Nitrous oxide gas emissions estimated by liquid-phase measurements: robustness and financial opportunity in single and multi-point monitoring campaigns.

A liquid-phase nitrous oxide sensor can be used as a proxy to estimate the gas emissions. Experiments conducted in a pilot-scale Anammox reactor, at different degrees of aeration intermittency, indicate a predictive error in the range of 13.4-19.3% during the stripping phase, with a higher error range in the unaerated phases (23.4-62.8%). The total emissions not explained by the aerated model amounted to 14.1%. Only a negligible fraction (3.6%) of the total nitrous oxide emissions were not captured by the unaerated phase model, indicating thus a minor concern for full-scale application. A sensitivity analysis performed on the present study indicates that the quality of the nitrous oxide measurement is of extreme importance to decrease the load prediction uncertainty. Air flow measurement errors have lower impact on the overall load prediction. The financial attractivity of this monitoring approach is significant in completely mixed tank reactors. In presence of a multi-point analysis, and starting from two monitoring points, the financial interest deteriorates by the relatively short lifetime of the commercially available liquid-phase nitrous oxide sensor.

Advanced biological activated carbon filter for removing pharmaceutically active compounds from treated wastewater.

Through their release of effluents, conventional wastewater treatment plants (WWTPs) represent a major pollution point sources for pharmaceutically active compounds (PhACs) in water bodies. The combination of a biological activated carbon (BAC) filter coupled with an ultrafiltration (UF) unit was evaluated as an advanced treatment for PhACs removal at pilot scale. The BAC-UF pilot plant was monitored for one year. The biological activity of the biofilm that developed on the granular activated carbon (GAC) particles and the contribution of this biofilm to the overall removal of PhACs were evaluated. Two different phases were observed during the long-term monitoring of PhACs removal. During the first 9200 bed volumes (BV; i.e., before GAC saturation), 89, 78, 83 and 79% of beta-blockers, psychiatric drugs, antibiotics and a mix of other therapeutic groups were removed, respectively. The second phase was characterized by deterioration of the overall performances during the period between 9200 and 13,800 BV. To quantify the respective contribution of adsorption and biodegradation, a lab-scale setup was operated for four months and highlighted the essential role played by GAC in biofiltration units. Physical adsorption was indeed the main removal mechanism. Nevertheless, a significant contribution due to biological activity was detected for some PhACs. The biofilm contributed to the removal of 22, 25, 30, 32 and 35% of ciprofloxacin, bezafibrate, ofloxacin, azithromycin and sulfamethoxazole, respectively.

Evaluation of the applicability of the aquatic ascomycete Phoma sp. UHH 5-1-03 for the removal of pharmaceutically active compounds from municipal wastewaters using membrane bioreactors.

Membrane bioreactors (MBRs) augmented with terrestrial white-rot basidiomycetes have already been tested for the removal of pharmaceutically active compounds (PhACs) from wastewaters. Within the present study, an aquatic ascomycete (Phoma sp.) was initially demonstrated to efficiently remove several PhACs at their real environmental trace concentrations from nonsterile municipal wastewater on a laboratory scale. Then, a pilot MBR was bioaugmented with Phoma sp. and successively operated in two configurations (first treating full-scale MBR effluent as a posttreatment, and then treating raw municipal wastewater). Treatment of influent wastewater by the Phoma-bioaugmented pilot MBR was more efficient than influent treatment by a concomitantly operated full-scale MBR lacking Phoma sp and posttreatment of full-scale MBR permeate using the pilot MBR. A stable removal of the PhACs carbamazepine (CBZ) and diclofenac (DF) (39 and 34% on average, respectively) could be achieved throughout the pilot MBR influent treatment period of 51 days, without the need for additional nutrient supplementation (full-scale MBR: on average, 15% DF but no CBZ removed during 108 days). The long-term presence of Phoma sp. in the pilot MBR could be demonstrated using fluorescence in situ hybridization analysis, but still open questions regarding its long-term activity maintenance remain to be answered.

Energy saving on wastewater treatment plants through improved online control: case study wastewater treatment plant Antwerp-South.

This work provides a case study on how activated sludge modelling and computational fluid dynamics (CFD) can help to optimize the energy consumption of a treatment plant that is already equipped with an advanced control based on online nutrient measurements. Currently, aeration basins on wastewater treatment plant Antwerp-South are operated sequentially while flow direction and point of inflow and outflow vary as a function of time. Activated sludge modelling shows that switching from the existing alternating flow based control to a simultaneous parallel feeding of all aeration tanks saves 1.3% energy. CFD calculations also illustrate that the water velocity is still sufficient if some impellers in the aeration basins are shutdown. The simulations of the Activated Sludge Model No. 2d indicate that the coupling of the aeration control with the impeller control, and automatically switching off some impellers when the aeration is inactive, can save 2.2 to 3.3% of energy without affecting the nutrient removal efficiency. On the other hand, all impellers are needed when the aeration is active to distribute the oxygen.