Characterization of fractionated dissolved organic matter in industrial estate wastewater using spectrofluorometry and pyrolysis GC/MS analysis

Abstract

The aims of this research were to investigate the dissolved organic carbon (DOC) mass distribution, trihalomethane formation potential (THMFP) and specific THMFP of dissolved organic matter (DOM) fractions in industrial estate wastewater and effluent water from the aeration, facultative, oxidation and detention ponds of the central wastewater treatment plant of the Northern-Region Industrial Estate, Lamphun province, Thailand. Pyrolysis gas chromatography mass spectrometer and three-dimensional fluorescent spectroscopy (fluorescent excitation-emission matrix, FEEM) analysis were utilized on the DOM fractions of all water samples to identify the fluorescent organic matter and chemical classes, respectively. Industrial estate wastewater and treated effluent from each pond were collected from June 2004 to July 2005. The resin fractionation technique, used with three different types of resins (i.e. DAX-8, AG-MP-50 and WA-10), was employed to characterize the DOC in all water samples into six fractions, namely hydrophobic neutral (HPON), hydrophobic base (HPOB), hydrophobic acid (HPOA), hydrophilic base (HPIB), hydrophilic acid (HPIA), and hydrophilic neutral (HPIN). The results showed that HPOA and HPIN were the major DOM fractions in the industrial estate wastewater and aeration pond effluent; summations of HPOA and HPIN were more than 50%. However, HPOA and HPIA were the dominant DOM fractions in the effluent from the facultative, oxidation, and detention ponds; summations of HPOA and HPIA were more than 50%. THMFPHPOA and THMFPHPIA were found in the largest quantities when compared with the THMFP of others species. In addition, the specific THMFPs of HPOA and HPIA were considerably high. The aliphatic hydrocarbon class (approx. 70%) was dominant in the industrial estate wastewater and in the treated effluent from each pond (25-58%). Aromatic hydrocarbon (20-55%) and ester (5-21%) were the major chemical classes of HPON; whereas carboxylic acid (27-75%) was the major chemical class of HPOB. Aliphatic (17-42%) and aromatic hydrocarbons (26-41%) were classified as the major chemical classes of HPOA. In the case of the hydrophilic organic (HPI) fraction, aliphatic hydrocarbon (45-71%) was identified as the major chemical class in HPIB, HPIA, and HPIN. Trihalomethanes could be easily associated with hydrophobic organic (HPO) fractions that are mainly composed of the aromatic hydrocarbon, carboxylic acids, phenol and ester classes, along with the aliphatic hydrocarbon class (C5≤ aliphatic hydrocarbon fragments ≤ C11). The aliphatic hydrocarbon (C18 ≤ aliphatic hydrocarbon fragments ≤ C24) and organic nitrogen classes (mainly composed of aliphatic organic nitrogen fragments), when combined with chlorine could be inactive and fail to form THMs. With regard to the FEEM results, tyrosine-like and tryptophan-like substances were classified as major fluorescent organic matter in HPON. For HPOA, tyrosine-like and humic and fulvic acids-like substances were the major fluorescent organic matter. In the HPI fractions, tyrosine-like and humic and fulvic acids-like substances were the dominant fluorescent organic matter of HPIB, HPIA, and HPIN. With regard to DOM reductions, the aeration and facultative ponds were the main processes that reduced HPON, HPIN, and HPIB. Only the aeration ponds reduced HPOA and HPIA, however, only moderately. In total, the aeration + facultative + oxidation ponds] reduced HPON, HPIN, HPIB, HPOA, and HPIA by 73%, 46%, 60%, 18%, and 11%, respectively.