Electrical stimulation for enhanced denitrification in woodchip bioreactors: Opportunities and challenges

Law, Ji Yeow; Soupir, Michelle L.; Raman, D. Raj; Moorman, T. B.; Ong, Say Kee

doi:10.1016/j.ecoleng.2017.10.002

Cited by 15 publications

(10 citation statements)

References 31 publications

(68 reference statements)

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“…Previous literature has not evaluated the costs of bioreactors scaled up in size to not have bypass flow; therefore, our study is compared to the unit cost of the bioreactors with bypass only. The unit costs of our study are generally similar but slightly higher than previously reported by Christianson et al (2013a), Christianson et al (2013b), andLaw et al (2018). Variations in assumptions in costs assessed account for the higher costs observed in our study; the other studies typically did not include operating or depreciation costs or had varying interest rates.…”

Section: Discussionsupporting

confidence: 72%

“…Variations in assumptions in costs assessed account for the higher costs observed in our study; the other studies typically did not include operating or depreciation costs or had varying interest rates. In the study by Law et al (2018), a 100 m 3 bioreactor was determined to have a NO3-N removal cost of $4.86/kg NO3-N, which ranges $3.30/kg NO3-N to $1.90/kg NO3-N less than the values observed in the similarly sized medium-scale bioreactor (127 m 3 ) with bypass flow in our study. Christianson et al (2013a) The large-scale bioreactor has the greatest yearly and total cost, however, it represents a more cost effective option when considering the number of pilot-, small-, and medium-scale bioreactors that would be needed to treat the same amount of flow as the large-scale bioreactor.…”

Section: Discussionmentioning

confidence: 48%

“…Our objectives were to (i) evaluate the cost for four scales of bioreactors operating under a variety of mass removal rates and HRTs, with bypass flow being used to achieve the varying HRTs, (ii) evaluate the cost for the same four scales of bioreactors re-sized to be operated with a low probability of bypass flow, allowing for different mass removal rates to occur, and (iii) compare the costs for the different scenarios and scales designed with and without expected bypass flow. Previous TEAs conducted for woodchip bioreactors focused on specific bioreactors that generally performed well (Christianson et al, 2013a;Christianson et al, 2013b;Law et al, 2018). This study developed a more generalized TEA to account for the great variation that has been observed in these systems, at a variety of bioreactor scales and operating conditions, to assess the cost-effectiveness of the different design scales.…”

mentioning

confidence: 99%

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Techno-Economic Analysis of Constant-Flow Woodchip Bioreactors

Hartfiel¹,

Soupir²,

Rosentrater³

2021

Transactions of the ASABE

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HighlightsTechno-economic analysis was performed for multiple scales of bioreactors operated under a variety of conditions.The unit cost decreased as the bioreactor size increased.The unit cost increased in bioreactors with longer HRTs and bypass flow due to reduced treatment capacity.One large bioreactor was more cost-effective than multiple smaller bioreactors.Abstract. Woodchip denitrification bioreactors are a relatively new, edge-of-field technology used to reduce nitrate-nitrogen (NO3-N) from subsurface tile drainage. The removal rate of nitrate is influenced by many factors, including temperature, dissolved oxygen, and hydraulic residence time (HRT). The objective of this study was to conduct a techno-economic analysis (TEA) for four scales of woodchip denitrification bioreactors operating at three HRTs (2, 8, and 16 h), designed with bypass flow or with a low probability of bypass flow, to determine the cost to remove 1 kg of NO3-N at each bioreactor scale and at each HRT. Several assumptions were made: the flow rate required to achieve a 2 h HRT on a per m3 basis could be achieved at all scales, the same mass removal of NO3-N was achieved on a per cubic meter basis, and the 2 h HRT did not have any bypass flow at each scale. With these assumptions, the lowest unit cost was observed for the large-scale bioreactor sized to have a low probability of bypass flow at 16 h HRT, with a resulting cost of $0.74 kg-1 NO3-N removed. The highest unit cost was observed for the pilot-scale bioreactor designed with bypass flow to achieve a 16 h HRT at a cost of $60.13 kg-1 NO3-N removed. At longer HRTs with bypass flow, a greater percent removal of nitrate has been observed with a lower mass removal rate. By having a low probability of bypass flow in the design, a higher mass removal and percent removal of nitrate were observed, leading to the above results. Contrasting this trend, the total and annual costs were highest for the large-scale bioreactor and lowest for the pilot-scale bioreactor. However, it was determined that 783%, 280%, and 54% increases in total cost for the pilot-, small-, and medium-scale bioreactors would be incurred to implement the number of bioreactors (66, 24, and 4, respectively) required to treat the same volume of flow as one large bioreactor. These results can be used to inform future design decisions and inform stakeholders of the approximate unit cost of installing a denitrifying woodchip bioreactor over a range of expected field conditions. While a larger bioreactor with a low probability of bypass flow may represent a more cost-effective investment, the potential for unintended, negative byproducts needs to be considered in the design. Keywords: Denitrification, Nitrate, Tile drainage, Water quality, Woodchip bioreactor.

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Section: Discussionsupporting

confidence: 72%

Section: Discussionmentioning

confidence: 48%

mentioning

confidence: 99%

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Techno-Economic Analysis of Constant-Flow Woodchip Bioreactors

Hartfiel¹,

Soupir²,

Rosentrater³

2021

Transactions of the ASABE

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“…In Iowa, average bioreactor installation cost currently ranges from $10,000 to $20,000, with most installations being partially supported by cost sharing (Christianson and Helmers, 2011b;McKinney, 2018). With an average removal rate of 43%, bioreactors have an estimated cost per kg of nutrient removed of (Christianson et al, 2013(Christianson et al, , 2018Law et al, 2018). Woodchip bioreactors have a wide variety of reported NO 3 − N removal rates, but typically range from 13 to 100% depending on conditions and location (Christianson et al, 2012b(Christianson et al, , 2018Greenan et al, 2009;Hassanpour et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Impact of hydraulic residence time on nitrate removal in pilot-scale woodchip bioreactors

Martin

Davis

Isenhart

et al. 2019

Journal of Environmental Management

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Nitrate (NO3−N) export from row crop agricultural systems with subsurface tile drainage continues to be a major water quality concern. Woodchip bioreactors are an effective edge-of-field practice designed to remove NO3−N from tile drainage. The NO3−N removal rate of woodchip bioreactors can be impacted by several factors, including hydraulic residence time(HRT). This study examined the impact of three HRTs, 2 h, 8 h, and 16 h, on NO3−N removal in a set of nine pilot-scale woodchip bioreactors in Central Iowa. NO3−N concentration reduction from the inlet to the outlet was significantly different for all HRTs (p < 0.05). The 16 h HRT removed the most NO3−N by concentration (7.5 mg L−1) and had the highest removal efficiency at 53.8%. The 8 h HRT removed an average of 5.5 mg L−1 NO3−N with a removal efficiency of 32.1%. The 2 h HRT removed an average of 1.3 mg L−1 NO3−N with a removal efficiency of 9.0%. The 2 h HRT had the highest NO3−N mass removal rate (MRR) at 9.0 g m−3 day−1, followed by the 8 h HRT at 8.5 g m−3 day−1, and the 16 h HRT at 7.4 g m−3 day−1, all of which were statistically different (p < 0.05). Significant explanatory variables for removal efficiency were HRT (p < 0.001) and influent NO3−N concentration (p < 0.001), (R2 = 0.80), with HRT accounting for 93% contribution. When paired with results from a companion study, the ideal HRT for the bioreactors was 8 h to achieve maximum NO3−N removal while reducing the impact from greenhouse gas emissions.

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“…To the authors' knowledge, a method yielding such a dramatic increase in NO 3 removal rates in woodchip bioreactors without requiring additional energy or chemical inputs (e.g., C dosing, heating, electrical stimulation, etc.) has not been reported (Cameron and Schipper, 2011;Law et al, 2018;Roser et al, 2018). Further research is required to quantify total C loss from woodchips since DRW cycles will decrease woodchip lifespan.…”

Section: Discussionmentioning

confidence: 98%

Increased Duration of Drying–Rewetting Cycles Increases Nitrate Removal in Woodchip Bioreactors

Maxwell

Bírgand

Schipper

et al. 2019

Agricultural & Env Letters

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Core Ideas Nitrate removal in woodchips increased linearly with drying–rewetting duration. Nitrate removal increased up to 172% in the longest drying–rewetting duration. Nitrate removal rates increased proportionally with dissolved organic C leaching. A previously reported experiment showed weekly drying–rewetting (DRW) cycles increase nitrate removal rates in woodchip‐based denitrifying bioreactors. A follow‐up experiment determined the effect of duration of unsaturated conditions on nitrate removal after rewetting. Three different levels of DRW duration were tested in a 105‐d column experiment (n = 2), with woodchips left unsaturated once a week for either 2 h, 8 h, or 24 h. Increasing duration of unsaturated conditions significantly increased nitrate removal rates. The longest DRW duration of 24 h resulted in the greatest increase in nitrate removal rates, relative to constantly saturated woodchips, with mean rate increases reaching 172% by the end of the experiment. Results suggest nitrate removal in denitrifying bioreactors is carbon limited, with labile carbon made available during aerobic periods of DRW cycles the most likely cause of observed rate increases. Both studies show DRW cycles dramatically increase the nitrate removal efficiency of denitrifying bioreactors.

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Electrical stimulation for enhanced denitrification in woodchip bioreactors: Opportunities and challenges

Cited by 15 publications

References 31 publications

Techno-Economic Analysis of Constant-Flow Woodchip Bioreactors

Techno-Economic Analysis of Constant-Flow Woodchip Bioreactors

Impact of hydraulic residence time on nitrate removal in pilot-scale woodchip bioreactors

Increased Duration of Drying–Rewetting Cycles Increases Nitrate Removal in Woodchip Bioreactors

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