Enhancing the membrane bioreactor efficiency: The impact of rotating membrane modules and aeration strategies on the transmembrane pressure.

The study analyses the performance of a pilot plant using a rotating hollow fibre (HF) membrane bioreactor system. The experiments evaluated the effect of operational parameters such as rotational speed, aeration strategies, and maintenance cleaning (MC) procedures on the efficiency of the system, in particular transmembrane pressure (TMP) and filtrate quality. The results indicate that the rotating membrane module reduces TMP increase and can operate for 48 days with satisfactory performance, even without aeration. This has the potential to significantly improve efficiency, resulting in significant energy savings. In addition, two MC methods, clean in air and clean in place, were tested and found to be efficient for weekly MC. It was observed that operating without aeration during colder seasons may not be effective. Therefore, adaptive strategies are needed to address seasonal temperature variations.

Modelling competitive adsorption of organic micropollutants onto powdered activated carbon in continuous stirred tank reactors for advanced wastewater treatment.

This work investigates the validation and application of a competitive model approach for full-scale wastewater treatment plants (WWTP) with external recirculation of partially loaded powdered activated carbon (PAC) for removal of organic micropollutants (OMP). It is based on the ideal adsorbed solution theory (IAST) for multisolute mixtures combined with calibration of fictive organic components and correction of single-solute model parameters for OMP by use of the tracer model (TRM). Adsorption kinetics are represented by a pseudo first order reaction (PFO) and compared to mass transfer calculated with the homogenous surface diffusion model (HSDM). Model validation with operational data from two different WWTPs showed a strong dependency of model results on the batch sample quality used for model calibration. In contrast, the kinetic approach is of less importance for predicting full-scale OMP removal with long PAC sludge retention times. Further model application demonstrated that external PAC recirculation significantly improves the OMP removal with regard to both adsorption capacity and compensation of competitive effects of Dissolved Organic Carbon (DOC).

Influence of effluent particles and particle-bound micropollutants on the removal of micropollutants and UVA254 in wastewater effluent ozonation.

This study systematically investigated the influence of effluent particles and activated sludge (AS) particles on the removal of micropollutants via wastewater effluent ozonation within typical effluent total suspended solids (TSS) concentrations. A series of batch experiments revealed that particle concentrations up to 30 mg/L had a minor impact on the removal of organic micropollutants (OMPs) in the aqueous phase. Moreover, the reduction of UV absorbance at 254 nm (UVA254) was negatively correlated to the level of particle concentration at ozone doses higher than 0.5 gO3/gDOC. It indicates that UVA254 abatement was more sensitive to the presence of particles compared to OMP removal. Organic micropollutants (OMPs) sorbed on effluent particles and sludge particles were extracted before and after ozonation. OMP sorption in effluent particles was 2-5 times higher than that in sludge particles. During the ozonation of raw secondary effluent, particle-bound micropollutants were removed comparably to the micropollutants in the aqueous phase. This suggests that the boundary layer surrounding the particle didn't affect the removal of OMPs in the particle phase. Furthermore, the removal of existing OMPs (irbesartan, sulfamethoxazole, and metoprolol) in the effluent was used to assess the ozone and •OH exposure. In water samples with and without particles, the elimination of OMPs could be reliably predicted (R² > 0.95) by calculated ozone and •OH exposures.

The impact of solid/floc holdup on oxygen transfer in a rotating hollow fiber membrane bioreactor under endogenous conditions.

A set of oxygen transfer experiments in clean water and three different activated sludge concentrations were conducted with fine and coarse bubble aeration in a rotating hollow fiber membrane bioreactor to observe the impact of different rotational speeds on the oxygen transfer rate. The results showed that with increasing membrane rotational speed, the oxygen transfer coefficient enhanced while the α-factor showed similar values at comparable sludge concentrations and solid/floc holdups. The highest improvement rates occurred during the experiments with coarse bubble aeration at 50 rpm and the lowest specific airflow rate. The solid/floc holdup appears to universally impact oxygen transfer depletion regardless of what reactor type, diffuser setup and membrane rotational speed were used in the wastewater experiments.

A new concept of a rotating hollow fibre membrane module:impact of rotation on fine-bubble aeration.

A new concept of a rotating membrane module in a membrane bioreactor (MBR) system was tested for its effect on oxygen transfer in clean water and wastewater. The membrane module consists of horizontally aligned hollow fibres connected to the vertically positioned permeate tube which rotates. The results indicated that oxygen transfer can be improved by up to 50% at the highest applied rotational speed (50 rpm) and that the additional energy demand required for the rotation can be compensated by the enhanced oxygen transfer. However, at the highest rotational speed (50 rpm), the fine bubbles bypassed the MBR module, and, consequently, could not contribute to any cleaning effect. The α-factors at different rotational speeds showed similar results. This indicates that the depletion was caused neither by surfactants nor by viscosity phenomena but rather by the floc/solid holdup of the sludge.

Development and application of a predictive model for advanced wastewater treatment by adsorption onto powdered activated carbon.

This work presents a mathematical method to describe adsorptive removal of organic micropollutants (OMPs) and dissolved organic carbon (DOC) from wastewater treatment plant effluent using powdered activated carbon (PAC). The developed model is based on the tracer model (TRM) as a modification of the ideal adsorbed solution theory (IAST) and uses the fictive component approach for organic matter fractionation. It enables the simulation of multisolute adsorption of OMPs considering competitive adsorption behavior of organic background compounds (OBC). Adsorption equilibrium data for DOC and seven different OMPs as well as kinetic data for DOC were derived from batch experiments performed with secondary clarifier effluent of two municipal wastewater treatment plants (WWTP 1 and WWTP 2). Two conventional PAC products were investigated as well as one biogenic PAC (BioPAC). Verification and validation of the fitting results based on operational data of WWTP 1 showed promising prediction of DOC and OMP removal efficiency. However, when applied to a static simulation of a full-scale PAC adsorption stage, the model overpredicts the removal efficiency of sulfamethoxazole and candesartan. For benzotriazole, carbamazepine or hydrochlorothiazide, predicted removal falls below operational removal. The model can be used to predict removals of good adsorbable OMPs but fails to accurately predict the removals of OMPs with variable or low PAC affinity. The model was further used for a dynamic simulation of DOC and diclofenac effluent concentrations of a full-scale PAC adsorption stage with varying operating conditions and influent concentrations. Results show that the hydraulic retention time (HRT) in the contact reactor is a decisive operational parameter for OMP removal efficiency besides the PAC dose.

Determination of antibiotic resistance genes in a WWTP-impacted river in surface water, sediment, and biofilm: Influence of seasonality and water quality.

Many pathogenic bacteria are adapted to live in aquatic habitats, which makes rivers possible sources and spread pathways of antibiotic resistance, since they usually receive effluents from wastewater treatment plants (WWTP), possibly containing antibiotic residues and also antibiotic-resistant bacteria. This study investigates different monitoring strategies to identify the occurrence of antibiotic-resistant bacteria in rivers. We analyzed the presence of 13 antibiotic resistance genes (ARGs) and seven gene markers for facultative pathogenic bacteria (FPB) with qPCR in sampling sites upstream and downstream of a small WWTP in Southern Germany. Five sampling campaigns were conducted from February to June 2019. Surface water, sediment, and biofilm samples were analyzed. The biofilm was collected from an artificial sampler placed in the river. blaTEM, ermB, tetM, and sul1 genes were detected in all samples analyzed. The results showed there was a previous background in the river, but the WWTP and the water quality of the river influenced the concentration and occurrence of ARGs and FPB. Genes representing resistance against strong or last-resort antibiotics, such as mecA, blaCMY-2, blaKPC-3, and mcr-1, and multidrug resistance were also detected, mainly in samples collected downstream of the WWTP. Downstream of the WWTP, the occurrence of ARG and FPB correlated with ammoniacal nitrogen, while upstream of the WWTP correlated with turbidity, suspended solids, and seasonal factors such as UVA radiation and the presence of macrophytes. Biofilm samples presented higher abundances of ARGs and FPB. The biofilm sampler was efficient and allowed to collect biofilms from specific periods, which helped to identify seasonal patterns.