Yuanping ZHANG,Xiaozhong ZHANG

Kocel Biochemistry Co.,Ltd.,Yinchuan 750200,China

Extraction and Characterization of Biological Humic Acids from Fermented Furfural Residue

Yuanping ZHANG*,Xiaozhong ZHANG

Kocel Biochemistry Co.,Ltd.,Yinchuan 750200,China

[Objective]This study aimed to eliminate the negative effects brought about by continuous,long-term accumulation of sodium ions in soil on soil environment.[Method]Biological humic acids(BHAs)were extracted from fermented furfural residue via alkali-dissolution and acidification.The effects of solid-liquid ratio(mass ratio of fermented furfural residue to water),alkali concentration,extraction temperature and extraction time on the content of BHA were investigated.Also its structure was characterized by FTIR.[Result]The optimal extraction conditions were as follows:solid-liquid ratio of 1:7,KOH concentration of 6%,extraction temperature of 70℃and extraction time of 1 h.Under the optimal conditions,the content of BHAs extracted was up to 8.5%.The infrared spectrum analysis indicated that BHA had more types of functional groups and lower molecular weight than commercial humic acid although they had similar structures.[Conclusion]The technique has the advantages of simple operation and good stability,and is suitable for extracting BHAs. BHAs have a good prospect in developing new types of humic acid fertilizers.

Fermented furfural residue;Biological humic acid;Extraction;Characterization

H umic acids(HAs)are a group of aromatic organic macromolecular weak acids.They have complex structures with multiple active functional groups,resulting in a very high reactivity,and are widely used in all aspects including agriculture,industry,medicine,environment protection and so on[1-5].In re cent years,the production of HAs by fermentation has attracted more and more attention both at home and abroad.The production of HAs by fermentation simulates the production process of natural HAs,which inoculates microorganisms into culture mediums to produce HAs through mi crobial fermentation[6].Such biological humic acids(BHAs),whose functional groups have strong permeability,are endowed with good water solubility as well as good resistance to acids and alkalis,and thus have wide application prospect.In the late 1980s,after four years of large-scale application tests and more thorough theoretical studies, it was found that HAs can be used in agriculture to improve soil quality, fertilizer efficiency,crop production, crop resistance and quality[7].In recent years,along with the rising awareness for environment protection and the development of green food and organic food,environment-friendly water-soluble fertilizers including BHAs have got a lot of attention.The growth rate of annual demand for water-soluble HA fertilizers has moved far beyond ordinary products.However,the traditional techniques,because extracting HA with alkali solution could create pollution to soil,has been questioned,resulting in poor utilization of watersoluble HA fertilizers[8-9].So,novel techniques for producing water-soluble HA fertilizers are urgently required.

There are problems with the conventional techniques adopted by domestic water-soluble HA industry recently.Most water-soluble HA components required by agricultural HA products at home and aboard need to be extracted with sodium hydroxide, inducing sodium ions which are use-

Materials and Methods

Experimental materials

Fermented furfural residue(self manufactured),tap water,high-quality potassium hydroxide(content≥90%, Inner Mongolia Rida Taifeng Chemical Co.,Ltd.).

Experimental methods

Extraction of BHAsThe fermented furfural residue was crushed and sieved with an 80-mesh sieve.The powder obtained was weighed accurately according to a certain soil-liquid ratio(mass ratio of fermented furfural residue to water)and added into to a 1 000 ml flask.After a certain mass of potassium hydroxide was added into the flask,stirring was carried out at a certain temperature to allow reaction for a certain time period.After standing overnight,the dark brown supernatant containing BHA was collected.The supernatant obtained above was adjusted with 10%sulfuric acid to pH 2.5, to get a lot of blown black precipitate. Vacuum filtration was carried out with a Buchner funnel,and the precipitate was collected and washed with 20 ml of distilled water for three times.Finally,the precipitate obtained was dried at 105℃to a constant weight,and weighed.

Detection and characterization of BHAsBHA content was determined by volumetric method according to provisions in NY1106-2010 Water-soluble fertilizers containing humic-acids;organic matter content was determined according to NYT 1976-2010 Watersoluble fertilizers-Determination of organic matter content;BHAs were mixed with KBr powder,and the mixture was subjected to grinding and tableting,and determined by an infrared spectrometer with a scanning range of 4 000-400 cm-1;and the total acidity,carboxyl group and phenolic hydroxyl group were determined using barium hydroxide method and calcium acetate[10].

Results and Analysis

Extraction of BHAs with potassium hydroxide

Influence of solid-liquid ratio(mass ratio of fermented furfural residue to water)on the content of extracted BHAsReactions were performed under an extraction temperature of 75℃at solid-liquid ratios of 1∶4,1∶5,1∶6, 1∶7,1∶8,1∶9,1∶10 and 1∶12 for 2 h,and the BHA contents in supernatants were determined.

As shown in Fig.1,the content of extracted BHAs increased with the increasing soli-liquid ratios of raw material,and then decreased.When the soli-liquid ratio was 1∶7,the BHA content in the supernatant after extracting with alkali was the highest,up to 8.5%. While the soli-liquid ratio continued to increase,the BHA content decreased gradually,because the increase of water as a liquid-phase medium diluted alkali,and thus reducing the ability of alkali for extracting BHAs in furfural residue.Therefore,the optimal solidliquid ratio was 1∶7.

Influence of the concentration of potassium hydroxide solution on the extraction of BHAsKOH solution could extract soluble humates, free HAs and partial insoluble humates from fermented furfural residue.Therefore,fermented furfural residue was first treated with KOH solution at different concentrations,then,BHA extraction was carried out at 70℃and solid-liquid ratio of 1H7 for 1 h to evaluate the influence of KOH solution on final BHA content.

As shown in Fig.2,the content of extracted BHAs increased with increasing concentration of KOH solutions,reached the maximum value 8.5%at KOH concentration of 6%,and then decreased.Consequently,KOH concentration of 6%was chosen to extract HAs in fermented furfural residue.

Influence of reaction time on the extraction of BHAsThe variation of BHA content with different extraction time under an extraction temperature of 70℃at a solid-liquid ratio of 1∶7 and a KOH concentration of 6%was studied.

Extraction time is a key factor to the extraction of BHAs.BHAs could not be extracted thoroughly if the extraction time was too short,resulting in a low BHA content in the supernatant of fermented furfural acid.Otherwise, the characteristics of BHA would be affected if the extraction time was too long,which was prone to cause the decomposition of BHA,thereby decreasing the extraction efficiency.In addition,prolonged extraction time would increase unit energy consumption and production cost.

As shown in Fig.3,with the reaction time of 60 min,a highest BHA content was achieved.When the extraction time was shorter than or longer than 60 min,the content of BHA extracted from fermented furfural residue became lower.The extraction was inadequate with short extraction time.However,more alkali was consumed during a longer time period of extractioin,and furthermore BHA would decomposed,resulting in a low content of BHA in the supernatant.

Influence of reaction temperature on the extraction of BHAThe variation of BHA content with different extraction temperatures under extraction time of 1 h at a solid-liquid ratio of 1∶7 and a KOH concentration of 6%was studied.

BHAs are a group of macro-molecular substances with multiple active groups,and the higher the reaction temperature,the faster the motion of the molecules,resulting in higher reaction rate.However,a too high reaction temperature could lead to the decomposition of organic matter in fermented furfural residue,following with increased energy consumption. Therefore,designing a proper temperature not only can accelerate reaction, but also can reduce product cost.It can be seen from Fig.4,BHA content increased with the increasing reaction temperatures rapidly at first,and decreased gradually after the optimal temperature of 70℃.As a result,70℃ was considered as the optimal temperature for BHA extraction.

Physical properties of BHA productThe BHA product extracted from fermented furfural residue with alkali, had a total acidity of 10.687 mmol/g, phenolic hydroxyl group of 6.238 mmol/g,carboxyl group of 4.792 mmol/g,an HA content of 88.4 g/L, and an organic matter content of 104 g/L,which indicated that,due to the dissociable hydrogen ions existing on the carboxyl groups and hydroxyl groups on aromatic rings and aliphatic chains,BHAs were endowed with acidity and exchange capacity,and meanwhile,the content of organic matter was also high.

Infrared spectrum analysis

FTIR was applied to qualitatively analyze the functional groups on BHAs.The infrared spectrum of BHAs is shown as Fig.5.The characteristic infrared absorption peaks and functional groups of BHAs are shown in Table 1.

These functional groups were in different chemical environments in BHA molecules,so the widths of their absorption peaks were different from each other.The experiments and related information indicated BHAs had the active functional groups including hydroxyl group(-OH),carboxyl group(-COOH)and carbonyl group(-C=O) thereon.These active groups render BHAs strong permeability,good water solubility,good resistance to acids and alkalis,and high absorptivity.Accordingly,the substances extracted in this study were BHAs.

Conclusions

In recent years,HAs are widely used for preparing agricultural fertilizers,and commonly extracted from peat and weathered coal,while the study of extracting BHAs from fermented furfural residue is still in lack.BHAs were extracted from fermented furfural residue through alkali-dissolution acidification method.The effects of solid-liquid ratio(mass ratio of fermented furfural residue to water),alkali concentration,extraction temperature and extraction time on the content of BHAs were investigated.Also their structures were characterized by FTIR.The results showed that the op-

Table 1Characteristic infrared absorption peaks and functional groups of BHAs

timal extraction conditions were as follows:solid-liquid ratio of 1∶7,and KOH concentration of 6%,extraction temperature of 70℃and extraction time of 1 h.Under these conditions,the content of extracted BHAs was increased to 8.5%.The infrared spectrum analysis indicated that BHAs had more types of functional groups and lower molecular weight than commercial humic acids although they had similar structures.The technique has the advantages of simple operation and good stability,and is suitable for extracting BHAs.BHAs have a good prospect in developing new types of humic acid fertilizers.

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Responsible editor:Qingqing YIN

Responsible proofreader:Xiaoyan WU

發(fā)酵糠醛渣中生化腐植酸的提取與表征

張院萍*，張曉忠
（寧夏共享生物化工有限公司，寧夏銀川750200）

［目的］解決腐植酸的水溶性問題以及鈉離子連續(xù)、長期在土壤中的累積對土壤環(huán)境帶來的不利影響。［方法］以發(fā)酵糠醛渣為原料，采用堿溶酸析法提取生化腐植酸(BHA)，考察固液比(糠醛渣與水的質(zhì)量比)、堿液濃度、提取溫度、提取時間對生化腐植酸含量的影響，并且通過紅外光譜對其結(jié)構(gòu)進行了表征。［結(jié)果］最佳的提取工藝條件為∶固液比1∶7、堿液濃度6%KOH、提取時間1 h、提取溫度70℃，此時生化腐植酸含量為8.5%。紅外光譜分析表明，提取得到的生化腐植酸和商品腐植酸結(jié)構(gòu)相似，但BHA官能團種類較多，分子量較小。［結(jié)論］該工藝生產(chǎn)操作簡單，穩(wěn)定可行，可用于提取生化腐植酸。利用BHA開發(fā)制備腐植酸類新型肥料有很好的發(fā)展前景。

發(fā)酵糠醛渣；生化腐植酸；提??；紅外光譜less,even harmful to the products. Because sodium is not a nutritional element for crops,continuous longterm accumulation of sodium in soil would bring negative effects on soil environment.

張院萍(1984-)，女，寧夏銀川人，工程師，從事腐植酸提取及腐植酸系列肥料技術(shù)研發(fā)工作，E-mail：zhangyuanping31045 @163.com。*通訊作者。

2015-04-03

修回日期 2015-05-18

*Corresponding author.E-mail:zhangyuanping31045@163.com

Received:April 3,2015 Accepted:May 18,2015