Indications of recent warm and dry summers' impact on private wells for drinking-water supply in Germany: a review of press articles.

Climatic changes lead to seasonal droughts with declining groundwater levels, and - especially in rural regions - private wells in the upper aquifer might fall dry. However, only limited information and no systematic administrative reporting of the extent are available for Germany yet. Therefore, a systematic analysis of newspaper articles as a promising source of information was conducted for the extraordinarily hot summers of 2018, 2019 and 2020. The results of the database searches were analysed with respect to frequency and local and regional hotspots, relations to climatic data, extent of the reported dry-fallings and emergency water supply. The analysis indicates hotspots particularly for the federal states of Saxony, where a subsidy programme for connecting to the public water supply was reissued in 2019, for Bavaria and North Rhine-Westphalia. Emergency supply was realised through various approaches. It was partly required until the winter months and did not always have drinking-water quality. As private wells are particularly vulnerable to the effects of climate change, their operators should be involved as a stakeholder group in future discussions about allocating water resources to increasingly competing uses in periods of scarcity.

The benefits of powdered activated carbon recirculation for micropollutant removal in advanced wastewater treatment.

PAC adsorption is a widespread option for the removal of organic micropollutants (OMP) from secondary effluent. For an optimal exploitation of the adsorption capacity, PAC recirculation is nowadays a common practice, although the mechanistic interrelations of the complex recirculation process are not fully resolved. In this work, extensive multi-stage batch adsorption testing with repeated PAC and coagulant dosage was performed to evaluate the continuous-flow recirculation system. Partly loaded PAC showed a distinct amount of remaining capacity, as OMP and DOC removals considerably increased with each additional adsorption stage. At a low PAC dose of 10 mg PAC L(-1), removals of benzotriazole and carbamazepine were shown to rise from <40% in the first stage up to >80% in the 11th stage at 30 min adsorption time per stage. At a high PAC dose of 30 mg PAC L(-1), OMP and DOC removals were significantly higher and reached 98% (for benzotriazole and carbamazepine) after 11 stages. Coagulant dosage showed no influence on OMP removal, whereas a major part of DOC removal can be attributed to coagulation. Multi-stage adsorption is particularly beneficial for small PAC doses and significant PAC savings are feasible. A new model approach for predicting multi-stage OMP adsorption on the basis of a single-stage adsorption experiment was developed. It proved to predict OMP removals and PAC loadings accurately and thus contributes towards understanding the PAC recirculation process.

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.