Algae trapping function of plant-bed/ditch systems
植物床-沟壕系统的藻类捕获功能

This case study corroborated the algae trapping function of plant-bed/ditch system through in situ field testing. Results showed that the system could effectively intercept and trap algae from source water. Under the driving of hydraulic gradients, about 35% source water flowed into the higher small ditch, and exuded through the root channel structure inside plant bed into the lower small ditch. The chlorophyll-a (Chl-a) concentration in the lower small ditch was significantly lower (P=0.0239) than that in the opposite higher small ditch. The decline percentage of Chl-a concentration amounted to 11.1 % between both sides of plant bed. The Chl-a concentration dropped down by 27.0 % at the outlet of examined root channel purification zone with plant-bed/ditch system as structure form. According to rough estimation, this patch of root channel purification zone could trap algae fresh biomass of about 122 kg/d. Shijiuyang constructed wetland contains altogether 11 patches of root channel purification zones and provides 250 000 t/d purified raw water for the drinking water plant. The total trapped algae fresh biomass reached up to about 1 100 kg/d.