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Highlights• Micropollutants are efficiently removed by both ozone and powdered activated carbon• Specific substances were removed more efficiently by ozone• Powdered activated carbon effectively removed a wider range of pollutants• Both treatments significantly reduced the toxicity of WWTP effluent AbstractMany organic micropollutants present in wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs). To reduce the release of these substances into the aquatic environment, advanced wastewater treatments are necessary. In this context, two large-scale pilot advanced treatments were tested in parallel over more than one year at the municipal WWTP of Lausanne, Switzerland. The treatments were: i) oxidation by ozone followed by sand filtration (SF) and ii) powdered activated carbon (PAC) adsorption followed by either ultrafiltration (UF) or sand filtration. More than 70 potentially problematic substances (pharmaceuticals, pesticides, endocrine disruptors, drugs metabolites and other common chemicals) were regularly measured at different stages of treatment. Additionally, several ecotoxicological tests such as the yeast estrogen screen, a combined algae bioassay and a fish early life stage test were performed to evaluate effluent toxicity. Both treatments significantly improved the effluent quality. Micropollutants were removed on average over 80% compared with raw wastewater, with an average ozone dose of 5.7 mg O 3 l -1 or a PAC dose between 10 and 20 mg l -1 . Depending on the chemical properties of the substances (presence of electron-rich moieties, charge and hydrophobicity), either ozone or PAC performed better. Both advanced treatments led to a clear reduction in toxicity of the effluents, with PAC-UF performing slightly better overall. As both treatments had, on average, relatively similar efficiency, further criteria relevant to their implementation were considered, including local constraints (e.g., safety, sludge disposal, disinfection), operational feasibility and cost. For sensitive receiving waters (drinking water resources or recreational waters), the PAC-UF treatment, despite its current higher cost, was considered to be the most suitable option, enabling good removal of most micropollutants and macropollutants without forming problematic by-products, the strongest decrease in toxicity and a total disinfection of the effluent.

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Abstract. This paper presents a theoretical model of flow and chemical transport processes in subterranean estuaries (unconfined brackish groundwater aquifers at the ocean-land interface). The model shows that groundwater circulation and oscillating flow, caused by wave setup and tide, may constitute up to 96% of submarine groundwater discharge (SGWD) compared with 4% due to the net groundwater discharge. While these local flow processes do not change the total amount of land-derived chemical input to the ocean over a long period (e.g., yearly), they induce fluctuations of the chemical transfer rate as the aquifer undergoes saltwater intrusion. This may result in a substantial increase in chemical fluxes to the ocean over a short period (e.g., monthly and by a factor of 20 above the averaged level), imposing a possible threat to the marine environment. These results are essentially consistent with the experimental findings of Moore [1996] and have important implications for coastal resources management. Although these discharge components have been studied previously, the above conceptual model of SGWD is proposed for the first time.Dn can be estimated using aquifer recharge data. It is normally small compared with the discharge due to river flows into the ocean, Dr; the estimate of D n as a percentage of D r ranges from 0.1 to 10 [Younger, 1996]. Note that we are considering these discharges over a large coastal area (e.g., a few hundred kilometers in the alongshore direction) and a long period (e.g., seasonal). Although they contribute greatly to D sowr>, the magnitudes of D w and D t have not been described in previous studies nor measured independently in the field.

[1] Wave and tide are important forcing factors that typically coexist in coastal environments. A numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a nearshore subterranean estuary. A hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide. The oscillating sea levels determined the seaward boundary condition of the coastal aquifer, where variably saturated, variable density flow was modeled. The simulation results showed that waves induced an onshore upward tilt in the phase-averaged sea level (wave setup). The resulting hydraulic gradient generated pore water circulations in the nearshore zone of the coastal aquifer, which led to formation of an upper saline plume (USP) similar to that formed due to tides. However, mixing of recirculating seawater in the USP with underlying fresh groundwater was less intensive under the high-frequency wave oscillations. In the case of combined forcing, wave-induced circulations coupled with the intratidal flows strengthened the averaged, circulating pore water flows in the nearshore zone over the tidal period. The circulating flows increased exchange between the subterranean estuary and ocean, contributing 61% of the total submarine groundwater discharge for the simulated condition in comparison with the 40% and 49% proportions caused by the same but separate tidal and wave forcing, respectively. The combined forces also created a more extensive USP with the freshwater discharge zone shifted farther seaward. The freshwater flow paths in the intertidal subterranean estuary were modified with a significant increase in the associated transit times. The interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater. These results further demonstrate the complexity of nearshore groundwater systems and have implications for future investigations on the fate of land-sourced chemicals in the subterranean estuary prior to discharge to the ocean.

Municipal wastewaters are contaminated by a wide range of chemicals, from surfactants to heavy metals, including pharmaceutical residues, personal care products, various household chemicals, and biocides/pesticides. Their release into the environment, where they may generate adverse effects on aquatic organisms, depends on their fate in wastewater treatment plants (WWTPs). The sources, the typical concentrations and the fate of more than 160 micropollutants of various classes in conventional WWTPs, were investigated in order to estimate surface water contamination, risks for aquatic organisms, and to propose means to reduce their release into the environment. Relatively hydrophobic pollutants such as heavy metals, persistent organic pollutants (POPs), brominated flame retardants, and several personal care products (PCPs), as well as easily biodegradable pollutants such as surfactants, plastic additives, hormones, several PCPs, some pharmaceuticals, and household chemicals, are usually well removed (>70%) in WWTPs, either by sorption onto sewage sludge or by biodegradation. Good removal efficiencies, however, do not mean that the effluent concentrations will not potentially affect aquatic life, as some of these compounds are toxic at very low concentrations. More hydrophilic and poorly-to-moderately biodegradable pollutants such as several pharmaceuticals, pesticides, and household chemicals (corrosion inhibitors, sweeteners, chelating agents, phosphorus flame retardants) are only poorly removed during treatments. To decrease their discharge into surface waters, source control combined to advanced treatments such as ozonation and adsorption onto activated carbon are necessary.

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