Production of Hydroxylapatite from Biowaste, Chicken Manure by Hydrothermal Process ()
1. Introduction
Production of poultry is rapidly expanding worldwide to meet the needs of the increasing human population. This cause an increased poultry biowaste, i.e. chicken manure [1]. Pollutants from improperly managed chicken manure can cause serious environmental problems for water and air. The huge amount of waste produced in a concentrated area requires urgent treatment and disposal solutions because of gaseous pollutants of ammonia and H2S as well as green house gases of CH4 and CO2. Besides, improper use of chicken manure can result in pollution of soil and groundwater [2].
Valuable material, Hydroxylapatite is a calcium orthophosphate with chemical composition of Ca10(PO4)6(OH)2. There are chemical similarities between Hydroxyapatite and the mineral part of human bone. Therefore it is highly used for biomedical applications [3-5].
Catalysts were used to enhance the reaction rate of the hydrothermal process in sub or supercritical water at low reaction temperature [6]. The addition of catalysts could also enhance the Hydrogen yield. The effects of the Na2CO3 and Ni catalysts as additives on the hydrothermal process of cellulose at 400˚C were reported [7]. The addition of the optimum amount of Na2CO3 increased Hydrogen yield and suppressed CO2 emission in the gas phase. Yanik et al. [8] reported that trona, red mud, K2CO3 and Raney-Ni were useful for lignocellulosic and proteinous materials. Watanabe et al. [9] studied the effect of ZrO2 as a catalyst, and reported that for glucose and cellulose, the Hydrogen yield with ZrO2 was almost twice as much as without the catalyst.
In earlier study, various catalysts and additives used for hydrothermal process were studied and Ca(OH)2 was found to be a suitable additive because it could suppress the production of heteroatom pollutants in the gas phase and enhance the Hydrogen yield. Ca(OH)2 is also reasonable than other additives and catalysts currently available. The additive cost is an important factor for treatment of a large amount of biowaste [10].
First, selecting and using pure test samples of O-phospho-DL-serine with P, as a model compound, the optimum conditions were determined for the hydrothermal process. Then, these conditions were applied to a real biowaste, chicken manure.
The objective of this study was providing production of Hydroxylapatite as a valuable material through the hydrothermal process by using biowaste, chicken manure with Ca(OH)2.
2. Experimental
2.1. Experimental Setup
The experimental setup is basically same as that reported the earlier study [10]. A reactor is a stainless steel (SUS 316 of 1/2 inch in O.D. 12 cm in length) 1), connected to the T-fitting 2). A strain amplifier 3) for pressure measurement (Kyowa-Dengyo, Co., Japan) was connected to the T-fitting, and the stop valve 4) was connected to the other side. A gas chromatograph oven (Hewlett Packard, 5890 GC) was used for heating the reactor to a controlled temperature.
2.2. Reagent
O-phospho-DL-serine, Ca(OH)2 which was used as the additive is of analytical grade, acetic acid which was used in purification process, pure Hydroxylapatite, and CaCO3 were purchased from Wako Chemical Co. Ltd (Japan).
Commercially available chicken manure was purchased from G. I. Ltd. (Japan). The chicken manure’s elemental compositions were 30.3% C, 4.7% H, 2.6% N, 0.8% S, 4.4% K [10].
2.3. Procedure
About 400 mg sample was put into the reactortogether with 1 mmol Ca(OH)2 and 5 ml water. Then, N2 gas was introduced to purge the residual O2 gas in the reactor. The reactor was put in the ovenand heated to 400˚C at 1.5˚C min−1. The reactor was maintained at 400˚C for 40 minutes to complete the hydrothermal process under the pressure of 26 - 27 MPa. Then, the oven was cooled down to 30˚C. And the generated components were analyzed.
2.4. Analytical Equipment
Ionic chemical species dissolved in the liquid phase were analyzed with an ion chromatograph (HIC-SP Suppressor Ion Chromatograph, Shimadzu). The parameters and conditions; Shimadzu IC-SC-1 Column for Cation (+), Shodex ICSI-50 Column for Anion (−), Oxalic acid 3.0 mM Mobile phase for Cation (+), Na2CO3 3.2 mM and NaHCO3 1.0 mM Mobile phase for Anion (−), 1.5 mLmin−1 flow for (+) Cation and Anion (−), 40˚C column temperature for Cation (+), 25˚C column temperature for Anion (−) were used for the IC [10].
An XRD system (RINT 2500/PC by Rigaku Co., Japan) was used for identification of residual solid samples. The diffraction data were collected from 20˚ to 60˚ in 2θ values with a step of 0.02˚. An elemental analyzer (Perkin Elmer 2400 Series II CHNS/O System) was used for determination of C, H, and N.
The resulting gaseous components were analyzed using a gas chromatograph (GC Shimadzu 5A) equipped with a thermal conductivity detector (TCD).
Porapak Q (length: 2 m, diameter: 3 mm) Column, Argon carrier gas, 98 kPa inlet pressure, 80˚C inlet temperature and 50˚C column temperature were used for H2 analysis as the parameters and conditions [10].
Porapak Q (length: 2 m, diameter: 3 mm) Column, Helium carrier gas, 170 kPa inlet pressure, 80˚C inlet temperature and 50˚C column temperature were used for CH4, CO, etc. analysis as the parameters and conditions [10].
2.5. Purification of Solid Residue (Hydroxylapatite) by Chemical Method
Acetic acid solution was usedas weak acidfor purification of Hydroxylapatite.
3. Results and Discussion
3.1. Hydrothermal Process of O-Phospho-DL-Serine
3.1.1. Liquid Phases
In the earlier paper, the effect of added Ca(OH)2 amount on the concentration of phosphate ion dissolved in the liquid phase for O-phospho-DL-serine was reported [10].
The temperature for the hydrothermal process was held at 400˚C, without the additive, 93.3% of sample phosphorus was converted to phosphate ion. As the amount of Ca(OH)2 was increased, the phosphate ion yield was suppressed [10].
3.1.2. Solid Phases
Figure 1 shows the XRD patterns of pure Hydroxylapatite (a) and crude residue from O-phospho-DL-serine with the different amounts of Ca(OH)2. With 1 mmol Ca(OH)2 (b), the similar pattern tothat ofHydroxylapatite is observed. With 2 mmol Ca(OH)2 (c), some peaks of Hydroxylapatite is recognized together with the CaCO3 peaks. With 3 mmol Ca(OH)2 (d) stronger of Hydroxylapatite peaks became weaker while the peaks of Ca(OH)2 and CaCO3.