Wastewater treatment wetlands in cold climates

Abstract

The best prospects for successful wetland treatment should be in the warmer regions of the world, but studies in North America and Scandinavia show that wetland treatment may be feasible also in cooler regions. A review shows that the number of wetlands of different types (free water surface, FWS; horizontal and vertical subsurface flow, SSF), treating different kinds of wastewater, is steadily increasing in most parts of the cold temperate regions of the world. The major wetland engineering concerns in cold climates, which are discussed in this paper, are related to: (1) ice formation, and its implications for hydraulic performance; (2) hydrology and hydraulic issues besides ice formation; and (3) the thermal consequences for biologically or microbiologically mediated treatment processes. Energy- and water-balance calculations, as well as thermal modeling, are useful tools for successful design and operation of treatment wetlands, but the shortage of data makes it necessary to adopt a conservative approach. The treatment processes often appear less temperature sensitive in full-scale wetlands as compared to laboratory incubations. Several possible explanations are discussed in the paper: (1) sedimentation playing a significant role, (2) overdimensioning in relation to some constituents, (3) seasonal adsorption (cation exchange) of ammonium, and (4) temperature adaptation of the microbial community. Experience shows that cold climate wetlands can meet effluent criteria for the most important treatment parameters. To gain wide acceptance, however, we need to become more specific about design and construction, and also about operation, maintenance and cost-effectiveness. These goals require detailed knowledge about processes in full-scale wetlands, including long-term changes and response to maintenance.

Enhancement of nitrate removal in constructed wetlands utilizing a combined autotrophic and heterotrophic denitrification technology for treating hydroponic wastewater containing high nitrate and low organic carbon concentrations

“…The temperature and seasonal conditions in a wetland can affect an array of both the physical and biological activities within the system (Kadlec, 1999). Plant and microbial activity, and community selection are sensitive to both the seasonal and temperature shifts (Wittgren and Maehlum, 1997). The seasonal effects on the BOD removal efficiencies were also evident, with the most consistent overall performance occurring during the summer and the worst during the winter months (Henneck et al, 2001;Karathanasis et al, 2003).…”

Efficiency of small constructed wetlands for subsurface treatment of single-family domestic effluent

“…Nitrogen (ammonia and total nitrogen) and phosphorus are also mitigated but with widely varying efficiencies compared with other pathogens (Nichols, 1983;Mann, 1990;UrbancBercic and Bulc, 1995;Koottatep and Polprasert, 1997;Cronk and Fennessy, 2001). Seasonal changes in load reduction efficiency appear to be minimal (Maehlum et al, 1995;Wittgren and Maehlum, 1997).…”

Lolium Perenne as the Cultivation Plant in Hydroponic Ditch and Constructed Wetland to Improve Wastewater Treatment Efficiency in a Cold Region

“…These measures include: (1) internal improvement of system design and setup of the system, (2) optimization of winter operation, (3) external incorporation of pre-and post-treatment technologies (Dong et al 2011;Giaever 2000;Jenssen et al 2005). Selecting plants cultivated in HDs and CWs is proved to have consistent effect on cold period performance by insulating the water surface from cold temperatures, trapping falling and drifting snow, and reducing the heat-loss effects of wind (Wittgren and Maehlum 1997).…”