Low Cost Wastewater Treatment and Potentials for Re-use A Cleaner Production Approach to Wastewater Management

Current mainstream technologies for wastewater treatment, such as activated sludge and tertiary nutrient removal are too costly to provide a satisfactory solution for the increasing wastewater problems in developing regions. Besides, these technologies do not allow for re-use of valuable energy and nutrients contained in the wastewater. This paper introduces a so called ‘Cleaner Production’ concept to sewage management, which combines two approaches: pollution prevention, and re-use. Pollution prevention includes the shift towards low water use or dry sanitation technology. The remaining, more concentrated waste, automatically becomes more attractive for re-use oriented treatment schemes. The combination of anaerobic treatment, for energy recovery, and duckweed-based lagoons for pathogen removal and nutrient recovery is presented as an example of possible re-use strategies. By selecting optimal applications of the duckweed biomass and lagoon effluent, nutrients will end up as fish protein (via duckweed feeding) and crop protein (via irrigation). The focus on duckweed as a key step in waste recycling is due to the fact that it forms the central unit of a recycling engine, driven by photosynthesis and therefore the process is energy efficient, cost effective and applicable under a wide variety of rural and urban conditions. Wastewater in a historical perspective The provision of high quality piped drinking water to households took a fast development during the second part of the 19 century as a response to the rapid expansion of cities and to the wide spread occurrence of cholera epidemics (referred to as the Asian disease) in Europe and the USA. The origin of water borne diseases was not well understood until the famous microbiologists Louis Pasteur and Robert Koch discovered the concept of pathogenic bacteria and their transmission via contaminated water. The resulting technology development for urban water management was based on the following concepts (Gijzen 1999; Harremoes, 2000): The prevention of water-borne diseases. This has been realised by introducing centralised potable water treatment facilities, extensive distribution systems and multiple tap connections in each household. The success of this approach is guaranteed only if (re-)contamination of purified water is prevented; this requires effective operation and maintenance of the infrastructure. Many cities in developing regions suffer from frequent pressure drops and as a result (waste)water may infiltrate into the distribution system. The use of water to transport waste out of the city. It is daily practice to use large quantities of clean ‘drinking’ water in the household to flush waste via toilets, kitchen sinks and washing machine into the sewer. The basic function of water in these cases is the collection and subsequent transportation of unwanted waste materials out of the city. The provision of water was, and to a large extend still is, supply driven. The above functions of water for cleaning and transport of waste materials requires large volumes of water to be