Interaction between Natural Organic Matter (NOM) Fractions and Nano-Zero Valent Iron(NZVI)

จาก ChulaPedia

Interaction between Natural Organic Matter (NOM) Fractions and Nano-Zero Valent Iron (NZVI)

Katika Intarasuwan1,2; Eakalak Khan3; and Thunyalux Ratpukdi4

1International Postgraduate Program in Environmental Management, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand 2Center of Excellence on Hazardous Substance Management (HSM), Bangkok 10330, Thailand 3Department of Civil and Environmental Engineering, North Dakota State University, Dept. # 2470, P.O. Box 6050,Fargo, North Dakota 58108-6050, USA. 4Department of Environmental Engineering, Faculty of Engineering, Khon Kaen University, Khon Kaen 40002, Thailand. (Corresponding author) E-mail: thunyalux@kku.ac.th

Nanoscale zero valent iron (NZVI) is a novel technology for site remediation according to its high efficiency on degradation or removal pollutants in groundwater. It is easy to operate and can be applied for in situ site remediation. Many researchers have investigated the application of the NZVI for contaminants removal such as arsenic, nitrate, and metolachlor. In groundwater, the presence of natural organic matter (NOM) which is major organic constituent could affect the contaminant removal by NZVI. NOM is a mixture of organic compound derived from the decomposition of living organisms; for example, animals, and plants. NOM could be classified into two main fractions based on polarity as hydrophobic, and hydrophilic. Moreover, subfraction can be divided into 3 fractions based on charge as acid, base and neutral. To study an effect of each kind of NOM, NOM surrogates (model compounds) could be used as representative of each NOM fraction. Through many years, the effects of NOM onto NZVI, and modified NZVI have been studied. However, there still have the controversies about inhibition or enhancement of NOM to NZVI reactivity according to various conditions in groundwater. Most research was studied only humic Acid (HA) and Suwannee River NOM. This is because they were investigated extensively by other researchers in area of water treatment. Some previous studies showed that the NZVI or modified NZVI reactivity onto contaminant removal was inhibited in the presence of humic acid (HA) while some studies indicated that some ranges of HA concentration also promoted the contaminant reduction.

Although the previous studies described the research on humic acid influenced onto NZVI reactivity for pollutants degradation, there still lack of knowledge about other NOM fractions. This study investigated the interaction of each type of NOM fraction including hydrophobic acid (HPOA), hydrophobic base (HPOB), hydrophobic neutral (HPON), hydrophilic acid (HPIA), hydrophilic base (HPIB), and hydrophilic neutral (HPIN) with NZVI. Kinetic study of NOM fraction and NZVI, and adsorption isotherm was performed using several model compounds representing individual NOM fraction. The results show that Humic acid (HPOA) has the highest interaction with NZVI base on disappearance of dissolved organic carbon (DOC) with time. This might be due to adsorption of NOM onto NZVI surface. However, the DOC results of other NOM surrogates ((L-tryptophan, HPON, (Aniline, HPOB), (Oxalic acid, HPIA), (L-asparagine, HPIB), (D-xylose, HPIN)) were relatively stable with time. Adsorption isotherm experiments were conducted for HPOA and HPIA fractions. Langmuir isotherms fitted with both fractions. This indicates that interaction between HPOA and HPIA fractions with NZVI to be monolayer adsorption on specific sites. Moreover, the interaction between fractionated NOM fractions from two sources including groundwater (GWNOM), Khon Kaen, Thailand and Suwannee River NOM (SRNOM), USA. with NZVI and also between bulk NOMs and NZVI. The NOM fractions were isolated by a novel solid-phase extraction technique. The results showed that at low pH (pH5) both GWNOM and SRNOM had more interaction than other pHs. HPOA of GWNOM had the highest adsorption capacity (qe) of 6.95 mg/g while HPIN yielded the lowest qe (1.42 mg/g) at pH 5. For SRNOM, HPIA had the highest qe of 18.66 mg/g at pH 5 whereas the lowest qe of 1.45 mg/g was obtained from HPIN at pH 7. For competition study from GWNOM bulk found that HPOA competed with HPON whereas the amount of HPOA was still the highest for SRNOM. This work illustrated NOM components difference which reacted with NZVI could show the different interactions. This may lead to the method how to apply NZVI for groundwater treatment.

Keywords: Dissolved organic matter; Natural organic matter; Groundwater; Suwannee River; Fractionation; Nano-zero valent iron