Zhang Beiping

Optimization of four kinds of constructed wetlands substrate combination treating domestic sewage

Based on the static and dynamic experiments, this paper has analyzed the adsorbing capacity for domestic wastewater pollutant (COD, NH4+-N and TP) of four kinds of constructed wetlands substrate which were fly ash, hollow brick crumbs, coal cinder and activated carbon pellets in single and combined condition. In the static experiments, the adsorbing capacity of four substrates all grew as the adsorbing dose increased. In adsorbing COD, each substrate’s adsorbing capacity rises with the adsorbing dosage. Simultaneously, experiments show that all the adsorption of the four kinds of substrate for COD, NH4+-N and TP follows the Freundich Rule. The dynamic experiment demonstrated that the adsorbing capacity of combined substrates is bigger than that of single substrate. Fly ash in combination with small coal cinder adsorbs COD the best, while it takes in NH4+-N and TP the best when working with hollow brick crumbs. The combination of the two raises the removal rates up to 89% and 81% respectively. Given high cost and low adsorbing effect, activated carbon is not a suitable candidate for constructed wetlands substrate.

Study on Improvement of Pollutants Removal Efficiency by Backside Aeration in Wavy Subsurface-Flow Constructed Wetland

Lower removal rates of ammonium nitrogen in the constructed wetlands were mainly caused by the lack of dissolved oxygen (DO). The traditional wavy subsurface-flow constructed wetland was modified to install an aeration tube in the third wave interval to increase DO and the nitrification rates within the constructed wetlands. As most COD had been removed in the second wave interval, nitrifying bacteria became dominant in the third wave interval, which led to the nitrification extent to reach more than 95%. The ability to endure the impact of hydraulic loading was also enhanced. The hydraulic loading of wetlands was raised up to 0.8m³/m²ldrd^-1, with a COD organic loading of 56-112 g COD/m²ldrd^-1, and ammonium loading rates about 20-28 g NH₄ ⁺-N/m²ldrd^-1. These values were much higher than those reported of nitrification in constructed wetlands.