Improving Nutrient Removal in Constructed Wetland Wastewater Treatment

Abstract

The percentage pollutant removal obtained by the previous work were very good in terms of BOD5 which was 95% removal, TSS was 97% removal, but unsatisfactory in terms of NH4-N, NO3-N and P which was 39%, 41% and 44% removal respectively
-The effect of recycling portion of the effluent discharged from the 2ND. Cell, of a VSSF constructed wetland back to the 1ST. cell on the nutrient removal efficiency of the wetland was studied in this research.
The intermittent feeding of influent and the recycled quantity had good effect on system aeration by dissolving the air trapped in the voids of the substrates before each doss and using it to activate aerobic bacteria.
The Nitrification and denitrification were enhanced by the recycling process. Recycling effluent with low BOD & COD when mixed with raw wastewater infeed will increase system aeration which helps the nitrification process and when most of the oxygen has been consumed, by microorganisms during biological and chemical degradation of pollutant, than the denitrification process will start and transfer the NO3-, ultimately, to N2 gas.
The hydrology condition of the system was good, the water was running in the constructed wetland in a laminar form and the detention time was highest in July and lowest in January as expected due to the effect of evapotranspiration which reaches its highest in July and lowest in January.
The maturity of reed plant and extension of their stems and roots may have a positive influence on:
- Aerobic condition required for the nitrification process and BOD5 removal by supplying more air from the outside atmosphere to the system.
- Adsorbing of heavy metal and metal ions on the extended roots of reed plant.
- Increased nutrient uptake by reed plants which results in lowering nutrient in effluent.