A process for anaerobic digestion of agroindustrial wastes containing mainly soluble pollutants has been developed utilizing fixed-bed reactors. A pilot plant at a sugar refinery with two reactors in parallel, respectively of 10 and 50 m3 operating volume, has functioned successfully in treating wastes produced in regenerating ion-exchange columns used to purify the sugar juices. With an hydraulic retention time (HRT) of less than one day, a maximum gas production of 11.5 volumes per operating volume of reactor per day was obtained together with a reduction of up to 80% of the biological oxygen demand for five days (BOD5), and volatile solids and up to 70% of the chemical oxygen demand (COD). The gas contained from 70 to 75% methane. On the basis of these results, a full-scale industrial plant was built which has produced up to 7500 m3 a day of biogas. The process has been found suitable for a large number of industrial wastes, especially when plants are seasonally operated.

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