Sewage treatment | EPFL Graph Search

Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems (including on-site treatment systems) to large centralized systems involving a network of pipes and pump stations (called sewerage) which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporate

Treatment of micropollutants in municipal wastewater: study of a sequential batch biofilter

Andreu Contijoch Culleré

A fungal biofilter composed of woodchips was designed in order to remove micropollutants from the effluents of waste water treatment plants. Two fungi were tested: Pleurotus ostreatus and Trametes versicolor in order to evaluate their efficiency for the removal of two micropollutants: the anti-inflammatory drug naproxen and the antibiotic sulfamethoxazole. Although Trametes versicolor was able to degrade quickly naproxen, this fungus was not any more active after one week of operation in the filter. Pleurotus ostreatus was, on contrary, able to survive more than 3 months in the filter, showing good removal efficiencies of naproxen and sulfamethoxazole during all this period, in tap water but also in real treated municipal wastewater. Several other experiments have provided insight on the removal mechanisms of these micropollutants in the fungal biofilter (degradation and adsorption) and also allowed to model the removal trend. Fungal treatment with Pleurotus ostreatus grown on wood substrates appeared to be a promising solution to improve micropollutants removal in wastewater.

2014

Characterisation of Hospital Wastewater: the Case of the CHUV

Laura Marie Blanc

The aim of this study was to characterize hospital effluents in investigating the CHUV importance as source of pollutants, the range and amounts of pharmaceuticals that are used in the hospital and the need of source treatment of the hospital sewage. The CHUV is the biggest hospital of Lausanne (Switzerland), and 71% of its beds are in a building named “BH” (Hospital Building). The BH treats around 609 patients a day and releases an important volume of water (735 litres per patient per day), potentially highly concentrated in pharmaceuticals. The drugs the most delivered to the BH patients are the analgesic Paracetamol (787 g/day) and two anti-inflammatory substances: Ibuprofen (106 g/day) and Mefenamic acid (78 g/day). Among the 39 analysed pharmaceuticals, the most concentrated in the BH effluents are Paracetamol (423 ng/l) and Ciprofloxacin (22 ng/l). The CHUV effluents plus many other wastes from Lausanne city (homes, other health centres, etc.) are treated in Vidy wastewater treatment plant (WWTP). The treated water is then released into Lake Geneva. The load of pharmaceuticals from the CHUV was found to be relatively small, compared to the total load entering in Vidy WWTP. Maximal percentages of the WWTP inputs from the BH effluents were shown by two antibiotics: Ciprofloxacin (2.8%) and Sulfamethoxazole (4.3%). This indicates that many drugs are excreted in domestic wastewater. Although the drug levels in the water from the hospital are low compared to the total levels reaching the WWTP, they still represent a significant point source and wastewater treatment at the hospital or in the WWTP is necessary. But Vidy WWTP was shown to be particularly inefficient in treating some of the pharmaceuticals that entered it. Therefore, the risk for the environment has been assessed. Diclofenac, Ibuprofen, Paracetamol, Propranolol, Ciprofloxacin, Clarithromycin, Sulfamethoxazole and 17α-Ethinylestradiol were from 2 to 601111 times more concentrated in Vidy WWTP effluents than acceptable in terms of calculated risk quotient (RQ) values. So, in some cases, a very important risk for the environment has been demonstrated here. Improvements of the WWTP efficiency are now in progress as a response to this. Treated water leaving Vidy WWTP is further diluted (at least 84.7 times) when it enters Lake Geneva, however this study revealed detectable levels of some pharmaceuticals in the lake itself, albeit below the predicted no effect concentration (PNEC) in all cases measured in this study.

2010

Pretreatment options for micropollutant abatement before aquifer recharge in drinking water production: Assessment of UV/H2O2 and dense membranes

Robin Wünsch

Micropollutants (MP) such as residues of pharmaceuticals, industrial chemicals or pesticides can be detected in almost all water resources. Various processes can be used to abate them in drinking water treatment, e.g., ozonation, advanced oxidation processes (AOP), adsorption on activated carbon or membrane filtration. The selection of a suitable process combination is a complex task for water suppliers.This thesis compares two process chains in the context of a multi-barrier system including managed aquifer recharge (MAR). To protect soils and aquifers from MP in the future, an additional barrier against MP upstream of the MAR was investigated: (1) a full-stream treatment using the AOP UV/H2O2, and (2) a side-stream treatment with low-pressure reverse osmosis (LPRO) or nanofiltration (NF) and ozonation of the retentate to treat the concentrated MPs.Pilot-scale experiments were conducted to determine the relative abatements of MP by UV/H2O2 treatment and by a subsequent soil column treatment. Compared to a soil column fed with water without UV/H2O2 pretreatment, the performance of the combined process (UV/H2O2 + soil column) was more efficient. However, this could be explained by an additive effect of the individual processes.Relative abatements in the UV/H2O2 process are mainly based on the introduced UV fluence and hydroxyl radical exposure. These parameters could be calculated with a model based on the measured relative abatements of two MPs (probe compounds) and their kinetic data (second-order rate constants for the reactions with hydroxyl radical, absorbance and quantum yield).With this information, the relative abatements of other MPs could be predicted with an accuracy of ±20%. A sensitivity analysis of the model showed that the relative abatements of the selected probe compounds should be >50%. In this case, the accuracy of the calculated parameters depends mainly on the precision of the kinetic data.In the case of membrane-based treatment of water by LPRO or NF, a concentrate is produced. Ozonation to treat MP in the concentrate is accompanied by a formation of the possibly carcinogenic bromate by oxidation of bromide. To achieve the highest possible MP abatement with simultaneously low bromate formation, both membrane selection and subsequent concentrate ozonation were investigated. In laboratory tests with standardized concentrates, neither the water source nor the membrane type caused a change in bromate yield for similar relative MP abatements. However, NF membranes have lower relative retentions of bromide and MP than LPRO membranes, making NF concentrates more suitable for ozonation with limited bromate formation.A comparison of UV/H2O2 with membrane treatment showed that full-stream treatment with UV/H2O2 has about four times lower costs and an about five times lower environmental impact. In addition it achieves significantly higher disinfection. In contrast, side-stream treatment with LPRO causes up to two times lower impacts for the environment when the electrical energy source is wind or hydropower. This study thus contributes technical, economic, and environmental aspects to a holistic evaluation of the two process options.

EPFL2022