Time filter

Source Type

Zürich, Switzerland

Kovalova L.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Siegrist H.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Von Gunten U.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Von Gunten U.,Ecole Polytechnique Federale de Lausanne | And 5 more authors.
Environmental Science and Technology | Year: 2013

A pilot-scale hospital wastewater treatment plant consisting of a primary clarifier, membrane bioreactor, and five post-treatment technologies including ozone (O3), O3/H2O2, powdered activated carbon (PAC), and low pressure UV light with and without TiO 2 was operated to test the elimination efficiencies for 56 micropollutants. The extent of the elimination of the selected micropollutants (pharmaceuticals, metabolites and industrial chemicals) was successfully correlated to physical-chemical properties or molecular structure. By mass loading, 95% of all measured micropollutants in the biologically treated hospital wastewater feeding the post-treatments consisted of iodinated contrast media (ICM). The elimination of ICM by the tested post-treatment technologies was 50-65% when using 1.08 g O3/gDOC, 23 mg/L PAC, or a UV dose of 2400 J/m2 (254 nm). For the total load of analyzed pharmaceuticals and metabolites excluding ICM the elimination by ozonation, PAC, and UV at the same conditions was 90%, 86%, and 33%, respectively. Thus, the majority of analyzed substances can be efficiently eliminated by ozonation (which also provides disinfection) or PAC (which provides micropollutants removal, not only transformation). Some micropollutants recalcitrant to those two post-treatments, such as the ICM diatrizoate, can be substantially removed only by high doses of UV (96% at 7200 J/m2). The tested combined treatments (O 3/H2O2 and UV/TiO2) did not improve the elimination compared to the single treatments (O3 and UV). © 2013 American Chemical Society.

Kaiser H.-P.,Zurich Water Works | Koster O.,Zurich Water Works | Gresch M.,Hunziker Betatech AG | Gresch M.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | And 5 more authors.
Ozone: Science and Engineering | Year: 2013

For real-time control of ozonation processes in water works, a sequencing batch reactor was constructed to measure the ozone decay rate constant (kO3) in short time intervals of about 15 min. The batch reactor is filled during the production process, immediately after dissolving ozone in water by a static mixer. On the basis of kO3 and the initial ozone concentration ([O3]0), and the experimentally determined ratio of the concentrations of •OH radicals to ozone (Rct), the degradation of micropollutants in ozone reactors (modeled as Continuously Stirred Tank Reactors - CSTRs) were calculated for compounds with known reaction rate constants with ozone and •OH radicals. Calculated degradation of atrazine, iopromide, benzotriazole and acesulfame are in good agreement with measured data. For acesulfame the following rate constants were determined in this study at 20 oC: reaction rate constant with ozone = 88 M-1s-1, reaction rate constant with •OH radical = 4.55 × 109 M-1s-1. For the ozone reaction an activation energy of 35 kJ/mol was determined. Similarly to micropollutants, the relative inactivation of microorganisms (N/N0) can be calculated based on the inactivation rate constant for ozone and if applicable the lag phase. The pI-value (= -logN/N0) was introduced and implemented in the process management system to calculate online the log inactivation of reference microorganisms such as B. subtilis spores. The system was tested for variation of pH (6.5-8.5), DOC (1.2-4.2 mg/L) flowrate 3.2-12 m3/h and temperature (5.7-9 oC). Furthermore, a given pI-value, e.g. 1 for a 1-log inactivation of B. subtilis spores, can be set as control parameter in the process management system. The ozone gas flow is then adjusted until the set pI-value is reached. The process control concept was validated with B. subtilis spores. Generally, a good agreement was found between calculated and measured inactivation data. It was also demonstrated, that a constant ozone residual may lead to insufficient disinfection or overdosing of ozone. The new process control concept for ozonations based on onsite measurement of the ozone decay rate constant and the pI-value allows to assess disinfection and degradation processes quantitatively in real-time. © 2013 Copyright 2013 International Ozone Association.

Neumann M.B.,Basque Center for Climate Change | Neumann M.B.,Ikerbasque | Rieckermann J.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Hug T.,Hunziker Betatech AG | Gujer W.,ETH Zurich
Journal of Environmental Management | Year: 2015

Well-planned urban infrastructure should meet critical loads during its design lifetime. In order to proceed with design, engineers are forced to make numerous assumptions with very little supporting information about the development of various drivers. For the wastewater sector, these drivers include the future amount and composition of the generated wastewater, effluent requirements, technologies, prices of inputs such as energy or chemicals, and the value of outputs produced such as nutrients for fertilizer use. When planning wastewater systems, there is a lack of methods to address discrepancies between the timescales at which fundamental changes in these drivers can occur, and the long physical life expectancy of infrastructure (on the order of 25-80 years). To explore these discrepancies, we take a hindsight perspective of the long-term development of wastewater infrastructure and assess the stability of assumptions made during previous designs. Repeatedly we find that the drivers influencing wastewater loads, environmental requirements or technological innovation can change at smaller timescales than the infrastructure design lifetime, often in less than a decade. Our analysis shows that i) built infrastructure is continuously confronted with challenges it was not conceived for, ii) significant adaptation occurs during a structure's lifetime, and iii) "muddling-through" is the pre-dominant strategy for adaptive management. As a consequence, we argue, there is a need to explore robust design strategies which require the systematic use of scenario planning methods and instruments to increase operational, structural, managerial, institutional and financial flexibility. Hindsight studies, such as this one, may inform the development of robust design strategies and assist in the transition to more explicit forms of adaptive management for urban infrastructures. © 2015 Elsevier Ltd.

Jeuch-Trommsdorff C.,Axpo Kompogas AG | Benz A.,Hunziker Betatech AG | Moser R.,Hunziker Betatech AG | Ulli A.,Axpo Kompogas AG
Water Practice and Technology | Year: 2011

A common valorization of digester gas and composting gas increases the efficiency of the co-generator installation by 10% to 15%. In this case study, a green waste fermentation and composting platform and its neighboring waste water treatment plant (WWTP) opted for a common co-generator: about 600,000 m 3 of digester gas and 1,900,000 m 3/year of fermentation gas (biogas) transformed into electricity and heat. The energy content of this combined gas source is about 13,800 MW/a, out of which about 38% is transformed into electricity, about 42% is converted into heat, and 20% is lost. The electrical energy produced (600 kW) is sold to the Swiss electrical grid (Swissgrid Program) as Ökostrom, or "green power," at a higher price than that of normal power. The heat produced (660 kWh) is used to heat the composter (60 kWh), the digester (125 kWh), and the buildings (25 kW). The excess heat (450 kWh) could also be used for a future low-temperature biosolids drying project, whose life-cycle costs would be counterbalanced by the reduction in disposal costs. This project allows for an optimal use of the energy content of biogas and digester gas. Once drying is implemented, the environmental impact will be even more beneficial with a reduction in transport and the facilitation of phosphorous recovery from dried biosolids. In this case study, the large amount of biogas produced would enable the implementation of low-temperature biosolids drying using the excess heat of the co-gen facilities. The ratio of the biogas to the digester gas production has to be at least 2.5 to 3.0 in order to produce sufficient excess heat for a low-temperature dryer. Low-temperature drying is the most ecological and sensible way of using locally produced waste-heat all year long. © IWA Publishing 2011.

Discover hidden collaborations