ANAEROBIC CO-DIGESTION OF ABATTOIR AND TEXTILE INDUSTRY WASTEWATER IN A UASB REACTOR. A thesis submitted in fulfillment of the requirements for the degree Magister Technologiae: Civil Engineering. In the Faculty of Engineering and Technology ONDARI JAMES MAATI 211123536 Highest Qualification: BSc. Civil Engineering SUPERVISORS: PROF. MAURICE NDEGE CO-SUPERVISOR: PROF. OCHIENG AOYI APRIL 2015 DECLARATION I hereby certify that this work is my own, except where otherwise acknowledged, and that it has not been submitted previously for a degree at this or any other university. JAMES MAATI ONDARI Signature: …………………… Date: ……………………… i DEDICATION This M-Tech dissertation is dedicated to my loving parents Richard and Sabina Ondari. May God bless them and keep them safe and healthy. ii ACKNOWLEDGMENTS I thank God in a very special way for being with me every step of the way. I wouldn’t have come this far without His grace and guidance. I thank my parents too whose encouragements and efforts made me feel comfortable and settled throughout my stay in South Africa. I also appreciate the efforts of my supervisor, Prof. Maurice Ndege and co-supervisor, Prof. Ochieng’Aoyi who gave me unforgettable insights as far as research is concerned. Let me also take this opportunity to acknowledge the following people and institutions, without them my study wouldn’t have seen the light of day; 1. Vaal University of Technology who provided the source of transport, laboratory equipment and general funding for the study; 2. A meat Abattoir plant in Parys from where I collected wastewater samples. 3. My research collegues especially Apollo Seth who was also doing anaerobic degradation. 4. Ambio water quality laboratory in VUT who trained me on how to do the preliminary tests especially BOD , Nitrates, Phosphates and turbidity. 5 iii ABSTRACT Textile industry effluents are carcinogenic and highly recalcitrant hence difficult to degrade especially through biological methods. Abattoir effluents are classified under high-strength wastewaters because of their characteristic high organic load hence highly biodegradable. Anaerobic co-digestion is the concept of degrading two effluent streams with complementary characteristics in order to improve the substrate removal rate. The feasibility of co-digesting abattoir and textile wastewater in a UASB reactor was evaluated at mesophilic and ambient temperature conditions. Preliminary experiments were conducted in 500 ml batch reactors to evaluate the optimum abattoir to textile synthetic wastewater ratio. The effect of COD, TVFA, alkalinity and pH on biogas yield was examined at both ambient and mesophilic temperatures. Anaerobic co-digestion of abattoir to textile wastewater in the ratio determined in the batch process was carried out in a 3 L UASB reactor by a continuous process. The continuous biodegradation process was executed at three different HRTs (22, 18 and 14 hrs) over a 60 day operation period. UASB reactor efficiency was achieved at organic loads ranging from 3.0 – 10.8 gCOD L-1 day-1. Continuous mode experiments were carried out at influent flow rates which corresponded to HRTs ranging between 1 to 8 days in order to evaluate the steady state operating parameters for the co- digestion process. The abattoir to textile effluent ratio was found to be 60:40 respectively. The COD, TVFA, alkalinity and pH and biogas yield followed a similar pattern over time at both mesophilic and ambient temperature conditions. Experimental data adequately fit the Grau first order kinetic model and average COD removal efficiencies of 85% and BOD of around 96% were achieved. 5 The average biogas yield remained essentially constant, around 0.19 L/g COD . The co- removed digested mixture was found to be biodegradable judging from the BOD:COD ratio of 0.53. TCOD removal efficiency decreased from 93% to 16% as HRT decreased from 8 days to 1 day. The kinetics of a UASB reactor co-digesting the mixture of synthetic abattoir and textile wastewater was evaluated in this study using Grau second order multicomponent substrate removal kinetic model. The Grau second order kinetic model, whose kinetic coefficient (k) was s 0.389, was found to be suitable for predicting the performance of a lab-scale UASB reactor. iv TABLE OF CONTENTS PAGE DECLARATION ..............................................................................................................................i DEDICATION ...............................................................................................................................ii ACKNOWLEDGMENTS................................................................................................................ iii ABSTRACT .................................................................................................................................. iv LIST OF ACRONYMS .................................................................................................................... x LIST OF SYMBOLS ....................................................................................................................... xi CHAPTER 1 . INTRODUCTION .................................................................................................1 1.1 Background information ................................................................................................................ 1 1.2 Kinetic Studies ............................................................................................................................... 3 1.3 Purpose of Study ............................................................................................................................ 4 1.4 Problem Statement ........................................................................................................................ 4 1.5 Objectives ...................................................................................................................................... 4 1.6 Thesis Layout. ................................................................................................................................ 5 CHAPTER 2 . LITERATURE REVIEW .........................................................................................6 2.1 Background Information .......................................................................................................... 6 2.2 Wastewater Treatment ............................................................................................................ 7 2.2.1 Pre-treatment procedure ........................................................................................................ 7 2.2.2 Physicochemical treatment. .................................................................................................... 7 2.2.3 Biological Treatment ............................................................................................................... 8 2.2.4 Tertiary treatment .................................................................................................................. 9 2.3 Environmental Impacts and Characterization of Wastewaters. ............................................... 10 2.3.1 Abattoir wastewater ............................................................................................................. 11 2.3.2 Textile Wastewater ............................................................................................................... 13 2.3.3 Effluent pre-treatment and synthesis .................................................................................... 14 2.3.4 Mixing ................................................................................................................................... 16 2.4 Anaerobic co-digestion ................................................................................................................ 16 2.5 UASB Reactor Performance .......................................................................................................... 18 2.6 Kinetics Models............................................................................................................................ 20 2.6.1 Substrate removal kinetics for single components. ................................................................ 20 2.6.2 Substrate removal kinetics for multicomponents. ................................................................. 21 v 2.6.3 Multicomponents kinetic model. ........................................................................................... 21 2.7 Current trends in Literature ......................................................................................................... 22 CHAPTER 3 . METHODOLOGY ..............................................................................................24 3.1 Wastewater sampling .................................................................................................................. 24 3.1.1 Abattoir wastewater ............................................................................................................. 24 3.1.2 Textile wastewater. ............................................................................................................... 24 3.2 Wastewater Pre-treatment Procedure ......................................................................................... 26 3.3 Experimental Unit ........................................................................................................................ 26 3.3.1 Preliminary Batch reactors .................................................................................................... 26 3.3.2 UASB reactor ......................................................................................................................... 27 3.4 Inoculum Preparation Process...................................................................................................... 27 3.5 Anaerobic Co-digestion Start-up Process ...................................................................................... 28 3.5.1 Inoculum ............................................................................................................................... 28 3.5.2 Preliminary treatment process .............................................................................................. 28 3.5.3 Continuous biodegradation process. ..................................................................................... 30 3.6 Analytical Methods ...................................................................................................................... 31 3.7 Statistical Analysis ........................................................................................................................ 31 CHAPTER 4 . RESULTS AND DISCUSSION..............................................................................33 4.1 Characterization of Wastewater ................................................................................................... 33 4.1.1 Abattoir wastewater ............................................................................................................. 33 4.1.2 Textile wastewater ................................................................................................................ 34 4.2 Optimum Co-digestion Ratio ........................................................................................................ 34 4.2.1 Performance of the preliminary anaerobic batch Reactors. ................................................... 34 4.3 Evaluation of Substrate and Dye Removal Efficiencies. ................................................................. 36 4.3.1 The effect of temperature on biodegradation. ...................................................................... 36 4.3.2 Batch experiment kinetic evaluation ..................................................................................... 41 4.3.3 Total Aromatic Amines removal efficiency and Methane yield ............................................... 42 4.4 Continuous Anaerobic Degradation of Pretreated Raw Abattoir Effluent. .................................... 46 4.5 Evaluation of anaerobic co-digestion feasibility in a continuous process. ..................................... 51 4.5.1 COD and BOD removal rate. ................................................................................................. 51 5 4.5.2 pH ........................................................................................................................................ 55 vi 4.5.3 Biogas production process .................................................................................................... 56 4.6 Evaluation of the Operating Parameters for Steady State Co-digestion Process in the UASB......... 57 4.6.1 Effect of OLR, HRT and flow rate on substrate removal.......................................................... 58 4.6.2 Grau second-order multicomponent substrate removal model ............................................. 64 4.6.3 Evaluation of the kinetic model ............................................................................................. 65 CHAPTER 5 . CONCLUSIONS AND RECOMMENDATIONS .....................................................68 5.1 Conclusion ................................................................................................................................... 68 5.1.1 Wastewater characterization. ............................................................................................... 68 5.1.2 Optimum abattoir to textile wastewater ratio ....................................................................... 68 5.1.3 Evaluation of the substrate and dye removal efficiencies of the co-digestion mixture at mesophilic and ambient temperatures........................................................................................... 68 5.1.4 Evaluation of the operating parameters for steady state co-digestion process in the UASB ... 69 5.2 Recommendations ....................................................................................................................... 69 REFERENCES .............................................................................................................................71 APPENDIX .................................................................................................................................79 APPENDIX A: UASB REACTOR SPECIFICATIONS DRAWN TO SCALE. ..................................................... 79 APPENDIX B: TABLE SHOWING STEADY STATE PARAMETERS. ............................................................. 80 APPENDIX C: GRAPH SHOWING HOW TO OBTAIN THE VALUE OF K AND K . ...................................... 81 1 2 APPENDIX D: APHA EXTRACTS FOR COD AND BOD . ........................................................................... 81 5 vii LIST OF FIGURES Page FIGURE 2.1: UNIT OPERATIONS IN PHYSICOCHEMICAL TREATMENT SYSTEMS ............................................................. 8 FIGURE 3.1: SCHEMATIC DIAGRAM OF THE BATCH REACTOR. .................................................................................. 26 FIGURE 3.2: SCHEMATIC DIAGRAM OF A SETUP OF THE CONTINUOUS BIOREACTOR. .................................................. 27 FIGURE 4.1: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN M1................................................................................................................................ 36 FIGURE 4.2: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN A1. ............................................................................................................................... 37 FIGURE 4.3: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN M2................................................................................................................................ 37 FIGURE 4.4: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN A2. ............................................................................................................................... 38 FIGURE 4.5: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN M3................................................................................................................................ 38 FIGURE 4.6: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN A3. ............................................................................................................................... 38 FIGURE 4.7: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN M4................................................................................................................................ 39 FIGURE 4.8: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN A4. ............................................................................................................................... 39 FIGURE 4.9: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN M5................................................................................................................................ 40 FIGURE 4.10: THE EFFECT OF INITIAL ORGANIC LOAD, PH, ALKALINITY AND TVFA ON BIOGAS YIELD FOR EXPERIMENTAL RUN A5. ............................................................................................................................... 40 FIGURE 4.11: EFFECT OF SUBSTRATE CONCENTRATION ON THE COD REMOVAL EFFICIENCY AND TAA CONCENTRATION IN UASB REACTOR. ........................................................................................................... 43 FIGURE 4.12: EFFECT OF SUBSTRATE CONCENTRATION ON TAA PERCENTAGE REMOVAL AND BIOGAS YIELD. ........... 44 FIGURE 4.13: INFLUENT AND EFFLUENT COD DYNAMICS THROUGHOUT THE OPERATION PERIOD. ............................. 46 FIGURE 4.14: BIOGAS YIELD AND COD REMOVAL EFFICIENCY (%) FOR DIFFERENT OPERATIONAL PERIODS............... 48 FIGURE 4.15: VARIATION OF THE INFLUENT AND EFFLUENT PH WITH REACTION TIME. ............................................. 48 FIGURE 4.16: THE EFFLUENT COD AND BOD5 (MG/L) AND THE BOD:COD RATIO OF THE EFFLUENT FROM THE REACTOR. ..................................................................................................................................................... 49 FIGURE 4.17: THE METHANE YIELD (%) OF THE BIOGAS. ......................................................................................... 50 FIGURE 4.18: CODIN, CODOUT, BOD5(OUT) AND COD REMOVAL EFFICIENCY AGAINST OPERATION TIME FOR SYNTHETIC ABATTOIR AND TEXTILE WASTEWATER MIXTURE. ........................................................................................... 51 FIGURE 4.19: CODIN, CODOUT, BOD5(OUT) AND COD REMOVAL EFFICIENCY AGAINST OPERATION TIME FOR SYNTHETIC ABATTOIR WASTEWATER ONLY...................................................................................................................... 52 FIGURE 4.20: CODIN, CODOUT, BOD5(OUT) AND COD REMOVAL EFFICIENCY AGAINST OPERATION TIME FOR SYNTHETIC TEXTILE WASTEWATER ONLY. ....................................................................................................................... 54 FIGURE 4.21: VARIATION OF THE PH WITH THE DIGESTION TIME FOR ALL THE THREE REACTORS............................... 55 FIGURE 4.22: VARIATION OF BIOGAS PRODUCTION AT DIFFERENT OLRS WITH THE DIGESTION TIME FOR ALL THREE REACTORS. ................................................................................................................................................... 56 FIGURE 4.23: VARIATION OF BIOGAS PRODUCTION AND PERCENTAGE METHANE YIELD WITH DIGESTION TIME FOR THE CO-DIGESTION REACTOR. .............................................................................................................................. 57 FIGURE 4.24: EFFECT OF REACTION TIME ON TCOD REMOVAL EFFICIENCY AT 0.375 L/D FLOW RATE. ...................... 57 viii FIGURE 4.25: THE EFFECT OF HRT VARIATION ON TCOD PERCENTAGE REDUCTION AND TVFA/ALKALINITY RATIO (P). .............................................................................................................................................................. 58 FIGURE 4.26: VOLUMETRIC PROPORTION OF CARBON DIOXIDE (CO2) AGAINST THE TVFA/ALKALINITY (P) RATIO. ... 60 FIGURE 4.27: INFLUENCE OF RESIDUAL SCOD ON TVFA/ALKALINITY (P) RATIO. ................................................... 61 FIGURE 4.28: PROPORTIONAL PERCENTAGE REDUCTION AGAINST VOLUMETRIC OLR (VOLR). ................................... 61 FIGURE 4.29: EFFECT OF VARYING VOLUMETRIC OLR (VOLR) ON THE RESIDUAL AND THEORETICAL SCOD (EQ. 4.3) CONCENTRATION. ......................................................................................................................................... 62 FIGURE 4.30: SCOD REMOVAL RATE (R) AGAINST THE VOLUMETRIC OLR (VOLR). .................................................. 63 FIGURE 4.31: EFFECT OF THE VOLUMETRIC OLR (VOLR) ON BIOGAS YIELD PER VOLUME OF INFLUENT (QM) AND PER VOLUME OF REACTOR (QM). .......................................................................................................................... 64 FIGURE 4.32: EVALUATION OF KINETIC CONSTANTS (A, B AND K) FOR GRAU’S SECOND-ORDER MULTICOMPONENT S SUBSTRATE REMOVAL MODEL. ...................................................................................................................... 65 LIST OF TABLES Page TABLE 3.1: COMPOSITION OF THE SYNTHETIC ABATTOIR EFFLUENT IN THIS STUDY. ................................................. 25 TABLE 3.2: COMPOSITION OF THE SYNTHETIC TEXTILE EFFLUENT IN THIS STUDY. .................................................... 25 TABLE 3.3: DESCRIPTION OF THE EXPERIMENTAL RUNS AT VARIOUS INITIAL SUBSTRATE CONCENTRATIONS. ............ 29 TABLE 4.1: CHARACTERISTICS OF RAW ABATTOIR EFFLUENT. ................................................................................. 33 TABLE 4.2: PARAMETERS OF THE SYNTHETIC ABATTOIR WASTEWATER. .................................................................. 34 TABLE 4.3: SYNTHETIC TEXTILE WASTEWATER PARAMETERS.................................................................................. 34 TABLE 4.4: BATCH REACTOR PERFORMANCE AT DIFFERENT EFFLUENT PROPORTIOS AFTER 11 DAY OPERATION PERIOD. .................................................................................................................................................................... 35 TABLE 4.5: GRADIENT (P) VALUES EVALUATED USING GRAU’S FIRST-ORDER KINETIC MODEL. ................................. 41 TABLE 4.6: KINETIC CONSTANT (K’1) VALUES EVALUATED USING GRAU’S FIRST-ORDER KINETIC MODEL. ................. 42 TABLE 4.7: UPFLOW ANAEROBIC SLUDGE BLANKET (UASB) DEGRADATION PROCESS PARAMETERS (MEAN±STD). .... 49 TABLE 4.8: STEADY STATE PARAMETERS AT VARIOUS HYDRAULIC RETENTION TIMES (HRTS)A. ............................... 59 TABLE 4.9: KINETIC PARAMETER OF UASB REACTOR TREATING ABATTOIR AND TEXTILE CO-DIGESTION MIXTURE. .. 66 TABLE 4.10: COMPARISON OF KINETIC CONSTANTS FOR CONTOIS, GRAU’S SECOND-ORDER AND MONOD KINETIC MODELS........................................................................................................................................................ 67 ix