Enhanced estrogen removal in activated sludge processes through the optimization of the hydraulic flow pattern.

The removal of ß-estradiol (E2) and α-ethinylestradiol (EE2) in biological wastewater treatment plants (WWTP) would need to be improved in order to comply with prospective Environmental Quality Standards (EQS) of 0.4 and 0.035 ng.L-1 respectively. The effluent concentration of a micropollutant in an activated sludge process is a function of the removal rate, the hydraulic retention time (HRT) and the flow pattern, which is usually overlooked. In order to better understand this aspect, we carried out tracer studies in eight WWTPs in the UK and found that relatively modest changes in aeration tanks would translate into tangible improvements in their flow pattern. We further evaluated the degradation rates for E1 (estrone), E2, E3 (estriol) and EE2 in each WWTP and we estimated that the modification of the flow pattern would be sufficient to place effluent concentrations of E2 (23.2 L∙gVSS-1∙d-1

A flow cytometry method for bacterial quantification and biomass estimates in activated sludge.

Absolute bacterial quantification receives little serious attention in the literature compared to sequencing, conceivably because it is considered unimportant and facile, or because existing methods are tedious, laborious and/or biased in nature. This is particularly true in engineered systems, including activated sludge, where such information underpins their design and operation. To overcome these limitations we built upon existing work and optimised and comprehensively validated, through comparison with epifluorescence microscopy (EFM), a rapid and precise flow cytometric protocol to enumerate total bacterial numbers in activated sludge. Insights into potential biases were evaluated using appropriate statistical analyses on this comparison, which spanned four orders of magnitude, as well as comparing volatile suspended solid (VSS) concentrations. The results suggest flow cytometry (FCM) is a rapid, reproducible and economical technique for quantifying total bacterial numbers and biomass concentrations in activated sludge, despite within order of magnitude discrepancies with EFM counts, which had inherent and evidently greater errors and biases than FCM. The use of FCM for routine monitoring over both EFM and VSS should help further understanding of the microbial ecology in, and the operation of, engineered systems.