Elimination of micropollutants from municipal wastewater by adsorption on powdered activated carbon and separation by innovative precoat filtration

Abstract

The removal of organic micropollutants from wastewater treatment plant (WWTP) effluent protects the aquatic ecosystems in the receiving water body. Activated carbon adsorption is a promising method for advanced wastewater treatment. The use of powdered activated carbon (PAC) requires a subsequent separation stage to avoid PAC leakage and thus desorption of harmful substances in the environment. So far, preliminary separation of the PAC by precipitation and sedimentation in combination with a sand filter has proven to be suitable. Separation using filtering separators in the form of candle filters is a space-saving alternative but has not yet been used on an industrial scale. The subject of this work is to fundamentally investigate the process design regarding the hydraulic properties, the retention and the effective filtration mechanism. After preliminary tests with a pressurized filter cell (PFC), a scale up to a pilot-scale candle filter under optimized conditions is carried out. The use of a precoat layer of cellulose is necessary to protect the fabric from blockage, to retain the PAC, and thus enables the flow to be maintained. Cellulose with medium fiber length with an applied quantity of ρ C = 1 kg·m −2 turns out to be suitable to obtain high filtrate throughput and clear filtrate. The use of precipitants (FeCl 3 ) in combination with sedimentation reduces the content of total suspended solids ( TSS ) of the wastewater PAC suspension and thus increases the throughput by factor 7. The precoat experiments with the candle filter show a complex superposition of the predominant filtration mechanism. In the beginning, clogging filtration predominates. During the filtration, separation inside the precoat, as well as the build-up of a thin cake of PAC particles, gain in importance.