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Hirtshals, Denmark

Rygaard M.,Technical University of Denmark | Godskesen B.,HOFOR | Jorgensen C.,DHI | Hoffmann B.,University of Aalborg
Science of the Total Environment | Year: 2014

Increasing stress on water resources is driving urban water utilities to establish new concepts for water supply. This paper presents the consequences of proposed alternative water supply options using a unique combination of quantitative and qualitative methods from different research fields. A former industrial harbor area in Copenhagen, Denmark, is currently under development and all infrastructure will be updated to accommodate 40,000 inhabitants and 40,000 jobs in the future. To reduce stress on water resources it has been proposed to establish a secondary water supply in the area as an alternative to the conventional groundwater-based drinking water supply. Four alternative concepts for a secondary water supply have been considered: 1) slightly polluted groundwater for use in toilets and laundry, 2) desalinated brackish water for use in toilets, laundry, and dishwashers, 3) desalinated brackish water for all uses, including drinking water, and 4) local reclamation of rain and gray water for use in toilets and laundry. The concepts have been evaluated for their technical feasibility, economy, health risks, and public acceptance, while the concepts' environmental sustainability has been assessed using lifecycle assessment and freshwater use impact methods. The holistic assessment method exposes conflicting preference solutions depending on assessment criteria, and reveals multi-faceted consequences for choices in urban water management. Not one concept turns out unambiguously positive based on the evaluation criteria included here, but the systematic evaluation will leave decision-makers informed on the consequences of their choices. © 2014 Elsevier B.V. Source


Mollerup A.L.,HOFOR | Mollerup A.L.,Technical University of Denmark | Mikkelsen P.S.,Technical University of Denmark | Sin G.,Technical University of Denmark
Environmental Modelling and Software | Year: 2016

This study focuses on designing an optimisation based control for sewer system in a methodological way and linking it to a regulatory control. Optimisation based design is found to depend on proper choice of a model, formulation of objective function and tuning of optimisation parameters. Accordingly, two novel optimisation configurations are developed, where the optimisation either acts on the actuators or acts on the regulatory control layer. These two optimisation designs are evaluated on a sub-catchment of the sewer system in Copenhagen, and found to perform better than the existing control; a rule based expert system. On the other hand, compared with a regulatory control technique designed earlier in Mollerup et al. (2015), the optimisation showed similar performance with respect to minimising overflow volume. Hence for operation of small sewer systems, regulatory control strategies can offer promising potential and should be considered along more advanced strategies when identifying novel solutions. © 2016 Elsevier Ltd. Source


Mollerup A.L.,HOFOR | Mollerup A.L.,Technical University of Denmark | Mikkelsen P.S.,Technical University of Denmark | Thornberg D.,BIOFOS | Sin G.,Technical University of Denmark
Environmental Modelling and Software | Year: 2015

A systematic methodology for regulatory control analysis and design is adapted for sewer system operation and evaluated. The main challenge with adapting the methodology is the handling of the stochastic and transient nature of the rainfall disturbances, inherent to sewer system operation. To this end, four distinct modes of operation are identified (dry weather, filling, saturation and emptying) and for each of these the process gain matrix is found. Based on the gain matrices a controllability analysis is performed, to screen for suitable pairings between measurements and actuators in the case study area of Copenhagen. The analysis effectively reduces the number of potential controlled variables, by considering the sensitivity of the measurements towards changes in the manipulated variables. Several potential pairings are generated and the best alternative is chosen for closed-loop testing. The methodology is a promising tool for systematic generation of solutions for sewer system control. © 2014 Elsevier Ltd. Source


Montgomery M.,Cowi A/S | Enemark A.,Cowi A/S | Hangaard A.,HOFOR
Journal of Failure Analysis and Prevention | Year: 2014

The titanium condenser has been in operation for 24 years at Amager unit 3 power plant. In February 2012, the plant was contaminated by seawater due to a failed condenser tube and some tubes were plugged. A month later, the plant tripped again. Small leaks were found again and finally approx. 200 tubes were plugged before the condenser was in service again. A series of inspections, NDT, and destructive examinations were conducted to try and understand the cause of failure in the tubes within the condenser. After such investigations, degradation mechanisms such as inner fouling, steam impingement, and fretting/erosion around the supports could be discounted. Ductile cracks were found in the tube within the tubesheet. From circumstantial evidence, it was concluded that failure was caused by a semi-filled condenser which led to a mismatch in expansion coefficients of filled tubes and unfilled tubes during a plant trip. In addition, small amounts of titanium hydride were revealed to be present in the tubes within the tubesheet indicating that the carbon steel tubesheet was corroding due to ingress of salt water. Although this was not the reason for the failure, it indicated the need for repair of the epoxy coating in the waterbox. © 2014 ASM International. Source


Godskesen B.,Technical University of Denmark | Hauschild M.,Technical University of Denmark | Rygaard M.,Technical University of Denmark | Zambrano K.,HOFOR | Albrechtsen H.-J.,Technical University of Denmark
Water Research | Year: 2013

Four alternative cases for water supply were environmentally evaluated and compared based on the standard environmental impact categories from the life-cycle assessment (LCA) methodology extended with a freshwater withdrawal category (FWI). The cases were designed for Copenhagen, a part of Denmark with high population density and relatively low available water resources. FWI was applied at local groundwater catchments based on data from the national implementation of the EU Water Framework Directive. The base case of the study was the current practice of groundwater abstraction from well fields situated near Copenhagen. The 4 cases studied were: Rain & stormwater harvesting from several blocks in the city; Today's groundwater abstraction with compensating actions applied in the affected freshwater environments to ensure sufficient water flow in water courses; Establishment of well fields further away from the city; And seawater desalination. The standard LCA showed that the Rain & stormwater harvesting case had the lowest overall environmental impact (81.9 μPET/m3) followed by the cases relying on groundwater abstraction (123.5-137.8 μPET/m3), and that desalination had a relatively small but still important increase in environmental impact (204.8 μPET/m3). Rain & stormwater harvesting and desalination had a markedly lower environmental impact compared to the base case, due to the reduced water hardness leading to e.g. a decrease in electricity consumption in households. For a relevant comparison, it is therefore essential to include the effects of water hardness when comparing the environmental impacts of water systems of different hardness. This study also emphasizes the necessity of including freshwater withdrawal respecting the relevant affected geographical scale, i.e. by focusing the assessment on the local groundwater catchments rather than on the regional catchments. Our work shows that freshwater withdrawal methods previously used on a regional level can also be applied to local groundwater catchments and integrated into the standard LCA as an impact category. When standard LCA is extended to include impacts of freshwater withdrawal, rain & stormwater and seawater (0.09-0.18 compared to 11.45-17.16 mPET/m3) were the resources resulting in least overall environmental impact. © 2013 Elsevier Ltd. Source

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