Sustainable clean-up of polluted ports
The German Seaport of Emden is facing a tough challenge:
Can they treat the environmental legacy pollution in the sediments and provide sufficient depth of water for port operation without spreading polluted materials to other parts of the harbor?
And do this in a climate friendly way and reduce carbon emissions?
During the process the harbor authorities must secure that any existing pollutants under no circumstances will be distributed to other port areas during the process.
This is a pilot project that began in 2020 with the extensive investigation of the actual pollution scenario by legacy contaminants in the harbour and culminated in 2021 in the kickstart of a field test and is still ongoing.
This is the question that the Port of Emden is trying to answer in their DUAL Ports Pilot Project where a promising in Situ pollutant treatment alternative is being investigated in a field experiment in a semi-enclosed section of the harbour.
Laboratory tests give strong indications that it works on a bigger scale.
Pollution from TBT
In parts of the port of Emden, the sediment presents environmental pollutants that entered the harbour mostly due to shipyard activities in the past decades, when several nowadays banned substances were still allowed. Near an old shipyard located at the inner part of the harbour, large quantities of PAHs (polyaromatic hydrocarbons) and TBT (Tributyltin) can be found.
A challenge the Port of Emden is facing is that the recirculation dredging procedures can only be carried out in areas where no pollutants are present in the sediment to be treated.
Any existing pollutants may under no circumstances be distributed to other port areas. This is not ensured by using the recirculation process used in the other parts of the port and therefore the potentially contaminated areas remained so far untouched.
This prevents the use of water depth conservation measures and thus the long-term use of certain parts of the harbour. Therefore, the harbour has seen a target to create an innovative, economically advantageous, and sustainable concept for the removal of pollutants in the port’s sediments, to maintain port operations there in the long term.
The port is located at the mouth of the River Ems, and this causes problems with large deposits of estuarine sediments in the port. It significantly affects the depth of the port, and it is necessary on an ongoing operation to remove the deposits on the bottom.
This is done by a method where the material, that would otherwise settle, is recirculated, and is turned into a navigable mud layer, also called fluid mud, providing an increased water depth in the harbor.
The adapted trailing suction hopper dredger is used for this. This vessel dredges the very fine sediment into its hold, putting it in contact with the atmospheric air. The constant mixing of the material hinders the settlement and consolidation of it and thus makes it possible to sail through this created fluid mud layer.
A purpose-built vessel constantly sucks up the deposits on the bottom and releases it out again like fluid mud through which the ships in the harbor can navigate.
The process is very simple yet innovative. Normally, sediment on the bounds would be removed completely from the port and sailed away to be dumped either at sea – if not polluted or transported to a land depot. Both methods are expensive and burden the climate with increased carbon emissions.
Sedimentation and thus lower depth are a challenge all ports struggle with.
The Port infrastructure company Niedersachsen Ports has been using the fluid mud method in the port of Emden since 1992 and has good experience with it. Since 2000 the water depth maintenance of the harbour has been done solely by the recirculation process.
The question then is how the port can keep the depth in the areas contaminated with the pollutant TBT from a nearby shipyard without the contaminated mud being spread out in the rest of the port.
“The use of our already established recirculation process not only as a port maintenance method but also as a tool to facilitate the degradation of pollutants is very promising and suitable in our particular case, since we are dealing with organic pollutants in a relatively low to moderate concentration. The TBT will eventually disappear, but it will take a very long time to degrade. We would like to propose a process that stimulates the natural biodegradation of these organic substances, speeding up the degradation process of TBT,” explains Daniela da Rosa, Niedersachsen Ports, Emden.
How is it done?
The degradation of TBT by microorganisms in the environment is a naturally occurring process. Usually, it happens quite slowly because TBT is a man made, persistent substance that is very hard to degrade. A number of methods have been developed over the years for the removal of contaminants from sediments with varying cost ranges, waste generations, energy demands, transport requirements, and so on. Based on the scientific findings regarding contaminants degradation, the processes that take place during the recirculation process may facilitate the natural biodegradation of these compounds and therefore represent an in situ treatment approach worth investigating.
The enrichment of the fluid mud with oxygen from the air can potentially create more favorable conditions for the degrading microorganisms that are present in the system and cause higher microbial degrading activity.
TBT is more quickly transformed into less harmful products thorough the microbial metabolism activity.
The goal of the process is to create improvements of the conditions to optimize naturally occurring processes.
Test area established
A survey was conducted to identify which parts of the harbor that was suitable to conduct a test of the designed process. Area 1 was the least contaminated and other investigated areas were not suitable for the decided process.
Back in September 2021 a “bio-reactor” was set up located at the Oil Harbour (see illustration) to test the process.
“We moved a small part of moderately polluted material from area 1 and brought it into the oil harbour to test the effect of the recirculation process on the TBT degradation rates. The test and the monitoring will run until April 2022. We collect data every second week and analyze this data very thoroughly in order to hopefully be able to evaluate the effectiveness of the process by the end of the project. We have good reason to believe that this method works,” concludes Daniela da Rosa.
The pilot will continue this spring, and port of Emden expects that the outcome will be positive. The goal is to integrate area 1 of the harbor into the regular maintenance schedule to secure nautical depth.
The results of the project regarding the success in the treatment of TBT are still under evaluation and the process can take a longer time in comparison to conventional approaches. In terms of the financial and environmental aspects, however, this is a highly promising approach. The pilot project of Port of Emden is a part of the Dual Ports project, and the preliminary data clearly indicates that the targets in cost and CO2 reduction will be exceeded and that it will improve the economy at the Port of Emden.
“We hope the results of the test will produce meaningful insights for us and that it hopefully will represent the treatment alternative that the port is seeking. We hope to make use of the recirculation process to achieve sustainable decontamination of sediments whilst at the same time to carry on with the more resource efficient port maintenance strategy,” says Daniela da Rosa.
The Pilot project at the Port of Emden supports the overall goals of the Dual Ports project which is 20% operating cost reduction, 20% total cost reduction, and 10% emissions reduction.
According to the calculations carried out by the HWWI the pilot in Emden fulfils all targets by over 90% when the new method is compared with the conventional approach (extraction of the contaminated material, transport to, and depot at a specialized facility).