food/products food food/products grey water water water water black water CO2 CO2 biomass biomass biomass residual heat high temperature energy net low temperature energy net low temperature energy net river valley port Ghent foodstock exchange Ghent greenhouses water treatment food production biomass production biomass processing organic waste treatment netwerken van het circulair metabolisme veduta di Gent 2030 - blauw-groene structuren streetview landbouwpark