**Abstract**

Azo dyes represent a broad group of environmental pollutants that comprise between 60 and 70% of all the dyes and pigments used. The conventional processes are not efficient in treating effluents from the textile industry. Biofiltration emerges as an unconventional, easy-to-use, effective, and low-cost technology for the treatment of textile effluents. Biofiltration uses microbial consortia that form a biofilm on a filter medium. Peat is an organic matter with the ability to retain high moisture content and represents an attractive option to treat these effluents due to its high porosity, sorption capacity, availability, and low cost. The packing materials used were: peat as an organic biomass, perlite as an inorganic material, and a mixture of peat and perlite. Sorption processes in the biofilter peat-packed material and perlite are discussed dealing with its treatment capacity and as potential removers of azo dyes, their advantages and disadvantages compared with other traditional methods, and a review of operating parameters and design criteria that allow its large-scale application as a possible nonconventional treatment technology. The biofilter with the highest removal capacity was the peat-perlite mixture that achieved a 91% for the organic matter (measured as COD), and a 92% for the color removal (Direct blue 2 dye). with a retention time of 1.18 days.

**Keywords:** azo dyes, biofiltration, peat, perlite, sorption, biomass
