Cold climate wetlands: design and performance

Abstract

Constructed wetlands are gaining widespread use as a simple, low cost means of wastewater treatment. Introduction of constructed wetlands technology into the northern United States has been limited by the ability of conventional wetland systems to operate without freezing during the winter. A design approach using subsurface-flow constructed wetlands covered with an insulating mulch layer has been demonstrated to prevent freezing. However, introduction of a mulch layer will affect oxygen transfer rates, pollutant removal performance, and plant establishment. These factors must be addressed for successful application of constructed wetlands technology in cold climates.

Study of a Novel Vertical Flow Constructed Wetland System with Drop Aeration for Rural Wastewater Treatment

“…The limited oxygen transfer capability of wetlands has led to the development of enhanced treatment systems which are capable of providing sufficient oxygen transfer for the removal of organic material and nitrification of ammonia, introducing oxygen to the system through frequent water level fluctuation (tidal flow; Austin et al 2003;Behrends et al 1996), passive air pumps (vertical flow; Green et al 1998), or direct mechanical aeration of the water in the gravel bed (horizontal flow ;Dufay 2000;Flowers 2002;Wallace et al 2001).…”

The effects of flow regime and temperature on the wastewater purification efficiency of a pilot hybrid constructed wetland

“…The initial phases of nitrification -nitrite production -was not limited by NH 4 -N availability. The next phase of nitrification, nitrate production -is limited by the production of nitrite, and thus the community of nitrite producers should be developing faster and should be located closer to the inflowing resource, NH 4 , especially in the case of diffusion-limited mass transport processes in the wetland substrate, which is discussed in greater detail by Austin et al [48]. We suggest that this situation should gradually change towards complete nitrification, especially when high recirculation rates are applied.…”

“…In the LWA system, recirculation regime had highly significant positive correlations with the purification efficiency of N tot (p<0.01, R 2 = 0.85), NH 4 4 -N had a non-significant tendency towards a negative relationship with hydraulic load (p=0.07, R 2 = 0.59). The more significant effect of the recirculation regime on the purification efficiencies of N-compounds is consistent with general knowledge about environmental needs for nitrogen processing pathways.…”

“…This is coherent with the data in the literature. In milder climatic conditions higher hydraulic loadings can be optimal [8] and also 100-200% recycling rate can give 52-65% N tot removal [17] and even 65-70% NH 4 -N removal with a detention time of only 3.5 days [19]. In tropical regions already 50% recirculation guarantees increase in NH 4 -N removal from 71 to 85% [22].…”

“…The idea of compact systems is to sustain systems with lower area requirement and lower building costs. In cold climates, CWs are often designed with a reserve in order to compensate for lower temperatures during winter [3][4][5]. Providing measures that can help achieve proper results without over-dimensioning would make CW a much more attractive wastewater treatment technology.…”