Feasibility of using rural waste products to increase the denitrification efficiency in a surface flow constructed wetland

Abstract

A surface flow constructed wetland (CW) was set in the Lerma gully to decrease nitrate (NO3 -) pollution from agricultural runoff water. The water flow rate and NO3concentration were monitored at the inlet and the outlet, and sampling campaigns were performed which consisted of collecting six water samples along the CW flow line. After two years of operation, the NO3attenuation was limited at a flow rate of ~2.5 L/s and became negligible at ~5.5 L/s. The present work aimed to assess the feasibility of using rural waste products (wheat hay, corn stubble, and animal compost) to induce denitrification in the CW, to assess the effect of temperature on this process, and to trace the efficiency of the treatment by using isotopic tools. In the first stage, microcosm experiments were performed. Afterwards, the selected waste material was applied in the CW, and the treatment efficiency was evaluated by means of a chemical and isotopic characterization and using the isotopic fractionation (ε) values calculated from laboratory experiments to avoid field-scale interference. The microcosms results showed that the stubble was the most appropriate material for application in the CW, but the denitrification rate was found to decrease with temperature. In the CW, biostimulation in autumn-winter promoted NO3attenuation between two weeks and one month (a reduction in NO3between 1.2 and 1.5 mM was achieved). After the biostimulation in spring-summer, the attenuation was maintained for approximately three months (NO3reduction between 0.1 and 1.5 mM). The ε 15 NNO3/N2 and ε 18 ONO3/N2 values obtained from the laboratory experiments allowed to estimate the induced denitrification percentage. At an approximate average flow rate of 16 L/s, at least 60 % of NO3attenuation was achieved in the CW. The field samples exhibited a slope of 1.0 for δ 18 O-NO3versus δ 15 N-NO3 -, similar to those of the laboratory experiments (0.9-1.2). Plant uptake seemed to play a minor role in NO3attenuation in the CW. Hence, the application of stubble in the CW allowed the removal of large amounts of NO3from the Lerma gully, especially when applied during the warm months, but its efficacy was limited to a short time period (up to three months).

Enhancing Nitrate Removal With Industrial Wine Residue: Insights From Laboratory Batch and Column Experiments Using Chemical, Isotopic and Numerical Modeling Tools

“…Limited NO 3 removal in the case of B-V might show larger fractionation (i.e., more negative 15 ε) values consistent with Mariotti et al (1988), who proposed that larger fractionation is expected for a lower denitrification rate. The ε 15 N NO3 and ε 18 O NO3 obtained in our work are consistent with values reported in the literature for denitrification, ranging from +6.5 to 39.0‰ and 1.0 to 30.4‰, respectively (Grau-Martínez et al, 2017;Margalef-Marti, Carrey, Merchán, et al, 2019) for freshwater denitrification studies, depending on the environmental conditions, organic matter source employed and biomass community. δ 15 N-NO 3 versus δ 18 O-NO 3 showed a positive linear correlation with a slope of 0.71 in B-L and 0.82 in B-V (Figure 4b), indicating a high enrichment effect on ε 15 N NO3 .…”

“…In 2015, a CW was built in the Lerma basin to remove N before discharge into the environment. Details on the construction and operation of the Lerma Basin CW can be found in Margalef-Marti, Carrey, Merchán, et al (2019) and Merchán et al (2015).…”

“…In long‐term nitrate remediation treatments, using pure organic carbon sources such as glucose, acetate, ethanol and methanol could be costly (Margalef‐Marti, Carrey, Merchán, et al., 2019). Therefore, the concept of the circular economy offers an optimal solution by transforming waste products into valuable resources.…”

Impact of fertilization with pig slurry on the isotopic composition of nitrate retained in soil and leached to groundwater in agricultural areas

“…The limited variation of δ 18 O NO3 values along the study indicated a negligible isotopic effect from plant uptake. Also, it pointed that denitrification was not significant along the experimental period even if organic carbon in pig slurry could have induced this process, especially during the spring-summer season due to the higher temperatures (Dawson and Murphy, 1972;Elefsiniotis and Li, 2006;Margalef-Marti et al, 2019). Hence, it was reinforced that the measured NO 2 and N 2 O during the experiment (Table S3) were produced from nitrification rather than denitrification (Beeckman et al, 2018;Caranto and Lancaster, 2017;Morley et al, 2008;Wunderlin et al, 2012).…”

Mean residence time of lagoons in shallow vegetated floodplains

“…CW facilitate the removal of chemicals from wastewater and also homogenize the physical and chemical characteristics of the flow (Schaafsma et al, 2000). As such, they offer low-cost and low-maintenance processes of removing wastewater N and P through precipitation into the soil bottom, soil adsorption of chemicals, plant uptake with organic matter accumulation, and microbial immobilization (Margalef-Martí et al, 2019). In addition, they provide new habitats for aquatic organisms, refuges for wildlife, and can be used as recreational or educational facilities (Zhang et al, 2020).…”