Presence of sub-inhibitory concentrations of quaternary ammonium compounds in water: effects on bacteria and their inactivation by ozone and monochloramine

Disinfection agents have been present in our daily lives for several decades in detergents or in personal care products, where their role is to prevent the spread of pathogenic microor-ganisms. One of the largest class of disinfection agents is quaternary ammonium compounds (QACs). Within this class, cetyltrimethylammonium chloride (CTMA) and benzalkonium chlo-ride (BAC) are widely used. QACs have a broad-spectrum effect on bacteria, where they pri-marily target the membrane. After use, QACs are partially discharged to municipal wastewaters, where they are diluted to concentrations in the sub-inhibitory range. These low concentrations of QACs can trigger resistance mechanisms in bacteria, including membrane modifications and the expression of efflux pumps.The aim of this thesis was to investigate the consequences and the impact of the presence of low concentrations of QACs in wastewater and surface water on the survival of bacteria. It could be demonstrated that strains of P. aeruginosa long-term exposed to constant sub-inhibitory concentrations of either BAC or CTMA showed decreased susceptibility to both QACs, regardless of which QAC the bacteria had been exposed to. However, no resistance to selected antibiotics was found after this exposure. Investigations of the membrane using atomic force microscopy showed an increase in surface roughness following exposure to both BAC and CTMA, demonstrating that QACs affect bacterial membranes.QACs are poorly biodegradable and their presence, even at constant sub-inhibitory concen-trations, affect bacteria. QACs are poorly reactive with chemical oxidants commonly used for water disinfection, which aims to inactivate microorganisms. Therefore, QACs remain present during water and wastewater treatment. Several methods of disinfection exist, where ozona-tion and monochloramination are widely applied worldwide. The effect of a pre-exposure of E. coli to CTMA and of the presence of CTMA during disinfection with ozone (O3) and mono-chloramine (NH2Cl) were investigated. The pre-exposure to CTMA led to contrasting results: inactivation of E. coli was enhanced when using ozone but decreased when using monochlo-ramine. This result demonstrates the different modes of inactivation of bacteria for ozone and monochloramine. Moreover, the role of efflux pumps during inactivation was tested with two strains of E. coli, expressing different efflux pump systems. These two strains showed contrasting behaviors when treated with either ozone or monochloramine. Nevertheless, we were unable to resolve the role of efflux pumps in this system. The presence of CTMA en-hanced the inactivation when concentrations were higher than 2 mgL-1 for ozone and 2.25 mgL-1 for monochloramine.Standard methods to determine the minimum inhibitory concentration use ideal conditions for bacterial growth, which do not occur in natural water. Therefore, the susceptibility of E. coli to CTMA in PBS, lake water (Lake Geneva, Switzerland) and a wastewater effluent was investigated and compared to nutrient broth. It could be shown that E. coli was significantly more susceptible to CTMA in dilute aqueous solutions compared to broth. These results are relevant to assess the effect of CTMA and potentially other biocides on bacteria under realis-tic conditions, as it is probably overestimated using the current standard methods for MICs determination.

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

Conception of a biological activated carbon filter for micropollutants removal in wastewater

Solène Gomez

The presence of micro pollutants in water is an important emerging problem because of their negative impacts on health and environment. The Swiss Federal Office of the Environment is planning to impose new regulations to reduce the load of micro pollutants in waste water. This paper assesses the use of biological activated carbon (BAC) to treat micro pollutants from small waste water treatment plant (WWTP). In a first part, articles were consulted to evaluate the state of the art of BAC filters: their properties, efficiencies, costs as well as the impact of parameters such as the empty bed contact time (EBCT), aeration and backwashing. In a second part, two BAC filters were designed for implementation in WWTP (Vidy, Lausanne, Switzerland) and laboratory. The dimensioned BAC filter for the WWTP has an EBCT of 90 min and treats 1.7 L day-1. The proposed carbon is the ‘DCL-G’ carbon type. Feed water is pumped from the aeration tank of the Vidy WWTP and rejected before the existing granular activated carbon filter. Backwashing consists in stirring the top layer of carbon bed weekly and no aeration is needed for the proposed implementation. Dissolved organic carbon and micro pollutants monitoring is planned. The BAC filters are expected to remove 90% of micro pollutants treated below a concentration of 10 ng L-1.

2013

Impacts of irrigation with industrial treated wastewater on soil properties

Pascal Boivin, André Mermoud

Wastewater reuse in agriculture is a widespread practice in developing countries, especially in urban areas where water shortage and poverty encourage people to use that marginal resource. Raw or treated wastewaters are used by farmers, but even treated wastewaters frequently do not meet WHO and FAO standards for irrigation water. Such practices may lead to health hazards, relatively well documented in the literature and to environmental damages. Adverse environmental impacts such as soil degradation and groundwater contamination are frequently associated with the use of wastewater from industrial sources. Previous studies have demonstrated that wastewater irrigation may decrease soil hydraulic conductivity and infiltration rate. Nevertheless, the effects on soil structural and chemical behaviors have been little studied so far and need further investigations. The impacts of irrigation with alkaline and sodic industrial wastewater previously treated in microphyte ponds on soil physical and chemical properties were studied downstream the sewage treatment plant of Kossodo in Ouagadougou, on plots cropped with eggplants. Plots irrigated with fresh water and non cropped, non irrigated plots were used as controls. Different soil properties were characterized: pore volumes determined by using shrinkage analysis, pH and electrical conductivity of water extracts, and major soluble and exchangeable cations (Ca, Mg, K, and Na). Organic matter characterization was performed by means of three dimensional fluorescence spectra analysis to determine its origin and evolution on irrigated soils. Plots irrigated with wastewater showed important structural damages, especially in the subsurface horizon where the soil pore network collapsed dramatically, resulting in a compact impermeable layer. Fluorescence spectra revealed that the organic matter contained in the wastewater was largely dissolved due to a sharp soil pH increase, resulting in black alkali formation at the surface: the soil became sodic, with an exchange complex dominated by sodium, whereas plots irrigated with fresh water kept properties comparable to that of non irrigated plots. Such a rapid soil sodication was seldom reported so far. The study emphasizes the need to carefully examine irrigation water quality and particularly calcite residual alkalinity and suggests that shrinkage analysis could be used to monitor the physical changes of soil properties upon sodication. Inadequate wastewater quality is likely to cause deep and irreversible damages to irrigated soils. (C) 2013 Elsevier B.V. All rights reserved.