Comparative multi -criteria performance assessment tool for alternative water infrastructure systems

Transcription

1 Comparative multi -criteria performance assessment tool for alternative water infrastructure systems C. Sartorius 1, P. Lévai 2, J. Niederste-Hollenberg 1, I. Nyga 3, C. Sorge 2 and T. Hillenbrand 1 1 Fraunhofer ISI, Karlsruhe, Germany 2 IWW, Mühlheim/Ruhr, Germany 3 Bauhaus Universität, Weimar, Germany IWA Pi 2017 Conference, Vienna, May

2 Alternative w ater infrastructure systems (WIS) a need for comparative assessment The project TWIST++* is part of the research programme "Sustainable Water Management" (NaWaM) sponsored by the German Federal Ministry of Education and Research Its purpose is the development of more sustainable water infrastructure systems After their first implementation the widespread dissemination of these innovative concepts is often hampered by uncertainty about their performance Need for a comparative and comprehensive performance assessment tool Innovative vs conventional Innovative vs innovative * Transition pathways water InfraSTructure systems 2

3 i. WET* an innovative decentralized WIS Recovery of heat from light (= weakly polluted) grey water Collection of light grey and rain water Treat both to become process water Blue path Green path Excess grey and rain water is treated in a horizontal soil filter ("energy alley") Use of water and nutrients for producing biomass (short-rotation coppice) Evaporated water improves micro-climate 3 *Integrated Water Energy Transition

4 Multi-criteria assessment General objective Basic objectives Specific objectives Criteria Indicators List of criteria: see DWA work sheet A 272 (2015), similarly Lienert et al. (2015) 4

5 Multi-criteria method: utility analysis Enables the comparison and aggregation of assessments based on a wide variety of different criteria For this purpose, normalized partial utility values (PUV) are determined for each criterion (and indicator) PUV 1 Max. permissible value PUV 1 Average value PUV 1 PUV 1 PUV 2 0,5 PUV 3 0 E 1 Emission 0 E 2 Emission 0 0% 100% R 3 Retention Bonus-malus systems are used to quantify more qualitative properties PUV are weighted (weights according to AHP method from survey) Weighted PUV are aggregated through adding up Highly transparent assessment process 5

6 Assessment results The conventional WIS is a large-size (> 100,000 p.e.) wastewater treatment plant (including anaerobic sludge digestion) with a combined sewer system. Its overall performance is above German average Compared with the conventional system, the innovative WIS including i.wet performs better in the following respects (exemplary): A smaller share of organic matter and nutrients in the wastewater is adsorbed in the soil filter (energy alley); the larger share arrives in the WWTP in a more concentrated form better cleaning All eco-toxic substances washed off by the rain are adsorbed completely in the energy alley With respect to greenhouse gas emissions i.wet earns higher credits for heat recovery from wastewater, produced biomass, substituted water supply etc. than debits for operation of processing the grey and process water 6

7 Assessment results (2) Compared with the conventional system, the innovative WIS (incl. i.wet) performs better in the following respects (exemplary), continued: 27 % of the water and small amounts of P and N are recycled, while no recycling takes place in the conventional WIS While i.wet is more costly owing to grey and rain water processing and heat recovery equipment, it benefits from making redundant the otherwise necessary retrofit of a separate sewer system The need for rehabilitation of the conventional WIS opens up a "window of opportunity" with respect to sunk cost The economic burden of the users of having to buy (decentralized) i.wet is relieved by the fact that a third party buys and operates it at a fixed monthly price ( adapted business model) Due to its decentralized nature, i.wet renders the innovative WIS more flexible with respect to changing conditions and the damage potential is more limited 7

8 Assessment results (3) Compared with the conventional system, the innovative WIS (incl. i.wet) performs worse in the following respects (exemplary), continued: Knowhow/experience of plumbers and operators with i.wet (also in case of trouble) is lower than with the conventional WIS Dependence on other infrastructures, in particular energy, is higher 8

9 Criteria Indicators Weight (%) Conventional i.wet 1. Ecological criteria Nutrient burden N, P Ecotoxic substances/water Cu, Zn, Diclofenac, Terbutryn Oxygen-consuming substances BOD Ecotoxic substances/ soil Cadmium, lead, PAK Greenhouse gas emission GHG equivalents Effect on micro climate Soil sealing, cold-air lanes Resource use Energy, operating materials Resource recovery P, N, H 2 O, C (organic) Land use r F -value Safety-relevant criteria a Germ infestation/hygiene Total bacteria count, Coliform cfu b Smell/turbidity TON, NTU Economic criteria (Net) costs Investment and operation Flexibility, system's readiness for change Depreciated cost, useful life Social criteria Convenience (Service quality) Expenditure of time Economic burden Special cost burden Nuisance Number of sensoric media Technical criteria Vulnerability to damage Spare capacity, damage potential Knowhow availability Effect of system failure Share of BOD in river/lake Supply of firefighting water Share of safe supply Flexibility w/ resp. to changing conditions Modularity Dependence Number/intensity Total

10 When is better better? Criteria Weight (%) Conventional i.wet 1. Ecological criteria Safety-relevant criteria Economic criteria Social criteria Technical criteria Total Aggregated PUV are higher for i.wet in four out of five categories appears unambigous, but is the difference between 0.67 and 0.72 significant? If PUV conv and PUV i.wet were determined independently: ΔPUV = PUV i.wet PUV conv = 0.72 (±0.04) 0.67 (±0.03) = 0.05 (±0.07) Weakly significant Since ΔPUV (and PUV conv ) is determined directly: ΔPUV = 0.05 (± 0.01); PUV i.wet = PUV conv + ΔPUV = 0.72 (±0.04) Highly significant 10

11 Conclusions The multi-criteria assessment method described above uses utility analysis and a set of 5 main objectives, 21 criteria and 33 indicators to enable a transparent and comprehensive assessment of alternative WIS Through normalization and the inclusion of weighting factors partial assessments are easily comparable (with respect to pros and cons) In order to arrive at an overall assessment, partial utility values can (but do not have to) be aggregated The significance of the comparative assessment is increased by determining the difference values directly (rather than as dependent on both, the reference and innovative WIS) As long as the system borders and the threshold values used for normalization are identical, quite different WIS in all kinds of model settings can be compared; on the other hand, case-by-case adjustments of the system borders can save time and effort required for the assessment 11

12 Thank you for your attention! 12