Degradation of 37 emergent contaminants by UV and neutral fenton and photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L␣1, and a real global quantity of micropollutants of 29.5 mg L␣1. The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV254) alone, dark Fenton (Fe2þ,3þ/H2O2) and photo-Fenton (Fe2þ,3þ/H2O2/light). Different irradiation sources were used for the photo-Fenton experi- ences: UV254 and simulated sunlight. Iron and H2O2 concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV254, 50 mg L␣1 of H2O2, with and without adding iron (5 mg L␣1 of Fe2þ added or 1.48 mg L␣1 of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treat- ments. As the H2O2 concentration increased (10, 25 and 50 mg L␣1), best degradations were observed. UV254, Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

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.

Elsevier Science Bv2013

Co-culture of microalgae and bacteria for wastewater treatment

Thierry Mounir

To address the problem of insucient wastewater treatment and eutrophication of lakes and rivers, the symbiotic association of microalgae and bacteria has shown great potential and numerous advantages. First, co-cultures can exhibit ecient treatment of domestic wastewater, with the combination of high nutrients (nitrogen and phosphorus) removal abilities of the microalgae and ecient degradation of organic matter by bacteria. Second, the symbiosis between microalgae and bacteria exchanging CO2 and O2 makes aeration not necessary, thus signicantly reducing the operating costs of the wastewater treatment plant. Third, recovered biomass of algae could be used as highpro t products like biofuels and food source. Fourth, the xation of the atmospheric CO2 by the microalgae through photosynthesis would contribute to greenhouse gas reduction in the atmosphere. Finally, the decayed microalgal biomass could serve as organic carbon source for denitrication by bacteria. However, this technology is not well-known yet, and further research on the in uence of the operating parameters have to be conducted. Furthermore, its main drawback is the harvesting of the microalgae. Due to their small size, microalgae demonstrate a low settling rate of 3.6 x 10􀀀3 m/h. A solution is to enhance aggregation of the biomass through occulation, followed by granulation to reach fully-developed microalgal-bacterial consortia. These granules exhibit high treatment performances and high settleability. The rst objective of this project was to identify the optimal microalgae:bacteria ratio for COD and nutrients removal. The second objective was to form fully-developed granules, starting from a co-culture, and assess the in uence of dierent agitation speeds on the granulation. The photobioreactor with a microalgae:bacteria ratio of 75:25 expressed the most promising results in COD removal eciency (95% after 8 days), nitrogen removal eciency (94% after 9 days), phosphorus removal eciency (93% after 7 days), and biomass productivity (144 mg/L/d). In this photobioreactor, nitrogen was removed by a combination of assimilation into microalgal biomass and nitrication/denitrication by the bacteria. The COD was removed by degradation by bacteria and mixotrophic microalgae that used the organic matter as carbon source. Finally, phosphorus was removed by assimilation into microalgal biomass. Although obvious aggregation between microalgae and bacteria could be observed, no fully-developed granules were formed after 89 batches of 24 hours. Because of low COD and nitrogen removals, no starvation period was experienced by the co-cultures. Therefore, extracellular polymeric substances were not released in sucient amounts to enhance the granulation. Furthermore, excessive stirring (200 rpm) may have lead to microalgal cells damage, thus promoting bacterial growth over microalgal growth. On the other hand, slower agitation speeds (80 and 120 rpm) seemed to enhance microalgal growth. Overall, the agitation speed appeared to have an indirect impact on the treatment performances and the settleability of the co-cultures, by signicantly in uencing the microalgal and bacterial growths.

2020

A strategy for xenobiotic removal using photocatalytic treatment, microbial degradation or integrated photocatalytic-biological process

Miléna Lapertot

According to the limited natural resources and due to the risks of anthropogenic pollution, it appears necessary to react efficiently in order to remove existing contaminations and avoid the creation of new ones. Therefore, the purpose of this thesis is to propose a sustainable strategy for treating problematic pollutants with the most adequate process. First, an overview of the different treatment processes has been given. In particular, biological, photocatalytic and integrated biological-photocatalytic treatments have been described as efficient methods to remove xenobiotics. Biological treatment of contaminated environments and industrial effluents has been presented as the most attractive method on a cost-benefit extent. But for biorecalcitrant substances, the Advanced Oxidation Processes (AOP) have remained the most efficient methods although expensive. Therefore, the coupling of biological-photocatalytic has emerged as the best compromise for removal of recalcitrant xenobiotics. The first step of the treatment strategy has consisted of evaluating the biotraitability of 19 chemicals: pesticides, pharmaceuticals and volatile organic compounds (VOCs) have been assessed according to three biodegradability methods (Zahn-Wellens, Manometric Respirometry, Closed-Bottle tests), whose official protocols had to be adapted to the compound specificities (volatility, hydrophobicity). Structure-Activity Relationship (SAR) estimation models have also been used to compare and validate the experimental results. For the compounds which have been assessed as biotraitable (VOCs), further biodegradation studies have been led in order to improve the treatment (batch with pulses of substrate): automated monitoring of the biodegradation process, increased degradation yields and biomass productivity have been successfully completed for Toluene, Ethylbenzene, Xylenes, Chlorobenzenze and Dichlorobenzene removal. Conversely, the compounds assessed as biorecalcitrant have been oriented towards the TiO2 and photo-Fenton photocatalytic treatments. Thus, the degradation of four p-halophenols by TiO2 photocatalysis has been investigated and has demonstrated the halogen effect on removal rates, aromatic intermediates and toxicity variations. Finally, the treatment of five bioreacalcitrant pesticides (Alachlor, Atrazine, Chlorfenvinphos, Diuron, Pentachlorophenol) has been studied in order to develop a coupled photocatalytic-biological system: first, enhanced biotreatability has been evaluated using the Zahn-Wellens procedure and then fixed-bed bioreactors have been operated and permitted to find out the best moment for coupling.

EPFL2006