Frederik Zietzschmann

Impact of EfOM size on competition in activated carbon adsorption of organic micro-pollutants from treated wastewater.

The competitive impacts of different fractions of wastewater treatment plant effluent organic matter (EfOM) on organic micro-pollutant (OMP) adsorption were investigated. The fractionation was accomplished using separation by nanofiltration (NF). The waters resulting from NF were additionally treated to obtain the same dissolved organic carbon (DOC) concentrations as the initial water. Using size exclusion chromatography (LC-OCD) it could be shown that the NF treatment resulted in an EfOM separation by size. Adsorption tests showed different competitive effects of the EfOM fractions with the OMP. While large EfOM compounds that were retained in NF demonstrated a reduced competition as compared to the raw water, the NF-permeating EfOM compounds showed an increased competition with the majority of the measured OMP. The effects of small size EfOM are particularly negative for OMP which are weak/moderate adsorbates. Adsorption analysis was carried out for the differently fractionized waters. The small sized EfOM contain better adsorbable compounds than the raw water while the large EfOM are less adsorbable. This explains the observed differences in the EfOM competitiveness. The equivalent background compound (EBC) model was applied to model competitive adsorption between OMP and EfOM and showed that the negative impacts of EfOM on OMP adsorption increase with decreasing size of the EfOM fractions. The results suggest that direct competition for adsorption sites on the internal surface of the activated carbon is more substantial than indirect competition due to pore access restriction by blockage. Another explication for reduced competition by large EfOM compounds could be the inability to enter and block the pores due to size exclusion.

Anthropogenic organic micro-pollutants and pathogens in the urban water cycle: assessment, barriers and risk communication (ASKURIS)

In urban areas, water often flows along a partially closed water cycle in which treated municipal wastewater is discharged into surface waters which are one source of raw waters used for drinking water supply. A number of organic micro-pollutants (OMP) can be found in different water compartments. In the near future, climatic and demographic changes will probably contribute to an increase of OMP and antibiotic-resistant pathogens in aquatic ecosystems. The occurrence of OMP, possible adverse effects on aquatic organisms and human health and the public perception must be carefully assessed to properly manage and communicate potentially associated risks and to implement appropriate advanced treatment options at the optimum location within the water cycle. Therefore, the interdisciplinary research project ASKURIS focuses on identification and quantification, toxicological assessment and removal of organic micro-pollutants and antibiotic-resistant pathogens in the Berlin water cycle, life cycle-based economic and environmental assessment, public perception and management of potential risks.

Pilot-Scale Investigation of Micropollutant Removal with Granular and Powdered Activated Carbon

Activated carbon is investigated as adsorptive barrier for organic micropollutants (OMP) within the Berlin water cycle. In a pilot plant using granular activated carbon (GAC) as upper layer in dual-media filtration, OMP concentrations in treated wastewater could be reduced without any negative impact on filtration efficiency. OMP breakthroughs occurred after shorter runtimes than estimated according to isotherm experiments with powdered activated carbon (PAC). Batch adsorption tests comparing the used GAC to new GAC showed that the capacity of the used GAC was not exhausted, indicating that besides direct site competition, pore blocking is also responsible for the poor GAC performance. A pilot plant application of PAC of the same type as GAC showed significantly higher OMP removals at lower dosages, taking advantage of immobilization of PAC particles in the filters. Both PAC and GAC applications can be integrated into tertiary wastewater treatment without significant constructional changes.

Impacts of coagulation on the adsorption of organic micropollutants onto powdered activated carbon in treated domestic wastewater

The application of powdered activated carbon (PAC) as an advanced wastewater treatment step for the removal of organic micropollutants (OMP) necessitates complete separation of the PAC particles, e.g. by coagulation. In this study, potential positive or negative indirect or direct effects of coagulation on the adsorption of OMPs onto PAC in treated wastewater were investigated. Although the concentration of dissolved organic matter (DOM) was significantly reduced by coagulation, the selective removal of mainly larger DOM components such as biopolymers and humic substances did not improve subsequent OMP adsorption onto PAC, demonstrating that coagulation has minor effects on DOM constituents that are relevant for direct competition or pore blocking. The combination of coagulation and adsorption yielded the sum of the individual removals, as adsorption predominantly affected smaller compounds. While the formation of flocs led to visible incorporation of PAC particles, no significant mass transfer limitations impeded the OMP adsorption. As a result, the dosing sequence of coagulant and PAC is not critical for efficient adsorption of OMPs onto PAC. The relationships between adsorptive OMP removal and corresponding reduction of UV absorption at 254 nm (UVA254) as a promising surrogate correlation for the real-time monitoring and PAC adjustment were affected by coagulation, leading to individual correlations depending on the water composition. Correcting for UVA254 reduction by coagulation produces adsorptive UVA254 removal, which correlates highly with OMP removal for different WWTP effluents and varying coagulant doses and can be applied in combined adsorption/coagulation processes to predict OMP removal and control PAC dosing.

Lab-testing, predicting, and modeling multi-stage activated carbon adsorption of organic micro-pollutants from treated wastewater

Multi-stage reuse of powdered activated carbon (PAC) is often applied in practice for a more efficient exploitation of the PAC capacity to remove organic micro-pollutants (OMP). However, the adsorption mechanisms in multi-stage PAC reuse are rarely investigated, as large-scale experiments do not allow for systematic tests. In this study, a laboratory method for the separation of PAC/water suspensions and the subsequent reuse of the PAC and the water was developed. The method was tested on wastewater treatment plant (WWTP) effluent in a setup with up to 7 PAC reuse stages. The tests show that the overall OMP removal from WWTP effluent can be increased when reusing PAC. The reason is that a repeated adsorption in multi-stage PAC reuse results in similar equilibrium concentrations as a single-stage adsorption. Thus, a single relationship between solid and liquid phase OMP concentrations appears valid throughout all stages. This also means that the adsorption efficiency of multi-stage PAC reuse setups can be estimated from the data of a single-stage setup. Furthermore, the overall OMP removals in multi-stage setups coincide with the overall UV254 removals, and for each respective OMP one relationship to UV254 removal is valid throughout all stages. The results were modeled by a simple modification of the equivalent background compound model (EBCM) which was also used to simulate the additional OMP removals in multi-stage setups with up to 50 reuse stages.

Impacts of ozonation on the competition between organic micro-pollutants and effluent organic matter in powdered activated carbon adsorption.

This study investigates if ozonation of wastewater treatment plant (WWTP) effluent can reduce the negative impacts of effluent organic matter (EfOM) on the adsorption of organic micro-pollutants (OMP) onto powdered activated carbon (PAC). Pre-treatment of the water included membrane filtration for the removal of suspended/colloidal organics, ozonation with various specific ozone consumptions, and subsequent OMP spiking to comparable initial concentrations in all of the ozonated waters. This approach allowed for comparative PAC adsorption tests. Adsorption analyses show that the adsorbability of EfOM decreases with increasing specific ozone consumptions. This is also reflected by liquid chromatography with online carbon and UV254 detection (LC-OCD) which shows the ozone-induced disintegration of large EfOM into smaller fragments. Also, small organic neutrals are decreased while the small organic acids peak continuously increases with rising specific ozone consumptions. UV254 demonstrates that the aromaticity of all LC-OCD fractions continuously declines together with increasing specific O3 consumptions. This explains the varying EfOM adsorbabilities that occur due to ozonation. The ozone-induced decrease of EfOM adsorbability directly translates into reduced adsorption competition against the adsorption of OMP. With higher specific ozone consumptions, OMP removal and OMP loadings increase. The reduced adsorption competition is reflected in the outputs from equivalent background compound (EBC) modeling. In each of the ozonated waters, correlations between the OMP removals and the UV254 removal were found.

Rapid small-scale column testing of granular activated carbon for organic micro-pollutant removal in treated domestic wastewater.

This study investigates the applicability of the rapid small-scale column test (RSSCT) concept for testing of granular activated carbon (GAC) for organic micro-pollutants (OMPs) removal from wastewater treatment plant (WWTP) effluent. The chosen experimental setup was checked using pure water, WWTP effluent, different GAC products, and variable hydrodynamic conditions with different flow velocities and differently sized GAC, as well as different empty bed contact times (EBCTs). The setup results in satisfying reproducibility and robustness. RSSCTs in combination with WWTP effluent are effective when comparing the OMP removal potentials of different GAC products and are a useful tool for the estimation of larger filters. Due to the potentially high competition between OMPs and bulk organics, breakthrough curves are likely to have unfavorable shapes when treating WWTP effluent. This effect can be counteracted by extending the EBCT. With respect to the strong competition observed in GAC treatment of WWTP effluent, the small organic acid and neutral substances are retained longer in the RSSCT filters and are likely to cause the majority of the observed adsorption competition with OMPs.

Linking UF reversible and irreversible fouling to the water quality of surface water and treated municipal wastewater

AbstractThe interdependencies between water quality parameters and ultrafiltration characteristics (reversible, and irreversible fouling) of surface water (SW) in comparison with treated domestic wastewater (TDW) were systematically investigated. A focus was set to the macromolecular dissolved fraction (“biopolymers”), accounting for about 50% of the full fouling resistance. Correlation matrices were used to point out overall differences of both waters, whereas seasonal monitoring was used to reveal different inter-annual variability. The correlation matrices show that biopolymer concentration significantly correlates with total and reversible fouling of both waters but not with irreversible fouling. The membrane rejection of SW biopolymers showed significant correlations to all parameters (biopolymer concentration, reversibility, etc.). We found significant correlations of temperature with total and reversible fouling (positive in SW but negative in TDW) and irreversible fouling (negative in SW but posit...

Stratification of Granular Activated Carbon Filters for Advanced Wastewater Treatment

Advanced wastewater treatment with granular activated carbon (GAC) is a promising option to reduce emissions of organic micropollutants (OMP) into the aquatic environment. Frequent back-washes of the GAC filters are required due to high particle concentration in the treated wastewater but lead to stratification. Differences in adsorption capacities of individual strata are not known. The present study aimed at investigating physical and chemical differences at different filter depths of a stratified GAC filter. Two different commercial products were stratified during repeated filter bed expansions and sectioned into vertical fractions. Bulk densities, grain size distributions and ash contents of the individual fractions differed significantly. Adsorption tests with pulverized GAC from different levels showed great vertical differences in adsorption properties. OMP removals determined in the upper part of a GAC filter therefore cannot be extrapolated downwards. Both physical and chemical vertical heterogeneities with regard to adsorption capacities and residence times at different filter depths should be considered in the filter design, in the monitoring of a GAC filter, and in the interpretation of the GAC filter performance. Good correlations between abatements of UV light absorption and OMP removals were found for the virgin GAC throughout the non-uniform filter.

Influence of dissolved organic matter and activated carbon pore characteristics on organic micropollutant desorption

By simulating decreasing inflow concentrations, the extent of desorption of organic micropollutants (OMP) from three activated carbons (AC) was examined in laboratory batch tests. The tested AC showed strong differences in pore size distribution and could therefore be characterized as typical micro-, meso- and macroporous AC, respectively. Adsorption and desorption conditions were varied by using drinking water (containing dissolved organic matter (DOM)) and DOM-free pure water as background solutions to examine the influence of DOM on OMP desorption for the different AC. Under ideal conditions (adsorption and desorption in pure water) adsorption of the tested OMP was found to be highly up to completely reversible for all tested AC. Under real conditions (adsorption and desorption in drinking water) additional DOM adsorption affects desorption in different ways depending on the AC pore structure. For the micro- and mesoporous AC, an increased irreversibility of OMP adsorption was found, which shows that DOM adsorption prevents OMP desorption. This could be referred to pore blockage effects that occur during the parallel adsorption of DOM and OMP. For the macroporous AC, DOM adsorption led to an enhanced OMP desorption which could be attributed to displacement processes. These results show that smaller pores tend to be blocked by DOM which hinders OMP from desorption. The overall larger pores of the macroporous AC do not get blocked which could allow (i) OMP to desorb and (ii) DOM to enter and displace OMP.