Screening of organic substrates for a permeable biobarrier to remediate nitrate contaminated groundwater

Abstract

Easily available organic substrates (e.g., peanut, walnut and almond shells and luffa sponge) were evaluated as potential filter material for permeable biobarrier systems. Higher removal efficiencies and rate constants were observed for lower (20%) substrate (e.g., peanut, walnut and luffa sponge) percentages indicating to the importance of substrate percentage. Rate constants were higher for total inorganic nitrogen removal (≥0.137 mg N/L/d) than for nitrate removal (≥0.127 mg N/L/d) in the batch bioreactors promising the capability of microorganisms in consuming substrate released nitrogen compounds. Continuous flow biobarriers revealed greater removal efficiencies (<1 mg NO3−–N/L) and rate constants (≥2.38 mg NO3−–N/L/d) that were related to better microbial performance with increased substrate contact. Different dissolved oxygen levels observed for peanut shell (≤7.45 mg O2/L) and luffa sponge columns (<3 mg O2/L) were indicating to the existence of different mechanisms and microorganisms during simultaneous heterotrophic nitrification and aerobic or anoxic denitrification. Luffa sponge was found to be the best candidate as a biobarrier substrate for a longer timescale, although walnut and almond shells may be excellent materials both supporting the denitrification process and permeability of barrier system.

Enhanced Biological Nitrate Removal from Groundwater in Humid Tropical Regions Using Corn Cob-Based Permeable Reactive Barriers: A Case Study from Panama

“…The relatively low concentrations of nitrogen species correlate with the corn cob's total nitrogen content of 0.07%, as determined during chemical characterization. This suggests a minimal risk of secondary contamination during denitrification, supporting conclusions drawn in previous studies [18,42,55].…”

“…Nitrogen released from corn cob primarily exists as nitrate, followed by ammonium and nitrite. However, the total nitrogen concentrations were comparatively lower than those observed in other reactive materials, such as mulch, compost [4], hazelnut shell [55], almond shell, and loofah sponge [4,18,55]. Carbon release amounted to 16.83 mg/g, contrasting with findings for almond shell and loofah sponge, which registered values of 6.32 mg/g and 21.95 mg/g, respectively [18].…”

“…However, the total nitrogen concentrations were comparatively lower than those observed in other reactive materials, such as mulch, compost [4], hazelnut shell [55], almond shell, and loofah sponge [4,18,55]. Carbon release amounted to 16.83 mg/g, contrasting with findings for almond shell and loofah sponge, which registered values of 6.32 mg/g and 21.95 mg/g, respectively [18]. Thus, corn cob as a reactive material demonstrates adequate release without accruing undesired compounds for groundwater remediation [54].…”

“…The reactors were agitated at 150 rpm at 28 ± 1 • C for 15 days. Total nitrogen was quantified by summing the concentrations of nitrate, nitrite, and ammonium [18]. Additionally, the organic carbon content of the corn cob was measured in terms of the chemical oxygen demand (COD) to evaluate its organic carbon capacity [42].…”

“…Such an abundance of waste presents an opportunity to use this resource for environmental remediation. Therefore, this study aimed to explore the potential of corn cobs for removing nitrate from contaminated groundwater Among the agricultural residues previously studied in the literature for their potential in nitrate removal are wheat straw [16], mulch [17], luffa [18], canal straw [19], and corn cob [20]. For instance, Xu et al [21] research demonstrated that corn cobs could remove over 90% of nitrate from wastewater, showcasing their potential as an economical and effective carbon source for denitrification.…”