Fluoride Removal from Antarctic Krill (Euphausia superba) By Donnan Dialysis

Fluoride removal from Antarctic Krill (Euphausia superba) by Donnan Dialysis

 

Guojia Yan^1,2, Yan Bao¹, Xiaolan Lu², Ming Tan^1*, Yang Zhang^1* 

 

¹Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, 189 Songling Road, Laoshan District, Qingdao 266101, PR China

²Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, PR China

*Corresponding author: tanming@qibebt.ac.cn (Ming Tan); zhangyang@qibebt.ac.cn (Yang Zhang)

Abstract:

Antarctic krill (Euphausia superba) has abundant species in the Southern Ocean which makes krill an alternative protein source for humans as well as rich fishery resource [1]. However, a high fluorine levels in Antarctic krill have attracted attention which is the reason why krill has not been widely used commercially. The total fluoride concentration in the exoskeleton of krill is 3828-4278 mg kg⁻¹ dry weight (DW), 178-285 mg kg⁻¹DW in muscle, and 1102-1432 mg kg⁻¹DW in whole krill [2]. Thus, fluoride should be removed and those expenses adversely affected the economics of krill exploitation. [3]

Donnan dialysis (DD) is a potentially attractive membrane-based equilibrium process for removing undesirable ions from solution [4]. Compared to other popular methods, a low purity of treated water is a serious problem by absorption [5]. Electrodialysis [6] may have high kinetics compared to DD, it has some disadvantages which is great strength of DD, i.e. economical, energy saving and need simple technology, etc. [4]

The effect of NaCl concentration (0.1, 0.5,1 and 2mol/L) on receiver cell, experiment stage (1^st, 2^nd and 3^rd) and flow velocity (0.01 and 0.03cm/s) were investigated by synthetic solution (43mg/L NaF and 4.15g/L NaCl) firstly. The results show that fluoride was removed 65% at first stage which is the most removal rate when receiver concentration was 1 mol/L. Higher receiver concentration provided higher driven force for chloride to pass through anion exchange membrane which is good for defluorine. However, higher receiver concentration also increased the percentage of other ion, such as sodium which may explain 1mol/L result is better than 2mol/L. Furthermore, flow velocity 0.01 cm/s offered high removal efficiency than 0.03cm/s at 65% and 62% respectively. More time for fluoride to be exchanged into receiver chamber at 0.01cm/s. When concentration and flow velocity were both optimized, three stages were investigated at 1 mol/L. The results were 65%, 85% and 93.6% at 1^st , 2^nd and 3^rd stage separately as displayed by Fig. 1.

After that, krill solution was operated by optimum parameters, leakage of protein and amino acids were investigated at the same time. Due to complex impurity characteristic of krill solution, the absence of other ion leakage cut down the removal rate. Nevertheless, fluoride removal by DD maintained more protein than absorption as well as higher purity of treated water.

Figure:

Fig.1 The effect of experimental stage at 1 mol/L receiver concentration.

References:

[1].   Xie, C.L., et al., Organic Acid Extraction of Fluoride from Antarctic Krill Euphausia superba. Fisheries and aquatic sciences, 2012. 15(3): p. 203-207.

[2].   Adelung, D., et al., Fluoride in tissues of krill Euphausia superba Dana and Meganyctiphanes norvegica M. Sars in relation to the moult cycle. Polar Biol 7:43-50. Polar Biology, 1986. 7(1): p. 43-50.

[3].   Schmidt, K. and A. Atkinson, Feeding and Food Processing in Antarctic Krill ( Euphausia superba  Dana). 2016: Springer International Publishing.

[4].   Ktari, T., C. Larchet and B. Auclair, Mass transfer characterization in Donnan dialysis. Journal of Membrane Science, 1993. 84(1-2): p. 53-60.

[5].   Engelo Lu, Y., E. K R and M. Ers Z, Removal of fluoride from aqueous solution by using red mud. Separation and Purification Technology, 2002. 28(1): p. 81-86.

[6].   Arahman, N., et al., The removal of fluoride from water based on applied current and membrane types in electrodialyis. Journal of Fluorine Chemistry, 2016. 191: p. 97-102.