Article pubs.acs.org/JAFC
Increased Agronomic and Environmental Value Provided by Biochars with Varied Physiochemical Properties Derived from Swine Manure Blended with Rice Straw Zhongmin Dai, Philip C. Brookes, Yan He, and Jianming Xu* Institute of Soil and Water Resources and Environmental Science, Zhejiang Provincial Key Laboratory of Subtropical Soil and Plant Nutrition, Zhejiang University, Hangzhou 310058, China S Supporting Information *
ABSTRACT: To compensate for the shortcomings of manure biochar, an lignocellulose-based feedstock (rice straw) was added into manure-based feedstock (swine manure) at 3:1, 1:1, and 1:3 (w/w) manure/straw ratios during biochar production within the pyrolysis temperature ranging from 300 to 700 °C. The results showed that the pyrolysis temperatures and the proportions of straw added both influenced the biochar properties. The overall properties of biochars at 300, 400, and 500 °C were thoroughly different from those at 600 and 700 °C by principal components analysis (PCA). The XRD, FTIR, and SEM spectra suggested that the addition of straw considerably changed the mineral crystals, functional groups, and porous structures in manure biochar, respectively. The Zn(II) adsorption batch experiments showed that the biochars with more proportions of manure had the largest Zn(II) adsorption capacity than other biochars at 300 °C, which was attributed to the mineral components, oxygen functional groups, and surface areas. To meet varied agronomic and environmental requirements, the different conditions including pyrolysis temperatures and proportions of straw added should be quantitated. KEYWORDS: feedstock blending biochar, swine manure, rice straw, Zn(II) adsorption, agronomic and environmental value
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were 1.33 and 2.98 cmol/kg, respectively.10 Previous studies suggested that manure biochar can absorb and immobilize heavy metals in soils and reduce Al toxicity to the crops.11−14 For instance, Xu et al.15 found that manure biochar can increase the adsorption capacities of Cd, Zn, and Cu, which is attributed to complexation and precipitation reactions. Due to the higher yield of manure biochar, fewer gases are produced during the pyrolysis process and larger fraction of manure biochars are produced per unit of feedstock, compared with other biochars. This suggests that biochar produced from manures can minimize the production costs, i.e., using the least feedstock and electrical energy required to obtain the largest amounts of biochars. However, some limitations of the manure biochar, e.g., the low C content, relatively low surface area, and high heavy metal concentrations, suggest that this biochar probably cannot be used in some applications, e.g., increased soil carbon sequestration. Thus, some new approaches should be introduced to improve the properties of manure biochar and to compensate for its shortcomings. In our study, different proportions of a lignocellulose-based feedstock, i.e., rice straw, were added to the manure-based feedstock, i.e., swine manure, followed by pyrolysis to change the physiochemical properties of the manure biochars. With the straw addition, the manure biochar was considered as a comprehensive and effective soil amendment, retaining its original advantages and correcting its
INTRODUCTION In China, hundreds of millions of tons of swine manures are generated in the agricultural industry annually. Swine manures can be utilized as organic fertilizers applied to soil, increasing soil fertility and enhancing crop growth. However, swine manures also have some inevitable negative effects when applied into soil. For example, they may release some poisonous gases that affect human health;1 some nutrients such as N and P may cause eutrophication,2 when transported into lakes or rivers by runoff and leaching; and the heavy metals in swine manures are toxic to crops if their concentrations exceed permitted limits.3,4 Thus, how to use the large quantity of swine manure effectively and efficiently is currently of great debate in the interdisciplinary areas of agriculture production, environment pollution, and waste management. Biochars are the products of pyrolysis, which converts organic matter into stable carbon solids under limited oxygen supply at relatively low pyrolysis temperatures (normally from 200 to 700 °C). In recent years, swine manures have been used as a principal feedstock to produce biochars for soil amendment. Compared with other biochars, the manure biochar has the highest yield, nutrients (P and K), ash content, and base cations, whereas its C and H contents are much lower than those of other biochars such as wood biochar and crop straw biochar.5−8 Qian et al.9 reported that manure-derived biochar can alleviate Al toxicity and can serve as a new material for aluminum detoxification in acid soils. Due to its relatively high pH and base cation concentrations, the swine manure biochar increased the soil pH by 1.27 and 2.26 units at 1% and 3% incorporation rates respectively in a red soil, and the corresponding figures for the decreases in Al concentration © 2014 American Chemical Society
Received: Revised: Accepted: Published: 10623
May 26, October October October
2014 7, 2014 11, 2014 11, 2014
dx.doi.org/10.1021/jf504106v | J. Agric. Food Chem. 2014, 62, 10623−10631
Journal of Agricultural and Food Chemistry
Article
Figure 1. (A) pH, (B) total C (%), (C) ash content (%), and (D) yield (%) of the biochars at five pyrolysis temperatures. Chemical and Physical Analyses. Yield (%) was calculated by the following equation: yield (%) = (weight of biochar)/(weight of feedstock) × 100. The ash content was determined as follows: 1.00 g of the ground biochar was heated at 700 °C for 2 h in a muffle furnace and the ash (%) calculated from ash (%) = (weight of ash)/(weight of biochar) × 100. The pH values of the biochars were determined in deionized water at the ratio of 1:10 w/w biochar/water with a pH meter. The total C, H, and N concentrations of the biochars were measured with a Flash EA 1112 elemental analyzer (Thermo Scientific, USA), and the total O concentration was determined by difference.6 The exchangeable base cations (K, Na, Ca, and Mg) and heavy metal (Cu, Zn, and Fe) concentrations of the biochar samples were extracted by 1.0 mol/L ammonium acetate using a ratio of 1:25 w/v biochar/ solution. The Ca, Mg, K, Na, Cu, Fe, and Zn concentrations were determined by a NovAA300 atomic absorption spectrometer (Analytikjena, Germany). The micropore area (MA), surface area (BET), total pore volume (TPV), average pore width (APW), and average particle size (APS) were measured using a Nova 2200e surface area analyzer (Quantachrome, USA) after degassing at 200 °C for 8 h. SEM-EDS, XRD, and FTIR Analyses. A Sirion 100 thermal field emission scanning electron microscope (FEI, Netherlands) equipped with a Genesis 4000 X-ray energy dispersive spectroscope (EDAX, USA) (SEM-EDS) was used to determine the biochar morphology. Xray diffraction (XRD) was used to observe the changes in mineral crystals in the biochars, using an X’Pert PRO computer-controlled diffractometer (PANalytical, The Netherlands). An Avatar370 Fourier transform infrared (FTIR) spectrometer with a Nicolet 380 spectrophotometer (ThermoNicolet, USA) was used to determine the functional groups on the biochar surface. The detail operations for the SEM-EDS, XRD, and FTIR analyses have been previously described.5 Batch Zn(II) Adsorption Experiments. Duplicate biochar samples of 0.1 g were added to 50 mL polypropylene tubes. The Zn(NO3)2 solutions were prepared with varying initial concentrations from 0 to 6.0 mM. The ionic strengths of the Zn(NO3)2 solutions
disadvantages, and this new concept was quite different from previous studies.16,17 Our aims were to (1) characterize the chemical and physical properties of biochars and investigate the mechanisms which led to these changes in properties; (2) investigate the heavy metal adsorption capacity of manure biochars, prepared with added straw feedstock using, as an example, Zn(II) adsorption; (3) assess the abilities of biochars prepared jointly from manures and plant materials as soil amendments, and suggest the appropriate proportions of straw addition and the pyrolysis temperature to suit different agronomic and environmental purposes.
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MATERIALS AND METHODS
Preparation of Biochars. The swine manure was obtained from a piggery in the suburbs of Hangzhou city, Zhejiang Province, China, where vegetables, corn, and wheat are provided as the diet of the pigs. The rice straw was collected from farmland near Zhejiang University, Zhejiang Province, China. The feedstocks were air-dried, crushed into pieces, and ground
