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Removal of heavy metals from wastewater using granular coal Saravanabawan, Thirugnana 1980

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REMOVAL OF HEAVY METALS FROM WASTEWATER USING GRANULAR COAL by TH-SRUGNANA SARAVANABAWAN B . S c , Un ivers i ty of Wales, 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of C i v i l Engineering) We accept th is thes i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January 1980 (^Thijrugnana Saravanabawan, 1980 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of E ^ i N E E f Q r J g , The University of Brit ish Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date MMLtU- \4 , WZo A B S T R A C T Batch tests were performed to evaluate the r e l a t i v e performance of four B.C. coals (Hat Creek Oxid ised, Ka i ser -s tock p i l e refuse, Ka i ser -specia l plant feed and Cominco Ash) in removing heavy metals copper, lead, z inc and mercury from f i l t e r e d primary sewage treatment plant e f f l u e n t . Emphasis was placed on metal concentrat ions of 10 mg/1 and less . Hat Creek coal was found to be much superior to the other three and i t s e f f i c i e n c y is comparable to that of Darco act ivated carbon 12 x 20. Hat Creek and Kaiser-stock p i l e refuse coals were further used in column tests to evaluate the r e l a t i v e performance of these coals in removing copper, lead and z inc under dynamic cond i t ions . Again emphasis was placed on in f luent metal concentrat ions of 10 mg/1 and less and once more the performance of Hat Creek coal was much super ior to that of Kaiser coa l . Tests with act ivated carbon ind icate Hat Creek coal to be a c lose competitor for use in advanced waste treatment for heavy metal removal. - i i i -TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v LIST OF FIGURES vi ACKNOWLEDGEMENT ix CHAPTER 1 INTRODUCTION AND RESEARCH RATIONALE 1 CHAPTER 2 MATERIAL AND PROCEDURE 5 2.1 Type of Coal 5 2.2 Coal Preparation 5 2.3 Wastewater 6 l.k Measurement of Concentration 7 2.5 Batch Test ing Procedure 7 2.5-1 Determination of Optimum Contact Time 7 2.5.2 Determination of Required Coal Quantity 9 2.5.3 Adsorption Isotherms 9 2.6 Column Test ing Procedure 11 2.6.1 Col umn Set Up 11 2.6.2 Experimental Procedure 12 CHAPTER 3 RESULTS AND DISCUSSION '7 3. 1 Batch Tests 17 3.1.1 E f f ec t of pH on E f f i c i e n c y 17 - i v-Page 3.1.2 Capacity of Coals 20 3.1.3 Overal l Ranking of the Coals 37 3.1 .4 General Comments 39 3.1.5 Comparison of Hat Creek Coal with Act ivated Carbon kO 3.2 Column Tests kl 3.2.1 Copper, Lead and Zinc kl CHAPTER k CONCLUSIONS Ik CHAPTER 5 RECOMMENDATIONS 77 REFERENCES 79 LIST OF TABLES Page TABLE 3. 1 Summary of Copper Adsorption Capac i t ies 24 3. 2 Summary of Lead Adsorption Capac i t ies 28 3. 3 Summary of Zinc Adsorption Capac i t ies 32 3. Summary of Mercury Adsorption Capac i t ies . . . 36 3-5 Summary of Comparison Between Act ivated Carbon and Hat Creek Coal 46 LIST OF FIGURES Page FIGURE 2.1 E f fec t of Contact Time on Adsorption of Copper . . . . 8 2.2 E f fec t of Coal Dosage on Metal Adsorption , 10 2.3 Breakthrough Curves for Copper Using Various Depths of Hat Creek Coal 14 l.k Breakthrough Curve for Copper with D i f fe rent Sorbstcs •••• •••• •••• •••• • > • « •••• 15 3.1 E f fec t of pH on Metal Removal at Lower Concentration . . . . 18 3.2 E f fec t of pH on Metal Removal at Higher Concentration , 19 3.3 Copper Adsorption Isotherms 21 3.4 Copper Adsorption Isotherms 22 3.5 Copper Adsorption Isotherms 23 3.6 Copper Removal E f f i c i e n c y 25 3.7 Lead Adsorption Isotherms 27 3.8 Lead Removal E f f i c i e n c y 30 3.9 Zinc Adsorption Isotherms 31 3.10 Zinc Removal E f f i c i e n c y J,k 3.11 Mercury Adsorption Isotherms 35 3.12 Mercury Removal E f f i c i e n c y 38 3.13 Copper Adsorption Isotherms k] 3 . H Lead Adsorption Isotherms kl 3.15 Zinc Adsorption Isotherms kk — v i ! — Page FIGURE 3.16 Mercury Adsorption Isotherms 45 3.17 Breakthrough Curve for Copper . . . **8 3.18 Breakthrough Curve for Copper ; 50 3.19 Breakthrough Curve for Copper 51 3.20 Comparison of Adsorption Capacity for Copper in Primary E f f luent at D i f fe rent Flow Rates . . . . 52 3.21 Comparison of Breakthrough Curve for Copper in Primary E f f luent and Water Solut ion 56 3.22 Comparison of Adsorption Capacity for Copper in Primary E f f luent and D i s t i l l e d Water 57 3.23 Breakthrough Curve for Copper 58 3.2A Breakthrough Curve fo r Copper 59 3.25 Comparison of Adsorption Capacity for Copper in Primary E f f luent at D i f fe rent Flow Rates . . . . 60 3.26 Comparison of Adsorption Capacity for D i f f e ren t Copper Influent Concentrations 61 3.27 Breakthrough Curve for Lead 63 3.28 Breakthrough Curve for Lead 64 3.29 Comparison of Adsorption Capacity for Lead in Primary E f f luent at D i f fe rent Flow Rates . . . . 65 3.30 Breakthrough Curve for Zinc 67 3.31 Breakthrough Curve fo r Zinc 68 3.32 Comparison of Adsorption Capacity for Zinc in Primary E f f luent at D i f fe rent Flow Rates . . . . 69 - v i i i -Page FIGURE 3.33 Breakthrough Curve for Zinc 70 3.3^ Breakthrough Curve for Zinc 71 3.35 Comparison of Adsorption Capacity for Z inc in Primary E f f l uent at D i f fe rent Flow Rates . . . . 72 3.36 Comparison of Adsorption Capacity for D i f fe rent Zinc Influent Concentrations 73 ACKNOWLEDGEMENT I am gratefu l to my research superv i sor , Dr. W.K. Oldham, for his patience and encouragement throughout th is study. His support and guidance were of the utmost importance and are s incere apprec iated. My thanks are a l so due to Dr. K. Hall for making a c r i t i c a l survey of my typescr ipt and weeding out some ana l y t i c a l e r ro r s . This study was supported by Grants from the M in i s t ry of Environment of the Province of B r i t i s h Columbia. 1 Chapter 1 INTRODUCTION AND RESEARCH RATIONALE Increasing populat ion and i ndus t r i a l growth has produced adverse e f fec t s on the environment and human l i f e such as the mercury con-tamination of f i s h and the subsequent human health hazards. S imi lar incidents have focused a t tent ion on the po l l u t i on potent ia l s of heavy metals in wastewater e f f l uen t s and rece iv ing waters. The p u b l i c ' s concern for the preservat ion of the environment has forced the Federal and Prov inc ia l Governments of Canada to enact s t r i c t po l l u t i on control standards for municipal and i ndus t r i a l e f f luent discharges. 1 2 A review of l i t e r a t u r e ' indicates that copper, z inc and lead contr ibute the bulk of the heavy metal loading to rece iv ing waters, and mercury with i t s inherent cumulative nature and mu l t ip ly ing e f f ec t in the food chain poses the utmost concern in the aquatic environment. Crushed anthrac i te coal has been used for many years as a f i l t e r i n g medium for water supp l ies . However i t s use as a sorpt ion medium for pur i f y ing wastewater has been examined only recent ly with 3 specia l emphasis towards the removal of organics from domestic sewage . A s i g n i f i c a n t advantage is that coal exhausted of i t s sorpt ion capacity is s t i l l p o t e n t i a l l y useful as an energy source. A U.S. Department 2 of Inter ior report"' recommends the use of coal for post, or " t e r t i a r y " treatment of secondary sewage treatment plant e f f l u e n t . The a b i l i t y of ce r t a in B r i t i s h Columbia coals to remove d isso lved k 5 const i tuents from water has been invest igated by Coulthard and Hendren and the i r f ind ings are encouraging. However, most of the work was ca r r ied out with r e l a t i v e l y high metal concentrat ions and with only two coals found in B r i t i s h Columbia. Recent studies by Riaz^ and Tin Tun^ were ca r r i ed out with r e l a t i v e l y lower copper, z i n c , lead and mercury con-centrat ions and the resu l t s obtained from both batch and laboratory sca le column tests are promising. Riaz^ ca r r i ed out batch tests with s ix coal samples: Kaiser coal - Special waste lagoon sample Kaiser coal - Stock p i l e refuse sample Kaiser coal - Special plant feed sample Kaiser coal - Oxidised stock p i l e sample Northern coal mines - Unoxidised sample and Northern coal mines - Oxidised sample. On the basis of batch test data obta ined, the best two coals (Kaiser coal - stock p i l e refuse and Kaiser coal - spec ia l plant feed) were tested in a continuous flow laboratory - sca le column. The emphasis was placed on metal concentrat ions of 2 mg/1 and less for copper, lead and z inc and 5 yg/1 for mercury. The e f f e c t of in f luent concentrat ion, flow rate through the column (contact t ime), pH of i n f l u e n t , and mixture of metals on the adsorpt ive capacity of coal were invest igated. On the basis of adsorpt ive capac i ty , Kaiser coal - S tockp i le refuse sample was found to be the best of s ix coals tested. Its metal removing e f f i c i e n c y 3 was compared with act ivated carbon and nitrohumic acid and resu l t s indicate that coal may be a f e a s i b l e a l ternate to remove heavy metals from waste e f f l u e n t s . T in Tun^ ca r r ied out batch tests with f i v e coal samples: Hat Creek oxid ised Hat Creek unoxidised Cominco oxid ised Cominco ashwaste and Cominco product ion. Based on batch test r e su l t s , the best performing coal from each of the Hat Creek and Cominco groups, namely Hat Creek oxid ised and Cominco ashwaste were tested on a continuous flow laboratory - sca le column. The in f luent concentrat ion was 2 mg/1 and less in the case of copper, z inc and lead and was 5 yg/1 and less for mercury. The e f f e c t of pH, in f luent metal concentrat ion, flow rate and the s yne rg i s t i c e f f ec t s of mul t ip le metals were invest igated. Hat Creek ox id i sed was found to be super ior to others with regard to adsorpt ive capacity and a lso compared favourably with Darco act ivated carbon. The study reported in th i s thes i s is an extension of the work ca r r i ed out by Riaz^ and T in Tun^. Readers are strongly recommended to refer to these references for fur ther background information on heavy metal po l l u t i on problems, t h e i r magnitudes, and methods present ly ava i l ab le and used to control them. Synthet ic waste waters produced by mix ing metal so lut ions with d i s t i l l e d water to des ired concentrat ions were used by the above workers in adsorption s tud ies . In the study reported here in , the performance of coal in removing heavy metals from sewage treatment plant e f f l uen t was invest igated. The s p e c i f i c object ives of th i s invest igat ion were 1. To evaluate the r e l a t i v e e f f i c i e n c i e s and capac i t ie s of four d i f f e r e n t B.C. coals in removing heavy metals from wastewater in batch te s t s ; 2. To evaluate heavy metal removal capacity of the best two coals in continuous flow column tes t s ; 3. To compare the metal removing capac i ty of coal from waste-water with that of Darco act ivated carbon grade 12 x 20. During the inves t i ga t i on , information was obtained on the i n -f luences of the fo l lowing c h a r a c t e r i s t i c s on removal e f f i c i e n c y and adsorption capaci ty of c o a l ; 1. Concentration of adsorbate; 2. Flow rate or contact t ime; 3. pH. 5 Chapter 2 MATERIAL AND PROCEDURE 2.1 Types of Coal Four d i f f e r e n t coal samples were used of which two were chosen from R iaz ' s^ study and the other two from Tin Tun 's^ work. Kaiser coal - Stock p i l e refuse (K.C. SPR)" Kaiser coal - Special plant feed (K.C. SPF) Hat Creek ox id i sed (H.C. OX) Cominco Ashwaste (CO. ASH) Act ivated carbon (ACT. CARB.) Abbreviat ions used throughout the text . The performances of the above four coals were compared with Darco act ivated carbon grade 12 x 20 by p a r a l l e l t e s t i n g . 2.2 Coal Preparation Coal was f i r s t washed with water to remove a l l foreign p a r t i c l e s and subsequently dr ied at room temperature. The dr ied coal was then crushed to the des ired grain s i ze (28/48 mesh) by passing i t f i r s t through a Taylor Gyrator and then through a Massco cone crusher. Crushed coal was dry sieved using 28/48 mesh screens and mechanical shaker. 6 The 28/48 mesh f r a c t i o n was then wet sieved and back washed in a p lex ig lass column to remove f i n e s . F i n a l l y , the granular coal was dr ied at 103°C for about 40 hours and stored in sealed bot t les f lushed with nitrogen gas. 2.3 Wastewater Wastewater was prepared from unchlorinated e f f l uen t from the Lions Gate Primary Sewage Treatment plant of the Greater Vancouver Regional D i s t r i c t . The primary e f f l u e n t , which has to ta l v o l a t i l e s of about 200 ppm and suspended v o l a t i l e s of about 70 ppm, was f i l t e r e d by vacuum into glass carboys using Whatman No. 5^ 1 f i l t e r paper and stored under r e -f r i ge ra ted cond i t ions . Removal of suspended so l i d s was necessary to prevent s e t t l i n g and entrapment of these so l id s during column tes t ing within the pore spaces of the 28/48 mesh coal column. As a r e s u l t , i t was poss ib le to achieve throughput volumes of up to 10 l i t e r s instead of less than one. The f i l t e r e d e f f l uen t with non-detectable i n i t i a l metal concentrations was " sp i ked " with standard metal so lut ions to des ired concentrat ions, and heated to room temperature (23°C) before use as wastewater for te s t i ng . Standard so lut ions used to spike the f i l t e r e d e f f l uent were copper, lead, z inc and mercury atomic absorption standard (stock) so lut ions with 1000 mg/1 (ppm) metal concentrat ion. Since the above standard metal so lut ions are a c i d i c , the spiked wastewater turned a c i d i c , the f i n a l pH depending on the quantity of metal so lu t ion added. Whenever the prepared wastewater was found to have pH less than 4.0, and pH was adjusted to 4.0 by add i t ion of sodium hydroxide which was shown by prel iminary tests not to i n te r fe re with the ad-sorpt ion process. If the pH of spiked wastewater was greater than 4.0, 7 pH adjustment was not c a r r i ed out. 2.k Measurement of Concentration A J a r r e l l Ash MV - 500 atomic absorption spectrophotometer was used for the measurement of metal concentrat ion. For copper, z inc and lead and mercury at concentrat ions of 2 mg/1 and higher the flame atomic absorption technique was used. For lower mercury concentrat ion the cold g vapour or f lameless method was u t i l i s e d . Samples having mercury con-centrat ions of 2 mg/1 and higher were a c i d i f i e d to pH below 2.0 using NHO^ and then analysed by the same method as copper, z inc or lead. 2.5 Batch Test ing Procedure Known quant i t ies of granulated coal were mixed with one hundred m i l l i l i t e r s of wastewater containing known concentrat ions of copper, z i n c , lead or mercury in a f l a sk fo r a predetermined contact time using a mechanical shaker. The mixture was then f i l t e r e d and the f i l t r a t e analysed to f ind the res idual metal concentrat ion. These tests were u t i l i s e d to study the r e l a t i v e e f f i c i e n c i e s of the d i f f e r e n t coals in removing heavy metals from wastewater. 2.5.1 Determination of Optimum Contact Time Batch tests were performed with d i f f e r e n t coals to determine equ i l i b r ium copper concentrat ion at d i f f e r e n t contact times and the resu l t s are shown in Figure 2.1. From these resu l t s the fo l lowing con-c lus ions were drawn. 8 0 1 2 . 3 0 I 2 3 Contact time - hours Figure 2.1 E f fec t of Contact Time on Adsorption of Copper 9 (a) Contact time of 90 minutes w i l l achieve about 35% of the ult imate removal, and i t was thus chosen as the optimum contact time for the rest of the study. (b) I n i t i a l metal concentrat ion and the pH of wastewater do not appreciably inf luence the optimum contact time. 2.5.2. Determination of Required Coal Quantity Batch tests were ca r r i ed out with wastewaters containing constant i n i t i a l concentrat ions of the various metals, but with varying quant i t ies of coa l . The volume of wastewater used for each test was 100 ml. Results obtained are shown in Figure 2.2. From these resu l t s the minimum quantity of coal necessary for e f f e c t i v e removal of heavy metals from 100 m i l l i l i t e r s of wastewater was determined to be one gram. 2.5.3- Adsorption Isotherms An adsorption isotherm which is derived from a ser ies of batch tests can be defined as a constant temperature p lot of the adsorbent capaci ty to remove a p a r t i c u l a r adsorbate from so lut ion against the concentrat ion of adsorbate in equ i l i b r ium with the adsorbent. Conditions used in the batch tests for the preparat ion of isotherms were as fo l lows: Quantity of coal 1 gram Coal s i ze 28/48 Volume of wastewater 100 ml Contact time 90 min Temperature 23 C (room temperature) pH of wastewater 4.0 10 0 0.5 I 1.5 Coa I do sage - q Figure 2.2 Ef fec t of Coal Dosage on Metal Adsorption 11 I n i t i a l metal concentrat ions: Emphasis was placed on low metal concentrat ions ( less than 10 mg/1) so that concentrat ions are of a s im i l a r order of magnitude to those found in municipal waste-waters that contain some indus t r i a l wastes. The s e n s i t i v i t y and minimum concentrat ion detectable by the atomic absorption technique were taken into cons iderat ion when choosing the minimum metal concentrat ions. Isotherms so developed reveal useful information in that they provide an easy comparison on the a b i l i t i e s of d i f f e r e n t absorbents to remove a common adsorbate from s o l u t i o n , and give some insight into design requirements for flow-through columns. 2.6 Columns Test ing Procedure 2.6.1. Column Set Up The a b i l i t y of coal to remove metals from wastewater under continuous flow condit ions was studied using column te s t s . This type of tes t ing simulates the use of packed, or sorpt ion towers which are designed to achieve mass t rans fer between the l i q u i d and s o l i d phases of the system. The set up used is s im i l a r to that employed by Riaz^ and Tin Tun^ 2 but with s l i g h t mod i f i ca t ions . F i f t y m i l l i l i t e r burettes of 0.9385 cm 2 7 (0.001 f t ) cross sect iona l area were used as columns. It has been shown 2 that for column contain ing 28/48 mesh s i ze p a r t i c l e s , 0.001 f t bed cross sect iona l area is greater than the c r i t i c a l area below which the column wall inf luences the f l u i d flow c h a r a c t e r i s t i c s and thereby s i g n i f i c a n t l y reduces adsorption capac i ty . Glass beads and glass wool were packed under the coal column to avoid plugging the out le t flow con-t ro l valve with coa l . The burette in le t opening was connected to an acid 12 washed 5 gal lon glass carboy which functioned as a wastewater reservo i r in the system. Care was taken to keep the rate of flow constant by frequent adjustments to the out le t valve. 2.6.2 Experimental Procedure The en t i r e study was intended to be ca r r ied out in a manner s im i l a r to those of Riaz^ and T in Tun^ so that comparisons could be drawn with respect to the a b i l i t y of coal to remove heavy metals from d i f f e r e n t types of wastewater. Most of the time th i s condit ion was s a t i s f i e d , but at other times some deviat ions were necessary to accommodate the d i f f e r e n t propert ies of the wastewater used, as discussed la ter in th i s chapter. Prel iminary column runs revealed that a column depth of 10 inches as chosen by Riaz^ and T in Tun^ was not su i t ab le for work with primary sewage treatment plant e f f l u e n t , s ince the column tends to plug due to microbia l growth on the surface before metal breakthrough occurs. T in Tun^ reported that microbia l growth on the coal surface was evident a f te r about 65 hours of contact with his simulated wastewater. With the wastewater used in th i s study, the column became completely plugged and no flow occurred a f t e r some 40 hours of use. S t e r i l i z a t i o n of the waste-water to overcome this problem was considered but not ca r r ied out s ince microbia l a c t i v i t y and i t s in ter ference is one of the more important c h a r a c t e r i s t i c s of t h i s type of wastewater. Since complete plugging occurred at about 40 hours, the coal column had obviously been m ic rob i a l l y ac t i ve for some time before that. Hence 20 hours was considered to be the maximum time the column should be operated to keep th i s inter ference to a minimum. This r e s t r i c t ed the 2 2 throughput volume to 5-5. l i t e r s at 4.88 ml/cm min. (l gpm/ft ) flow 13 rate and 27.5 l i t e r s at 24.41 ml/cm . min. (5 gpm/ft ). To se lec t a su i t ab le column depth tests were ca r r ied out with coal columns with depths of 19.1 > 12.7 and 6.4 c m . (7.5, 5.0 and 2.5 inch re spec t i ve l y ) . Emphasis was placed on breakthrough c h a r a c t e r i s t i c s of Hat Creek ox id i sed coal which performed best in batch te s t s . A flow 2 2 rate of 4.88 ml/cm . min. (lgpm/ft ) was chosen for these tes t s . 2 Figure 2.3 indicates that for a flow rate of 4.88 ml/cm . min. using Hat Creek coa l : (1) A column height of 19-1 cm (7.5 inches) is too. great as no s i g n i f i c a n t breakthrough had occurred a f t e r 5 l i t e r s had been passed through the column. (2) A column height of 6.4 cm (2.5. inches) is not adequate s ince metal penetrat ion occurred at an ear ly stage. (3) A column height of 12.7 cm (5.0 inches) is more su i t ab le s ince metal concentrat ion in the e f f l uen t was constant and less than one-tenth of the in f luent concentrat ion upto a throughput volume of 1 l i t e r , and increased with increas ing throughput volume therea f te r . However complete breakthrough was not achieved with a throughput volume of 5 l i t e r s , ind ica t ing that optimum column depth for Hat Creek coal is smaller than 12.7 cm. and greater than 6.4. cm. Test resu l t s with Kaiser coal and act ivated carbon p lot ted in Figure 2.4 ind icate that a column height of 12.7 cm is not adequate for these adsorbates under stated operating cond i t ions , s ince metal penetrat ion occurred at ear ly stages of such runs. From resu l t s of these tests i t is obvious that one column height w i l l not s a t i s f y adsorption c h a r a c t e r i s t i c s of the three adsorbates to be s tud ied. A l so , 0 I 2 3 4 Throughput volume - liters F i g u r e 2.3- B r e a k t h r o u g h C u r v e s f o r Copper U s i n g Depths o f Hat C reek Coa l 0 I 2 3 4 5 Throughput volume - liters vn Breakthrough Curve fo r Copper With D i f f e r e n t Sorbates 16 d i f f e r e n t metals would require d i f f e r e n t heights of adsorbate columns to exh ib i t adsorption and breakthrough c h a r a c t e r i s t i c s . It is extremely important to note that these column tests were devised and car r ied out only for the comparison of the performances of d i f f e r e n t coals and not to obtain absolute values for the adsorption capac i ty , minimum e f f l uen t metal concentrat ion, e t c . By a l t e r i n g the flow rate or column depth the e f f l uen t metal concentrat ion can be s i g n i f i c a n t l y changed. For comparative purposes, the d i f f e r e n t coals must be tested under exact ly s im i l a r cond i t ions . That i s , the same column height should be used for a l l coals in a l l tests i f the e f fec t of the other parameters ( i n f luent concentrat ion, flow rate, etc.) were to be examined. Hence d i f f e r e n t column heights should not be used for d i f f e r e n t coa l s , to su i t t h e i r ind iv idua l c h a r a c t e r i s t i c s . If for a p a r t i c u l a r column height and flow rate, breakthrough was not obtained with say, coal A and metal penetrat ion was obtained with coal B, it goes to prove that in order to remove that metal from waste-water coal A is much more su i tab le than coal B. Further column tests with coal A would be required in order to obtain more information, such as the minimum e f f l uen t concentrat ion a t t a i nab le , breakthrough con-cent ra t i on , optimum flow rate and column depth e tc . Since th i s study is to obtain information such as the former and not the l a t t e r , a column depth of 12.7 cm (5.0 inches), which is between the requirements of Hat Creek and Kaiser coa l s , was considered su i t ab le and was used ih column te s t i ng . Chapter 3 RESULTS AND DISCUSSION 3.1 Batch Tests 3.1.1 E f fec t of pH on E f f i c i e n c y Batch tests were ca r r ied out to examine the e f fec t of pH on the e f f i c i e n c y of heavy metal removal. The resu l t s are shown in Figure 3.1 and 3.2. Hat Creek coal was chosen for these tests s ince i t had continuously d isp layed greater adsorpt ive e f f i c i e n c y than the others. Tests were performed at pH values of 3.0, 4.0,5-5 and 7.0. With i n -creasing pH, an increase in metal removal e f f i c i e n c y is ev ident. The inf luence of pH is greater in the adsorption of z inc than in the case of copper or lead, poss ib ly due to p r e c i p i t a t i o n of z inc at higher pH. Compared to work car r ied out by Riaz^ and Tin Tun^, the overa l l metal removal e f f i c i e n c y has dropped s i g n i f i c a n t l y in treated sewage e f f l u e n t , as shown in Figure 3.1. This might be due to competition with organics for adsorption s i t e s , resu l t ing in fewer s i t e s being ava i l ab le for heavy metals. This very important d i f f e rence between pure so lut ion and wastewater is discussed in de ta i l l a ter in th i s chapter. 18 100 20 10 ]• Distilled water O Cu . ^ 2„ jPrimary effluent Init ial cone. 8 2mg/L Coa I used - H.C. OX Coa I weight * I g 7 6 Figure 3-1 pH Ef fec t of pH on Metal Removal at Lower Concentration Figure 3.2 E f fec t of pH on Metal Removal at Higher Concentration 20 3.1.2 Capacity of Coals (a) Copper Copper adsorption isotherms obtained from batch tests are shown in Figures 3-3 to 3-5. Under batch test condit ions already def ined, the fo l lowing coal propert ies were noted. (Refer to Table 3.1). (1) The copper adsorption capacity of coal increased with increasing equ i l ib r ium concentrat ion of the metal. (2) By comparison to R iaz ' s^ work in the 10 to 30 mg/1 equ i l i b r ium concentrat ion range, coals have shown greater trace metal removal capac i t i e s from sewage e f f l uen t than from water so lu t i on . (3) Under much lower equ i l i b r ium concentrations (0.1 to 1.0 mg/l) , the adsorpt ive capac i t i e s of the various coals have decreased s i g n i f i c a n t l y from those obtained with water so lut ions of copper. (4) Hat Creek coal had the a b i l i t y to produce a res idual supernatant concentrat ion of less than the detectable l im i t of 0.03 mg/1 from an i n i t i a l so lu t ion containing 0.1 mg/1 of copper. (see Figure 3.5). (5) In decreasing order of removal e f f i c i e n c y the four coals could be ranked (see Figure 3.6) as fo l lows: Hat Creek ox id i sed coal sample Kaiser - Stock p i l e refuse j / No s i g n i f i c a n t Kaiser - Special plant feed r d i f fe rence between j these three coa l s . Cominco - Ash / 5 22 Equi l ibr ium c o n e - mg/L Figure 3.H Copper Adsorption Isotherms 0.018 o . o i o O -Coa l - H.C. OX Coa I weight = Ig pH = 4.0 0 0.1 0.2 Equi l ibr ium c o n c . - m g / L Figure 3-5- Copper Adsorption Isotherms 2k TABLE 3-1 SUMMARY OF COPPER ADSORPTION CAPACITIES | Equi 1 i b r i um mg Adsorbed/g Coal Coal Type | C o n c e n t r a t i o n Water S< s l u t ion T r e a t e d ( p r i m a r y ) j mg/1 R i a z ^ Ti nTun ^  Sewage E f f l u e n t H.C.OX 3-7 5.5 Co.Ash I.A 2.3 K.C. SPR 0.85 2.5 K.C. SPF 0.7 2.9 H.C.OX 10 3-0 3-7 Co.Ash 1.25 1.3 K.C. SPR 0.71 1-7 K.C. SPF 0.6 1.2 H.C.OX 5 2.5 1.9 Co.Ash 0.9 0.2 K.C. SPR 0.6 Q.k K.C. SPF 0.5 0.2 H.C.OX 1.0 1.0 0.32 Co.Ash 0.5 0 K.C. SPR 0. 10 0.2 0 K.C. SPF 0.15 0 100 80 — • n H.C.OX K.CSPF Cn • A<?H • ® A u 60 A / ® A Q A O K.C.SPR 40 Coa l weight - Ig 20 — 1 1 1 1 1 1 | KJ C ) 10 20 30 40 50 60 70 I n i t i a l cone - mg / L Figure 3-6" Copper Removal E f f i c i ency 26 The above resu l t s could be explained using the p r i n c i p l e s of complex formation . Assuming that complex forming react ion between metal ions (M) and organic reactant (L) occur rap id ly and reve r s i b l y , they may be treated as a system in equ i l i b r i um. M + L . = ML u * ML Hence K = M . L Where K is the comp1 ex-format ion or s t a b i l i t y constant. Applying Le C h a t e l i e r ' s p r i n c i p l e ^ to the above system, when metal ions are present in high concentrat ions (as in item 2 above) the equ i l i b r ium w i l l s h i f t to the r ight re su l t i ng in s i g n i f i c a n t metal-organic complex concentrat ion. Thus the higher adsorption capacity obtained with primary e f f l uen t compared to pure so lut ion is probably due to metal adsorption both d i r e c t l y and complexed with organics. However when metals are present in lower concentrations (as in item 3 above) the equ i l i b r ium w i l l s h i f t to the l e f t re su l t i ng in much reduced meta1-organic complex concentr t ion. Hence the metal ions and complexed organics w i l l have to compete with high concentrat ions of organic species that have no metal ions at tached, fo r adsorption s i t e s and the l a t t e r is favoured s ince they are vas t ly more numerous. (This phenomenon is comparable to "compet i t i ve i n h i b i t i o n " in enzymatic react ions). (b) Lead Lead adsorption isotherms obtained from batch tests are shown in Figure 3.7. The fo l lowing coal propert ies were noted: (Refer to table 3.2) . Equ i l ib r ium c o n e - m q / L Figure 3-7 Lead Adsorption Isotherms 28 TABLE 3-2 SUMMARY OF LEAD ADSORPTION CAPACITIES Equilibrium mg adsorbed/g coal Coal Type Concentration water s( l u t i o n treated (primary) mg/1 R i a z 6 Ti nTun ^  sewage effluent H.C.OX 8 5 0.17 CO. Ash 2.1 0.35 H.C.OX 6 5 0.125 CO. Ash 2.0 0.01 H.C.OX 4 5 0.085 CO. Ash 1.9 0 K.C. SPR 1.45 0.01 K.C. SPF 1.55 0 H.C.OX 1 4.65 0.02 CO. Ash 1.7 0 K.C. SPR 1.9 0 K.C. SPF 1.07 0 (l) The metal adsorption capacity of coal increased with increasing equ i l i b r ium concentrat ion of lead; ( l l ) By comparison to R iaz ' s^ work in the less than 10 mg/1 equ i l ib r ium concentrat ion range the adsorpt ive capac i t i e s of Kaiser coals are much lower with Sewage than with water, as in item 3 above, ( i l l ) Lead removal with Hat Creek coal is much greater than with the other coa l s . (IV) In decreasing order of removal e f f i c i e n c y the four coals could be ranked as fo l lows: (Refer to Figure 3-8) Hat Creek ox id i sed Kaiser - stock p i l e refuse Kaiser - spec ia l plant feed Cominco ash (c) Zinc Z inc adsorption isotherms obtained from batch tests are shown in Figure 3-9- Under test condit ions already defined the fo l lowing coal propert ies were noted: (Refer to Table 3- 3) • (l) Metal adsorption capaci ty of coals increased with increasing equ i l i b r ium concentrat ion. (11) Hat Creek coal had the a b i l i t y to produce a residual z inc concentrat ion of 0.14 mg/1 from an i n i t i a l concentrat ion of 0.5 mg/1 No s i g n i f i c a n t d i f f e rence between these three coa l s . 100 80 o | 601 <v a. ^ 40 Coal we i g ht = I g 20 1 .2 3 F igure 3-8 H.C.OX Co'ASH.K.C.SPF.K.C.SPR 4 5 6 7 Initial concentration - mg/L Lead Removal E f f i c i e n c y 8 10 0.20 • • H.C.OX O Co ' A SH A K.C. SPR x K.C.SPF pH = 4 .0 Coal weight - Ig I 2 3 Equ i l i b r i um c o n c . - m g / L Figure 3-9 Zinc Adsorption Isotherms 32 TABLE 3-3 SUMMARY OF ZINC ADSORPTION CAPACITIES Coal Type Equ i1i br i um mg Adsorbed/g Coal Concent r a t i on Water ' o1ut ion T r e a t e d ( p r i m a r y ) mg/1 R i a z 6 Ti nTun ^  Sewage E f f l u e n t H. C. OX It 0.9 0.19 Co.Ash 0.4 0.06 H.C.OX 2 0.6 0.17 Co.Ash 0.3 0.01 H.C.OX 0.4 0.28 • 0. 15 Co.Ash 0.07 0 H.C.OX • 3 • 19 0.14 H.C.OX 0.2 0.11 0. 13 Co.Ash .03 0 K.C. SPR 0. 18 0 K.C. SPF 0. 10 0 H.C.OX .1 .03 0.002 33 ( i l l ) By comparison with R iaz ' s work at 0.2 mg/1 n equ i l i b r ium concentrat ion, Kaiser coals have shown s i g n i f i c a n t l y reduced metal adsorption c a p a c i t i e s : (IV) In decreasing order of removal e f f i c i e n c y the four coals could be ranked (Refer to Figure 3-10) as fo l lows: Hat Creek oxid ised Kaiser - Stock p i l e refuse j No s i gn i f i can t Kaiser - Special plant feed d i f fe rence between these coa l s . Cominco Ash (d) Mercury Mercury adsorption isotherms obtained from batch tests are shown in Figure 3.1.3- Under test condit ions already defined the fo l lowing coal propert ies were noted; (Refer to Table 3-4). (l) Capac i t ies of Cominco ash and KC. SPR to remove mercury increase up to an i n i t i a l concentrat ion of about kO mg/1 and atta ined capac i t ie s of 0.3 and 0.6 mg/g re spec t i ve l y . The r e l a t i v e increase at higher concentrat ions were very smal l . KC. SPF was able to adsorb mercury only at i n i t i a l concentrat ions higher than 20 mg/1. ( l l ) The lowest residual concentrat ion was produced by H.C. OX and was 2.5 mg/1 from an i n i t i a l concentrat ion of 5 mg/1. No measurable reduction in concentrat ion was obtained with i n i t i a l concentrat ions of less than 5 mg/1. T in Tun^ was able to obtain res idual concentrat ions as low as 0.005 mg/1 from pure so lut ion of 0.03 mg/1 i n i t i a l mercury concentrat ion, while i t was poss ib le down to only 2.5 mg/1 with treated 100 0 I 2 3 4 5 Init ial concent ra t ion - mg /L Figure 3-10 Zinc Removal E f f i c i ency -t-Equ i l i b r i um c o n e - m g / L F i gure 3-11 Mercury Adsorption Isotherms ^ 36 TABLE 3-4 SUMMARY OF MERCURY ADSORPTION CAPACITIES Coal Type Equilibrium Concentration mg/1 mg adsorbed/g coal Water Solution Treated (Primary) Riaz" | TinTun^ | sewage e f f l u e n t K.C. SPR K.C. SPF K.C. SPR K.C. SPF K.C. SPR K.C. SPF H.C. OX CO. Ash H.C. OX CO. Ash H.C. OX 40 30 10 .2 .01 .005 0.6 1.2 0.55 1.1 0.4 0.7 0. 145 0.015 0.0035 0.0026 0.0008 0.55 1.2 0.5 0. 35 0 0 0 0 sewage e f f l u e n t ; ( i l l ) By comparison to R i az ' s^ work, within a range of 30 to 40 mg/1 mercury equ i l i b r ium concentrat ion, Kaiser coals produced comparable adsorption capac i t ie s between treated sewage e f f l uen t and water s o lu t i on . Under lower equ i -l ibr ium concentrations ( less than 10 mg/1) greater adsorption capac i t i e s were obtained with water so lu t ion than from treated sewage e f f l u e n t . Again, these resu l t s can be explained using the same theory as in sect ion (a). (IV) In decreasing order of removal e f f i c i e n c y the four coals could be ranked (Refer to Figure 3.12 as fo l lows; Hat Creek ox id i sed sample Kaiser - Stock p i l e refuse Kaiser - Special plant feed) 3.T.3 Overal l Ranking of the Coals The resu l t s of the batch tests show that of the four d i f f e r e n t coals tes ted, H.C. Oxidised was far super ior compared to the other three in the removal of copper, lead, z inc and mercury from wastewater. K.C.SPF, K.C.SPR, and CO. Ash exhib i ted metal removing e f f i c i e n c i e s very much s im i l a r to each other and no s i g n i f i c a n t d i f f e rence was present between these three. H.C. OX seem to belong to a c lass of i t s own. Its adsorption capacity was often observed to be more than double that of any other used. This observation suggests that H.C.OX has much greater surface area per unit weight and/or has greater concentrat ion of ac t ive sorpt ion s i t e s per unit surface area than any of the other three coals tested. 100 Coo I weight = Ig • Initial co ncentra tion - mg / L F i gure 3-12 Mercury Removal E f f i c i ency CO 39 Hence in decreasing order of e f f i c i e n c y the four could be ranked fo l lows; Hat Creek Oxidised Kaiser - Stock p i l e refuse ,, . . , , No s i g n i f i c a n t d i f fe rence Kaiser - Special plant feed , . , , K v between these three coals Cominco Ash 3.1.4. General Comments Changes in adsorpt ive capacity or metal removing e f f i c i e n c y of coals w i l l be described as " s l i g h t " , " s i g n i f i c a n t " , "marked" e t c , and the use of actual quant i ty , percentage, e t c , w i l l be avoided in most cases. Since th i s study is for comparative purposes on ly, the actual values have no s i g n i f i c a n t meaning s ince they are dependent on so many var iab les . Riaz chose to develop isotherms by changing the i n i t i a l concentrations of the metal ions while keeping the coal weight constant. Tin Tun^ in most cases changed the coal weight and kept the i n i t i a l concentrat ion constant. The isotherms developed by these methods w i l l be ident i ca l within a small concentrat ion range but w i l l be d i f f e ren t outside i t . To be able to make accurate comparisons, i t is necessary . that the data taking procedures are cons i s tent . As long as a l l coals were tested in the same manner, the comparisons are v a l i d . Since isotherms in th is study were developed by changing i n i t i a l concentrat ions, K.C. SPR and K.C. SPF can be compared with R iaz ' s^ resu l t s while H.C. OX and CO. Ash cannot be compared with Tin Tun's^ resu l t s except when i n i t i a l concentrations are s im i l a r . 3.1.5- Comparison of Hat Creek,wjth Act ivated Carbon Metal adsorbing capacity of H.C. OX was compared with Darco act ivated carbon grade 12 x 20, which is a commercially ava i l ab le adsorbent. Batch tests were performed with H.C. OX and act ivated carbon, using metal d isso lved in both water and primary e f f l u e n t . Copper: Adsorption isotherms for copper removal using act ivated carbon and H.C. OX are shown in Figure 3.13. Act ivated carbon exhibited better metal adsorption capacity than H.C. OX under test condi t ions . The d i f f e rence between the two is comparatively uniform and the performance of H.C. OX is cons i s tent l y lower over the concentrat ion range tested. The increase in adsorption capacity for copper in water so lut ion as compared to that in primary e f f l uent is as much as 100%, p a r t i c u l a r l y for higher equ i l ib r ium concentrat ions. Lead: The a b i l i t y of both H.C. OX and act ivated carbon to adsorb lead from both primary e f f l uen t and water so lut ion was tested and the isotherms are shown in Figure 3.1**. Within the concentrat ion range tested, both removed lead from water so lut ion completely. The capacity was s l i g h t l y lower for act ivated carbon and tremendously reduced for H.C. OX when used to treat primary e f f l u e n t . This marked reduction makes H.C. OX much i n f e r i o r to act ivated carbon in removing lead from primary e f f l u e n t . E q u i l i b r i u m c o n e - m g / L F i gure 3-13 Copper Adsorption Isotherms hi Equilibrium cone. - mg/L Figure 3- 14 Lead Adsorption Isotherms ^3 Z i nc: Adsorption isotherms are given in Figure 3 . 1 5 - The a b i l i t y of H.C. OX to remove z inc from water so lut ion and from primary e f f luent was better than that of act ivated carbon. Furthermore, the metal adsorption capac i t ies of both H.C. OX and act ivated carbon were higher when t reat ing primary e f f l uent than when t reat ing a water so lut ion of z inc . These observations are opposite to what were observed with copper and lead. Thus H.C. OX seems to be a better choice than act ivated carbon with regard to z inc removal from wastewater. Mercury: The performance of H.C. OX was compared with act ivated carbon (see Figure 3-16) in the removal of mercury from primary e f f l u e n t . Act ivated carbon produced s i g n i f i c a n t l y better resu l ts than H.C. OX. The d i f fe rence between the two was 100% or greater over the concentra-t ion range tested. 3 0 2 4 6 8 10 12 Equilibrium cone.-mg/L Figure 3 . 1 P Mercury Adsorption Isotherms Summary: Table 3-5* Summary of Comparisons Between Act ivated Carbon and Hat Creek Oxidised Coal Act i vated Carbon Hat Creek Oxidised Coal Metal Water Pr imary Water Pr imary Solut ion Sewage Ef f luent Solut ion Sewage Ef f luent Coppe r 1 2 3 k Lead 1 2 3 Z i nc k 3 2 1 Mercury 1 2 3 Numbers 1 to k denote batch systems in decreasing metal removal e f f i c i e n c y . (See Figures 3.13 to 3-16). Act ivated carbon has much greater surface area per unit weight than Hat Creek oxid ised coa l . Also a much greater percentage of surface area in act ivated carbon is ava i l ab le for sorpt ion processes while only smaller percentage is ava i l ab le in the case of coal due to the presence of various surface depos i ts . Hence the former can be expected to show greater metal adsorption capacity than the l a t t e r . Out of four metals tes ted, act ivated carbon was superior to H.C. OX with regard to adsorption of copper, lead and mercury, and i n f e r i o r to H.C. OX with regard to adsorption of z i n c . This is poss ib ly due to the removal of z inc from so lut ion by chemical react ions with surface deposits on c o a l , than by sorpt ion means. For reasons discussed e a r l i e r in th i s chapter, greater metal adsorption can be expected to occur in water so lut ion than in primary sewage e f f l uen t . Out of four metals tes ted, greater adsorption capac i t ie s were obtained with water so lut ion of copper, lead and mercury, and primary sewage e f f l uent gave higher z inc adsorpt ion. Thus in both cases z inc behaved in a manner opposite to other three metals. (Refer Table 3 _5)• L i t e ra tu re research did not reveal this type of anomaly, nor did i t suggest any reason why z inc might act d i f f e r e n t l y . This behaviour is poss ib ly due to greater s t a b i l i t y of the z inc -organ ic complex that is formed, compared to the other three metal-organic complexes. 3.2 Column Tests : Compared to batch te s t i ng , column tests represent continuous systems. As in batch te s t s , the capacity of coal to adsorb heavy metals can be ca l cu la ted . A plot of metal concentrat ion in column e f f luent against volume passed through.gives the "breakthrough curve" from which metal adsorption capac i t ie s can be ca l cu l a ted . Thus th is method of test ing can a l so be used to compare the performance of d i f f e r e n t metals, but th is time in a dynamic system. Sample ca l cu l a t i ons showing the pro-6 cedure for ca l cu l a t i ng adsorption capacity is shown in Appendix 11. Adsorbing materia ls for these tests were H.C. OX, K.C. SPR and Act. Carb. (Darco act ivated Carbon grade 12 x 20). 3.2.1 (a) Copper The f i r s t run was car r ied out with an inf luent copper concentrat ion 2 of k mg/1 at a flow rate of 1 gpm/ft . The breakthrough curves obtained from th is run are shown in Figure 3-17. Breakthrough was not attained ACT. CARB o — -Influent cone. pH*4.0 Flow rote * Igpm/ft. Column depth 5" Coal weight 1 K.C. SPR = 9.5g ACT. CARB = 5.0g H.CR. ' 7.75g H.CR. 10 II Throughput volume - liters Figure 3-17 Breakthrough Curve for Copper h3 with H.C. OX c o a l , due to b io log i ca l a c t i v i t y which plugged the column a f te r a throughput of 12 l i t e r s . From the breakthrough curves obtained i t is evident that a column height of 5 inches is too great for H.C. OX, but not enough for K.C. SPR and Act ivated carbon to show metal breakthrough c h a r a c t e r i s t i c s . The plots obtained with act ivated carbon and K.C. SPR a l so indicate com-parat ive ly low rates of adsorption and low metal adsorption capac i t i e s . The reasons for choosing a column height of 5 inch are explained in sect ion 2.6.2. In Figures 3- 18 and 3-19 are shown breakthrough curves obtained 2 with 5 gpm/ft flow rate. From Figures 3.17, 3- 18 and 3.19 adsorption capac i t ie s for the coals and act ivated carbon were ca lcu la ted and plotted against the r a t i o of e f f l uen t to in f luent metal concentrat ions (C/Co) in Figure 3.20. From Figure 3.20 i t is evident that; (l) Adsorption capacity of coals increase with increas ing e f f luent concentrat ion: (higher C/Co) (11) For the same e f f l uen t concentrat ion each coal has a higher adsorption capacity at the lower flow rate due to the higher contact time: ( i l l ) Under column operating cond i t ions , the three adsorbents can be ranked in the decreasing order of removal e f f i c i e n c y as: Hat Creek Coal Act ivated Carbon Kaiser - Stock P i l e Refuse. 1.5 2 2.5 Throughput volume ACT. CARB Influent cone. H pH = 4.0 Flow rate = 5gpm/ft Column depth 5" Coa I weight « K.C. SPR = 9.5g ACT. CARB =5.0g H. CR. = 7.75g 3 liters 3.5 4.5 F i gu re 3-18 Breakthrough Curve for Copper cn I o c o c 3 UJ "pH = 4.0 Flow rate B 5gpm/ft' Column depth * 5" Coal weight' K.C. SPR = 9.5g ACT. CARB = 5.0g H.CR. = 7.75g Influent cone. K.C.SPR ACT. CARB 1 1 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Throughput volume - liters 0.8 0.9 Figure 3- 19 Breakthrough Curve for Copper COAL ROW RATE O H.CR. I gpm/ft S • Q H.CR. 5 • • ACT. CARS I O O ACT.CARB 5 A A KCSPR I A A K C S P R 5 pH = 4.0 INFL .CONC = 4 m g / L COLUMN DEPTH = 5" COAL WEIGHT : K.C. SPR = 9.5g ACT. CARB = Sg H.CR. = 7.75g / P » 0.25 0.50 C/ Cr 0.75 Figure 3.20 Comparison of Adsorption Capacity for Copper in Primary E f f luent at D i f fe rent Flow Rates The e f f l uent metal concentrat ion before breakthrough is a funct io of the rate of adsorpt ion, where the rate of adsorption is defined as the net quantity of metal ions which adsorb on the coal surface per unit time. This rate of adsorption is usual ly dependent on inf luent metal concentrat ion, form of metal in s o l u t i on , a v a i l a b i l i t y of adsorption s i t e s , temperature and pH. Since a l l other parameters are kept constant throughout a column run, the e f f l uent metal concentra-t ion in our tests is a funct ion of ava i l ab le adsorption s i t e s . Usual ly "Tota l s i te s o r i g i n a l l y present" is a constant. " S i te s already used" increases with increasing time. During the adsorption process s i t e s already occupied are s t i l l ac t i ve though they don't con-t r ibu te to net adsorbt ion. By a process of adsorption and desorption state of equ i l ib r ium is approached on those s i t e s while unused s i te s a s t i l l providing a net adsorpt ive trend. Since the wastewater used in th i s study is primary e f f l uent from a sewage treatment p lant , i t is r i ch in microorganisms and b i o l o g i c a l l y very ac t i ve . When th i s waste-water is passed through a column of c o a l , microorganisms w i l l attach themselves to coal and begin to mult ip ly i f environmental condit ions are favourable. Continuous supply of d i sso lved oxygen and substrate provided by the flow of wastewater, and the a v a i l a b i l i t y of su i t ab le growth sur face, make environmental condit ions ins ide the coal column ideal for growth and m u l t i p l i c a t i o n of microorganisms. Microbia l growth is usua l ly in the form of an expanding layer on the media surface, hence i t tends to reduce the a v a i l a b i l i t y of the surface for adsorption continuously. Common fecal bacter ia (Esh. c o l i ) which predominate among the aerobic commensal organisms present in the 12 healthy gut, thus abundant in the wastewater used, are capable of mult ip ly ing once every 15 to 20 minutes under ideal condi t ions . With 2 a column flow of 1 gpm/ft , the time required to pass 0 .08 1 of waste-water through the column is s u f f i c i e n t to double the number of Esh. co l i present. This microbial growth on s o l i d surfaces resu l t s in a microbial f i l m , which due to i t s viscous nature, great ly reduces the rate of 13 d i f fu s i on of the adsorbate through i t . Hence, by b i o l og i ca l a c t i v i t y , an e f f e c t i v e blanketing of coal surface occurs, and the rate of d i f f u s i on could be so reduced that a coal surface covered by microbial growth has a much reduced c a p a b i l i t y for adsorpt ion. Hence the " t o t a l s i te s o r i g i n a l l y present" w i l l continuously decrease and can be compared to a s i tua t i on where the height of column is being continuously decreased by removing coal and thereby making i t not ava i l ab le for adsorpt ion. Hence the adsorption capaci ty of the coal can be expected to be lower when used to treat sewage e f f l uen t compared to pure metal s o l u t i on . Another very important d i f fe rence between sewage e f f l uen t and metal so lu t ion is that the former contains d i s so lved organics in a r e l a t i v e l y high concentrat ion whi le the l a t t e r has none. As discussed in sect ion 3.1.2 (a) the presence of organics can be expected to inf luence metal adsorption c h a r a c t e r i s t i c s . Depending on the type of adsorbate ( i on i c charge, and s ize) type of adsorbent (pore s izes) and re l a t i ve concentra-t ion of metal and organics , the rate of adsorption and adsorption capacity w i l l be in f luenced. This could be as a resu l t of d i r ec t com-pe t i t i on between organic molecules and metal ions for adsorption s i t e s or due to the formation of organo-metal complexes (as opposed to aquo complex) having a much slower or fa s ter react ion rate for adsorption on to s i te s with in the coal p a r t i c l e s . 55 The combined e f f ec t s of competition for adsorption s i te s between metal ions, organo-metal complexes and organic molecules and the blanket-ing e f fec t of microbia l growth with in the adsorption column on the breakthrough curve are unknown. Perhaps the gradual and continuous r i se in the e f f l uent metal concentrat ion as observed with H.Cr coal in Figure 3.18 was due to the inf luence of above combined e f f e c t s . Tests ca r r ied out with water so lu t ion produced constant e f f l uen t metal con-centrat ion t i l l breakthrough was achieved. Column runs were a l so ca r r i ed out with copper so lu t ion in water 2 of k mg/1 concentrat ion at 1 gpm/ft , with the resu l t s shown in Figure 3.21. Adsorption capac i t ie s were ca lcu la ted and given in Figure 3.22. Results indicate that Hat Creek and Kaiser coals have reduced adsorption capac i t ies in primary e f f l uen t and i t is somewhat unchanged for act ivated carbon. Hat Creek coal performed better than act ivated carbon under both condi t ions . Column tests were ca r r ied out with sewage containing a copper 2 concentrat ion of 10 mg/1 at 1 and 5 gpm/ft flow rates, and the break-through curves are in Figure 3-23 and 3.2k re spect i ve ly . Adsorption capac i t ies at these two flow rates were ca lcu la ted and shown in Figure 3.25. Again Hat Creek coal has shown a d i s t i n c t super io r i ty over act ivated carbon at both flow rares. Comparison of metal adsorption capac i t ies for d i f f e r e n t copper in f luent concentrations are shown in Figure 3.26. Greater adsorption capac i t ie s were obtained with higher in f luent metal concentrat ions. (b) Lead Column runs were ca r r i ed out with an in f luent lead concentrat ion 2 of k mg/1 at 1.0 and 5.0 gpm/ft flow rates, with breakthrough curves Eff luent c o n c . - m g / L — ro ui ro in oi c fD O -I o — • 3 3 XI QJ —1 ~\ ZT -< . —\ o m O c -u 3 |Q-h 3-— • o T3 c -tl C ro 3 CO rt re vol QJ QJ c 3 3 O-rt a zrs: - i i QJ o rt c ID a ZT -i O o c — • -1 c < rt ro O -ti 3 o -\ c~> O T3 X) ro 3 9 5 Figure 3-22 Comparison of Adsorption Capacity for Copper in Primary E f f luent and D i s t i l l e d Water Influent cone. pH = 4.0 Flow rote 5 lgpm/ft' Column depth * 5" Cool weight » K.C. SPR * 9.5g ACT. CARB = 5g H.CR.= 7.75g ACT. CARB 2 2.5 3 3.5 Throughput vo Iu me - li ters H.CR. 4.5 Breakthrough Curve for Copper 10 Influent cone. ACT. CARB pH * 4.0 Flow rote 3 5gpm/ft' Column depth - 5" Coo I weight' K.C. SPR = 9.5g ACT.CARB - 5g H. CR.= 7.75g I 1 2 2.5 3 3.5 Throughput volume - liters Breakthrough Curve for Copper 4.5 o 4| o •o 2 31 •o o o> E o a Cool Flow rote H.CR. "J ACT.CARB J Igpm/fl K.C.SPR " O — H.CR •- . •> - ACT.CARB J5gpm/(t' -- K.C.SPR J pH = 4 . 0 Influent conc. = 4 m g / L Co Iu mn de pth = 5 " Cool weight^ K . C . S P R = 9 . 5 g ACT.CARB s 5 g H. CR. = 7. 7 5 g / 0.2 0.3 c/c_ 0.4 0.5 0.6 Figure 3-25 Comparison of Adsorption Capacity for Copper in Primary E f f luent at D i f fe rent Flow Rates o } 10 m g / L - C r - H.CR.OX — A C T . CARB --Q— H.CR.OX •( } 4mg / L ACT .CARB 1 pH = 4 .0 Co Iu mn depth - 5" F low rote : I gpm/f t J I I L 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 C/C„ Figure 3-26 Comparison of Adsorption Capacity for D i f ferent Copper Influent Concentrations being shown in Figure 3-27 and 3-28 re spec t i ve ly . Again, an inc l ined slope was obtained probably due to microbia l growth as explained e a r l i e r . For both act ivated carbon and Hat Creek coal a high degree of scat ter with regard to data points was obtained. The scat ter seemed rather confined at ear ly stages but developed over a larger range at la ter stages. The reason for th i s behaviour is unknown. It could be that lead ions were complexed to a p a r t i c u l a r type of organics which was used as a substrate by ce r t a in groups of microorganisms and thus got absorbed into microbial c e l l s , a f t e r which due to c e l l u l a r ion ic regula-t ion by osmotic processes were excreted outs ide the microbial c e l l s . Rate of substrate intake and c e l l u l a r metabolism of microorganisms are dependent on the phase of microorganisms' l i f e cyc le (lag phase, growth phase, mul t ip ly ing phase etc) and hence apart from the inf luence of adsorption c h a r a c r e r i s t i c s of the coa l s , i t is poss ib le that e f f l uen t metal concentrat ion has a l so been inf luenced by the phase of micro-organisms' l i f e cyc l e . Answers to such questions are not known at this time. Adsorption capac i t ie s were ca lcu la ted from the l ines of best f i t from Figures 3.27 and 3-28 and p lot ted in Figure 3.29. Hat Creek coal and act ivated carbon performed in a much superior manner to Kaiser c o a l , with act ivated carbon performing somewhat better than Hat Creek c o a l . Under column operat ing cond i t ions , the three adsorbents can be ranked in the decreasing order of removal e f f i c i e n c y as: Act ivated Carbon Hat Creek Coal Kaiser - Stock P i l e Refuse Influent cone. Throughput volume - l iters Figure 3-27 Breakthrough Curve for Lead ON Influent cone. E I o u c 3 Q H.CR-• ACT. C A R B •a K . C SPR. pH = 4 . 0 F l ow ro te = 5gpm/I t Co lumn depth - 5" Coo I weight : K C S P R = 9.5g A C T . C A R B = 5g • H.CR. = 7.75g D • 1 I 2 3 Th rough tpu t v o l u m e - l i ters Figure 3-28 Breakthrough Curve for Lead ' ON -E-CA vn Figure 3-29 Comparison of Adsorption Capacity for Lead in Primary E f f luent at D i f ferent Flow Rates 66 (c) Zinc Column runs were ca r r i ed out with an inf luent z inc concentrat ion 2 of 0.5 mg/1 at 1.0 and 5.0 gpm/ft flow rates , with breakthrough curves shown in Figures 3-30 and 3-31 r e spec t i ve l y . Adsorption capac i t i e s were ca lcu la ted from these and are shown in Figure 3-32. As expected Hat Creek and act ivated carbon performed much superior to Kaiser coa l . As with Copper, once again Hat Creek performed better than act ivated carbon. More column tests were performed with in f luent z inc concentrat ion 2 of 2.0 mg/1 at 1.0 and 5.0 gpm/ft flow rates and breakthrough curves are shown in Figure 3-33 and 3.3** re spec t i ve ly . Capac i t ies ca lcu la ted from these are shown in Figure 3-35. Again Hat Creek and act ivated carbon performed much super ior to Kaiser coal and Hat Creek had much higher adsorption capacity than act ivated carbon under these column test ing cond i t ions . Greater adsorption capac i t ie s were obtained with higher in f luent metal concentrat ions. Under column operat ing condit ions the three adsorbents can be ranked in the decreasing order of removal e f f i c i e n c y as: Hat Creek Coal Act ivated Carbon Kaiser - Stock P i l e Refuse. 0.5 _i 0.41 E I 0 .3 u c o o 0.2 c 3 5 o . UJ Influent cone. K.C.SPR. pH =4.0 Flow rate s I gpm/ ft Column depth 8 5 " Coo I weight 8 K.C. SPR * 9.5g ACT. CARB - 5g H.CR. « 7.75g ACT.CARB H.CR. I 2 3 Throughput volume - l i ters Figure 3-30 Breakthrough Curve for Zinc ON Influent cone, pH = 4.0 Flow ro te = 5gpm/ft Column depth B 5" C o o l weight* K . C . S P R = 9.5g ACT.CARB * 5g H.CR. = 7.75g H.CR. Throughput volume - l i ters Figure 3-31 Breakthrough Curve for Zinc 0.3 o o u 1 0.2| o in •o o CP E Cool Flow rote - O - H.CR. , — • — ACT.CARB I gpm/ f t * —Cr- K.C.SPR J --D-- H.CR. -, ACT.CARB 5 gpm/ft - • 6 — K.C.SPR J pH = 4.0 Influent c o n c . - 0 . 5 m g / L Co lumn depth : 5" C o a l , weight^ K.C. SPR = 9.5g ACT. CARB = 5g H . C R . : 7. 75 g " 0.1 o a. o O 0.1 0.2 0.3 0.4 C/C r 0.5 0.6 0.7 0.8 Figure 3-32 Comparison of Adsorption Capacity for Zinc in Primary Ef f luent at D i f ferent Flow Rates ON Throughput volume - ii*ers —i o Figure 3-33 Breakthrough Curve for Z i n c 0 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 Throughput volume - liters F i gure 3-34 Breakthrough Curve for Zinc 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 C/C 0 Figure 3.35 Comparison of Adsorption Capacity for .Z inc in Primary E f f luent at D i f fe rent Flow Rates 0.35 0 .30 o o » 0.25 •o JO I 0 .20 o cn E 0.15 o a. « 0.10 0 .05 i t r / H.CR.OX ACT. CARB } 2 m g / L --Q-- H. CR.OX 1 n _ .. f 0.5 m g / L - - • — ACT. CARB pH = 4.0 Column depth = 5" Flow rate - Igpm/ft 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 .8 0.9 'o C / C , 1.0 Figure 3 - 3 6 Comparison of Adsorption Capacity for D i f ferent Zinc Influent Concentrations 7k Chapter k CONCLUSIONS Under batch test condit ions with concentrat ion ranges spec i f i ed in the text ; 1. Of four coals (Hat Creek Oxid ised, Kaiser - stock p i l e refuse, Kaiser - spec ia l plant feed, Cominco-Ash) tes ted, Hat Creek coal had the a b i l i t y to remove heavy metals from f i l t e r e d primary sewage treatment plant e f f l uen t better than the other th ree; 2. With regard to removal of copper, Hat Creek coal was able to a t t a in about 80% removal e f f i c i e n c y while the others managed about 60%; 3. With regard to lead, removal e f f i c i e n c i e s obtained were very low. Hat Creek oxid ised was about 17% e f f i c i e n t while the others were about 5%; k. With regard to removal of z i n c , Hat Creek coal was able to a t t a i n 80% removal e f f i c i e n c y whi le the others atta ined about 15%; 5. With regard to mercury Hat Creek coal had about 65% e f f i c i e n c y while the others had about 15%; 76 6 . The adsorption a f f i n i t i e s of the four metals tested towards Hat Creek coal ranked in a descending order were copper, z i n c , lead and mercury; 7- When Hat Creek coa l ' s performance was compared with that of ac t ivated carbon the l a t t e r was found to possess greater capaci ty to adsorb copper, lead and mercury while the former was super ior with regard to removal of z i n c ; 8. A l l four coals had lower metal adsorption capac i t ie s from primary e f f l uen t than from water s o lu t i on . 9 . A l l coals indicated increasing adsorption capacity with increas ing pH. Under.column test condit ions with in f luent concentrat ions spec i f i ed in the text , the fo l lowing conclusions were drawn; 10. Of the two coals tes ted, Hat Creek coal had better a b i l i t y to remove heavy metal from f i l t e r e d priamary e f f l u e n t better than the Kaiser coal sample; 11. Column tests were inf luenced by the growth of micro-organisms on coal surface and eventual plugging; 12. When the performance of Hat Creek coal is compared to that of ac t ivated carbon, the l a t t e r was found to possess greater capacity to adsorb lead whi le the former was superior with regard to adsorption of copper and z i n c ; 13. A f i v e - f o l d increase in flow rate through the column reduced adsorption capac i t ie s of both coals and the act ivated carbon; 14. Greater adsorption capac i t i e s were obtained at higher in f luent metal concentrat ions; 76 15- Adsorption a f f i n i t i e s towards Hat Creek coal ranked in the descending order are copper, z i n c , and lead; 16. Of the four coals studied Hat Creek coal proved to be the most e f f e c t i v e in heavy metal removal from wastewater and i t s adsorption capac i t i e s were comparable to that of the act ivated carbon tested. 77 Chapter 5 RECOMMENDATIONS 1. Hat Creek coal was proven to be much superior to other B.C. coals tested with regard to heavy metal removal from wastewater and hence any fur ther deta i led study should be r e s t r i c t e d to th is coa 1 . 2. Further studies with Hat Creek coal should be ca r r ied out in p a r a l l e l with d i f f e r e n t grades of act ivated carbon for com-parat ive purposes. 3. Comparative studies between ch lor inated and unchlorinated waste-waters must be ca r r ied out to evaluate the e f f e c t of ch l o r i na t i on on microbial a c t i v i t y . k. Studies should be ca r r i ed out to i dent i f y the type of micro-organisms most predominant in the column and i t s inf luence on column proper t ie s . 5. If poss ib le microorganisms should be made to a s s i s t in heavy metal removal s ince some forms have the a b i l i t y to absorb heavy metals. 78 6. The a b i l i t y of Hat Creek coal to remove d isso lved organics from treated sewage e f f l uen t should be invest igated, as should the inf luence of microbia l growth on that removal process. 7. If microorganisms cannot be made to work to advantage, methods of stopping or c o n t r o l l i n g t h e i r growth on coal surface should be invest igated. 8. Work should be d i rec ted to a r r i ve at optimum flow ra te , column depth, and p a r t i c l e s i z e to y i e l d high adsorption c apac i t i e s . 9 . Minimum equ i l ib r ium e f f l uen t metal concentrat ions and maximum adsorption capac i t i e s obtained at optimum operat ing condit ions should be determined and compared with that for act ivated carbon. 1 0 . Influence of pH on column performance should be s tud ied, taking into cons iderat ion i t s e f f e c t on microorganisms. Microbia l a c t i v i t y is s en s i t i ve tc pH cond i t i on . Also a f f ec t of pH on com-plexat ion and p r e c i p i t a t i o n of d i f f e r e n t metals should be considered. 1 1 . An economic f e a s i b i l i t y study of using Hat Creek coal in advance waste treatment should be ca r r ied out taking into cons iderat ion i t s poss ib le use as an energy source a f te r waste treatment. 12 . If coal is to be burned as a f u e l , fa te of metals adsorbed should be determined. If metals escape with stack gases, i n s t a l l a t i o n of a i r po l l u t i on control devices may be necessary. If metals remain in ash i t s d isposal method should minimise escape of metal by leaching. These facts should be taken into account when conducting any f e a s i b i l i t y study. 79 REFERENCES 1. Buhler, D.R., Environmental Contamination by Toxic Metals. Heavy metals in the Environment. Water Resources Research In s t i tu te , Oregon State Un i ve r s i t y , SEMN WR016 73:1-36, January 1973. 2. Argo, D.G. and G.L. Culp, Heavy Metals Removal in Wastewater Treatment Processes : Part 1 Water and Sewage Works 119(8):62-65» August 1972. 3. Development of Coal Based Sewage Treatment Process. Research and Development Report No. 55. O f f i c e of Coal Research, U.S. Department of I n ter io r , Washington, D.C. 1971. 4. Coulthard, T .L . and Mrs. Samia Fad l , The Adsorption of Water Po l lutants by a Coal Sorption Process. Paper No. 73 -506 presented at Can. Soc. Agr. Eng. Annual Meeting at V i c t o r i a , B.C. August 1973-5. Henren, M.K., Heavy Metals Removal by Using Coal . Unpublished M.A.Sc. Thesis , Un iver s i ty of B r i t i s h Columbia, Vancouver, B.C. 1974. 6. R i az , M. , Removal of Heavy Metals Using Granular Coal. Unpublished M.A.Sc. Thes i s , Un iver s i t y of B r i t i s h Columbia, Vancouver, B.C., 1974. 7. T in Tun, U., Adsorption of Heavy Metals at Low Concentration Using Granular Coal . Unpublished M.A.Sc. Thes i s , Un ivers i ty of B r i t i s h Columbia, Vancouver, B.C., 1974. 8. Determination of Mercury by Flameless Atomic Adsorption J a r r e l l Ash - Atomic Absorption Ana l y t i ca l Method. No Hg-1, August 1970. 9. F a i r , G.M., J . C . Geyer and D.A.Okun, Water and Wastewater  Engineering, Volume 2, Chapter 28. John Wiley and Sons Inc. New York, 1968. 10. Sawyer, C.N. and P.L. McCarty, Chemistry for Sanitory Engineers, Chapter 2. McGraw-Hill Book Company, New York 1967. 80 11. Lehniger, A . L . , Biochemistry. Chapter 8. Worth Pub l i shers , Inc. New York, 1971. 12. Cruickshank, R., Medical Microbio logy, Chapter 18, Church i l l L iv ingstone, London, 1972. 13. Atkinson, B., Biochemical Reactors, Chapter 7, Pion L imited, London, 197**. \ 

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