Determination of first order rate constants for wetlands treating livestock wastewater in cold climates

Abstract

Four years of performance data from a free-water surface constructed wetland receiving dairy wastewater in Nova Scotia was used to compute first order reaction rate constants (Ka) for several parameters including BOD5, TP, TKN, NH4+-N, FC, and TSS. Flow rates at the inlet and outlet of the 5 m wide × 20 m long wetland were continuously measured to assess how external hydrologic influences affected the water budget of the wetland and the system treatment performance. The Ka values were calculated using inlet and outlet concentrations and an assumption of plug flow hydraulics. Adjusted rate constants (Kac) were also computed, in which the effects of dilution and concentration on pollutant concentrations were considered. Precipitation, runoff, and evapotranspiration had a large influence on the wetland water budget. Values of Ka were higher than Kac for all wastewater parameters, illustrating the effects of dilution on outlet pollutant concentrations and the importance of accurately characterizing wetland hydrology when determining or using rate constants. The Kac values did not appear to be influenced by temperature or solar radiation, but were positively correlated with the hydraulic loading rate for most parameters. Rate constants were lower than those reported in the literature for livestock wastewater treatment wetlands operating in warmer climates. This could be due to differences in climate, but could also be attributed to the relatively high strength wastewater and low hydraulic loading rate (0.1 m month–1) used in this study. Key words: treatment wetlands, cold climate, agricultural wastewater, design, rate constants.

Constructed Wetlands for Agricultural Wastewater Treatment in Northeastern North America: A Review

“…However, from the data presented in this review both SSF and SF wetlands have also been found effective during winter (Table 3). Two studies [23,39] examined the year-round performance of SF CWs in Atlantic Canada and found that even with the seasonal fluctuations, SF CWs performed well and were suitable water treatment options. Steps can be taken to further improve winter performance of CWs, such as allowing snow and dead vegetation to accumulate on the surface of the wetland to help insulate the system [2,49] and supplemental aeration can prevent freezing [49].…”

“…Of the plug flow assumptions required for the use of this model [64], the most inaccurate is the assumption that inflow and outflow are equal [23]. External hydrologic factors (surface flow into or out of the CW, precipitation, and ET) play important roles in either concentrating [44,65] or diluting [21,23,24,66] wetland effluent, which can skew treatment efficiency calculations.…”

“…Applications include the treatment of milkhouse wash water and farmyard runoff [19][20][21][22][23][24][25][26][27], tile drainage outflow [28][29][30][31]), aquaculture wastewater [32,33] abattoir wastewater [34], and winery process water [35]. CWs are engineered to optimize naturally occurring biological, chemical, and physical processes to treat wastewaters.…”

Performance of a Constructed Wetland and Pretreatment System Receiving Potato Farm Wash Water

“…Therefore, ammonification and nitrification were limiting reactions for further N removal in pretreatment. This could be due to a lack of DO supply for biological degradation of organic matter and nitrification, especially in the winter (Figure 2) [12]. A nitrifying intermittent sand filter or subsurface flow wetland, like W3 in Kadlec et al, 1997, could be beneficial for increasing nitrification.…”

Estudio de los Humedales Artificiales de Flujo Superficial del Tancat de la Pipa como instrumentos para la restauración ambiental del lago de l'Albufera de Valencia

“…Algunos ejemplos de aplicaciones se pueden ver en Di Toro et al (1971), Mesplé et al (1995), Martín et al (1998), Broekhuizen et al (2012). En este estudio, todas las constantes calculadas, excepto la referente a la materia orgánica, están significativamente correlacionadas con la CH aplicada al sistema (Tabla 6-117,Figura 6-124), de acuerdo con otros autores (Coveney et al, 2002;Braskerud et al, 2002a;Jamieson et al, 2007;Trang et al, 2010;Chen et al, 2015). Esto nos permite estimar valores de K para las CH más altas.…”