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Biochar is defined as the carbon-rich product which is produced by pyrolysis of organic material such as wood, manure under limited supply of oxygen (Lehmann and Joseph, 2009). Carbon atoms in biochar are organized in aromatic rings of six carbon atoms linked together without Oxygen or hydrogen. However, arrangements of Carbon atoms in biochar are more irregular, complexity and variability due to affects of mineral content of feedstock (Schmidt and Noack, 2000). There are many terms that have been used to describe carbon-rich material such as black carbon, activated carbon and char. Black Carbon is a term widely used to describe the spectrum of rich carbon materials such as graphite, char, charcoal and biochar. The term includes the solid carbonaceous residue of combustion and heat, as well as the condensation products, known as soot (Schmidt and Noack, 2000). Activated carbon is a term used to define rich carbon substances that is treated by steam or CO2 or chemicals, often at high temperature (>700°C) (Boehm, 1994). Char is a term is often used to refer to carbon material that is produced by fires (Schmidt and Noack, 2000).
1.2 Nutrient content and availability of biochar
Despite massive effort has been paid to study using biochar, research related to contents and availability of nutrients in biochar is still limited. Moreover, information provided by these studies has been incomplete. However, this data is variable that may be attributed to using different material and manufacture operation condition. The nutrients content of biochar depend upon many factors such as the feedstock biomass type and the operating conditions of pyrolysis. Changing pyrolysis operation parameters can produce biochar have different nutrients content form same feedstocks. Chan et al. (2007a) reported that total nitrogen content of poultry litter biochar was 20 g kg-1 when it made at 450°C, while this concentration was 7.5 g kg-1at 700°C. In addition, phosphate and nitrogen content of biochar produced from sewage sludge and broiler litter feedstocks are higher than those from plant biomass at same pyrolysis conditions. For example, total nitrogen content of biochar from sewage sludge was 6400 mg kg-1(Bridle and Pritchard, 2004) while it was 1700 mg kg-1in biochar made from green waste (Chan et al., 2007a). Wood biochar had low total phosphate content by 127 mg kg-1 and available phosphate was low by <7.8 mg kg-1.wherase total phosphate in poultry biochar was very high by 5763 mg kg-1 and available phosphate was between 1555 mg kg-1 to 2446 mg kg-1(4"Singh et al., 2010).
Information about available nutrient contents has been limited. From the limited data available, inorganic forms of nutrients is very low (Chan and Xu, 2009). Available form of nutrients is a small fraction of total content which organisms can uptake (Keeney, 1982). Chan and Xu (2009) point out that the total elemental contents of nutrients in biochar are not an indicator on the availability of these nutrients to organisms. For example, although total nitrogen contents in biochar produced from sewage sludge was 6.4%, the concentration of inorganic forms (ammonium and nitrate) was negligible after 56 days of incubation (Bridle and Pritchard, 2004). Ammonium nitrogen form and available phosphate were reduced in soil treated by11% w/w biochar compared with the control (6"Van Zwieten 6"et al., 2010). Lehmann et al. (2003) and Rondon et al. (2007) studied the causes of reduction of available nutrients in biochar. It is attributed to immobilization of mineral nitrogen because of its high C/N ratio.
1.3 Effects of biochar on crop and microorganisms responses
Crops and microorganisms response to applying biochar is related to increases nutrients (Lehmann et al., 2003; Chan et al., 2007b; Van Zwieten et al., 2007) and improves chemical and physical characterization of soil. Added biochar have direct effects related to increase nutrients value, while indirect vale is attributed to improve chemical and physical characterization of soil. However, Addition of biochar to soil which have sufficient amounts of nutrients could not significantly increase plant production (Blackwell et al., 2009).The indirect positive impacts of biochar benefit crops production more than direct impacts (Chan and Xu, 2009). One of the positive indirect effects of adding biochar is increasing of pH acidic soils due to the alkaline nature of the biochar. Van Zwieten et al. (2007) reported that the wheat height was increased by 30% to 40% in acidic soil when biochar was applied at a rate of 10t ha-1 to an acidic soil but not to a neutral soil. That increased in wheat yield attributed to overcoming toxic effects of exchangeable aluminum (Al) of the acidic soils (Van Zwieten et al., 2007). However, the alkaline nature of the biochar might be harmful to calcifuge plant species (Mikan and Abrams, 1995). For example, Kishimoto and Sugiura (1985) reported applied biochar to soil by rate at 5t ha-1 and 15t ha-1 reduce soybeans by 37% and 71% respectively, and they attributed this to reduction availability of micronutrient due to increasing of pH. The positive indirect effects such as increased fertilizer-use efficiency in soil treated with biochar by reduction nutrients loss via leaching (Lehmann, 2007, 6"Van Zwieten 6"et al., 2010), improved soil physical properties such as increase in water-holding capacity (Iswaran et al, 1980) and reduced soil strength (Chan et al., 2007b). According to 6"Van Zwieten et al. (2010) combine biochar and Nitrogen fertilizer was significantly increased both microbial activity and Crop production in sandy soil, while nitrogen fertilizer application did not in¬‚uence microbial activity or Crop production.
1.4 Effect pyrolysis condition on nutrient content of biochar
Many type of organic material can conversed to biochar such as poultry litter, sewage sludge, green waste and wood. (Bridle and Pritchard, 2004; 4"Singh et al., 2010). Different feedstock materials under different pyrolysis operation conditions give the vast differences in the biochars properties in term of nutrient contents and their availability. The main important operation parameters affect on biochar properties are higher temperature (Lang et al., 2005;4"Singh et al., 2010), heating rate and retention time (Lang et al., 2005). Lang et al. (2005) Pointed out that, total nitrogen content of biochar made from sewage sludge was reduced from 3.8% at 400°C to 0.94 % at 950°C. It is attributed to loss of volatile organic matter (Bagreev et al., 2001). During the thermal conversion, chemical, structural properties of feedstocks and functional groups will change depending on operation condition (Chan and Xu, 2009). Increased pyrolysis temperature from150°C to 550°C there were decreased in amounts of OH and CH3 an increase in C=C. these changes attributed to change from aliphatic to aromatic C structure of the biochar (Chan and Xu, 2009). As a consequence, low temperature biochars are found to have higher amounts of acid-basic surface functional groups. The changes of aliphatic group to aromatic were caused reduction in availability of nutrients that are bound in the organic structure, such as N, P and S (Chan and Xu, 2009). Furthermore, Yu et al. (2005) found about half of the total potassium and sodium content was lost by vaporization when temperature increased from 473°C to 673°C and water-soluble form of potassium which is bioavailable is decreased from 90% of total potassium to 20%. Exchangeable and acid extractable form of potassium is increased. Changes in chemical forms of can attributed to switch bound between potassium and oxygen atoms as ionic phenoxides to incorporation of potassium into the silicate structure, which is expected to be much less bioavailable (Wornat et al., 1995). However, 4"Singh et al. (2010) reported that available phosphate in poultry biochar was increased from 1756 mg kg-1 to 2446 mg kg-1 with increased pyrolysis temperature from 400 ÌŠC to 550 ÌŠC.
1.5 Biochar Effects on Nutrient Leaching
Leaching is an important aspect affect on fertilizer-use efficiency and health of environmental. It occurs when nutrients migrate outside the rooting zone and plants cannot uptake them. Leaching can be spatially and temporally highly variable (Major et al., 2009). According to Lehmann et al. (2004) leaching contributed to lose by up to 80% of applied nitrogen. Mueller et al. (1995) reported that the levels of the nitrate in 26% of water well intensive agricultural areas of the US were exceeded the maximum contaminant level in1991. Many researches have been performed to investigate the effect adding biochar on leaching of nutrients. Ability of biochar to adsorbed nutrients and pesticides is not only to reduce the leaching and enter local water sources which cause eutrophication problem but also reduce the need for fertilizer application ( Takagi and Yoshida, 2003; 1"Ding et al., 2010; 3"Laird et al., 2010). In addition, in high rainfall climates, Adding mixture of biochar with mineral fertilizer improved yield of plants by more than using biochar, due to reduction of nutrients leaching (Chan and Xu, 2009). For example, in soil treated with both nitrogen fertilizer by 100kg N ha-1 and biochar by 11t ha-1, dry matter of sorghum is increased by up to 266 compared to a control that received the same amount of N but no biochar (Chan and Xu, 2009). Total nitrogen and phosphate lost via leaching was decreased by 11% and 69%, respectively in soil column treated by biochar and manure, this treatment was increased total nitrogen by up to 7% in this soil (3"Laird et al., 2010). Moreover, increasing of yields is not only due to reduction of nutrients leaching, but also reduction of some toxic compound. For example, decreasing of available Al in Colombia and Indonesia and tropical soils of Brazil was a result of adding wood or rice husk biochar (Lehmann et al., 2003; Yamato et al., 2006; Steiner et al., 2007).
Mechanisms that affect on lose nutrients via leaching, were studied by Major et al. (2009), Dünisch et al. (2007) and Lehmann et al. (2003). Biochar have physical characteristics such as pore-size distribution, surface area and water holding capacity that could alter retention times of water and water flow rate in soil (Major et al., 2009). This may result in decrease nutrients leaching (Lehmann et al., 2003; Dünisch et al., 2007). Lehmann et al. (2003) suggested that reduction of water mobility by increased plant biomass and evaporative surfaces was main mechanism in a biochar/clay Amazon mixture. While in biochar/sandy soil mixture increase water holding capacity was mechanism that reduced nutrient leaching. However, sorption capacity of biochars is high. Therefore, sorption could reduce nutrients that lose via leaching. For example Downie et al. (2007) found that biochar removed up to 52% of dairy farm effluent phosphorus when chicken litter biochar added by ratio 100:1 effluent/biochar. That is due to precipitate as calcium phosphate. Adsorption of phosphate by biochar was readily, while ammonium adsorption was intermediate, and nitrate was not adsorbed at all (Lehmann et al., 2002). In the greenhouse, lysimeters shown that mixture of typical Hapludox soil with biochar made locally reduced leaching of ammonium by up to 60% over 40 day of cropping rice compared to treatments not receiving biochar (Lehmann et al., 2003).
1.6 Sorption ability of biochar
Sorption is an important process, affects on availability, leaching and behavior of chemicals in the environment (Downie et al., 2007). It occurs when chemical engage to charge on surface area of particles or collides. There are many factors affect on sorption such as salinity (3"Rysgaard et al., 1999; 2"Hou et al., 2003), type of function groups (1"Hina et al., 2010), feedstocks materials (Chan et al., 2007a) and thermal conversion condition (Wornat et al., 1995; Chan and Xu, 2009). According to Hou et al. (2003) and Rysgaard et al. (1999) salinity has great influence on ammonium sorption capacity of estuarine sediments. it is found that ammonium adsorption capacity of Danish estuarine sediment was significantly decreased when salinity was increased from 0 â€° to 10 â€° (3"Rysgaard et al., 1999) . However, increased salinity over 10 â€° did not have significantly affects on ammonium sorption (Wornat et al., 1995; Chan and Xu, 2009). Ability of biochar to sorbs ammonium is attributed to functional groups rather than surface area. Hina et al. (2010) reported that Type of functional groups on biochar surface area has more influence on ammonium sorption than the total surface area charge. Carboxyl and carbonyl functional groups have main affects on cation adsorption sorption (Hina et al., 2010; 8"Uchimiya et al., 2010). Result from Hina et al. (2010) shown that despite the total surface area of biochar treated with alkaline slurry was decreased comparison with untreated , removal percentage of ammonium was increased from 61% to 83% of the total amount
2 Materials and Methods
2.1 Soil sample
The soil used in this study was obtained from the Newcastle low school building construction site on the Newcastle University campus in the U.K. The soil was sieved (< 4.0 mm).The solid density was 2.5 g cm-3. The soil pH was 7.74±0.026.
The biochar used in this study was obtained from Environmental Power International EPI (Wiltshire, UK) and produced from wood chips in a fixed bed reactor by fast pyrolysis at high temperature (800°C). It had a C: N: S ratio of 86.5:1.2:0.3. The biochar was ground to a particle size of < 163 Î¼m. The solid density was 0.361 g cm-3, and biochar had a pH of 9.25±0.16.
2.3 Ammonium, nitrate and phosphate sorption isotherms:
A batch method was used to obtain ammonium, nitrate and phosphate isotherm for soil, soil&2% activated carbon, soil&2% biochar, activated carbon and biochar. 0.1 g of activated carbon or 0.1 g of biochar or 5 g of soil or 5g of soil &2% activated carbon, 5g of soil&2% biochar was added to 50 ml centrifuge tubes. 6-7 different ammonium loadings ranged from 0 -400 mg l-1 or 6-7 different nitrate loadings ranged from 0 -20 mg l-1 or 6-7 different phosphate loadings ranged from 0 -20 mg l-1 were added to centrifuge tubes.
To assess the influence of competition of other cations on sorption of ammonium, ammonium chloride was dissolved in 0.01 molL-1 of calcium chloride (CaCl2) and 6-7 different ammonium loadings ranged from 0 - 400 mg L-1 were used in batch experiments to obtain ammonium isotherm for soil, soil&2% activated carbon, soil&2% biochar, activated carbon and biochar.
In addition, centrifuge tubes without sorbent material or soil were served as blank. All tubes were shaken for 20 h at 120 rpm to establish equilibrium. After which the slurries were centrifuged at 4,000 rpm for 8 min and the supernatant was immediately filtered by using Syringe Filter (pore size 0.2µm, diam. 25mm). Changes in ammonium , nitrate or phosphate concentration from the initial were used to calculate the sorbent ammonium , nitrate or phosphate (ug g-1). Adsorption isotherms were fitted with the Langmuir model according to (2) to check linearity.
where is amount adsorbed (ug g-1), is maximum amount adsorbed (ug g-1), k is Langmuir equilibrium constant and is equilibrium aqueous concentration.
2.4 Ammonium quantification:
Ammonium determination was carried out using Steam distillation methods. Analysis was performed on Vapodest 30s steam distillation system (Gerhardt, Northlands, UK).The sample of equilibrium solution (50 ml) was steamed for 4 min, and Ammonia was received in 50 ml of indicating boric acid solution(4% boric acid). The ammonia released in the distillation system was back-titrated with standard 0.02 M sulfuric acid (H2SO4). The concentration of ammonium was calculated according to equation (3)
where is Volume of sulfuric acid which used in sample (ml) and is Volume of sulfuric acid which used in Blank (ml).
2.5 Nitrate and phosphate quantification
Nitrate and phosphate Analysis was performed on a Dionex ICS 1000 Ion Chromatography system provided with conductivity detector (Dionex, Sunnyvale, CA, USA). The sample (5mL) of equilibrium solution was injected by a Dionex AS40 automated sampler. The separation was performed on an Ionic pac AS14A analytical column (250m m * 4 mm i.d) (Dionex, Sunnyvale, CA, USA). The Ion Chromatography was held isothermally at 20°C with 8.0mM Na2CO3/1.0 mM NaHCO3 solution as the move phase (flow rate of 1 mL min-1, initial pressure 1800 psi ). Instrumental qualification was calibrated using standard NO2, NO3 and PO4 at a three point calibration.
3 Result and discussion
3.1 Effects of material type on nutrient sorption
The effects of soil, biochar and activated carbon on sorption of nitrate, phosphate and ammonium sorption isotherms are shown in fig. 1. The ability of activated carbon, biochar on sorption of ammonium ion is very high. For example, maximum amount adsorbed () of activated carbon was 90090 ug g-1, while of biochar was 20000 ug g-1 (table 1). However, maximum amount adsorbed of soil was lower than biochar. It was 272.48 ug g-1. Moreover, sorption capacity of activated carbon for phosphate was slightly higher than biochar. Soil had lowest phosphate sorption capacity (fig. 1 b). were 2094.8 ug g-1, 1655.8 ug g-1 and 59.75 ug g-1 respectively. Maximum amount adsorbed of nitrate by activated carbon was 549.5 ug g-1 whereas it was 189.5 ug g-1. However, this value was 0.0 ug g-1 in soil.
High ability of material to adsorption ammonium ion may attribute to domination negative charge on surface area of particles and collides due to high pH that increase negative charge. While positive charges that engage anions such as nitrate are very low. High sorption capacity of activated carbon could attributed to it have higher surface area than biochar and soil. Thus activated carbon have higher amount on negative charge.
Fig. 1 sorption isotherms for (a) nitrate, (b) phosphate and (c) ammonium on (â-²) soil, (â™¦) biochar and (â-‹) activated carbon
Table 1- Isotherm parameters of used materials
Soil&2% activated carbon
Comparison between measured and calculated sorption isotherms of nitrate, phosphate and ammonia in soil&2%biochar and soil&2% activated carbon is shown in fig. 2. Despite calculated sorption isotherms of ammonium and phosphate was higher than measured, the difference between measured and calculated isotherms was little. Competition between ammonium ion and other cations in soil solution for negative charge on surface area could cause reduction in sorption capacity in measured isotherm comparable calculated isotherm. It is assumed that calcium carbonate and alkaline functional group on surface area of biochar and activated carbon had main influence on sorption phosphate and there is no competition between phosphate and other anions on calcium carbonate and alkaline functional group. Therefore, that explain why the difference between calculated and measured isotherms is little.
As shown in fig.2, measured nitrate isotherm was higher than calculated isotherm??? (discuss with David)
Fig. 2 Comparison between sorption isotherms for ( a) nitrate, (b) phosphate and (c) ammonium on (â-²)soil&2% biochar (calculated), (â™¦)soil&2% biochar (measured), (â-‹)soil&2% activated carbon (calculated) and (â-¡)soil&2% activated carbon (measured).
3.2 Effects of calcium chloride solution on ammonium sorption
Comparison between sorption isotherm of ammonium in calcium chloride solution and ammonium in deionised water is shown in fig. 3. As it shown, the adsorbed mass of ammonium was significantly decreased in experiments that used calcium chloride solution for all type of materials. Therefore, was reduced. For example, of activated carbon was decreased by 92.08% in calcium chloride solution treatment (table 1). It was decreased from 90090 ug g-1 in deionised water treatment to 7127.7 ug g-1 in calcium chloride solution treatment. Biochar, soil and soil &25 biochar or activated carbon had same trend with different percentage of change. The change of sorption capacity could attribute to competition between ammonium and calcium on sorption site on surface area.
Fig.3 Comparison between sorption isotherms for ammonium on ( a) soil, (b)biochar and (c) activated carbon using different solution, (â-)ammonium in Deionised water and (â™¦)Calcium chloride solution.