Date of Award

2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. munjed Maraqa

Second Advisor

R.L. Droste

Third Advisor

Dr. Mohamed Abdul Kareem

Abstract

Phenols are present in discharge effluents of many heavy industries such as refineries. They are regulated and monitored by environmental authorities. Emirates National Oil Company (ENOC) processes condensate oil and produces wastewater that is treated at the ENOC Processing Company's (EPCL-refinery) wastewater treatment plant (ETP) through the use of physical, chemical and biological treatment processes. This study provides an in-depth description of the unit processes employed to treat the different waste streams generated at the EPCL refinery and identifies the different types of phenols which are formulated in the processes. Characterization of phenol level at EPCL-ETP and assessment of the effectiveness of employed pollution control technologies in reducing phenol level at the treatment plant have been conducted in this study. In addition, the study explores the potential correlation between phenol level and other water quality parameters in the treated wastewater.

A thorough review of the adverse effects of phenols on the receiving environment has been provided in this study. It is well documented that phenol and its derivatives pose a danger to humans and marine life in their varying toxicities. Such toxicity depends on the solubility and persistence of the phenolic compounds in the system. The literature reveals that the sources and formation of phenol and its derivatives are based on many complex reactions.

It was found that the main sources of phenol in the received waste streams at ENOC-ETP are the crude oil tank wastewater drain (average 65.34 mg/l), the desalter effluent (average 0.95 mg/l) and the neutralized spent caustic (average 180 mg/l) waste streams. However, there are large fluctuations from the average phenol level within each waste stream. Also, the level of phenol and its derivatives in these streams vary significantly with phenol, m-p-cresols, o-cresol, tri and tetra-chlorophenols and to a lesser extent 4-chloro-3-cresol are common among these streams. Based on the average concentration from samples collected during this study and based on the average production of these streams, typical phenol loadings from tank wastewater drain, neutralized spent caustic and desalter wastewaters are 69.3 kg, 1497.8 kg and 131.5 kg per year, respectively. Other waste streams have been tested for phenol, but the contribution of the other waste streams to phenol loading was found to be insignificant due either to the low flow rate or low phenol levels in the stream.

The processes employed in the treatment plant vary from a semi-continuous flow process (i.e. CPI, IGF) to a completely mixed batch reactor followed by continuous flow packed bed reactors. The study shows variations in water quality parameters at early stages of treatment but the waste stream is homogenized in the SBR and a more or less uniform treated waste stream enters the sand filter and the carbon bed.

The effluent in the wastewater treatment plant, basic odour, colour and clarity improves significantly through the stages of treatment. The study further showed that the most effective process employed in the reduction of phenols within the plant is the Sequencing Batch Reactors (SBR). This is also true for the organic loading which is reduced mainly by the SBR and to a lesser extent by the carbon reactor. The reduction of sulphides, like phenols, is almost entirely dependant on the performance of the SBR units.

Based on the analysis of five years (2000-2004) of daily data, it was found that the correlation between phenol level in the discharged treated effluent and levels of COD, BOD5 and sulphides are weak although statistically significant in most cases. The relationship between BOD5 and COD in the final effluent has been established with a ratio (COD:BOD5) of 1.6 to 1 and an average non-degradable COD of about 55 mg/l. However, the relationship is again weak due to the scatter of the data as reflected by the low value of the coefficient of determination.

Recommendations are given mainly focusing on conducting further studies, such as characterization of waste streams at different condensate oil refineries, ETP performance, and process optimization. In addition, further investigation is needed to optimize SBR operations by characterizing and enriching microorganisms that specifically degrade phenol. It is also recommended to study the ETP performance on removal of other aromatic hydrocarbons.

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