Objectives were to evaluate microbial populations in two free-water surface (FWS) constructed wetland cells receiving secondary treated pulp-mill wastewater, identify the microorganisms having decomposition activity of selected organic substances and discuss diversity of actinomycetes isolated from soil, plant and wastewater samples.

The populations of microorganisms in soil samples in the two wetland cells showed similar size in both cells; 6–7 × 106 cfu/g, 0.7–1.0 × 106 cfu/g, and 0.8–1.0 × 104 cfu/g, respectively, for total bacteria, actinomycetes and fungi. The population of bacteria in wastewater was similar in size to bacteria isolated from soil, but those of actinomycetes and fungi exhibited a very small size: 2–3 × 103 cfu/ml and only about 10 cfu/ml, respectively. In the populations on the surface of bulrush stems, the number of bacteria, actinomycetes and fungi found on the top portion of the stems was 4 × 105 cfu/cm2, 1.4 × 103 cfu/cm2 and 0.5 × 102 cfu/cm2, respectively. Actinomycetes and fungi occurred in very low numbers on the bottom of stems. More than 90% of actinomycetes isolated from the wetland cells had amylase activity, and 60 and 25% of them had chitinase and xylanase activity, respectively. Approximately 70 and 50% of fungi had protease and amylase activities, respectively. Fungi also had xylanase activity in about 40% of isolates. On the other hand, about 40% of bacteria exhibited protease activity, but a very low proportion of them had chitinase and xylanase activities. The number of actinomycete species isolated from wastewater and the surface of plant stems was restricted in comparison to that of actinomycetes isolated from soil.