Abstract
The much over-looked element in new sanitation, the transport systems which bridge the source and treatment facilities, is the focus of this study. The knowledge of rheological properties of concentrated domestic slurry is essential for the design of the waste collection and transport systems. To investigate these properties, samples were collected from a pilot sanitation system in the Netherlands. Two types of slurries were examined: black water (consisting of human faecal waste, urine, and flushed water from vacuum toilets) and black water with ground kitchen waste. Rheograms of these slurries were obtained using a narrow gap rotating rheometer and modelled using a Herschel-Bulkley model. The effect of concentration on the slurry are described through the changes in the parameters of the Herschel-Bulkley model. A detailed method is proposed on estimating the parameters for the rheological models. For the black water, yield stress and consistency index follow an increasing power law with the concentration and the behaviour index follows a decreasing power law. The influence of temperature on the viscosity of the slurry is described using an Arrhenius type relation. The viscosity of black water decreases with temperature. As for the black water mixed with ground kitchen waste, it is found that the viscosity increases with concentration and decreases with temperature. The viscosity of black-water with ground kitchen waste is found to be higher than that of black water, which can be attributed to the presence of larger particles in the slurry.
Highlights
Critical evaluation of our current sanitation system has led to the introduction of a new sanitation paradigm
The steady-state laminar data was used in creating these rheograms
Rheograms were obtained for various total suspended solids (TSS) concentration and temperatures of slurries
Summary
Critical evaluation of our current sanitation system has led to the introduction of a new sanitation paradigm (see e.g. KujawaRoeleveld et al, 2006; Tervahauta et al, 2013; Zeeman et al, 2008). The new paradigm is based on source separation of the waste (as depicted in Fig. 1) and minimizing the use of water for transport This source separated waste consists primarily of faecal matter from vacuum toilets, toilet paper and grinded kitchen waste arising from the use of food waste disposers. These domestic waste streams are subsequently treated with the objective to minimize energy use during treatment while maximizing the recovery of resources present in the wastewater, namely: bio-energy (generated from the anaerobic transformation of organic material), nutrients (nitrogen, phosphorus, potassium and sulphur), and water. For any further development of the ‘source-separated sanitation’ approach, both transport and treatment are inseparable parts of the entire sanitation system and requires full assessment in order to evaluate its potentials for future waste handling (Larsen et al, 2009)
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