Waste stabilization ponds are a long established technology that is steadily regaining popularity and is increasingly acknowledged as a high potential wastewater treatment option of the future due to ponds' capacity to enhance biodiversity and aesthetic value of the environment. Recent years have seen continuing development in the understanding of the fundamental processes involved in the various types of pond and in their practical implementation separately and in combination; there is also a new interest in devices such as baffles, recirculation systems and gravel filters. This growing complexity of pond technology and the demand for greater performance predictability require more in depth knowledge of the mechanisms involved and the effect of meteorological factors. All these topics were considered at IWA's 7th ponds conference after which participants submitted nearly a hundred papers for full peer review, which led to the selection of the 31 papers in this issue.
The papers selected are grouped under the headings of: design and modeling of waste stabilization ponds; nutrient removal in waste stabilization ponds; upgrading waste stabilization ponds; advancement in waste stabilization ponds technology; and industrial and agricultural wastewater treatment. Together they provide an unrivalled insight into the state of the art in research into and application of waste stabilization ponds.