Ship repair and maintenance activities constitute not only a costly source of water discharge, but also a major environmental threat with the release of potentially toxic effluents. Surface treatment of ship hulls involves the consumption of high quantities of fresh water and results in the generation of large amounts of wastewater. These effluents are characterised by increased concentrations of chemicals, such as heavy metals, tributyltin (TBT), PCBs and oils that may be harmful. Periodic maintenance for removing old paint layers, surface coatings, biological fouling, such as algae and mineralogical depositions makes the situation even worse. A new research project PI-WAMAS explored a three-step treatment process of the generated dock wastewater without employing any chemical additions or energy intensive procedures.
Unlike other industries, the quality and quantity of dock wastewater is extensively varied depending on the activities and local surroundings. Appropriate wastewater treatment technologies need to cope with this variability in the most safe and cost-effective way. To answer this need, the PI-WAMAS project realised a closed cycle water management system that integrates three technologies. These involve a polyphase separator, an activated knitted carbon membrane system and a low energy desalination system. While the polyphase separator allows the simultaneous separation of suspended solids and oils, the Knitted Activated Carbon (KAC) membrane system is aimed at the separation of smaller particles. This material displays increased capabilities to absorb heavy metals, as well as TBT a potentially toxic anti-fouling agent, in very high rates. The membrane unit has a reduced reactor size and an improved efficiency of utilisation of adsorption material.
Based on laboratory adsorption tests, two different KAC prototype designs were developed and tested under real environments. A spiral design allows effluents running along and between lengths of rolled KAC. On the other hand, the second design that is based on Granular Activated Carbon (GAC) treatment beds, offers permeation of wastewater between pieces of folded KAC. The derived results were compared against those collected through test trials using conventional adsorption techniques and are available to naval communities and environmental agencies.