不同壳聚糖改性黏土对小球藻的絮凝效应及絮凝条件优选
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摘要
微藻个体微小,不易采收,为其开发利用带来了很大困难。利用酸性壳聚糖对3种不同类型的黏土矿物(膨润土、硅藻土、沸石)进行改性,制备无公害复合絮凝剂,探究其对小球藻(C.pyrenoidosa)的絮凝效果,并考察了复合絮凝剂的浓度、静置时间、藻液p H值和壳聚糖与黏土矿物的比例对絮凝率的影响。结果表明:复合絮凝剂的絮凝效果明显高于壳聚糖。其中壳聚糖改性硅藻土对小球藻的絮凝效果最佳,其最佳絮凝条件为p H值为8,壳聚糖和硅藻土的配比为1∶6,浓度为0.2 g/L,沉降120 min。在该条件下,小球藻的絮凝采收率可达到约96.16%。复合絮凝剂无毒环保,不会造成二次污染影响微藻生物质后续加工利用,是一种环境友好,安全健康的微藻絮凝剂,具有良好的应用前景。
The harvest of algal cells is difficult since the algal biomass density is usually less than 1 g/L and the cells have a small size(3-30 μm). At present, harvesting of microalgal is done with widely used techniques including coagulation–flocculation and sedimentation. Metal salts and macromolecule polymers(polyferric chloride and polyaluminum chloride) are common chemical flocculants for harvesting microalgae, but these metallic compounds may cause pollution. Therefore, it is necessary to develop efficient and non-polluting flocculants. Chitosan is a kind of non-toxic biodegradable polymer with good adsorption properties and important functions including electrical neutralization, bridging, and netting. At present, chitosan has been extensively used as effective flocculant, fungicide and ion exchanger for water treatment. It is widely used in food, agricultural, pharmaceutical, and chemical industries. Chitosan can be used as an environment-friendly, healthy, and safe flocculant for microalgae. However, chitosan is only soluble in acids, thus limiting its application in the flocculation process. Therefore, it is necessary to modify chitosan or adopt a composite material of chitosan with inorganic materials for the purpose of harvesting algae. Inorganic materials like metal salts may cause pollution. Clay minerals, cheap and conveniently available natural pollution-free materials, have been applied for algal flocculation. This study aims to develop non-toxic and efficient flocculant for harvesting microalgae. Three different types of clay minerals, i.e. bentonite, diatomite and zeolite, were modified with acidic chitosan to prepare 3 new types of composite flocculants, named CMD, CMB and CMZ, respectively. The flocculation efficiency(FE) was compared by flocculant concentrations, sedimentation time, pH values and the ratio of chitosan to clay minerals. The results indicated that the FE of modified flocculants was all obviously higher than chitosan for harvesting Chlorella pyrenoidosa. Among them, CMD flocculant had the best FE(95%) with a flocculant dosage of 0.2 g/L. Chitosan can change the surface electrical properties of diatomite in a way that the surface of diatomite becomes positively charged. The surfaces of microalgae are often negatively charged. This way has caused the FE of C. pyrenoidosa to be greatly improved. Moreover, the FE reaches the maximum of 93% with the ratios of 1:6(chitosan:diatomite). When the ratio was changed to 1:14, the FE decreased by 10% because excessive diatomite was not mixed with chitosan. The best FE of C. pyrenoidosa was 94% at pH value of 8 and 91% at pH value of 9 with a dosage of 0.2 g CMD after 120 min sedimentation. The FE was about 28% higher than the values at pH value of 4 or 6. When the pH value was increased to 11, the FE was decreased by 17%. Therefore, the optimum pH value for the flocculation of C. pyrenoidosa was set as 8. In a word, the best FE reached 96.16% under the CMD flocculant dosage of 0.2 g/L and the pH value of 8 after 120 min sedimentation. In this study, the raw materials are non-toxic and without secondary separation for harvesting algae from water, which can be further utilized or processed for wide application.
The harvest of algal cells is difficult since the algal biomass density is usually less than 1 g/L and the cells have a small size(3-30 μm). At present, harvesting of microalgal is done with widely used techniques including coagulation–flocculation and sedimentation. Metal salts and macromolecule polymers(polyferric chloride and polyaluminum chloride) are common chemical flocculants for harvesting microalgae, but these metallic compounds may cause pollution. Therefore, it is necessary to develop efficient and non-polluting flocculants. Chitosan is a kind of non-toxic biodegradable polymer with good adsorption properties and important functions including electrical neutralization, bridging, and netting. At present, chitosan has been extensively used as effective flocculant, fungicide and ion exchanger for water treatment. It is widely used in food, agricultural, pharmaceutical, and chemical industries. Chitosan can be used as an environment-friendly, healthy, and safe flocculant for microalgae. However, chitosan is only soluble in acids, thus limiting its application in the flocculation process. Therefore, it is necessary to modify chitosan or adopt a composite material of chitosan with inorganic materials for the purpose of harvesting algae. Inorganic materials like metal salts may cause pollution. Clay minerals, cheap and conveniently available natural pollution-free materials, have been applied for algal flocculation. This study aims to develop non-toxic and efficient flocculant for harvesting microalgae. Three different types of clay minerals, i.e. bentonite, diatomite and zeolite, were modified with acidic chitosan to prepare 3 new types of composite flocculants, named CMD, CMB and CMZ, respectively. The flocculation efficiency(FE) was compared by flocculant concentrations, sedimentation time, pH values and the ratio of chitosan to clay minerals. The results indicated that the FE of modified flocculants was all obviously higher than chitosan for harvesting Chlorella pyrenoidosa. Among them, CMD flocculant had the best FE(95%) with a flocculant dosage of 0.2 g/L. Chitosan can change the surface electrical properties of diatomite in a way that the surface of diatomite becomes positively charged. The surfaces of microalgae are often negatively charged. This way has caused the FE of C. pyrenoidosa to be greatly improved. Moreover, the FE reaches the maximum of 93% with the ratios of 1:6(chitosan:diatomite). When the ratio was changed to 1:14, the FE decreased by 10% because excessive diatomite was not mixed with chitosan. The best FE of C. pyrenoidosa was 94% at pH value of 8 and 91% at pH value of 9 with a dosage of 0.2 g CMD after 120 min sedimentation. The FE was about 28% higher than the values at pH value of 4 or 6. When the pH value was increased to 11, the FE was decreased by 17%. Therefore, the optimum pH value for the flocculation of C. pyrenoidosa was set as 8. In a word, the best FE reached 96.16% under the CMD flocculant dosage of 0.2 g/L and the pH value of 8 after 120 min sedimentation. In this study, the raw materials are non-toxic and without secondary separation for harvesting algae from water, which can be further utilized or processed for wide application.
引文
[1]霍书豪,陈玉碧,刘宇鹏,等.添加沼液的BG11营养液微藻培养试验[J].农业工程学报,2012,28(8):241-246.Huo Shuhao,Chen Yubi,Liu Yupeng,et al.Experiment on microalgae cultivation in BG11 nutrient solution adding biogas slurry[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2012,28(8):241-246.(in Chinese with English abstract)
[2]孔维宝,李龙囡,张继,等.小球藻的营养保健功能及其在食品工业中的应用[J].食品科学,2010,31(9):323-328.Kong Weibao,Li Longnan,Zhang Ji,et al.Healthcare functions and applications in food industry of Chlorella[J].Food Science,2010,31(9):323-328.(in Chinese with English abstract)
[3]马志欣,尚春琼,胡小丽,等.微藻絮凝采收的研究进展[J].基因组学与应用生物学,2016,35(4):942-948.Ma Zhixin,Shang Chunqiong,Hu Xiaoli,et al.Research progresses on microalgae harvesting by flocculation[J].Genomics and Applied Biology,2016,35(4):942-948.(in Chinese with English abstract)
[4]Divakaran R,Pillai V N.Flocculation of river silt using chitosan[J].Water Research,2002,36(9):2414-2418.
[5]Huang C,Chen S,Pan J R.Optimal condition for modification of chitosan:A biopolymer for coagulation of colloidal particles[J].Water Research,2000,34(3):1057-1062.
[6]Jean R,Maurice V V,Eric G.Chitosan for the coagulation and flocculation of mineral colloids[J].Journal of Dispersion Science&Technology,2005,25(5):663-677.
[7]Fernández M,Fox P F.Fractionation of cheese nitrogen using chitosan[J].Food Chemistry,1997,58(4):319-322.
[8]Hwang D C,Damodaran S.Selective precipitation and removal of lipids from cheese whey using chitosan[J].Journal of Agricultural&Food Chemistry,1995,43(1):33-37.
[9]Knorr D.Use of chitinous polymers in food:A challenge for food research and development[J].Food Technology,1984,38(1):85-97.
[10]彭超,苏会波,熊强,等.絮凝剂对雨生红球藻采收的影响[J].生物加工过程,2017,15(2):1-6.Peng Chao,Su Huibo,Xiong Qiang,et al.Effects of flocculants on recovery of Haematococcus pluvialis[J].Nutrition and Health Research Institute,2017,15(2):1-6.(in Chinese with English abstract)
[11]Zhou W,Gao L,Cheng W,et al.Electro-flotation of Chlorella sp.assisted with flocculation by chitosan[J].Algal Research,2016,18:7-14.
[12]钱宝钢,黄力群,冯波,等.枯草芽孢杆菌产絮凝剂的发酵条件及絮凝特性研究[J].水处理技术,2011,37(8):26-30.Qian Baogang,Huang Liqun,Feng Bo,et al.Study on fermentation conditions and flocculation characteristics of bacillus subtilis flocculant[J].Technology of Water Treatment,2011,37(8):26-30.(in Chinese with English abstract)
[13]蒋茜茜,张小凤,陈文清,等.壳聚糖改性黏土絮凝去除水中铜绿微囊藻[J].四川化工,2017,20(1):54-58.Jiang Qianqian,Zhang Xiaofeng,Chen Wenqing,et al.Chitosan modified clays flocculate removing microcystis aeruginosa in water[J].Sichuan Chemical Industry,2017,20(1):54-58.(in Chinese with English abstract)
[14]王洪亮.颗粒物对藻华生物的絮凝作用及其分形数值模拟研究[D].青岛:中国科学院(海洋研究所),2010.Wang Hongliang,Study on the Flocculation of HABOrganisms by Particles and Its Fractal Numerical Simulation[D].Qingdao:Chinese Academy of Sciences(Institute of Oceanology),2010.(in Chinese with English abstract)
[15]Guenther M,Bozelli M.Factors influencing algae-clay aggregation[J].Hydrobiologia,2004,523(1/2/3):217-223.
[16]Pierce R H,Henry M S,Higham C J,et al.Removal of harmful algal cells(Karenia brevis)and toxins from seawater culture by clay flocculation[J].Harmful Algae,2004,3(2):141-148.
[17]侯伟,孙韶华,陈求稳,等.黏土改性技术用于絮凝除藻的研究进展[J].生态科学,2014,33(6):12-18.Hou Wei,Sun Shaohua,Chen Qiuwen,et al.Research progress of modified clay flocculating harmful algae[J].Ecological Science,2014,33(6):12-18.(in Chinese with English abstract)
[18]潘君廷,马俊怡,郜天磊,等.膨润土改善鸡粪厌氧消化产酸产甲烷特性[J].农业工程学报,2016,32(8):246-252.Pan Junting,Ma Junyi,Gao Tianlei,et al.Improving production characteristics of methane and organic acid during anaerobic batch digestion of poultry manure by adding bentonite[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2016,32(8):246-252.(in Chinese with English abstract)
[19]卢光远.改性黏土治理藻华对主要营养元素循环及藻毒素的影响[D].青岛:中国科学院(海洋研究所),2014.Lu Guangyuan.Effects of HABs Mitigation by Modified Clay on Major Nutrient Cyclings and Algal Toxins[D].Qingdao:Chinese Academy of Sciences(Institute of Oceanology),2014.(in Chinese with English abstract)
[20]Wu Z C,Zhu Y,Huang W Y,et al.Evaluation of flocculation induced by p H increase for harvesting microalgae and reuse of flocculated medium[J].Bioresource Technology,2012,110(2):496-502.
[21]Ahmad A L,Yasin N H M,Derek C J C,et al.Optimization of microalgae coagulation process using chitosan[J].Chemical Engineering Journal,2011,173(3):879-882.
[22]Dong C,Chen W,Liu C.Flocculation of algal cells by amphoteric chitosan-based flocculant[J].Bioresource Technology,2014,170(5):239-247.
[23]吴春笃,侯纯莉,杨峰,等.海泡石、膨润土改性壳聚糖对景观水絮凝效果的研究[J].生态环境学报,2008,17(1):50-54.Wu Chundu,Hou Chunli,Yang Feng,et al.Flocculation effect of sepiolite and bentonite modified chitosan on landscape water[J].Ecology and Environment,2008,17(1):50-54.(in Chinese with English abstract)
[24]杜胜蓝,刘文杰,臧常娟.壳聚糖-沸石复合体对铜绿微囊藻的去除效果[J].水资源保护,2013(4):87-90.Du Shenglan,Liu Wenjie,Zang Changjuan.Removal of microcystis aeruginosa by chitosan-zeolite composite[J].Water Resources Protection,2013(4):87-90.(in Chinese with English abstract)
[25]李凯,刘汉湖,周子森.壳聚糖-海泡石复合黏土去除铜绿微囊藻的试验研究[J].供水技术,2017,11(2):11-15.Li Kai,Liu Hanhu,Zhou Zisen.Removal of microcystis aeruginosa by chitosan-sepiolite composite[J].Water Technology,2017,11(2):11-15.(in Chinese with English abstract)
[26]黄斌,余国忠,栗印环.沸石去除铜绿微囊藻的试验研究[J].信阳师范学院学报(自然科学版),2004,17(4):433-436.Huang Bin,Yu Guozhong,Li Yinhuan.Removing of microcystis aeruginosa by use of zeolite powder[J].Journal of Xinyang Normal University(Natural Science Edition),2004,17(4):433-436.(in Chinese with English abstract)
[27]刘恋,陈兵,王志红.壳聚糖改性黏土对高藻水中藻类的絮凝去除[J].环境工程学报,2010(6):1296-1300.Liu Lian,Chen Bin,Wang Zhihong.Flocculation and removal of algae in algae-bloom water by chitosanmodified clays[J].Chinese Journal of Environmental Engineering,2010(6):1296-1300.(in Chinese with English abstract)
[28]Strand S P,Nordengen T,Ostgaard K.Efficiency of chitosans applied for flocculation of different bacteria[J].Water Research,2002,36(19):4745-4752.
[29]Pan J R,Huang C,Chen S,et al.Evaluation of a modified chitosan biopolymer for coagulation of colloidal particles[J].Colloids&Surfaces A Physicochemical&Engineering Aspects,1999,147(3):359-364.
[30]Kubota N,Tatsumoto N,Sano T,et al.A simple preparation of half N-acetylated chitosan highly soluble in water and aqueous organic solvents[J].Carbohydrate Research,2000,324(4):268-274.
[2]孔维宝,李龙囡,张继,等.小球藻的营养保健功能及其在食品工业中的应用[J].食品科学,2010,31(9):323-328.Kong Weibao,Li Longnan,Zhang Ji,et al.Healthcare functions and applications in food industry of Chlorella[J].Food Science,2010,31(9):323-328.(in Chinese with English abstract)
[3]马志欣,尚春琼,胡小丽,等.微藻絮凝采收的研究进展[J].基因组学与应用生物学,2016,35(4):942-948.Ma Zhixin,Shang Chunqiong,Hu Xiaoli,et al.Research progresses on microalgae harvesting by flocculation[J].Genomics and Applied Biology,2016,35(4):942-948.(in Chinese with English abstract)
[4]Divakaran R,Pillai V N.Flocculation of river silt using chitosan[J].Water Research,2002,36(9):2414-2418.
[5]Huang C,Chen S,Pan J R.Optimal condition for modification of chitosan:A biopolymer for coagulation of colloidal particles[J].Water Research,2000,34(3):1057-1062.
[6]Jean R,Maurice V V,Eric G.Chitosan for the coagulation and flocculation of mineral colloids[J].Journal of Dispersion Science&Technology,2005,25(5):663-677.
[7]Fernández M,Fox P F.Fractionation of cheese nitrogen using chitosan[J].Food Chemistry,1997,58(4):319-322.
[8]Hwang D C,Damodaran S.Selective precipitation and removal of lipids from cheese whey using chitosan[J].Journal of Agricultural&Food Chemistry,1995,43(1):33-37.
[9]Knorr D.Use of chitinous polymers in food:A challenge for food research and development[J].Food Technology,1984,38(1):85-97.
[10]彭超,苏会波,熊强,等.絮凝剂对雨生红球藻采收的影响[J].生物加工过程,2017,15(2):1-6.Peng Chao,Su Huibo,Xiong Qiang,et al.Effects of flocculants on recovery of Haematococcus pluvialis[J].Nutrition and Health Research Institute,2017,15(2):1-6.(in Chinese with English abstract)
[11]Zhou W,Gao L,Cheng W,et al.Electro-flotation of Chlorella sp.assisted with flocculation by chitosan[J].Algal Research,2016,18:7-14.
[12]钱宝钢,黄力群,冯波,等.枯草芽孢杆菌产絮凝剂的发酵条件及絮凝特性研究[J].水处理技术,2011,37(8):26-30.Qian Baogang,Huang Liqun,Feng Bo,et al.Study on fermentation conditions and flocculation characteristics of bacillus subtilis flocculant[J].Technology of Water Treatment,2011,37(8):26-30.(in Chinese with English abstract)
[13]蒋茜茜,张小凤,陈文清,等.壳聚糖改性黏土絮凝去除水中铜绿微囊藻[J].四川化工,2017,20(1):54-58.Jiang Qianqian,Zhang Xiaofeng,Chen Wenqing,et al.Chitosan modified clays flocculate removing microcystis aeruginosa in water[J].Sichuan Chemical Industry,2017,20(1):54-58.(in Chinese with English abstract)
[14]王洪亮.颗粒物对藻华生物的絮凝作用及其分形数值模拟研究[D].青岛:中国科学院(海洋研究所),2010.Wang Hongliang,Study on the Flocculation of HABOrganisms by Particles and Its Fractal Numerical Simulation[D].Qingdao:Chinese Academy of Sciences(Institute of Oceanology),2010.(in Chinese with English abstract)
[15]Guenther M,Bozelli M.Factors influencing algae-clay aggregation[J].Hydrobiologia,2004,523(1/2/3):217-223.
[16]Pierce R H,Henry M S,Higham C J,et al.Removal of harmful algal cells(Karenia brevis)and toxins from seawater culture by clay flocculation[J].Harmful Algae,2004,3(2):141-148.
[17]侯伟,孙韶华,陈求稳,等.黏土改性技术用于絮凝除藻的研究进展[J].生态科学,2014,33(6):12-18.Hou Wei,Sun Shaohua,Chen Qiuwen,et al.Research progress of modified clay flocculating harmful algae[J].Ecological Science,2014,33(6):12-18.(in Chinese with English abstract)
[18]潘君廷,马俊怡,郜天磊,等.膨润土改善鸡粪厌氧消化产酸产甲烷特性[J].农业工程学报,2016,32(8):246-252.Pan Junting,Ma Junyi,Gao Tianlei,et al.Improving production characteristics of methane and organic acid during anaerobic batch digestion of poultry manure by adding bentonite[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2016,32(8):246-252.(in Chinese with English abstract)
[19]卢光远.改性黏土治理藻华对主要营养元素循环及藻毒素的影响[D].青岛:中国科学院(海洋研究所),2014.Lu Guangyuan.Effects of HABs Mitigation by Modified Clay on Major Nutrient Cyclings and Algal Toxins[D].Qingdao:Chinese Academy of Sciences(Institute of Oceanology),2014.(in Chinese with English abstract)
[20]Wu Z C,Zhu Y,Huang W Y,et al.Evaluation of flocculation induced by p H increase for harvesting microalgae and reuse of flocculated medium[J].Bioresource Technology,2012,110(2):496-502.
[21]Ahmad A L,Yasin N H M,Derek C J C,et al.Optimization of microalgae coagulation process using chitosan[J].Chemical Engineering Journal,2011,173(3):879-882.
[22]Dong C,Chen W,Liu C.Flocculation of algal cells by amphoteric chitosan-based flocculant[J].Bioresource Technology,2014,170(5):239-247.
[23]吴春笃,侯纯莉,杨峰,等.海泡石、膨润土改性壳聚糖对景观水絮凝效果的研究[J].生态环境学报,2008,17(1):50-54.Wu Chundu,Hou Chunli,Yang Feng,et al.Flocculation effect of sepiolite and bentonite modified chitosan on landscape water[J].Ecology and Environment,2008,17(1):50-54.(in Chinese with English abstract)
[24]杜胜蓝,刘文杰,臧常娟.壳聚糖-沸石复合体对铜绿微囊藻的去除效果[J].水资源保护,2013(4):87-90.Du Shenglan,Liu Wenjie,Zang Changjuan.Removal of microcystis aeruginosa by chitosan-zeolite composite[J].Water Resources Protection,2013(4):87-90.(in Chinese with English abstract)
[25]李凯,刘汉湖,周子森.壳聚糖-海泡石复合黏土去除铜绿微囊藻的试验研究[J].供水技术,2017,11(2):11-15.Li Kai,Liu Hanhu,Zhou Zisen.Removal of microcystis aeruginosa by chitosan-sepiolite composite[J].Water Technology,2017,11(2):11-15.(in Chinese with English abstract)
[26]黄斌,余国忠,栗印环.沸石去除铜绿微囊藻的试验研究[J].信阳师范学院学报(自然科学版),2004,17(4):433-436.Huang Bin,Yu Guozhong,Li Yinhuan.Removing of microcystis aeruginosa by use of zeolite powder[J].Journal of Xinyang Normal University(Natural Science Edition),2004,17(4):433-436.(in Chinese with English abstract)
[27]刘恋,陈兵,王志红.壳聚糖改性黏土对高藻水中藻类的絮凝去除[J].环境工程学报,2010(6):1296-1300.Liu Lian,Chen Bin,Wang Zhihong.Flocculation and removal of algae in algae-bloom water by chitosanmodified clays[J].Chinese Journal of Environmental Engineering,2010(6):1296-1300.(in Chinese with English abstract)
[28]Strand S P,Nordengen T,Ostgaard K.Efficiency of chitosans applied for flocculation of different bacteria[J].Water Research,2002,36(19):4745-4752.
[29]Pan J R,Huang C,Chen S,et al.Evaluation of a modified chitosan biopolymer for coagulation of colloidal particles[J].Colloids&Surfaces A Physicochemical&Engineering Aspects,1999,147(3):359-364.
[30]Kubota N,Tatsumoto N,Sano T,et al.A simple preparation of half N-acetylated chitosan highly soluble in water and aqueous organic solvents[J].Carbohydrate Research,2000,324(4):268-274.