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This study assessed the accumulation of Cd (II), Hg (II), Cr (VI) and Pb (II) in Gynerium sagittatum (Gs), Colocasia esculenta (Ce) and Heliconia psittacorum (He) planted in constructed wetlands treating synthetic landfill leachate. Sixteen bioreactors were operated in two experimental blocks. Metal concentrations in the influent and effluent; root, stem, branch and leaves of plants were analysed, as well as COD, N-NH4+, TKN, T, pH, ORP, DO, and EC. Average removal efficiencies of COD, TKN and NH4+-N were 66, 67 and 72%, respectively and heavy metal removal ranged from 92 to 98% in all units. Cr (VI) was not detected in any effluent sample. The bioconcentration factors (BCF) were 10(0) -10(2). The BCF of Cr (VI) was the lowest: 0.59 and 2.5 (L kg(-1)) for Gs and He respectively; whilst Cd (II) had the highest (130-135 L kg(-1)) for Gs. Roots showed a higher metal content than shoots. Translocation factors (TF) were lower, He was the plant exhibiting TFs>1 for Pb (II), Cr (T) and Hg (II) and 0.4-0.9 for Cd (II) and Cr (VI). The evaluated plants demonstrate their suitability for phytoremediation of landfill leachate and all of them can be categorized as metals accumulators.

This paper discusses the applicability of effluent reuse in agriculture after treatment in a series of anaerobic, facultative and maturation ponds. The WSP system is located in Ginebra municipality, a small town in southwest Colombia. The total HRT is 12 days. Several samples of the final effluent were taken over a 55 day period and were analysed for E. coli, Streptococcus spp. and helminth eggs. Some additional grab samples were taken to determine the presence of pathogenic bacteria such as Salmonella spp. and Shigella spp. The results showed that the system was able to remove 4 log units of E. coli, 1 log unit of Streptococcus spp. and 100% of helminth eggs. Meanwhile, Salmonella spp. were detected in the effluent of the facultative pond whilst Shigella spp. were not detected in any sample. The main species of helminth eggs encountered were Taenia spp., Ascaris spp., Trichuris spp., Hymenolepis nana, H. diminuta and Enterobius vermicularis. Removal efficiencies were satisfactory despite the relatively short HRT. Nevertheless, WHO guidelines were slightly surpassed in the case of E. coli for unrestricted irrigation. The helminth egg value was always below the maximum WHO limit. Hence, this effluent can be safely used for restricted irrigation provided that field workers are protected from direct contact with wastewater given the presence of Salmonella spp. in the facultative pond effluent.

The simulation of hydrodynamics and transport phenomena in waste stabilization ponds is a developing tool worth studying in order to understand their internal processes and interactions. Pond design involves several physical, hydrological, geometric and dynamic variables so as to provide high hydrodynamic efficiency and maximum substrate utilization rates. CFD modelling allows the combination of these factors to predict the behaviour of ponds having different configurations. The two-dimensional depth-integrated model MIKE 21 was used in this study to simulate hydrodynamic and advection-dispersion processes in a full-scale anaerobic pond (AP) located in southwest Colombia. A set of 12 configurations including sludge contents, inlet-outlet positioning, baffling and pond geometry were modelled. Results showed that a crosswise (diagonally opposite) inlet-outlet layout, a length-to-breadth ratio of 2:1, plus provision of two cross baffles at 1/3 L and 2/3 L were the most effective measures to improve overall AP hydrodynamics and dispersion patterns.

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The design procedure for anaerobic ponds is based on calculations of the influent volumetric organic load as a function of temperature and wastewater strength. Hydraulically either a plug flow or a completely mixed model is assumed. However, factors such as sludge sedimentation patterns, biogas bubbling and sludge accumulation may influence the hydrodynamic behaviour of the pond and hence its removal efficiency. The results obtained show that sludge accumulation and incorrect positioning of inlets and outlets influence the hydraulic performance of the ponds. The dispersion number values obtained from experimental data (δ> 0.01) show the predominance of flow mixing patterns within the ponds. Nevertheless, short-circuiting as well as dead zones coexist. Pond desludging as well as improvement of the inlet-outlet arrangements increased the removal efficiency of both BOD and TSS. It would seem that desludging of the anaerobic pond has a higher impact on the effluent quality compared with improvements to the inlets and outlets. Furthermore,the removal efficiency of suspended and soluble organic matter might be improved by enhancing mixing within the pond volume. Finally, apart from conventional dispersion studies, other tools like computational fluid dynamics are essential in order to understand the complex hydrodynamic phenomena taking place in anaerobic ponds.