Background Wastewater treatment plants face recurrent problems such as sludge production and the toxicity of treated effluents. Technological solutions have already been tested at research scale with significant results, particularly in terms of sludge production. When the technology was applied to municipal wastewater, the results showed a drastic reduction of organic and nitrogen load with a negligible excess of sludge production. Objectives The PERBIOF project aimed to develop at demonstration scale an innovative technology for treating municipal and/or industrial wastewater. The technology was based on a submerged biofilter that operates in a "fill and draw" mode. In this biofilter all the phases of the biological treatment (i.e., carbon removal, nitrogen removal, secondary sedimentation) were carried out in a single operative unit. The proposed technology is characterized by high depuration efficiencies (more than 10 times higher than conventional ones) and very low sludge production. The following results were expected in comparison with conventional technologies: a greater conversion capacity (up to 6-10 times) and lower reaction volumes (this means smaller plants with lower environmental impact); a reduction of sludge production by up to 10 times in the case of municipal wastewater and up to 40 times for tannery wastewater; a 50% reduction in treated effluent toxicity; and finally, a 40% saving in operating costs, increasing the competitiveness of potential industrial stakeholders (even SMEs) that will adopt such a new technology. Results The PERBIOF project achieved great results in treating urban and tannery wastewater. In particular for urban wastewater treatment it demonstrated: A conversion capacity up to 5-7 times greater than with traditional technologies; A reduction in sludge production of up to 90% in comparison with traditional technologies; The reaction volume of PERBIOF technology was found to be 20% of that of traditional technologies; As a consequence an 80% reduction in investment costs has been achieved; A 40% reduction in operating costs; A reduction of the environmental impact of the new technology by some 70% in use of resources and by some 90% in the contribution to global warming and eco-toxicity in comparison with traditional technologies. For tannery wastewater treatment it obtained: High compactness of the plant in comparison with traditional plants: the footprint is some 25% of that of a standard plant; The sludge production is about one thirtieth of the amount produced by a traditional plant; Investment costs are some 10% higher than for a standard plant; Operating costs are one-third of those of a traditional plant; All emissions show lower toxicity levels: in particular, human toxicity decreases by 74%, terrestrial eco-toxicity decreases by 64%, and freshwater aquatic eco-toxicity decreases by 50%.The effectiveness of the PERBIOF technology stems from the fact that the biomass, growing as granules, are four-to-five times more dense than that of conventional activated sludge granules, making it possible to treat concentrated wastewater over a shorter time-scale and in very small reactors. In the case of recalcitrant pollutants (tannery wastewater, for example) a chemical oxidation step is added to the biological treatment process, in order to obtain a transformation of the complex molecules into simpler biodegradable molecules. The reproduction potential in the same sector of activity (waste water treatment) is high. The beneficiary, being a governmental Institute (IRSA), it has made its beneficial outputs public and exploitable by whatever potential stakeholders in technical, socioeconomic or commercial terms. The system is much more cost effective than the current technologies. The beneficiary intends to continue the project by experimenting this treatment process to different types of industrial effluents in order to find further applications of the technology. Lariana Depur S.p.A., a company operating in Northern Italy in the field of textile waste waters treatment has contacted the beneficiary, to this end, with a request for collaboration. In addition further experiments will be carried out in order to test the possibility to apply the new PERBIOF technology to sections of the urban depuration plants other than the biological treatment one. The LIFE PERBIOF project was awarded the Premio Impresa Ambiente by the Italian Environment Ministry in recognition of its achievements. A further honour was bestowed when the IWA Biofilm Technologies Conference in Singapore in January 2008 named PERBIOF's presentation the best of the conference. Further information on the project can be found in the project's layman report (see "Read more" section).