Effect of Wood Biochar in Manure-Applied Sand Columns on Leachate Quality

Biochar impacts on soil nitrogen and carbon dynamics in a Spodosol amended with biosolids and inorganic fertilizer

Despite evidence suggesting that biochar can retain nutrients, particularly nitrogen (N), and reduce the risks of transport, research on the co-application of biochar with organic and inorganic fertilizer sources is limited. Three laboratory studies (herein referred to as static incubation, column leaching, and batch sorption) were conducted to evaluate the impacts of two biochar materials (pine and grass biochar generated at temperatures of 800 and 400°C, respectively) on N and carbon (C) dynamics in soils amended with different N sources (ammonium nitrate, Class B, and Class AA biosolids). Nitrogen sources were applied at an equivalent rate of 180 kg N ha-1 while biochar was applied at a 1% (w/w) rate. Biochar effects on soil N and C dynamics were variable and dependent on biochar and N sources. A negligible but significant effect of pine biochar in reducing NH4 leaching was observed; however, both biochar materials were ineffective in reducing NO3 or inorganic N leaching. Reductions in leachate NH4 by pine biochar were attributed to relative greater ability of this material to retain NH4 than grass biochar. Both biochar materials exhibited no ability to sorb NO3 . Similarly, biochar had no effect on soil N2 O emissions. Class B biosolids resulted in greater N leaching and soil N2 O emissions compared to other fertilizers. This response was likely due to inherently high levels of inorganic N and moisture, which possibly favored denitrification. Further research is warranted to better understand the underlying mechanisms controlling soil N and C dynamics and responses to co-application with fertilizer sources.

Biochar-blended manure modified by polyacrylamide to reduce soil colloidal phosphorus leaching loss

Combined application of biochar and organic fertilizer improves soil structure and crop yield but may lead to increased loss of phosphorus (P). To reduce the P loss risk in this case, rice straw biochar (BC) and sheep manure (SM) were modified using polyacrylamide (PAM). The effects of using organic amendments (BC, SM, and PAM-modified organic mixtures) and no amendments (CK) on soil total and colloidal P leaching loss from paddy soils were evaluated through soil column leaching experiments. The soil leachate volume was increased by 8.91% with BC treatment and reduced by 15.3% with SM treatment. The total P leaching loss (973.9 μg kg^-1) from the BC-treated soil was higher than that from other treatments (541.4-963.5 μg kg^-1). However, there was much more colloidal P loss (480.0 μg kg^-1) from SM treatment. The optimal conditions for the preparation of BC and SM modified using polyacrylamide (PSB) for reducing P leaching loss were SM/BC = 4:1, 1% PAM, and 100 °C. Molybdate-unreactive P accounts for 58.61-86.89% of the colloidal P in the soil leachate with organic amendments. PSB reduced colloidal P loss (particularly in 10-220 nm range) by ~ 50% compared with BC and SM treatments. The colloidal P concentration in the leaching solutions was significantly correlated with TOC and susceptible to Fe and Al concentrations. Using PAM-modified mixture instead of manure and biochar as a soil amendment can effectively control P leaching from fields.

Combined effects of biochar and fertilizer applications on yield: A review and meta-analysis

The use of biochar is changing, and the combined application of biochar with fertilizer is increasingly gaining acceptance. However, the yield gains results reported in the existing literature through the co-application of fertilizer with biochar are conflicting. To resolve this, we utilized a meta-analysis of 627 paired data points extracted from 57 published articles to assess the performance of the co-application of biochar and fertilizers on crop yield compared with the corresponding controls. We also studied the impact of biochar characteristics, experimental conditions, and soil properties on crop yield. Our analysis showed that individually, biochar and inorganic fertilizer increased crop yield by 25.3% ± 3.2 (Bootstrap CI 95%) and 21.9% ± 4.4, respectively. The co-application of biochar with both inorganic and organic fertilizers increased crop yield by 179.6% ± 18.7, however, this data needs to be treated with caution due to the limited dataset. The highest yield increase was observed with amendments to very acidic soils (pH ≤5), but the benefits of biochar were not affected by the rate and the time after the application. In addition, the effects of biochar are enhanced when it is produced at 401-500 °C with a C:N ratio of 31-100. Our results suggest that the co-application of biochar with either inorganic and/or organic fertilizers in acidic soils increase crop productivity compared to amendment with either fertilizer or biochar. Our meta-analysis supports the utilization of biochar to enhance the efficiency and profitability of fertilizers.

Use of biochar to produce reclaimed water for irrigation use

Emerging contaminants, especially, pharmaceutical and personal care products (PPCPs) are not removed well during conventional wastewater treatment and hence pose water quality risk to the environment and potentially to public health. Long-term use of reclaimed wastewater for irrigation can lead to accumulation of trace contaminants in the soil, ground water and their subsequent uptake by plants and potentially can enter human food chain. This paper uses biochar as an adsorbent to remove emerging contaminants from treated wastewater by performing fixed bed experiments. Ten emerging contaminants namely, carbamazepine (CBZ), caffeine, diethyltoluamide (DEET), diphenhydramine (DPH), meprobamate (MPB), primidone (PMD), sulfamethoxazole (SMX), fluoxetine (FXT), perfluorooctanoic acid (PFOA) and trimethoprim (TMP) were monitored during lab scale experiments. Results from the continuous flow runs showed that the breakthrough curve for compounds caffeine, CBZ, DEET and PFOA follow second order Thomas model with adsorption capacities of 396 μg g^-1, 392 μg g^-1, 1160 μg g^-1 and 32 μg g^-1 biochar, respectively. Whereas compounds such as DPH, TMP and FXT were completely removed throughout the column runs by biochar. Results for rest of the compounds were interfered by leaching of these compounds from biochar. It was observed that commercially available GAC performed much better than biochar for all the compounds considered. Even at 1% of obtained capacity, biochar amendment to soils where reclaimed water is used for irrigation can reduce the uptake of these compounds by plants.

Treatment of horizontal silage bunker runoff using biochar amended vegetative filter strips

Horizontal silage bunkers produce leachate that contains contaminants that can be detrimental to the environment if released untreated. Vegetated filter strips are used to treat silage bunker runoff to prevent contamination of surface waters via infiltration, however increased infiltration poses risks to groundwater, particularly for nitrate (NO₃^-). Vegetated filter strip plots with a sandy loam soil, half of which are amended with biochar, were investigated to assess the treatment of silage bunker runoff over 20 application events. The subsurface effluent biological oxygen demand (BOD₅), chemical oxygen demand (COD), and total phosphorus (TP) were reduced on average by 40%, 46%, and 75%, respectively, and there was no statistical difference between treatments. The total nitrogen (TN) was reduced by 49 and 64% for control and biochar plots, respectively, which was significantly different between treatments. Biochar significantly reduced nitrate nitrogen (NO₃^--N) leaching by 40% compared to the control, however, the NO₃^--N concentration in leachate was still high ranging from 0.19 to 191.04 mg NO₃^--N L^-1 and 0.18-108.89 mg NO₃^--N L^-1 for control and biochar plots, respectively. A mass balance suggests the primary mechanism for a decrease in TN and NO₃^--N leaching from biochar amended plots was greater retention of NO₃^--N and organic N (ORG-N) within the soil/biochar matrix. The development of oxygenated functional groups and/or formation of organomineral layer on the biochar surface likely enhanced N retention.

Soil Amendment with Biochar Affects Water Drainage and Nutrient Losses by Leaching: Experimental Evidence under Field-Grown Conditions

Leaching of soluble elements from cultivated soils is a major concern to meet the target of agricultural sustainability in most areas. The effect of biochar application to a cultivated soil on water drainage and the consequent solute losses was assessed during a trial carried out over two consecutive growing seasons. Biochar was added to a loam-texture soil, at 0, 1, and 2% d.w. rates. A lysimeter-like set-up arranged in the experimental field-unit, allowed collecting the percolating water. Two multiple linear regressions (ANCOVA models) were applied to detect biochar effect on: (1) The seasonal amount of drained water; and (2) the concentration of solutes in the drained water. The statistical comparison among a set of slope coefficients as affected by treatments (growing season and biochar) was used as modelling approach. The lower biochar application rate (1%) significantly reduced both the amount of drained water and its concentration in solutes. Conversely, the higher biochar application rate (2%) showed no significant effects. Nitrate and chloride showed a significant interaction with biochar application rates. Higher biochar application increased nitrate leaching while reduced that of chloride. Biochar application within a rate no more than 1% resulted in a useful and quite effective technical operation.

Evaluation of Biochar Nitrate Extraction Methods

Biochar amendment to soil is a method used to mitigate losses of nitrogen leaching through agricultural soils. Multiple methods for extraction of nitrogen have been used, and recent studies have indicated that traditional soil extraction methods underestimate biochar nitrate. This study evaluated the nitrate extraction efficiency of a KCl extraction method under different temperature (20 and 50 °C) and duration (24 and 96 h) conditions. Increasing the duration of extraction from 24 to 96 h did not have a significant impact on extraction efficiency. However, increasing temperature resulted in nitrate extraction efficiencies above 90%. Rinsing the biochar once with deionized (DI) water following filtration after extraction increased the extraction efficiency significantly, but any subsequent rinses were not significant. This study recommends extracting nitrate from biochar using 2 M KCl at 50 °C for a period of 24 h with one additional rinse to increase nitrate recovery above 90%. However, future studies should evaluate this procedure for different types of biochar produced from alternative biomasses and at varying temperatures.

Nitrate sorption to biochar following chemical oxidation

Biochar amendments can reduce nitrate (NO₃) leaching in agricultural soil. It has been hypothesized that functional groups on the biochar surface from oxidation can increase NO₃ sorption. This study evaluates the effect of chemical oxidation of biochar on NO₃ sorption characteristics. Eight biochars, made from wood and corn cobs, underwent sodium hypochlorite (NaClO) and hydrogen peroxide (H₂O₂) oxidation and then assessed for NO₃ sorption capacity using batch isotherm methods. The unoxidized and oxidized biochar produced at low temperatures (400 °C) had no significant NO₃ sorption. Oxidized biochars produced at higher temperatures (600 °C and 700 °C) had calculated maximum NO₃ sorption capacities (S_max) ranging from 0.50 to 3.97 mg NO₃-N g^-1. Biochar oxidations with 50 mmol NaClO g^-1 (N50) in combination with an acid wash (AW) had the largest estimated sorption capacities of 3.68, 3.97, and 1.46 mg NO₃-N g^-1 for CT_N50,AW, BW3_N50,AW, and CC3_N50,AW, respectively. Sorption capacity of wood-based biochars was higher than corn cob biochars due to increased oxidation as measured by total acid group content (TAGC). Wood biochar Smax values were correlated with ΔTAGC (R²= 0.86), with a slope of 1.2 μmol NO₃-N μmol TAGC^-1 suggesting that cationic bridging of NO₃ to oxidized sites is the primary mechanism for NO₃ sorption.

Phosphorus sorption capacity of biochars from different waste woods and bamboo

Four biochars were made via pyrolysis at 500 °C using different waste plant materials, including tree branches from Cinnamonum campora (L.) Pres (CCP), Eriobotrya japonica (Thunb.) Lindl (EJL), Rohdea roth (RR) and bamboo shoots (Phyllostachys sulphurea) (PS). Phosphorus sorption capacities of the biochars were studied by isothermal experiments on their sorption kinetics. Results show that P sorption to the three wood biochars (CCP, EJL, and RR) fitted well with Lagergren pseudo second order model. However, P release was found in the PS biochar and sand amended with the PS biochar treatments during the isothermal sorption experiment. Phosphorus sorption capacity of the CCP biochar, EJL biochar and RR biochar was 4,762.0, 2, 439.0 and 1, 639.3 mg/kg, respectively. The CCP biochar showed the highest P sorption capacity due to its higher pH, lower dissolved P content, larger surface area (23.067 m²/g) and pore volume (0.058 cm³/g). The PS biochar showed the lowest P sorption due to its higher dissolved P content, more carboxyl groups, and smaller surface area (2.982 m²/g) and pore volume (0.017 cm³/g). Results suggest that the CCP biochar could be a potential alternative adsorbent for P sorption, such as removing P in wastewater treatment by constructed wetlands.

Biochar and Water Quality

Biochar application is considered to be an emerging strategy to improve soil ecosystem services. However, implications of such application on water quality parameters have not been widely discussed. This paper synthesizes the state-of-the-art research on biochar effects on water erosion, nitrate leaching, and other sources of water pollution. Literature indicates that in general, biochar application reduces runoff by 5 to 50% and soil loss by 11 to 78%, suggesting that it can be effective at reducing water erosion, but the magnitude of erosion reduction is highly variable. Co-application of biochar with other organic amendments (i.e., animal manure, compost) appears to be more effective at reducing water erosion than biochar alone. A main mechanism by which biochar can reduce water erosion is by improving soil properties (i.e., organic C, hydraulic conductivity, aggregate stability), which affect soil erodibility. This review also indicates that biochar reduces nitrate leaching, in most cases by 2 to 88%, but has mixed effect on phosphate and dissolved C leaching. Additionally, biochar effectively filters urban runoff, adsorbs pollutants, and reduces pesticides losses. Biochar feedstock, pyrolysis temperature, application amount, time after application, and co-application with other amendments affect biochar impacts on water quality. Biochar erosion and potential reduction in nutrient and pesticide use efficiency due to the strong adsorption are concerns that deserve consideration. Overall, biochar application has the potential to reduce water erosion, nitrate leaching, pesticide losses, and other pollutant losses, but more field-scale data are needed to better discern the extent to which biochar can improve water quality.

Using biochar capping to reduce nitrogen release from sediments in eutrophic lakes

The effects of reduced nitrogen release from sediments were studied using biochar (BC) capping in simulated water-sediment systems. Dried solid waste of Phyllostachys pubescens was used to produce BC, which was then pyrolyzed at 500 °C. Subsequently, 14 sediment cores were collected, including the sediment-water interface and some overlying water, from two sites in Baiyangdian Lake (China). The sediment cores were split into two batches (A and B), and then two each were capped with soil, BC or a BC/soil mixture, and incubated for 30 days. In the BC capped cores, the ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and total nitrogen (TN) concentrations decreased from 0.90 mg·L^-1 to 0.05 mg·L^-1, 0.88 mg·L^-1 to 0.18 mg·L^-1, 6.93 mg·L^-1 to 2.81 mg·L^-1, respectively, in batch A and 3.51 mg·L^-1 to 0.11 mg·L^-1, 0.92 mg·L^-1 to 0.61 mg·L^-1, 8.88 mg·L^-1 to 3.32 mg·L^-1, respectively, in batch B. The sediments to water fluxes of NH₄⁺-N, NO₃^--N and TN were greatly reduced or reversed. Compared with other cappings, the BC layer was shown to absorb more NH₄⁺-N from the pore water, thereby breaking the diffusion gradient of NH₄⁺-N at the sediment-water interface, and has a good inhibitory effect on the endogenous release of NH₄⁺-N from the sediments. Additionally, in the BC capped cores, the redox potential remarkably increased and dissolved oxygen was comparatively high. This study suggests that BC capping can reduce the amount of nitrogen released from polluted sediments because the diffusion of nitrogen to the overlying water is chemically blocked by the cap.

Mushroom cultivation in the circular economy

Commercial mushrooms are produced on lignocellulose such as straw, saw dust, and wood chips. As such, mushroom-forming fungi convert low-quality waste streams into high-quality food. Spent mushroom substrate (SMS) is usually considered a waste product. This review discusses the applications of SMS to promote the transition to a circular economy. SMS can be used as compost, as a substrate for other mushroom-forming fungi, as animal feed, to promote health of animals, and to produce packaging and construction materials, biofuels, and enzymes. This range of applications can make agricultural production more sustainable and efficient, especially if the CO₂ emission and heat from mushroom cultivation can be used to promote plant growth in greenhouses.

Can Biochar Covers Reduce Emissions from Manure Lagoons While Capturing Nutrients?

The unique physical and chemical properties of biochars make them promising materials for odor, gas, and nutrient sorption. Floating covers made from organic materials (biocovers) are one option for reducing odor and gas emissions from livestock manure lagoons. This study evaluated the potential of floating biochar covers to reduce odor and gas emissions while simultaneously sorbing nutrients from liquid dairy manure. This new approach has the potential to mitigate multiple environmental problems. Two biochars were tested: one made via gasification of Douglas fir chips at 650°C (FC650), and the other made from a mixture of Douglas fir [ (Mirb.) Franco] bark and center wood pyrolyzed at 600°C (HF600). The HF600 biocover reduced mean headspace ammonia concentration by 72 to 80%. No significant reduction was found with the FC650 biocover. Nutrient uptake ranged from 0.21 to 4.88 mg N g biochar and 0.64 to 2.70 mg P g biochar for the HF600 and FC650 biochars, respectively. Potassium ranged from a loss of 4.52 to a gain of 2.65 mg g biochar for the FC650 and HF600 biochars, respectively. The biochars also sorbed Ca, Mg, Na, Fe, Al, and Si. In a separate sensory evaluation, judges assessed odor offensiveness and odor threshold of five biocover treatments including four biochars applied over dairy manure. Reductions in mean odor offensiveness and mean odor threshold were observed in three treatments compared with the control. These results show that biochar covers hold promise as an effective practice for reducing odor and gas emissions while sorbing nutrients from liquid dairy manure.

Nutrient conservation during spent mushroom compost application using spent mushroom substrate derived biochar

Spent mushroom compost (SMC), a spent mushroom substrate (SMS) derived compost, is always applied to agriculture land to enhance soil organic matter and nutrient contents. However, nitrogen, phosphate and organic matter contained in SMC can leach out and contaminate ground water during its application. In this study, biochars prepared under different pyrolytic temperatures (550 °C, 650 °C or 750 °C) from SMS were applied to soil as a nutrient conservation strategy. The resultant biochars were characterized for physical and mineralogical properties. Surface area and pore volume of biochars increased as temperature increased, while pore size decreased with increasing temperature. Calcite and quartz were evidenced by X-ray diffraction analysis in all biochars produced. Results of column leaching test suggested that mixed treatment of SMC and SMS-750-800 (prepared with the temperature for pyrolysis and activation was chosen as 750 °C and 800 °C, respectively) could reduce 43% of TN and 66% of COD_Cr in leachate as compared to chemical fertilizers and SMC, respectively. Furthermore, increasing dosage of SMS-750-800 from 1% to 5% would lead to 54% COD_Cr reduction in leachate, which confirmed its nutrient retention capability. Findings from this study suggested that combined application of SMC and SMS-based biochar was an applicable strategy for reducing TN and COD_Cr leaching.

Phosphorus removal from secondary sewage and septage using sand media amended with biochar in constructed wetland mesocosms

To improve the performance efficiency of subsurface constructed wetlands (CWs), a variety of media have been tested. Recently, there has been a rising interest in biochar. This research aims to develop the effectiveness of sand media amended with biochar and two plants species (Melaleuca quinquenervia and Cymbopogon citratus) in removing phosphorus from sewage effluent in CWs. The experimental design consisted of vertical flow (VF) mesocosms with seven media treatments based on the proportions of biochar in the sand media which ranged from 0 to 25% by volume. During the first 8months, the mesocosms were loaded with secondary clarified wastewater (SCW) then septage was used for the remaining 8months. Inflow and outflow were monitored for total phosphorus (TP) and PO4-P. Plants were harvested at the end of the experiment and TP biomass was determined. Removal efficiencies of TP in the mesocosms loaded with SCW and septage ranged from 42 to 91% and 30 to 83%, respectively. Removal efficiencies of PO4-P ranged from 43 to -92% and 35 to 85% for SCW and septage, respectively. The results revealed that the sand media performed better than the biochar-amended media; increasing the proportion of biochar in the media decreased removal efficiency of phosphorus. However, after flushing due to major rain event, there was no significant difference between sand and sand augmented with 20% biochar. Total plant P ranged from 1.75g in the 20% biochar mesocosm to 2.10g in the sand only mesocosm. Plant uptake of P, at least in part, may be accredited for the better P removal efficiency in the sand media compared to the biochar-amended media.