Background Some 40 per cent of national production of leather in Spain takes place on the La Serrata industrial estate in Lorca, Murcia. The industrial estate houses 24 industrial units all responsible for leather tanning, employing 1 100 workers directly and 3 300 indirectly. The first process in the preservation of leather skins is based on salting. Before and after tanning, skins reach a level of moisture or swelling of the live animals, in order to recover their original flexibility, softness and fullness, as well as to make the penetration and absorption of tanning products easier. Due to the moisture in the hides, high saline effluents are produced. These have negative environmental impacts. In the past, in order to reduce this pollutant discharge enterprises would simply dilute the waste water and then dump it in the nearby river Guadalentin. This resulted in high levels of salinity and high organic and mineral pollution. In addition, it produced unpleasant odours and created a health risk, as well as having a negative effect on the environment. In the medium to long-term it was feared this could lead to the closure of the factories. Objectives The aim of the project was to develop a new wastewater treatment system for the tanning sector, based on membrane techniques, designed to lower the water salinity to levels suitable for re-use at an agricultural and industrial level. The chosen treatment was ultra-filtration (UF) of the water coming from the biological reactor, followed by reverse osmosis (RO). The rejections and purges from the whole process were dried out using thermal techniques and treated by an authorised administrator. Results The project was a success from a technical point-of-view and achieved its main objective. The plant treatment scheme now produces 8 000 m3/day of water that can be recycled and used for agricultural and industrial purposes. The scheme involved the development of the following:  A 4 000 m3 biological reactor with aeration and agitation elements to continuous treatment of wastewater from tannery industries.  Ultra-filtration membranes: 2 646 m2 to produce 5 000 m3/day of treated water.  Reverse Osmosis: 234 membranes equivalent to 1 326 m2 to obtain 200 m3/h of treated water from ultra-filtration.  Evaporator: The brine from reverse osmosis (55-60 m3/h) was treated to obtain a solid (20-30 Tm/day) as a final waste of the treatment plant. The project allowed for a sustainable development in the tanning industry in Lorca, as the infrastructure of waste management now in place will allow any industry located on the industrial estate to meet its environmental obligations. This project has been selected as one of the 24 "Best" LIFE Environment projects in 2004-2005