Research On The Clogging Development And Mechanism Of Constructed Wetlands

Constructed wetland is a kind of ecological treatment technology which has many advantages such as low construction cost, simple operation and maintenance requirements and so on. Constructed wetland has been widely used in the improvement of water environment. But when coming to the engineering practice, it has been gradually found that clogging is a widespread operational problem which would greatly restrict the application of the wetlands. Hence, in this paper, we firstly studied the clogging development and influence factors, and then discussed the clogging mechanism. Finally, effects of resting operation on the recovery of the wetlands clogging were assessed. The main contents in this paper are as follows:(1) Six experimental devices were built to study the clogging of stormwater wetlands and the inflow was the semi-synthetic rainwater. The results showed that the constructed wetlands can be divided into two sections, according to the clogging mechanism, i.e., Section I and Section II, where clogging is induced primarily by either solid entrapment or biofilm development, respectively. In Section I, the biological activities alleviated the clogging. Overall, the solids entrapment in the front section was the key of the wetlands clogging. With theclogging development, short flow region, hydraulic efficiency, and mean hydraulic retention time all increased slightly. The presence of the vegetation can change the flow path, which has an influence on the mean hydraulic retention time (HRT) and volumetric efficiency.(2) By studying the different clogging phenomenon, the clogging mechanism was discussed further, and the effect of the microorganism on clogging was analyzed. It was found that in four kinds of clogging phenomenon, inorganic particles clogging was a process of internal clogging, and serious clogging area was located in the front section (0-30 cm). However, in the rest of clogging phenomenon, the clogging area was in the surface layer. The results showed that biofilm growth didn’t only occupy the effective space, reduced the porosity and permeability coefficient of the wetlands, but also enhanced the interception, bonded the particulate matter together, and accelerated the wetlands clogging.(3) In this paper, the recovery regulations of different clogging phenomenon in the resting operation was studied. The results showed that in addition to the inorganic particles clogging, the rest three kinds of the clogging could recover significantly. In the enough resting period, these could restore the initial state of the model devices. In these clogging phenomenon, the biofilm clogging recovered fastest and the organic particles clogging recovered slowest. In this process, the microbial played a key role. Biofilm clogging recovery was due to the lack of external nutrients, and microbial death. This changing process could be simulated using microbial decay equations. The recovery of the organic particles clogging was the result of the microbial degradation and the reducing of the clogging matters.