Transportability of domestic slurries

Delft University of Technology and Deltares have been awarded a research grant (from technology foundation STW) to investigate the transportability of domestic slurries, which is the missing link for future sanitation systems. Many researchers of future treatment concepts have claimed that low dilution enhances treatment efficiency and is essential for the success of future sanitation systems. However, the minimum required dilution and other properties of domestic slurries (that is to say, toilet flushing and biodegradable “kitchen” slurries) have yet to be determined. A preliminary assessment of transportation concepts for future sanitation systems shows that the most promising transportation concepts are single-phase slurry transport and a two-phase (air-water) transportation concept. The Dutch Foundation for Applied Research on Water Management and Wastewater Treatment (STOWA) has recently recommended the further investigation of new black-water transport concepts.

Experimental facility of Deltares, ALPHA loop, in which the Domestic Slurry experiments will be conducted

Characteristics of domestic slurry

A domestic slurry is a non-Newtonian mixture of cohesive solids (faeces), fibres (toilet paper, hair, etc.), kitchen waste from grinders and liquids (water, urine). Deltares researches a number of transportability issues for new sanitation concepts relating to the dilution, or equivalently the solids content, that have been largely neglected. Key elements in this research project include:

  1. Rheological characterisation of domestic slurries, including cohesive properties, as a function of solids content, particle size and other parameters. To this end, 500 samples of domestic sludges have been analysed with respect to viscosity, cohesion, surface tension and density at different temperatures.
  2. Experiments with artificial sludges will be set up and carried out in our large-scale lab facilities (ALPHA Loop at Deltares). The reasons for not using real-life sludge in these experiments is that domestic sludges are not stable due to bio-chemical breakdown processes, repeatability of experiments and HSE regulations.
  3. Development of a 1D multi-phase simulation model for the transportation of a domestic slurry, starting from 3D analyses of critical phenomena.
  4. Monitoring of transient flow properties in the lab and possibly a full-scale vacuum sewer, resulting in validation data for the numerical models.

Two doctorate researchers have been appointed to carry out this challenging research project: one will focus on the experimental work and the other on the numerical modelling and validation.