Micropollutants (MPs) are ubiquitous in wastewater and are not effectively removed by the existing conventional treatment processes, resulting in increased environmental pollution. Nowadays, dosing of powdered activated carbon (PAC) prior to membrane filtration has emerged as an advanced wastewater treatment method for MPs removal. This study investigated the carbon agglomerate formation in the PAC stock suspension and its influence on MPs removal in PAC-capillary membrane filtration processes at both lab- and pilot-scale levels. Both lab- and pilot-scale membrane filtration results revealed that MPs removal efficiency is affected with the increase of PAC concentration in the stock suspension. For example, one of the investigated pilot tests showed a significantly reduced removal of good adsorbable MPs (from 57 to 17%) when stock suspension concentration was increased from 0.2 to 20 g/L. It is assumed that PAC agglomerates led to a slower adsorption kinetic and an inhomogeneous distribution of PAC in the membrane system. Maintaining PAC concentration in the stock suspension as low as possible (below 0.2 g/L for investigated PAC) certainly would help to avoid agglomeration problems and enhance the overall performance of the processes.

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Results from a lab-scale investigation of a hybrid in/out ultrafiltration and powdered activated carbon adsorption PAC/UF for removal of diclofenac (c= 5 mg/L) are presented. The efficiency of the process was compared for single pulse and continuous carbon dosing (PAC dose 5 mg/L) in dechlorinated tap water under fluxes of 87 and 135 L/(m h). For higher flux conditions, it was observed that single pulse dosing has an advantage over continuous dosing procedure when comparing cycle average removal efficiency. Increase of carbon dose under these conditions increased cycle average removal only to a limited extent. PAC dose above 15 mg/L did not give improvements of the removal. Hypothesis was made that non-effective carbon distribution might be the possible reason.

Producing drinking water from raw waters like river bank filtrate nowadays requires the safe removal of ever new emerging organic substances. At present, in Germany perfluorinated organic compounds are heavily discussed. When it comes to trace organics removal, reverse osmosis (RO) and nanofiltration (NF) are alternatives to conventional bank filtrate treatment technologies like ozonation and activated carbon adsorption. However, the trace organics removal capabilities of dense membranes are still under investigation. Questions about concentrate disposal strategies are still open. The paper presents results from lab-scale and pilot studies which were conducted for the project planning of a 1,100 m3/h NF plant treating river Rhine bank filtrate. Membranes from loose NF to dense RO were investigated spiking the raw waters with trace organic substances which usually pass the soil passage and to some extent even the conventional treatment process. The results showed high retention capabilities of the more dense membranes, even under ageing conditions.

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