Anaerobic biodegradability and toxicity of eucalyptus fiber board manufacturing wastewater

Wastewater from eucalyptus fiber board manufacturing (EFBM) was characterized and studied for its treatability by anaerobic digestion. The characteristics of the wastewater (in mg dm⁻³), are as follows: COD (42 000), SS (550), SO 42− (1200), PO 43−.P (50), NH 4+.N (15), VFA (710), phenol (20), p‐cresol (125), tannin COD (1460) and pH 2.8. Approximately 60% of the COD is composed of carbohydrates. The continuous treatment of EFBM wastewater resulted in 93% COD removal and 78% COD methanogenized, with influent COD values of 20 g dm⁻³ and OLR of 17 kg COD m⁻³ d⁻¹. The biodegradation reached 94% of influent COD and 74% of influent ultraviolet absorbance (215 nm). EFBM wastewater supplied at 20 g COD dm⁻³ (1:1 tap water diluted) caused 50% methanogenic toxicity, which did not disappear when tannins were removed by adsorption on PVP (polyvinylpyrrolidone). The toxicity decreased to 25% once the wastewater was autoxidized with air at high pH values. However, the effluent of the continuously fed column didn't show methanogenic toxicity, therefore the main toxic compounds in the wastewater were removed during anaerobic treatment.