ABSTRACT
Huge quantities of industrial oil are consumed as a result of their extensive application (more than 310 kt consumed in Spain in 2009) in a broad range of industrial processes. Once used, the resulting oils are considered toxic and hazardous showing fairly low chemical or biological degradability. The amount of these residues has been estimated at around 90 kt in Spain (2009). The used industrial oils (UIO) contain hazardous and toxic compounds, e.g. naphthalene, benzene derivatives and toluene, whose presence in the environment can cause severe damage. The waste hierarchy postulated in the 2008/98/EC European Directive includes valorization as one preferential strategy for waste management. [1] In Spain, recycling of 65% of UIO has been postulated as an objective. [2] Although it is still early to assess the impact of the new regulations, it is expected that the legal framework will reinforce oil recycling and regeneration objectives that will result in additional volumes of aqueous off-streams from these
operations, usually including different stages of metal precipitation, extraction and distillation. [3] These effl uents are characterized by high contents of organic solvents, hydrocarbons and suspended solids (SS), relatively high viscosity and poor biodegradability, making their treatment by conventional biological systems diffi cult. Nevertheless, biological techniques developed in the last two decades have shown their potential to deal with a broad range of industrial wastewater. In particular, anaerobic systems are an attractive option for the treatment of high-strength wastewater with an associated potential for methane generation. [4] A fi rst approach to the anaerobic treatment by a two-step process of a synthetic wastewater simulating the effl uents from UIO recycling operations showed COD removal effi ciencies higher than 83%. [5] However, application to real wastewater has not been reported so far.
