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Evaluation of a Sequencing Batch Reactor Followed by Media Filtration for Organic and Nutrient Removal from Produced Water

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Evaluation of a Sequencing Batch Reactor Followed by Media Filtration for Organic and Nutrient Removal from Produced Water EVALUATION OF A SEQUENCING BATCH REACTOR FOLLOWED BY MEDIA FILTRATION FOR ORGANIC AND NUTRIENT REMOVAL FROM PRODUCED WATER by Emily R. Nicholas A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Masters of Science (Civil and Environmental Engineering). Golden, Colorado Date ____________________________ Signed: ______________________________ Emily R. Nicholas Signed: ______________________________ Dr. Tzahi Y. Cath Thesis Advisor Golden, Colorado Date ____________________________ Signed: _______________________________ Dr. John McCray Professor and Head Department of Civil and Environmental Engineering ii ABSTRACT With technological advances such as hydraulic fracturing, the oil and gas industry now has access to petroleum reservoirs that were previously uneconomical to develop. Some of the reservoirs are located in areas that already have scarce water resources due to drought, climate change, or population. Oilfield operations introduce additional water stress and create a highly complex and variable waste stream called produced water. Produced water contains high concentrations of total dissolved solids (TDS), metals, organic matter, and in some cases naturally occurring radioactive material. In areas of high water stress, beneficial reuse of produced water needs to be considered. Sequencing batch reactors (SBR) have been used to facilitate biological organic and nutrient removal from domestic waste streams. Although the bacteria responsible for the treatment of domestic sources cannot tolerate the high TDS concentrations in produced water, the microorganisms native to produced water have the functional potential to treat produced water. In a bench scale bioreactor jar test using produced water from the Denver-Julesburg Basin, the produced water collected was determined to be nutrient limited with respect to phosphorus. By adding a phosphorus supplement, soluble chemical oxygen demand (COD) removal was increased by over 20% and ammonia removal increased by approximately 40%. Various supplements including KH2PO4, centrate from an anaerobic digester, and activated sludge from a municipal SBR were tested to see how treatment changed with phosphorous type. A pilot scale SBR followed by media filtration was used to evaluate the effects of operating conditions on produced water treatment. The hydraulic residence time ranged from 1.67 to 8.3 days during various phases of operation, with no measured effect on treatment performance. Adding 7.5 mg-P/L of KH2PO4 as a phosphorus supplement had the most significant effect on treatment performance on the system. The majority of COD removal switched locations from the filter columns to the bioreactors. Comparing total organic carbon (TOC) to COD, the biologically available portion of COD appears to be treated in the SBR treatment train while recalcitrant carbon and inorganic material may need to be removed via physical or chemical methods. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................................ iii LIST OF FIGURES …………………………………………………………………………………………..…...vi LIST OF TABLES …………………………………………………………………………………………………x ACKNOWLEDGEMENTS ......................................................................................................................... xii CHAPTER 1 INTRODUCTION .................................................................................................................. 1 1.1 Significance of oilfield waste ........................................................................................................... 1 1.2 Oil and gas waste streams .............................................................................................................. 1 1.3 Produced water management ......................................................................................................... 2 1.4 Challenges to reuse of produced water………………. .................................................................... 3 1.5 Produced water treatment methods…….. ....................................................................................... 3 1.6 Sequencing batch reactors….. ........................................................................................................ 4 1.7 Media filtration…… .......................................................................................................................... 5 1.8 Treatment potential of microorganisms native to produced waters….. ........................................... 5 1.9 Research objectives….. ................................................................................................................... 8 CHAPTER 2 MATERIALS AND METHODS.............................................................................................. 9 2.1 Produced water feed ....................................................................................................................... 9 2.2 Bench scale experimental setup ..................................................................................................... 9 2.3 .Pilot scale experimental setup…...................................................................................................11 2.4 Analytical procedures… ................................................................................................................ 12 2.5 Microbial analysis ...………………………………………………………… ……………………………13 2.6 Statistical analysis ………………………………………………………………………………………...14 CHAPTER 3 RESULTS AND DISCUSSION ........................................................................................... 15 3.1 Bench scale jar testing ……………………………………………………………………………………15 3.1.1 pH and conductivity ……..……………………………..………………………………....………….15 3.1.2 COD and sCOD removal………………………………………………………………………...…..16 3.1.3 Nitrogen removal….…………………………………………………………………………..………19 3.1.4 Phosphorus effects….……………………………………………………………………………..…20 3.1.5 Suspended solids and turbidity ..………………………………………………………...…………21 iv 3.1.6 PW2 bioreactor jar………….……………………………………………………………………..….23 3.2 Pilot system…..………………………………………….....................................................................25 3.2.1 pH and conductivity ..……………………….……………………………………………………......25 3.2.2 Organic removal…….………………………………………………………………..…………...….27 3.2.3 Nitrogen removal……………………………………………………………………………………...31 3.2.4 Iron removal…………………………………….………………………………………..……………34 3.2.5 Phosphorus supplement ………………………….…………..……………………………..……...36 3.2.6 Suspended solids and turbidity …………………………….…………………..………………..…37 3.4 Microbial analysis…………………………………………………...…………………………………....38 3.5 Bench and pilot system comparison .…………………………………………………………………...41 CHAPTER 4 CONCLUSION .................................................................................................................... 43 REFERENCES ........................................................................................................................................ 44 APPENDIX A ........................................................................................................................................... 47 v LIST OF FIGURES Figure 1.1 Stages in a sequencing batch reactor, starting with fill where raw influent enters the bioreactor followed by a mix stage, where activated sludge is dispersed throughout the bioreactor. The react stage allows the microbial communities in the mixed liquor to consume contaminants such as organics and nutrients. After the react stage, the bioreactor proceeds to settle before decanting off the clarified supernatant. During the decant stage activated sludge is left in the bioreactor to introduce microorganisms into the next batch of raw wastewater. ................................................................................................ 4 Figure 1.2 Relative distribution of 16S rRNA gene sequences for bacteria in a Pennsylvania well using (a) tag-encoded pyrosequencing and (b) clone libraries.27 Microbial communities changed over time, indicating that the produced water has native microbial communities, which were not introduced by the source water used for hydraulic fracturing. ....................... 6 Figure 1.3 Level 1 functional categories found in DNA segments from source water (SW), and produced water (PW) from days one and nine in a Marcellus Shale natural gas well in Westmoreland County, Pennsylvania.26 ................................................................................. 8 Figure 2.1 The bench scale system consisting of a standard jar tester and six 2 L jars. An air pump was used to intermittently supply aeration to all the jars. .....................................................10 Figure 2.2 Picture of pilot system (top) and sketch of hydraulic flow through the pilot system (bottom). Raw produced water is introduced to the bioreactors through an actuated ball valve at the bottom of each conical-bottom tank. After each batch cycle is over, supernatant drains into a holding reservoir, until it is pumped continuously through media filter. Treatment trains 1 and 2 are identical except for the media types with train 1 using recycled crushed glass, and train 2 using silica sand……………………………………………………………... .11 Figure 3.1 pH as a function of time for feed water and mixed liquor in the (a) baseline jar, AS addition jar, probiotic addition jar, KH2PO4 addition jar, centrate addition jar, attached growth jar, and H2O2
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