AIS CESIO ENVIRONMENTAL SURFACTANT MONITORING PROGRAM .1. LAS MONITORING STUDY IN DE-MEERN SEWAGE-TREATMENT PLANT AND RECEIVING RIVER LEIDSCHE-RIJN/

This manuscript reports on the outcome of a 7-day pilot monitoring stu dy on the anionic surfactant linear alkyl benzene sulfonate (LAS) at t he ''de Meem'' municipal sewage treatment plant. The receiving surface water, the Leidsche Rijn is a straight river - about 20 m wide and 1. 5 m deep - and dilutes the sewage discharge by a factor 3. The monitor ing study illustrates an effective removal of LAS of 99.9% during dry weather and normal operating conditions. The LAS concentrations in dai ly composite raw sewage samples varied between 3.1 and 7.2 mg/L, with corresponding effluent concentrations generally under the analytical d etection limit of 8.1 ug/L. During this same period, total LAS concent rations in the river varied between <2.1 ug/L (detection limit) and 2. 9 ug/L in samples taken above the sewage outfall and between <2.1 ug/L and 7.1 ug/L for samples taken below the sewage outfall. Malfunctioni ng of the primary settler during heavy rainfall conditions, resulted i n throughput of primary sludge particles to the aeration tank. The rem oval of LAS, BOD, SS, and TOC decreased significantly during this peri od, resulting in higher effluent concentrations. In addition, analyses of river samples taken during and after the rainfall indicated the pr esence of a sewage overflow which was discharged upstream of the sewag e treatment plant outfall.