Influence of the fetch parameter on results from empirical correlations for estimating odorous emissions at passive liquid surfaces

Passive liquid surfaces in wastewater treatment plants may be potential sources of odorous emissions. This study investigates the occurrence and significance of deviations that may originate from the use of the effective diameter as fetch parameter in the empirical correlations utilised by the WATER9 model to estimate odorous emissions at passive liquid surfaces. A sensitivity analysis was performed using benzene as a model compound and considering representative conditions of wind speed and wind alignment. The gas-film mass transfer coefficient (k_G) was found relatively insensitive to the choice of the fetch parameter, deviating less than 15% for aspect rations up to 15. The calculation of the liquid-film mass transfer coefficient (k_L) was much more sensitive (positive extreme of 126.98% and negative extreme of −54.80%), partially because of the use of different equations for different fetch-to-depth ratios. For more volatile compounds, such as benzene, these discrepancies will be significantly manifested in the estimated emission rate. When appropriate, the use of the actual fetch instead of the effective diameter is recommended.