August 31 - 0153 - Arvydas Povilaitis
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Activated carbon and biochar additions improved nitrate removal efficiency in denitrifying woodchip bioreactors, especially at low temperatures below 10°C. Woodchips amended with activated carbon or biochar had higher carbon-to-nitrogen ratios and reduced carbon losses compared to woodchips alone. While woodchips alone or with activated carbon effectively removed phosphates, biochar additions risked releasing phosphates and other inorganic elements into outflow. Activated carbon shows potential to develop more efficient bioreactors with prolonged longevity and higher nutrient removal capacity than woodchips alone.
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August 31 - 0153 - Arvydas Povilaitis
- 1. The Effect of Three Types of Amendments on Nutrient Removal from Tile Drainage Water Using Denitrifying Woodchip Bioreactors Arvydas Povilaitis Vytautas Magnus University, Lithuania 11th International Drainage Symposium August 30 – September 2, 2022 Des Moines, Iowa, USA
- 2. Drained Agricultural Land (ditches and tile drains in Lithuania)
- 3. Nutrient losses Nitrate-N: 3-30 mg/L from tile-drained fields Total P: from 0.05 to 0.15 mg/L Annual Losses: - from 3 to > 50 kg N/ha - 0.05-0.40 kg P/ha Eutrophication Image source: Smith et al., 2018
- 4. Expected climate change impact on nutrient loads to surface waters in LT 2000-2019 2040-2059 2080-2099 Plungė S.,Gudas M., and Povilaitis A., 2022. Ecohydrology & Hydrobiology 22. SWAT model results: national-scale outputs, t/year EURO-CORDEX meteodata EURO-CORDEX
- 5. Pilot scale field trials denitrifying bioreactors Study period: July 2017 – May 2022 Abbreviations: W1-W2 – woodchips only (alder & pine tree mixture; size d50=3 cm; bulk density 260 kg/m3); DB – denitrification bioreactor; W-AC – woodchips amended with 10% v/v activated carbon; W-FSC – woodchips amended with 10% v/v flax seed cake WB-10 and WB-20 – woodchips amended with 10% and 20% v/v biochar
- 6. Additives: Activated carbon; flax-seed cake & biochar cm cm 10% by volume Properties Activated carbon Flax-seed cake Biochar Source material Steam activated coal Flax seeds Pyrolyzed at 850oC deciduous woodchips Dominant particle size 3 mm 3 cm 2 mm Bulk density, kg/m3 450 570 300 BET surface area, m2/g 950 - 445 pH 8.5 7.3 8.3 C, % 90.0 - 80.6 N, % - - 0.33 S, % - - 0.03 Total P, % - - 0.10 Labile P2O5, mg/kg - - 664.8 Total Fe, mg/kg - - 957.6 Total Ca, % - - 0.52 Sum: Ca, Fe, S, N, P < 10 % Granular AC FSC
- 7. Biochar granule’s images at different magnifications Scanning electron microscope (SEM) images
- 8. NO3-N dynamics in Bioreactors Measurements from start Concentrations: Inlet O2 = 3.1 ÷ 4.9 mg/L Outlet O2 = 0.0 ÷ 1.1 mg/L Inlet NO3 = 6.3 ÷ 30.0 mg N/L Outlet NO3 = 3.3 ÷ 22.1 mg N/L Temperature 0 5 10 15 20 25 1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 Inflow water T ( o C) 0 5 10 15 20 25 30 1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 NO 3 -N (mg/L) INFLOW W1 W-AC W-FSC 0 5 10 15 20 25 30 1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 NO 3 -N (mg/L) INFLOW W2 WB-10 WB-20 Experiment 1 Experiment 2
- 9. Removal Efficiency vs. Inflow Water Temperature Woodchips only bioreactors y = 16,95 e0,066 x R² = 0,694 0 10 20 30 40 50 60 70 80 0 5 10 15 20 Removal efficiency % Water temperature oC y = 15,84 e0,067 x R² = 0,755 0 10 20 30 40 50 60 70 80 0 5 10 15 20 Water temperature oC Temperature range: from +1.8 to +21.7 °C Experiment 1: Experiment 2: Min: 13.7 15.3 Max: 75.0 61.0 Ave ± STD 40.1 ± 12.9 39.2 ± 11.3
- 10. Temp > 10°C Abbreviations: W1-W2 – woodchips only; W-AC – woodchips amended with activated carbon; W-FSC – woodchips amended with flaxseed cake WB-10 and WB-20 – woodchips amended with 10% and 20% v/v biochar Effect of amendments Temp < 10°C Bolded boxplots = higher values at p<0.050
- 11. Total Carbon Loss* Biochar amendment yW2 = 1,617·e0,113x R² = 0,786 yWB-20 = 1,639·e0,047x R² = 0,721 yWB-10 = 2,326·e0,055x R² = 0,715 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 Temperature (°C) W2 WB-20 WB-10 yw1 = 0,194·e0,288x R² = 0,725 yW-AC = 0,046·e0,255x R² = 0,728 yW-FSC = 0,668·e0,213x R² = 0,703 0 2 4 6 8 10 12 14 16 18 0 5 10 15 20 Total carbon loss (g) Temperature (°C) W1 W-AC W-FSC Activated carbon amendment Flax seed cake *Organic + inorganic Experiment 2 Experiment 1
- 12. N mass removal vs. total C loss (C-to-N ratio) yW1 = 0,087x + 0,581 R² = 0,709 yW-AC = 0,509x + 0,521 R² = 0,714 yW-FSC = 0,074x + 0,522 R² = 0,741 0 0.5 1 1.5 2 2.5 0 2 4 6 8 10 12 14 16 N removal (g) Total carbon loss (g) W1 W-AC W-FSC yW2 = 0,578·ln(x) - 0,029 R² = 0,705 yWB-20 = 0,302·e0,426x R² = 0,765 yWB-10 = 0,208x + 0,126 R² = 0,714 0 0.5 1 1.5 2 2.5 0 2 4 6 8 10 12 14 16 Total carbon loss (g) W2 WB-20 WB-10 Abbreviations: W1-W2 – woodchips only; W-AC – woodchips amended with activated carbon; W-FSC – woodchips amended with flaxseed cake WB-10 and WB-20 – woodchips amended with 10% and 20% v/v biochar, respectively Experiment 1 Experiment 2
- 13. PO4-P removal in bioreactors Abbreviations: W1-W2 – woodchips only; W-AC – woodchips amended with activated carbon; W-FSC – woodchips amended with flaxseed cake WB-10 and WB-20 – woodchips amended with 10% and 20% v/v biochar Removal efficiency 29% 39% 33% Release Removal 24% Ca- Fe-bound phosphates Bolded boxplots = higher values at p<0.050 Up to 3-fold higher PO4-P outflows ! Experiment 1 Experiment 2
- 14. PO4-P release Biochar amended bioreactors Accompanying Total Fe, Ca, Mg, Na, K, Cl concentrations 0.000 0.050 0.100 0.150 0.200 0.250 0.300 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 PO 4 -P (mg/L) Measurements from start in July, 2018 till May, 2022 INFLOW W2 - woodchips only WB- biochar 10% v/v WB- biochar 20% v/v
- 15. Summary - Nitrate removal efficiency increased in denitrifying bioreactors by the addition of 10% v/v activated carbon or 20% v/v biochar; - Woodchips amended with activated carbon or biochar have higher efficiency of NO3-N removal at low temperatures (below 10°C); - Activated carbon and biochar are effective additives that significantly reduce C losses and support the lowest C-to-N removal ratios; - Woodchips alone and/or amended with activated carbon are a suitable medium for PO4-P removal; - The biochar can lead to large PO4-P and other inorganic element releases. Biochar itself has shown to be a potential PO4-P source with the risk of large initial and long-term release. - The addition of activated C may serve to develop a more efficient bioreactor with prolonged longevity and higher NO3-N and PO4-P removal capacity.
- 16. Thanks for attention ! arvydas.povilaitis@vdu.lt
Editor's Notes
- Lithuania is located in a temperate climate zone with an average annual air temperature of +7 C. Therefore, Artificial drainage is a common agricultural practice. In Lithuania, about 74 % of the agricultural land is tile-drained. The country remains one of the most extensively drained countries in the world. This practice helps to effectively remove excess water and significantly increase (up to 40% in wet years) crop yields. However, the introduction ... Causes environmental concerns.
- This is how it is. The process of nutrient leaching is very complex process. Despite generally spread opinion, this is is not only the result of agricultural activity. It is highly affected by the wet deposition as well as nutrient balance and transformations in the soil and many more. Long lasting dry periods followed by intensive rainstorms can also affect the leaching. It is expected that Climate change can also affect this process.
- Climate change projections for the near-future and distant-future time periods show that there will be significant alterations in seasonal river runoff followed by nutrient loads in Lithuanian rivers. It is expected that river runoff significantly increase during the winter months and a fairly high decrease occurring in the spring and early summer months. Moreover, sudden short-term increases can be expected due to heavy rainstorms in July, August and October. This could result much higher nitrogen losses from the soil trough tile drainage in winter months in particular. These challengers require new solutions. There are many uncertainties in these predictions....
- However, this is a biological process which is negatevely impacted by low inflow water temperatures as well as organic flushes (carbon loss). Therefore, the goal is to increase N removal at low temperatures and reduce C loss at high temperatures. The passibilities to remove PO4 were also tested. Therefore,Two parallel experiments with a 1-year lag between their starting times were performed at the field laboratory. Each experiment consisted of three pilot scale woodchip filled bioreactors amended with different additives. In 1 experiment, one bioreactors was filled with only woodchips and the other two were amended with either a mixture of woodchips and 10% by volume activated carbon or a mixture of woodchips and 10% flaxseed cake. In experiment two one was filled with woodchips only, but the other two were amended with ether a mixture of woodchips and 10% and 20% biochar, respectively The locally sourced mixture of woodchips were predominantly from alder and pine trees.
- The granular activated carbon produced by high-temperature steam activation of coal was obtained from DESOTEC company. This is highly porours material with high surface area. Flaxseed cake is a by-product of local flaxceed oil production. It was added to woodchips as a supplementary C source to enhance denitrification under lower temperature conditions.
- Biochar has received increased attention in environmrental applications in recent years. A by-product of thermochemical conversion (pyrolysis) of carbonaceous biomass (agri residues, algal biomass, forest residues, activated sludge, energy crops) at high temperature (up to 900 °C) under O2-limiting conditions. In this experiment it was produced at high temperature from decidiuous woodchips. FLUID company.
- The results showed that all organic materials can support NO3 removal. The DO concentrations in both experiments in all bioreactors was close to zero. This implied that DO was consumed by hetertrophic bacteria and biological activity facilitated the reduction of NO3. The outflow concentrations were always lower than the inflow. However, the removal process was affected by the inflow water temperature.
- The resulting NO3 removal efficiency ranged from 13 to 75 %. The avarege was around 40 %. While the temperature was ranging between 5 and 10 C the removal efficiency was around 25%.
- However, bioreactors with additives have shown slightly higher efficiencies at both lower and higher temperatures. In absolute values, the increase was not very significant at all. Just 4-5% higher at temperatures below 10C, and . However, statistically higher efficiencies were observed in bioreactors amended with activated carbon and 20% vv biochar. This could be attributed to the effect of AC and biochar.
- Organic carbon (bioavailable carbon) supply to denitrifying microorganisms is a key determinant of NO3 removal. Total carbon loss was positively correlated with the inflow water temperature. Higher T contributed to higher C losses. Organic carbon releases were from 6 to 10 fold higher in woodchips only and flaxceed cake amended bioreactors than in activated carbon and biochar amended bioreactors. The AC and biochar amended bioreactors were less temperature dependent. In particular, FSC has shown to be highly degradable material. The highest retention was in AC bioreactor. The effects was most profound at low T interval. This shows that AC as filling material can substantially reduce C losses while maintaining denitrification.
- Therefore the same amendments also supported the lowest C-to-N ratios (i.e., carbon loss to N removal). In AC bioreactor the average C/N ratio was less than 1, while in Biochar amended from 3 to 4, and woodchips only bioreactors from 5 to 6. In general, N mass removal increased with carbon loss but in different proportions. This means that the same N removal was associated with different C losses. So bioreactors amended with AC and B supported higher N removal for the lesser C loss.
- The experiment revealed that both PO4 removal and release occurred in bioreactors with different fillers. The removal took place in all bioreactors of E1. with much higher values observed in the AC bioreactor (average 39%). Similarly, the removal was determined in bioreactor W2 with woodchips only. However, a 3 fold higher outflows compared to their inflows were observed in bioreactors with biochar. They highly differed from the other bioreactors. The PO4 removal to some extent can be attributed Ca-and Fe phosphate precipitation and due to the activity of PAO. The removal in AC occurred through the chemical reactions of Fe-phosphate compounds forming strong precipitates.
- Concerning the P release from B bioreactors The outflow concentrations were vey high. Biochar acted as a P source. After startup the PO4 outflows were even higher (up to 0,6 -0,85 mgL). Later, over time, they started to decrease. The PO4 release was accompanied by the increased concentrations of Ca, Mg, total Fe. Compared to other bioreactors these concentrations at the outlet increased more than twice. The highest increase 3 times was observed in the total Fe concentrations. This implies these elements were extracted from biochar. The result suggest that PO4 was extracted either from Fe or Ca based compounds present in biochar. Due to the decomposition of P-bounded compound. However, the decresing PO4 release patern indicates that this process over the course of time may be finite and may switch to PO4 removal. This highlights the significance of determining the ability of biochar to retain relevant substances prior to its application. For example, a laboratory scale isothermal study could be useful to determine the P sorption capacity of biochar.