In regions with arid climates, like the Middle East, there is a shortage of water. Improvement of sanitary techniques and use of the treated wastewater could reduce the demand on fresh water sources in these regions. The general objective of the research in the CORETECH project is therefore to integrate sanitary engineering with environmental and agricultural engineering for a cost-effective optimisation and safe usage of the limited water and nutrient resources in the region. Moreover, to diminish the discharge of raw domestic sewage in the environment, stimulate the use of treated wastewater for irrigation and fertilisation in agriculture, therewith to reduce the health risks and environmental pollution.

Due to the limited presence of water as resource, the conventional sanitation system is highly questionable under arid climate conditions. Minimising water consumption at the household requires other sanitation techniques. Source separation of solids at the household could be an alternative, particularly for rural areas. In such systems house-on-site (modified)-septic-tanks (Zeeman&Lettinga, 1999) for the treatment of domestic sewage, can be combined with small bore sewer systems, which are connected to a community-on-site (post)-treatment to meet the required effluent criteria. Separation of black and grey wastewater is to be considered in areas where so far no, or limited, sanitary services are available. The latter option has the advantage that the toilet waste water which contains the bulk of the pathogens, nutrients and salts, is separated from the diluted water streams, which has important advantages for the post-treatment and use of diluted streams. When toilet waste water is collected with or without a very limited amount of flushing water, the so called night soil production, it could be digested in accumulation systems (Zeeman et al. 2000). The digested slurry can be used in agriculture as soil conditioner and fertiliser.

Depending on the type of agricultural usage of the treated effluent, the anaerobically pre-treated water requires some additional post-treatment. In the post treatment a multiple approach is chosen, covering natural extensive systems which can be implemented in rural areas and villages, but also compact systems suitable for implementation in highly densely populated areas. The treatment systems include:

the soil-based or land-treatment systems (slow rate or rapid sand filtration, overland flow systems, constructed and natural wetlands) and

the aquatic-based systems (aquatic plant treatment systems, constructed and natural wetlands, and pond systems) (Angelakis and Tchobanoglous, 1995).

Development of appropriate irrigation/fertilisation methodologies will be coupled to the (community) on-site treatment systems. Its goals are to select the most suitable agricultural crops, including the cropping pattern, which can be grown on the treated sewage, to study the environmental impact of the usage of treated sewage on the soil and underground water reservoirs with regard to the fate of micro pollutants. Moreover to assess and develop improved methods for the identification and enumeration of various kinds of pathogenic organisms -in treated effluents, crops and soils. Agricultural aspects will be discussed in an additional paper.

Starting from households, the chosen sanitation strategy determines the collection and treatment