Biofilm bacteria attached to submerged surfaces play a major role in organic matter degradation in free-water-surface(FWS) constructed wetlands used for wastewater treatment. Effective specific surface area (as) available for the biofilm bacteria is an important parameter in organic matter degradation and in describing the biofilm kinetic models used in the design and operation of constructed wetlands. In this study, kinetic models based on two possible biofilm geometries were developed for the determination of as and its non-dimensionalised value or area factor (δ). The as and δ values were estimated for a laboratory FWS constructed wetland treating domestic wastewater based on the chemical oxygen demand (COD) removal performance and other kinetic parameters. With the assumption of slab geometry for the biofilm, the values of as and δ were found as 3.15 m2/m3 and 2.2 for the lab unit having 80% mass COD removal, whereas by considering the cylindrical geometry for the biofilm attached on the lateral roots higher values of as and δ were obtained.

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