There is growing interest in the recovery of energy and resources from wastewater. In order to achieve an efficient recovery, it is important that the concentrations in the wastewater be increased. This can be done by adding more organic waste to the water and by reducing the amount of water. The so-called ‘new water cycle’ achieves this: after being processed by a food waste disposer, food waste is discharged into the wastewater stream, together with concentrated toilet wastewater (‘black water’), and is then digested at a wastewater treatment plant (WWTP). We need to study whether current indoor sewer installations are capable of transporting food-waste-disposer waste, especially in apartment buildings. This means ensuring no clogging or other undesirable consequences (such as corrosion or increased methane emissions) occur. Research has so far focused mainly on the impact on the public sewer system and the WWTPs, but the effects on the indoor sewer system have received little attention. This is an area where we need to gain more insight and experience to be able to meet the challenges and seize the opportunities.
The concentration of organic material in wastewater can be increased through the use of food waste disposers in households. It is important to investigate the possibility of discharging organic kitchen waste into the sewer system, after it has been processed by a food waste disposer, while avoiding any clogging or other undesirable consequences. In addition, future scenarios, involving ‘new’ water use (water-saving appliances) and the water use of food waste disposers themselves, also need to be taken into account. The impact on the sewer system of developments in rainwater harvesting also need to be considered, since the resulting reduced flow of rainwater in the sewers could have consequences for the flushing process in light of the higher wastewater concentration caused by the presence of ground organic waste.
Experience and knowledge are being developed through a literature study, lab experiments, and a pilot study in households in the municipality of Leidschemdam-Voorburg. These will then be combined with the results of SIMDEUM and other hydraulic models of indoor sewer pipes, to produce a full picture of the possibilities for the use of food waste disposers. Additionally, a Life Cycle Assessment will explore the associated environmental benefits, and a study will be conducted on the current prohibition of the discharge of cut and/or ground waste.
By performing lab experiments and designing a pilot study, more insight will be gained into the use of food waste disposers and their effects on indoor sewer pipes. In addition, other scenarios will be tested through modelling exercises, which will enable the development of guidelines for the installation of food waste disposers. Legal guidelines will also be drawn up.