Decentralised Sanitation and Reuse

(DESAR)

Domestic solid waste and wastewater form a potential source of nutrients, energy and water. In the current centralized approach of collection and treatment their useful value is for a large part lost. Source separation and decentralized treatment lead to efficient utilization of valuable components and to at least 25% saving in the drinking water consumption.

Decentralised Sanitation and Reuse (DESAR)

By implementation of the decentralised approach in the public sanitation sector, stimulation of reuse of recovered by-products can be obtained. Decentralised sanitation focuses on source separated collection of waste(water), treatment on- or close to the location and maximization of the possibilities to recover and reuse nutrients, water and energy.

Figure 2. Closing cycles in water chain

In the Netherlands, Wageningen University and LeAF in cooperation with a large number of partners work on the development of DESAR systems. 

In the considered DESAR concept ‘extremely’ low flush vacuum toilets together with the belonging transport system for black water are used.  Thanks to low flush water use, the black water is strongly concentrated and with a high-energy content. Implementation of anaerobic digestion enables to recover biogas. The biogas production can be further increased when organic kitchen waste is co-digested. The produced biogas is suitable for heating and/or electricity generation, while the remaining digested material is rich in nutrients (nitrogen, phosphorus, potassium) which can be recovered and  used as fertilizer in agriculture.

Figure 3. Vacuum toilet (Roediger) and black water digestion pilot-plant at Wageningen University

The grey water can be treated on location. Various treatment systems are available, like compact and extensive (micro) aerobic treatment, constructed wetland systems and membrane filtration. Treated grey water can be infiltrated in the soil together with the rain water or used as a source of water for ponds, parks or canals.

Current drinking water– and wastewater management

The current sanitation system in the Netherlands and in most of industrialised countries is characterised by a high drinking water consumption, complex sewer infrastructure, large waste water treatment systems and a high production of waste. The drinking water consumption in the Netherlands amounts approximately at 50 m³ per person per year. Only a little fraction of that (10%) is used for direct consumption (drinking, cooking). The rest of the water is (miss)used for flushing the toilet, washing and cleaning purposes. Finally, all wastewater streams disappear in a complex sewer network transporting them for long distances to large wastewater treatment plants (WWTP). In WWTPs wastewater is treated using energy intensive methods. The potentially interesting minerals are removed and a large amount of polluted wastewater sludge is produced.

Figure 1. Water-, nutrients - and energy streams in current wastewater management

Large-scale sanitation systems hardly comply with requirements of sustainable development, known to focus on minimizing use of resources, maximizing reuse of useful components (from waste) and on decentralization, to lower the vulnerability of the system.

Implementation of sewer network in urban infrastructure means a serious confiscation of underground space with consequences, such as considerable nuisance at construction and maintenance. In addition, rain- and other reusable water are transported outside the urbanized areas, causing water shortage in some cases. Because of increasing rain water drainage, sewer overflow frequency increases, leading to pollution of local water systems.

To reach sustainable protection of ground- and surface water, future developments in water management should focus on closing cycles and saving energy. Latter is already implemented progressively in the industrial sector in the Netherlands.  The public sector is following slowly.

DESAR demonstration projects

The first demonstration based on DESAR principles is being constructed for 32 houses in Sneek, Friesland and will be started in june 2006.

In Germany different examples of vacuum technology application for collection of black water exist.

Calculation example Amsterdam/Diemen

Table 1 gives a calculation on an exaapplication of a DESAR system in an imaginary residential area Amsterdam/Diemen (750.000 inhabitants) where environmental profits regarding water, nutrients and energy are quantified. The use of water saving toilets is shown to lead to 25% reduction in drinking water consumption, while approximately 27,7 mln m³ of treated water becomes available for, for instance, flushing the canals. Moreover a substantial amount of nutrients can be recovered and generated energy amounts approximately 408 thousand GJ.

Table 1. Potential environmental profits when implementing DESAR concept in Amsterdam/Diemen (750.000 inhabitants)

* production black water and organic waste = 100 g BOD per person a day; 1 kg BOD – 0.35 m³ methane at 273 K and p = p_o; energy content methane = 35,8 MJ/m³.

Contacts:

Dr. ir. Grietje Zeeman

E-M: Grietje.Zeeman@wur.nl

Dr. ir. Katarzyna Kujawa-Roeleveld

E-M: Katarzyna.Kujawa@wur.nl

Dr. Ir. Adriaan Mels

E-M: Adriaan.Mels@wur.nl