Reversing clogging in subsurface-flow constructed wetlands by hydrogen peroxide treatment: two case studies

One of the most frequently encountered operational problems in subsurface-flow constructed wetlands is clogging. Traditionally, the restoration procedure is to remove the clogged gravel or sand and replace it with clean material. This method, while effective, is costly and may require sections of the facility to be taken offline for extended periods of time. Another common remediation strategy is to have a resting period for each wetland cell, although this is not an option for very small systems which often consist of only one treatment cell. Recently, a more radical approach has been tested on a number of lab-scale and pilot-scale setups which consists of an aggressive oxidation of organic matter by means of hydrogen peroxide (H2O2). Results indicate that after treatment, clogging was substantially reduced and that H2O2 did not appear to have a long-term negative effect on plants and biofilms. The outcomes of two full-scale tests are discussed in this paper.