Flocculation Analysis

Project Description

Chemical treatment on New Zealand earthworks sites is now commonplace and has provided a significant advantage and ability to achieve much more stringent water quality standards. Auckland Council first introduced this concept and the development of rainfall activated systems has now been supplemented with flow activation and many other forms of flocculation delivery.

The chemicals used have also changed and we have relied heavily on Polyaluminium Chloride (PAC) as the stalwart flocculant of choice for many years with significant success. We are also aware that due to a range of factors including soil pH, soil organic content and soil texture, that alternative flocculants are necessary in some circumstances. These alternatives, and many varying sources of PAC, are now available for use on sites.

The knowledge of the flocculants, their effectiveness and residual impacts are however not well understood by many and often are “promoted” by those selling these products. We acknowledge that these suppliers have significant intel and knowledge but the driving principle that needs to be applied is ensuring we have an effective flocculant for the specific site in question and that this can be used within the limits of a formal Chemical Treatment Management Plan while ensuring no residual effects of its use.

This Project is designed to take the mystery of flocculants away and with independence and lab and field testing confirm the options that exist and the criteria that these flocculants must meet. Phase 1 of the Project will involve working with the numerous products available and in collaboration with university testing achieve this overall objective. Phase 1 will also collate the existing data and information available. Phase 2 of the project will take these Phase 1 outcomes and assess and consider flocculation delivery systems that achieve optimisation and ultimately the water quality outcomes required.

Project Manager

Graeme Ridley will project manage this project.

Delivery Outcome and Timeframe

Phase 1 of the Project is at inception stage with discussions ongoing with universities with a delivery date expected at the end of the 2021/2022 earthworks season. The Phase 1 outcome will be a technical paper that will be circulated and discussed with the earthworks industry including through conference papers.