Constructed Wetland For Denitrification Enhanced By Solid Carbon Source

Recently, anthropogentic nitrogen pollutants inputs have been greatly increased, leading to the heavier eutrophication of lakes and rivers.Treated water produced from municipal sewage treatment plants is regularly regarded as a source of ground water bodies, which is called low-contaminated water. The nitrogen pollutants contained in the treated water still pose threats to the receiving waters. According to the water quality of low-contaminated water, we used two-stage constructed wetlands with aeration phase and anoxic phase which added a new type of solid carbon GC-5 as denitrification carbon sources and biofilm carriers. Denitrification of GC-5 performances, the appropriate supplement amount and two-stage constructed wetlands nitrogen removal performances were studied in this paper. The results showed that:(1) There were significant differences in the start-up time and the denitrification performances of GC-5 and sawdust with the start time were 11 d, 20 d, and the removal rate of NO3- N were 98.86%,53.62%,respectively.The removal rates of nitrate were 0.20 mg N/(L·h·g C) and 0.04 mg N/(L·h·g C) for GC-5 and sawdust respectively in batch mode tests. GC-5 had a better carbon-releasing control capability than sawdust. These conclusions were supplied as basis for the descendant experiments.(2) According to the dentrification performances and carbon-releasing characteristics, six reactors numbered as 1# to 6# were designed, which supplied different amount of GC-5. The NO3--N removal rate varied with the amount of GC-5 supplied into constructed wetlands.When the supplement amount of GC-5 <5.0%, the removal rate of NO3--N raised with the increase of GC-5 supplement amount. When the supplement amount of GC-5 =5.0%, the removal rate of NO3--N reached 95.0% or more. When the supplement amount of GC-5 >5.0%,the removal rate of NO3--N would no longer raise with the increase of GC-5 supplement amount.The order of the organics concentration in effluent was 1#<2#<3#<4#<30.0mg/L<5#<6#.1# and 2# system had accumulated a certain amount of NO2--N,however,5# and 6# system existed an amount of NH4+-N accumulation,and the NO2--N,NH4+-N concentrations were maintained at a low leval in 3# and 4# system.In conclusion the appropriate supplement amount of GC-5 was 5.0% under experiment conditions.(3) The nitrogen removal efficiency had been improved by supplying the GC-5 to constructed wetlands.With supplying the GC-5 to constructed wetlands, the removal rate of TN increased from 34.91% to 64.62%. The results indicated that temperature was an important factor to impact the removal effect of NH4+-N,NO3--N, TN and meanwhile hydraulic loading mostly impacted the removal effect of TN in the system.