will then theoretically increase at the anode as well.

Chloride from marine sediments is a significant concern and in many cases can limit the beneficial use options for sediment material. It also is fairly conservative and its behavior is important in understanding that of other elements or contaminants. Each of the five sampled sections was analyzed for total chloride with a chloride probe and pH/mV meter. Prior to measurement the sediment samples are baked in a muffle furnace at 350°C for 2 hours to remove organic interferences. Then they are stirred in DI water at a L/S ratio of 5 for 24 hours and filtered with a 0.45 µm filter. The results show clearly that chloride is effectively reduced from all sections of the sediment after 33 days except that at the cathode, particularly after dewatering, and is likely being evolved as Cl₂ gas from the anode (Figure 8).

The last set of data gathered during this reporting period is that of metals. Figure 9a and Figure 9b show the results of arsenic, calcium, cadmium, chromium, copper, iron, lead, and zinc. Selenium was measured below the detection limits by both UNH and the external laboratory, Eastern Analytical Inc. (EAI). Metals concentrations at the cathode were less after 33 days of remediation than after 15 days, except in the case of cadmium and calcium. Zinc had variable results for both the pre- and post-remediation samples with large standard deviations for duplicate samples. Another interesting result is that after the 33-day experiment, cadmium, chromium, copper and iron had an increase in concentration at the anode, which seems to be an anomaly in that sample or simply that a percentage of the metals did not migrate towards the cathode in that reactor.

Results obtained by UNH using the Dutch availability method for digestion were on average 65% less than the results reported by EAI, which uses microwave digestion to leach metals from sediments (Figure 10). UNH and EAI presented comparable results for calcium and cadmium only, suggesting that in only these cases are the total metals related to the leachable metals.

Difficulties
The greatest difficulty is with the GC-MS purchased last year for organic analysis. The machine has been consistently malfunctioning and needs manufacturer’s maintenance nearly every other week. This impediment is affecting several researchers in their sample analysis. Unfortunately, electrochemically-remediated sample extracts have been in queue for several weeks prior to this progress report, however, are still not able to be analyzed for PAHs on the GC-MS.

Second, black (soot) carbon content of the current pre- and post-remediation samples has not yet been measured but will be analyzed using thermogravimetric analysis (TGA) for the next reporting period.

Tasks and activities for next reporting period

Tasks for next reporting period

• Analyze all current and backlogged samples for 16 PAHs using GC-MS system.
• Analyze all current and backlogged samples for black (soot) carbon using TGA.
• Determine the behavior of PAHs under direct current electroremediation systems.
• If applicable, conduct two experiments using a surfactant and a cosolvent to mobilize PAHs.
• If results show promising migrations/removals of PAHs, prepare a scientific paper to be submitted for potential journal publication.

Concerns or difficulties
None, as long as GC-MS is maintained.

Expenditures
Expenditures are as anticipated for the current period.