Overview of the biological processes available for the treatment of sugarcane mill wastewater

Cane sugar production generates a high volume of wastewaters (1-20 m/sugarcane tonne) heavily polluted by suspended solids (5-12 g/l) and organic matter (2-8 g COD/l). Consequently, these wastewaters cannot be discharged directly in the environment without causing a negative impact and must be submitted to a physico-chemical treatment for removing the suspended solids followed by a biological treatment for removing soluble organic matter. The COD/BOD5 ratio of these wastewaters indicates that they are easily biodegradable and practically amenable to any kind of biological treatment. A brief description of the existing different types of treatment is given in the article focussing on the advantages and disadvantages of each one. A table comparing them on the basis of the treatment unit size (volume and area), energy consumption, sludge production, final wastewater quality and staff qualification is given for a mill with the capacity to process 4,000 sugarcane tonne/day. It appears from the discussion that the treatment scheme which seems to be economically the most convenient consists of an anaerobic pre-treatment followed by an aerobic polishing. In some instances, the water produced by the anaerobic treatment may be of good enough quality to be at least re-used in sugarcane washing or irrigation.