ABSTRACT
The use of constructed wetlands for a variety of treatment objectives has been underway for over 10 years. The system has proven effective in reducing the 5-day biochemical oxygen demand (BOD5) concentration of a secondary-treated effluent. Pulp mill effluents are complex mixtures of wood-derived organics as well as some inorganic ions and compounds. In untreated effluents, the BOD5 is high (generally in the range of 200 to 800 mg/L). The compounds responsible for the BOD5 of untreated effluents are primarily simple sugars, organic acids (e.g., acetic) and alcohols (e.g., methanol). Well-treated secondary effluents demonstrate no acute toxicity and little chronic toxicity using standard bioassay protocols. Some studies have found pulp mill effluents to cause biochemical and histological effects on fish and invertebrates. Two pilot studies have been conducted to determine the practicality of treating pulp mill effluents with constructed wetlands. Both utilized the subsurface flow/gravel matrix design.
