Tracing the role of endogenous carbon in denitrification using wine industry by-product as an external electron donor: Coupling isotopic tools with mathematical modeling

Abstract

Nitrate removal through enhanced biological denitrification (EBD), consisting of the inoculation of an external electron donor, is a feasible solution for the recovery of groundwater quality. In this context, liquid waste from wine industries (wine industry by-products, WIB) may be feasible for use as a reactant to enhance heterotrophic denitrification. To address the feasibility of WIB as electron donor to promote denitrification, as well as to evaluate the role of biomass as a secondary organic C source, a flow-through experiment was carried out. Chemical and isotopic characterization was performed and coupled with mathematical modeling. Complete nitrate attenuation with no nitrite accumulation was successfully achieved after 10 days. Four different C/N molar ratios (7.0, 2.0, 1.0 and 0) were tested. Progressive decrease of the C/N ratio reduced the remaining C in the outflow and favored biomass migration, producing significant changes in dispersivity in the reactor, which favored efficient nitrate degradation. The applied mathematical model described the general trends for nitrate, ethanol, dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentrations. This model shows how the biomass present in the system is degraded to dissolved organic C (DOC) and becomes the main source of DOC for a C/N ratio between 1.0 and 0. The isotopic model developed for organic and inorganic carbon also describes the general trends of δC of ethanol, DOC and DIC in the outflow water. The study of the evolution of the isotopic fractionation of organic C using a Rayleigh distillation model shows the shift in the organic carbon source from the WIB to the biomass and is in agreement with the isotopic fractionation values used to calibrate the model. Isotopic fractionations (ε) of C-ethanol and C-DOC were -1‰ and -5‰ (model) and -3.3‰ and -4.8‰ (Rayleigh), respectively. In addition, an inverse isotopic fractionation of +10‰ was observed for biomass degradation to DOC. Overall, WIB can efficiently promote nitrate reduction in EBD treatments. The conceptual model of the organic C cycle and the developed mathematical model accurately described the chemical and isotopic transformations that occur during this induced denitrification.

Evaluating the potential use of a dairy industry residue to induce denitrification in polluted water bodies: A flow-through experiment

“…However, to promote groundwater remediation within the aquifer, liquid compounds are preferable as they could be easily applied by injection through already constructed wells. In this context, a wine industry residue was recently tested to promote heterotrophic denitrification (Carrey et al, 2018). The use of whey may also be an economically feasible solution to attenuate NO3pollution, while providing waste recycling.…”

“…The observed isotopic fractionation (ε) of N and O from dissolved NO3can be used to estimate the efficacy of induced denitrification (Mariotti et al, 1988). Furthermore, the isotopic characterization (δ 13 C) of dissolved organic and inorganic carbon (DOC and DIC) during denitrification might provide knowledge on the fate of the added organic C source (Carrey et al, 2018;Nascimento and Krishnamurthy, 1997).…”

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

“…Since the use of pure reagents such as glucose, acetate, or ethanol may be expensive in long-term treatments, the use of industrial or agricultural residues that are rich in organic C could represent a more sustainable solution. Solid products such as animal or vegetal waste (Grau-Martínez et al, 2017;Si et al, 2018;Trois et al, 2010), as well as industrial liquid by-products (Carrey et al, 2018;Margalef-Marti et al, 2019), have already been reported as being useful for promoting denitrification.…”

Effects of C/N ratio on pollution removal efficiency and cell proliferation during the bioconversion of wastewater by photosynthetic bacteria

“…The C/N ratio is the ratio of COD to total nitrogen (TN) or biochemical oxygen demand (BOD) to TN [8,9]. It is not only a key factor for microorganism growth, but it is also an important wastewater quality index [10][11][12].…”

“…The optimal C/N ratio for conventional aerobic treatment is 20. In recent years, low C/N ratios (<5) have been frequently studied [9][10][11] and so low C/N ratios of 5, 2, 1, 0.5 and 0.1 were also included. A middle value of 10 was also chosen between 20 and 5.…”