Micropollutant removal from municipal wastewater

Many micropollutants present in municipal wastewater, such as pharmaceuticals and pesticides, are poorly removed in conventional wastewater treatment plants (WWTPs), and may generate adverse effects on aquatic life. The objective of this thesis was to study and develop various options to improve micropollutant removal from municipal wastewaters. Various technologies were investigated, from conventional biological treatments to advanced physico-chemical and biological processes such as ozonation, activated carbon adsorption, enzymatic bio-oxidation with laccase and biodegradation with white-rot fungi. The potential of ozonation and powdered activated carbon (PAC) adsorption was assessed with two large-scale pilot systems at Lausanne WWTP. Micropollutants were removed on average over 80%, with an average dose of 5.7 mg/l O3 or 10 to 20 mg/l PAC. Both advanced treatments led to a clear reduction in toxicity of the effluents, and appeared to be feasible in large municipal WWTPs. The role of nitrification on micropollutant removal in WWTPs was investigated with aerobic granular sludge reactors, operated with or without nitrification. Out of the 36 micropollutants studied, 5 were significantly better removed in the reactor with nitrification. For the other pollutants, aerobic heterotrophic microorganisms played probably a role much more important than nitrifying bacteria. The potential of laccase, an oxidative enzyme produced by many white-rot fungi and bacteria, was assessed for the removal of 39 micropollutants. 9 were oxidized by laccase alone, and three others were degraded in case of addition of a mediator. Despite the limited range of pollutants degraded, laccase (with or without mediators) was able to oxidize several substances of concern. The influence of pH, temperature, laccase concentration and reaction time on the oxidation kinetics by laccase of four micropollutants was investigated. All four factors have a significant effect on the micropollutant oxidation with the greatest influence shown by pH. Optimal conditions for micropollutant oxidation ranged between pH 4.5 to 6.5 and between 25°C to more than 40°C. The influence of pH, mediator, enzyme and pollutant concentrations on sulfamethoxazole and isoproturon oxidation kinetics with laccase-mediator systems (LMS) was investigated. The mediators were consumed during the reaction (no catalytic cycles observed). Faster oxidation kinetics were observed at lower pH, but also higher mediator/pollutant ratios were required. Transformation product mixtures were always less toxic than untreated pollutants. LMS appears to be a promising option to treat concentrated and potentially toxic effluents, but does not seem adapted for the treatment of low micropollutant concentrations in municipal wastewaters. Finally, a sequential batch fungal filter (SBFF), composed of woodchips as substrate and support for the mycelium of Pleurotus ostreatus, was designed and operated during more than 140 d with unsterile wastewaters. A wide range of micropollutants was removed well by a combination of fungal and microbial degradation and adsorption. The SBFFs were able to compete with ozonation and PAC adsorption regarding the average removal efficiency (up to 82%) of 27 micropollutants in municipal wastewaters. This thesis opened new perspectives regarding biological treatment of micropollutants in wastewater, highlighting also the challenges of applying fungal and oxidative enzyme treatments in WWTPs.

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

David Andrew Barry, Luiz Felippe De Alencastro, Anoys Magnet, Jonas Margot, Luca Rossi

Many 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 O3 l-1 or a PAC dose between 10 and 20 mg l-1 (Figure 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.

2013

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

David Andrew Barry, Luiz Felippe De Alencastro, Anoys Magnet, Jonas Margot, Luca Rossi

Many 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, drug 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 O3 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.

Elsevier2013

Bacterial Resource Management for Nutrient Removal in Aerobic Granular Sludge Wastewater Treatment Systems

David Gregory Weissbrodt

The approach of wastewater treatment has shifted towards a holistic view in order to achieve sustainability in addition to environmental protection. The aerobic granular sludge (AGS) technology, which relies on the use of fast-settling granular biofilms called granules, is progressively becoming a new standard for high-rate biological nutrient removal (BNR) and secondary clarification in single sequencing batch reactors (SBR). The AGS intensive process has been related with definite savings in land area, construction, and operation costs. In an economical analysis, theoretical savings of CHF 0.45 per m3 (1 Swiss franc CHF ≈ 0.83 €) were computed for a Swiss wastewater treatment plant (WWTP) of 200’000 capita removing all nutrients biologically. Besides scale-up, fundamental research was required to understand and tailor the structure of underlying bacterial communities that form granules and remove nutrients. Mechanisms of bacterial selection were investigated in a systems approach to propose strategic axes for optimal management of the bacterial resource for efficient process performances. This research led to the following advances. After having designed a flexible reactor infrastructure for AGS research, a mathematical modeling methodology was developed to understand the hydraulic and biological processes involved during plug-flow transport of wastewater across the settled AGS bed during the feeding phase. BNR relies on the preferential selection of polyphosphate-accumulating organisms (PAO) by proper uncoupled supply of electron donors and electron acceptors. A bed height to diameter ratio of 6 was deduced to be optimal for full bed loading and efficient anaerobic acetate uptake under reference simulation conditions (20°C, pH 7.0). A bioinformatics methodology called PyroTRF-ID was developed for the identification of bacterial relatives involved in BNR processes by combination of terminal-restriction fragment length polymorphism (T-RFLP) and pyrosequencing data. This procedure provided high resolution of bacterial community structures and dynamics of AGS systems. Electrical conductivity and polyphosphatase assays were proposed for rapid and low-cost assessment of the fractions of active PAO and of the dephosphatating potential of activated sludge and granular sludge. Positive linear correlations were obtained between the fraction of PAO, the biomass specific rate of conductivity evolution measured in anaerobic metabolic batch tests, and the polyphosphate-hydrolyzing enzymatic activity of cell extracts. Wash-out conditions used to stimulate granule formation were shown to exert a selection pressure not only on physical properties of early-stage granules, but also on the underlying bacterial community composition. Operation with constant volumetric organic loading rates (OLR) during wash-out resulted in the formation of slow-settling fluffy granules dominated by filamentous Burkholderiales affiliates formed under low aeration (< 2 cm s-1) and high mesophilic temperature (30°C), and of fast-settling dense granules dominated by Zoogloea spp. under high aeration (4 cm s-1) and with an inoculum originating from a BNR-WWTP. These exopolysaccharide producers were considered as model organisms for granulation. However, their proliferation over PAO and nitrifiers correlated with poor BNR. PAO estab-lished at mature stage as soon as sufficient AGS was present to fully remove volatile fatty acids (VFA) during the anaerobic feeding phase. Without purge of excess sludge, glycogen-accumulating organisms (GAO) competed with PAO at a later stage of reactor operation. Granulation was shown to occur in stirred-tank SBRs operated under steady-state condi¬tions to cultivate PAO and GAO enrichments. The Accumulibacter- and Competibacter-dominated communities displayed granulation potential without involvement of Zoogloea spp. Fast-settling nuclei formed despite initial operation with a settling time as high as 60 min, and evolved towards granules after decrease of settling time to 10 min. Dynamic control of the OLR, anaerobic contact time, and sludge retention time (SRT) selected for active PAO in early-stage granules. Confocal laser scanning microscopy (CLSM) revealed that granula¬tion mechanisms depend on the predominant organisms involved. Fast-growing Zoogloea spp. formed smooth biofilm continuum matrices. The slower-growing PAO and GAO formed het¬erogeneous granular structures by proliferation in compact colonies around flocs. Fluctuations in operation variables were shown by multivariate statistics to impact on process performance and bacterial community structures in anaerobic-aerobic AGS-SBRs. The size of granules impacted on nitrification and dephosphatation by affecting oxygen mass transfer. Efficient BNR was obtained with at least 500 mgCOD L-1of acetate, 30 gCOD gP-1, and 10 gCOD gN-1. Although clades of PAO can denitrify, nitrogen removal was thus not restricted only to PAO. A broad denitrifying community was identified. The bacterial community continuum comprised two major opponent clusters, composed of members of the core microbiome of full-scale BNR-WWTPs. The first mainly comprised Accumulibacter, Nitrospira, Xanthomonadaceae, and Aminobacter affiliates selected by conditions of efficient BNR. The second mainly comprised Competibacter, Sphingobacteriales, Cytophaga, and Tetrasphaera affiliates correlating with periods of low BNR. Bacterial selection in AGS systems was mainly impacted by pH, according to multifactorial experiments. Accumulibacter and BNR were favored with alkaline pH, low mesophilic temperatures, and in the presence of propionate. Competibacter proliferated with acidic pH, temperature close to 30°C, and only acetate. Tetrasphaera spp., potential major PAO of certain full-scale plants, withstood Competibacter-selective conditions. Enhanced BNR was obtained under non-limiting conditions with food-to-microorganism ratios above 25 mgCODs gCODx-1. With fixed 2-h starvation, dephosphatation was only complete with full aeration. Since alternating aerobic-anoxic starvation conditions led to partial conversions, the length of starvation phases should be controlled in function of the redox conditions applied. Overall, optimal bacterial resource management in AGS systems requires full control of system behavior by taking advantage of the flexibility of the SBR technology. A methodology is proposed to this end, comprising milestones for wastewater characterization, SBR design, “anaerobic selector” design, control of the starvation phase length, shaving of fluctuations in operation variables, purge of excess sludge, proper selection for a stable, active and cooperative bacterial community, as well as efficient BNR. As key research perspective, investigations with real wastewater should validate the knowledge gained on bacterial behaviors under low-complexity conditions. Significant differences in predominant bacterial relatives were detected between lab-scale and full-scale BNR sludge. Metagenomics will provide a broader view on key organisms and functions of BNR and AGS microbiomes.

EPFL2013

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

David Andrew Barry, Luiz Felippe De Alencastro, Anoys Magnet, Jonas Margot, Luca Rossi

2013

Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon?

David Andrew Barry, Luiz Felippe De Alencastro, Anoys Magnet, Jonas Margot, Luca Rossi

Many 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, drug 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 O3 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.

Elsevier2013

Bacterial Resource Management for Nutrient Removal in Aerobic Granular Sludge Wastewater Treatment Systems

David Gregory Weissbrodt

EPFL2013