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- Evaluation of different substrates to support the growth of Typha latifolia in constructed wetlands treating tannery wastewater over long-term operationPublication . Calheiros, Cristina S. C.; Rangel, António O. S. S.; Castro, Paula M. L.The aim of this study was to investigate the performance of horizontal subsurface flow constructed wetlands planted with Typha latifolia treating tannery wastewater under long-term operation. Two expanded clay aggregates (Filtralite® MR3–8-FMR and Filtralite® NR3–8-FNR) and a fine gravel-FG were used as substrate for the constructed wetland units plus one unit with FMR was left as an unvegetated control. The systems were subject to three hydraulic loadings, 18,8 and 6cm d⁻¹, and to periods of interruption in the feed. The relationship between the substrate, plant development and removal efficiency, especially of organic matter, was investigated. Organic loadings up to 1800 kg BOD5 ha⁻¹ d⁻¹ and 3849 kg COD ha⁻¹ d⁻¹ were applied leading to mass removals of up to 652 kg BOD₅ ha⁻¹ d⁻¹ and 1869 kg COD ha⁻¹ d⁻¹, respectively. The three different substrates were adequate for the establishment of T. latifolia, although the clay aggregates allowed for higher plant propagation levels. The units with FNR and FMR achieved significantly higher COD and BOD₅ removal when compared to the FG and to the unplanted units. The systems proved to be tolerant to high organic loadings and to interruptions in feed suggesting this technology as a viable option for the biological treatment of tannery wastewater.
- Constructed wetland pilot units for wastewater treatment in the tannery industryPublication . Calheiros, Cristina S. C.; Rangel, António O. S. S.; Castro, Paula M. L.Constructed wetlands can be used for primary and secondary treatment of domestic wastewaters and for the treatment of a variety of other water sources including stormwaters, landfill leachate, industrial and agricultural wastewaters and acid mine drainage. For the treatment of tannery wastewater no detailed studies using constructed wetlands are known in the literature. Frequent problems occur in this industry concerning the effluent with high organic loadings. In these situations, a constructed wetland can be potentially used to support the existing wastewater treatment. The present study refers to the applicability of subsurface horizontal flow constructed wetlands for the treatment of tannery wastewater in two series of pilot units planted with Typha latifolia and Phragmites australis. The units were subject to different hydraulic loadings, 180 mm/d and 60 mm/d, and the organic matter removal efficiency was evaluated. The average COD for the inflow of the units was 1579 mg/l for an hydraulic loading of 180mm/d (1421 KgCOD/had) and 1297 mg/l for an hydraulic loading of 60mm/d (385 KgCOD/had). Maximum removal efficiencies, in terms of COD, for hydraulic loading of 180 and 60 mm/d in Typha unit were 63% and 92%, respectively. For Phragmites, the maximum values were 64% and 92%. The decrease in COD, BOD5 and TSS at the outflow of the units was found to increase with their influent values in a linear correlation. This behavior corresponds to a first order kinetics, showing that the pollutant removal rate was proportional to the influent strength. There was no significant difference between the two systems in series, indicating that the type of plant did not influence the treatment performance.