This Great Ships Initiative (GSI) technical report describes outcomes from land-based tests conducted in August through October 2010 on three versions of the AlfaWall PureBallast® ballast water treatment system (BWTS). One version (hereafter referred to as v.1) of the PureBallast® BWTS received Type Approval by Det Norske Veritas (DNV) on behalf of the Norwegian Administration in June of 2008, following successful land-based testing at the Norwegian Institute of Water Research (NIVA). The second version (v.2), designed to conserve power relative to the first, was still undergoing International Maritime Organization (IMO) certification testing, and had completed successful land-based tests at NIVA immediately prior to testing at GSI during early summer 2010. The third version was a hybrid of versions 1 and 2, hereafter referred to as version 3 (v.3), and combined the 40 ?m filtration of PureBallast® BWTS v.2 with the advanced oxidation system of PureBallast® BWTS v.1. Unfortunately both v.1 and v.2 of the PureBallast® BWTS encountered mechanical filter failures such that no valid trials were completed. Instead, GSI tested the hybrid version (v.3) under a set of GSI source water conditions less challenging than those required by IMO and Environmental Technology Verification (ETV) Program, strictly for research and development purposes. Overall, the PureBallast® BWTS v.3 performed without interruption during the first two trials under the less challenging conditions. During the third and final trial, the PureBallast® BWTS v.3 encountered a filter failure, and the trial was stopped and restarted under ambient Duluth-Superior Harbor conditions. No residual toxicity was detected in the discharge waters of the PureBallast® BWTS v.3. The BWTS did not effectively reduce live organism densities in the two regulated size classes despite the fact that ambient densities were well below IMO and ETV testing intake thresholds. Part of the problem likely resided with filter ineffectiveness given filamentous algal forms in Duluth-Superior Harbor water. At the same time, very low ambient UV transmittance of Duluth-Superior Harbor water (naturally caused by tannins) during these tests likely impeded effectiveness of the advanced oxidation system. These two conditions also likely account for discrepancies between performance outcomes at GSI versus NIVA. Globally, the risk of very low UV transmittance conditions is not unique to Duluth-Superior Harbor, but it is relatively rare and can be anticipated in advance. Thus, this problem could be mitigated with management practices such as open ocean BWE in combination with treatment. Conditions present in Duluth-Superior Harbor likely leading to filter malfunction, on the other hand, may be relatively common to many fresh water and brackish water harbors.