Review of total residual chlorine discharge consent for wastewater discharge

Dr Mike Stewart provided scientific evidence to support an application by Van Den Brink Poultry (Brinks) for a variation of consent for the discharge of total residual chlorine (TRC) from their plant in Karaka, Auckland. Brinks are required to use an accredited laboratory for measurement and reporting of TRC concentrations in their discharge. However, they were advised by the laboratory that they could not measure TRC reliably to the level required. This meant that meeting the consent condition was problematic. A review by Dr Stewart of information associated with the 2012 discharge consent renewal application failed to provide the scientific basis for the derivation of the consent limit for TRC in the wastewater effluent. a Discussions with two analytical laboratories indicated that TRC was not able to be measured using standard analytical methodology. Dr Stewart concluded that an alternative practical discharge consent limit was required, that was measurable and would not impact the marine receiving environment.

Dr Stewart initially considered the existing guidelines as the basis for his assessment. However, the assessment was complicated as ANZECC (2000) provide only a low reliability trigger value for TRC in marine water, which was not updated in the more recent 2018 ANZ guidelines. Conservative and more robust marine chlorine guidelines proposed by Batley and Simpson (2020) were considered more appropriate and were used for the assessment. By applying these updated guidelines to previously derived worst-case (lowest) dilutions of the discharge in the receiving environment, an updated higher consent limit was derived that could be accurately measured and was protective of the marine receiving environment. Auckland Council have agreed to allow Brinks to use this updated consent limit, without the need for a consent variation application. This pragmatic approach to resolving an otherwise unachievable consent condition highlights the value of science-based derivation of consent conditions.

Brown chicken with an egg.