Monitoring Methods of EGCS Washwater - For Measurement of Turbidity and Concentration of Polycyclic Aromatic Hydrocarbon

Abstract

Turbidity and concentrations of polycyclic aromatic hydrocarbons (PAHs) of washwater circulated in a closed-loop scrubber were measured to evaluate the washwater monitoring methods that were approved by the International Maritime Organization (IMO). In turbidity measurements, the turbidity is increased with circulation time, since exhaust gas soot particles are trapped in the washwater and are not removed during circulation. Several turbidimeters were tested to determine whether the trapped soot particles, i.e. sludge, will affect turbidities or not. Turbidimeters with single nephelometric detector were saturated in the high-turbidity range due to the existence of light-absorbing black sludge in the washwater. On the other hand, turbidimeters with two detectors that compensate for the effect of the light absorption showed linear response even with relatively higher turbidities. The observed turbidities depended on the sludge amount and also might be affected by the physical properties of sludge such as size and/or color. In the case of PAH measurements, the measured values are influenced by suspended particles in washwater, i.e. turbidity, because the PAH measurement is based on the fluorescence detection of PAHs. Then the observed PAH concentrations were numerically corrected using turbidity values. The corrected PAH concentrations were consistent with those of washwater in which the suspended particles were filtered to physically remove the effect of turbidity. The results confirmed that the turbidity correction of PAH concentrations was reliable.