Effect Of Earthworms On Integrated Vertical Flow Constructed Wetland Purification Capacity

As a kind of constructed wetland technology, The integrated vertical flow constructed wetland has better features and purifying effects due to its aerobic and anaerobic areas resulted from distinctive downstream and upstream water flow mode. However, constructed wetland have clogging problem when it operated longer time. The effect of addition earthworms and different substrates to purifying capacity was researched in this thesis. The main results were shown as following:(1) The removal efficiency of major pollutants is enhanced significantly when earthworrm (Eisenia foetida) were added into integrated vertical flow constructed wetland; The removal efficiency of P was higher in constructed wetland with mixture with Qing sand and river sand than with Qing sand. The two constructed wetland with adding earthworms increased average removal efficiency of ammonia nitrogen, total nitrogen, total P and CODcr by5.23%and5.93%,4.14%and3.32%,2.41%and5.31%, and5.31%and4.98%, respectively.(2) Addition of earthworm(Eisenia foetida) into integrated vertical flow constructed wetland is beneficial to the activity of different enzyme in the substrates, such as catalase, urease, cellulase, and invertase. The higher catalase, cellulase, and invertase were found in substrates of mixture with Qing sand and river sand, while the higher urease was higher in river sand substrate. Compared with the constructed wetland without earthworms, adding earthworms into the two constructed wetland increased catalase activity in the upper layer substrates by6.34%and13.07%; its increased urease activity11.45%and7.16%, by cellulase14.66%and19.02%, and by invertase8.70%and15.80%, respectively.(3)Addition of earthworm(Eisenia foetida) into integrated vertical flow constructed wetland improved the potential of nitrification and denitrification. Compared with constructed wetland without earthworms, the nitrification and denitrification potential capacity of substrate was increased by26.62%and3.64%, and12.82%and4.17%, respectively for nitrification and denitrification potential capacity. Compared with the substrates of mixture with Qing sand and river sand, the nitrification and denitrification potential capacity of the river sand substrate increased by22.16%and13.72%, respectively。(4)Addition of earthworm(Eisenia foetida) into integrated vertical flow constructed wetland improved the uptake of nitrogen and phosphorus, substrate as mixture with Qing sand and river sand is more beneficial the uptake of phosphorus by wetland plants. The absorbed N by canna, yellow iris, water iris, reeds, wild rice and cattails in constructed wetland with river sand and earthworms were3.85,4.69,6.92,1.14,2.03and7.60times as the constructed wetland without earthworms, respectively; similarly, it absorbed P was3.50,3.27,8.10,2.25,1.88and4.38times as the constructed wetland without earthworms for P uptake by wetland plants, respectively. For constructed wetland with river sand and Qing sand, the N absorbed by canna, yellow iris, water iris, reeds, wild rice and cattails in constructed wetland with earthworms was3.83,3.56,7.11,1.33,2.43and10.73times as the constructed wetland without earthworms, respectively. Similarly, it absorbed P was3.96,3.44,9.26,2.75,2.36and6.29, respectively.