Seawater Scrubber Effluent from Flue Gas Treatment – An Evaluation of Possible Ecological Consequences

Abstract

Two alternative arrangements for scrubber effluent discharge are considered: to the surface layer together with the cooling water, or from a separate outlet at about 50 m depth. Effects are considered both for untreated effluent and with lime treatment and aeration of the effluent. The extention of water volumes with effluent concentrations above given limits are estimated for proposed power plant sites in the outer Oslofjord, and effects with respect to pH, oxygen, metals and polycyclic aromatic hydrocarbons are considered. The study indicates that mixed discharge of scrubber effluent and cooling water to the surface layer without treatment may harm the marine communities by causing mean pH reduction close to 0.5 units in the upper 10 m of the outer part of the Oslofjord. Treatment of the effluent will reduce the seriously affected area and volume of surface water masses by at least 90%. No significant harmful oxygen effects are indicated for a surface discharge. By deep water discharge of untreated scrubber effluent pH would be lowered only in intermediate layers, and in a relatively minor part of the total pelagic environment, making this discharge arrangement more acceptable as regards effects from acidification. The oxygen deficit will not be serious in the primary recipient area, but there may be unacceptable reduction of oxygen renewal in the deeper layers of the inner Oslofjord. Treatment will make pH-effects from a deep discharge negligible, and reduce oxygen demand by 80%, making the effluent acceptable in these respects for many recipients. Risk of metal effects seems moderate or small, while the data on discharge of polycyclic aromatic hydrocarbons (PAH) were too uncertain for conclusions at the time of the study.