Effect of Different Factors on Nitrogen Removal Rate in Constructed Wetlands

Factors affecting total nitrogen(TN) removal rates in constructed wetland were investigated by intermittent operation in the subsurface flow(SSF) constructed wetland system.The results demonstrated that removal rates of TN increased with the rising of TN pollution load(1.40-12.40 g/m2) when the retention time was determined by 60% TN removal efficiency(n=180,p<0.05) in SSF wetlands.The maximum TN removal rate was 1.71 g/(m2·d) in SSF Phragmites australis-soil-slag system.TN removal rates were affected by total phosphorus load in case of higher TN load.TN removal rates in SSF Phragmites australis wetlands were greater than that in SSF Calamagrostis angustifolia wetlands at the same experimental cycle.Effect of wetland substrates on TN removal rates varied with the pollutants loading in SSF constructed wetland system,plant species and plant-growing period.

A Lab-scale Study on the Routes of Nitrogen and Phosphorus Removal in Gravel-based Reed Bed Systems

The removal of ammonia and phosphorus from an artificial wastewater was studied in two lab-scale reed beds.During batch and continuous operations,it was found that ammonia was removed from the wastewater via a two-step process,sorption inside bed matrices followed by nitrification into nitrite and nitrate.Rapid decrease in the concentration of ammonia in the artificial wastewater was observed during the batch operation,whereas during the continuous operation,which lasted for 39 days,the percentage removal of ammonia decreased gradually with time before stabilizing at around 20%.The efficiency of phosphorus removal exhausted rapidly during the continuous operation,from 39% on the first day of operation to virtually zero after only 5 days.The results suggest that sorption(which may include ion exchange,adsorption,and biomass assimilation) serves as an initial step to remove ammonia and phosphorus from the wastewater,prior to any microbial transformations.

Wetland Definitions:Creation,Evolution and Application

In this paper,we review the creation,evolution and application of wetland definitions.Varying wetlands are found from the tundra to the tropics and on every continent except Antarctica in the planet.Wetlands have many distinguishing features,the most notable of which are water presence,unique soil conditions,and biota that are adapted to or tolerant of saturated soils.Many wetland definitions have been developed by scientists,U.S.federal agencies,and the Ramsar Convention for both scientific and regulatory purposes.Wetlands are not easily defined but a well-conceived,science-based definition of wetlands is important for scientists and resource managers to understand the nature of wetlands and/or to use and protect wetlands.A scientific definition is the basis for wetland classification.Developing an effective wetland classification system requires a well-conceived,science-based definition and clearly explicit guidance on the appropriate use of various wetland indicators to verify the presence of wetlands on the ground.Based on a well-accepted wetland definition,both wetland classification and inventory further provide needed information and a working frame for wise use and management of wetlands.