Abstract
Leachate was generated when precipitation percolated through a pile of woodwaste, including trimmings, off-specification wood chips, shredded bark and roots, and sawdust from several cedar processing mills. The “young” woodwaste leachate produced in the pile's placement period was amber, acidic (pH 3.4–3.7), nutrient-poor (inorganic nitrogen 1.4–3.2 mg L-1, orthophosphate 3.3–4.3 mg P L-1), of very high oxygen demand (chemical oxygen demand 12,559–14,254 mg L-1, tannin and lignin 3066–5150 mg L-1 as tannic acid, volatile fatty acids 1564–2132 mg L-1), and very toxic to aquatic life (96-h median lethal concentration of 0.74% leachate). The leachate at 1.5 years old in the closure period had lower oxygen demand and higher ammonia, and became less acidic and darker. The leachate had a 5-day biochemical oxygen demand to chemical oxygen demand ratio of 0.33 in the placement period and 0.14 in the late closure period. Volatile fatty acids accounted for 6 to 34% chemical oxygen demand, varying as the pile developed and with woodwaste age. Tannin and lignin accounted for 33 to 45% chemical oxygen demand. More than 98% contaminants were in dissolved form. The monthly variation of leachate quality was likely a result of both temperature and precipitation. pH was significantly correlated to chemical oxygen demand, tannin and lignin, and volatile fatty acids.
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