Impact of Prior Physico-Chemical Treatment on the Clogging Process of Subsurface Flow Constructed Wetlands: Model-Based Evaluation

The objective of this study was to check the effect of the use of a physico-chemical treatment on the clogging process of horizontal subsurface flow constructed wetlands by means of dynamic modelling. The hydraulic submodel was based on series as well as parallel branched complete stirred tanks of equal volume. The model was validated with data obtained from 2 identical experimental wetlands, which had a surface area of 0.54 m² and a water depth of 0.30 m, and that were monitored over a period of 5 months. One of the wetlands was fed with settled urban wastewater, whereas the other with the same wastewater, but previously treated with a physico-chemical treatment. In the model, pore volume reduction depends on the growth of bacteria and on solids retained. The effluent concentrations of COD and ammonium in both experimental wetlands were very similar in all the conditions tested, and therefore the physico-chemical treatment did not improve the removal efficiency. The model indicated that after 120 days of operation in some regions of the wetland fed with settled wastewater the porosity decreased in a 17%, whereas in the other wetlands it only decreased as much as 6%. The use of a prior physico-chemical treatment is a good alternative for avoiding an anticipated clogging of subsurface flow constructed wetlands.