Treatment of Water by Granular Activated Carbon - ACS Publications

13 Pilot Scale Evaluation of Ozone-Granular Activated Carbon Combinations for Trihalomethane Precursor Removal Downloaded by UNIV OF CINCINNATI on June 4, 2016 | http://pubs.acs.org Publication Date: March 15, 1983 | doi: 10.1021/ba-1983-0202.ch013

WILLIAM H. GLAZE—University of Texas at Dallas, Graduate Program in Environmental Sciences, Richardson, T X 75080 JAMES L. W A L L A C E , D O U G L A S WILCOX, K. R. JOHANSSON and K. L. DICKSON—North Texas State University, Denton, T X 76203 BOBBY SCALF and ROGER NOACK—Henningson, Durham, and Richardson, Dallas, T X 75230 ARTHUR W. BUSCH —Oligodynamics Corporation, Dallas, T X 75225 1

The biological activated-carbon process for removing trihalomethane precursors in drinking water was investigated at a pilot water treatment research facility. A series of carbon columns was used that allowed the regular monitoring of water chemistry and biological parameters. It was found unlikely that the events taking place on the GAC could be explained by purely physical processes, and a largely microbiological mode is indicated for the last several weeks of the study.

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HIS REPORT DESCRIBES a pilot water treatment research facility that was operated to evaluate the so-called biological activated-carbon process for removal of trihalomethane (THM) precursors in a drinking water source. The pilot plant included a package water treatment plant with the capability of supplying 10 gallons/min (GPM) of settled/filtered water of low turbidity. This water provided the test medium for the evaluation of granular activated carbon (GAC), with and without preozonation, for T H M precursor removal. Various water chemistry and biological parameters were monitored on a regular basis to determine to what extent Current Address: University of Texas at Dallas, Graduate Program in Environmental Sciences, Richardson, T X 75080. 1

0065-2393/83/0202-0303$06.00/0 © 1983 American Chemical Society

McGuire and Suffet; Treatment of Water by Granular Activated Carbon Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

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precursor levels were removed by various unit processes in the plant and how treatment could be improved by control of process variables such as ozone contact time. Most importantly, the project was designed to determine to what extent GAC columns maintained sustained removal capabilities past the time of expected exhaustion and hopefully to determine the role microorganisms played in the purification process.

Downloaded by UNIV OF CINCINNATI on June 4, 2016 | http://pubs.acs.org Publication Date: March 15, 1983 | doi: 10.1021/ba-1983-0202.ch013

Pilot Plant Facility The entire pilot plant with the exception of the raw water intake line [5-cm (2-in.) black steel] and pumps was housed in a 12.2-m (40-ft) dropframe trailer (similar to a moving van). The trailer was located within the gates of the Thomas L. Amiss Water Treatment Plant in Shreveport, La, and utilized raw water taken directly from Cross Lake, the principal source of water for the city. The pilot plant (Figure 1) had the capability for preoxidation of raw water with ozone, chlorine dioxide, and perhaps other oxidants, but in this study no preoxidant was used. Raw water was first filtered through a Sinflex strainer [0.08-cm (0.03-in.) perforations] and then flowed directly to a 10 GPM-rated Neptune-Microfloc "Waterboy" package treatment plant with four chemical feed options, tube settler, and multimedia filter. This unit was operated near rated capacity with the product water ultimately being split between three treatment trains, each with two carbon columns in series. The train with Columns 5 and 6 was a "control" train in that no ozone contacted the water prior to entering the carbon columns. Trains with Columns 1-4 received water which had been oxidized in the ozone contact basin. This contact basin utilized a highspeed turbine injector designed by Kerag (Switzerland) and manufactured by Howe-Baker (Tyler, TX). At 6.0 GPM, retention time in the contact basin was approximately 3.3 min. Ozone was generated from dry cylinder oxygen using a Howe-Baker " E S C O Z O N E E4" generator capable of producing up to 20 g/h of ozone. Water from the ozone contact basin (6.0 GPM) was split into a 2.0-GPM stream to Columns 1 and 2 and a 4.0-GPM stream was sent to an ozone detention basin. Retention time in the ozone detention basin was an additional 30 min, after which 2 GPM of water was pumped to Columns 3 and 4. A total of eight carbon columns was included in the pilot plant, each 30 cm (12 in.) diameter 304 SS, schedule 12 pipe. With 1.2 m (4 ft) of GAC, each carbon column had an empty bed contact time (EBCT) of 12 min at 2.0 GPM. In the first phase study, six carbon columns were operated in pairs (1 and 2; 3 and 4; 5 and 6). Each pair had its own backwash storage basin receiving water from the respective column pairs, a backwash pump, a feed pump, and fittings for air sparging as a part of the backwash procedure. Before and after each column a pressure gauge was


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Pilot Scale Evaluation of Ozone-GAC Combinations


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mounted in-line to provide a basis for initiation of backwash, which was a manual procedure. Also between Columns 3 and 4, 1 and 2, and 5 and 6, in-line injectors for oxygen enrichment were provided. Filtrasorb 400 carbon was provided gratuitously by Calgon Corp. as a means of assisting this research. Weekly composite samples were taken from the pilot plant by timer controlled valves located at the sampling points shown in Figure 1. Samples were taken at 4-h intervals; they were not of equal volume, however, since the sample points were at different pressures and therefore delivered different volumes of water when opened for a set interval. Water was transferred through 0.3 cm (1/8 in.) diameter black Teflon tubing to glass containers in refrigerators positioned close to the point of sampling. On the date composite samples were collected, discrete samples also were taken at each point by manually opening the valves. These samples were used for the analysis of inorganic carbon, ozone residual, dissolved oxygen, ammonia, nitrate, and microbiological parameters. Trihalomethane formation potential (THMFP), total organic carbon (TOC), color, UV absorbance, conductivity, and pH were measured on composite samples. T H M F P was determined by chlorinatiorf of samples at 20-mg/L dose at ambient temperature and at a buffered pH of 6.5. Incubation was for 3 days, at which point the T H M yield had leveled. T O C and inorganic carbon were determined using the Dohrmann DC-54 analyzer following the manufacturer s directions. Microbiology studies were divided into two components: a microbial identification component and a microbial activity component. The methods of analysis for total plate counts, total coliforms, and fecal coliformjs were taken from "Standard Methods for the Examination of Water and Wastewater" (i). Some procedural modifications were implemented in the total plate count method, i.e., changes in culture media (from tryptone glucose yeast agar to soil extract agar), incubation temperature (from 35°C to 28°C), and incubation period (from 48 h to 7 days (2). Total coliform and fecal coliform densities were calculated according to the membrane filtration method outlined in Reference 1 and EPA Document No. 600/8-70-017 (3). Isolation of major groups of microorganisms was accomplished by plating on soil extract agar. The dominant organism (colonies) were subcultured, gram stained, and processed through a determinative scheme. Isolated colonies also were evaluated using five routine selective media: 1. McConkey: gram negative organisms 2. Actinomycete isolation agar: Actinomycetes 3. Pseudomonas isolation agar: specific types of Pseudomonands such as P. fluorescens 4. Burkes: nitrogen fixing bacteria such as Azotobacter sp.


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307 Pilot Scale Evaluation of Ozone—GAC Combinations

5. Cooke rose bengal agar: most types of fungi Cell counts of organisms associated with the carbon particles were determined by sonication of the carbon sample for 1 min at 60 watts in a phosphate buffer to dislodge the microorganisms. An aliquot of the phosphate buffer containing dislodged microorganisms was then plated on soil extract agar and incubated for 5-7 days.


Pilot Plant Operational Parameters The Shreveport pilot research facility was operated from Dec. 29, 1979 to July 23,1981. This report describes the first 60 weeks of operation extending to March 6, 1981. During this period, the following operational conditions were used. The alum dose was 50 mg/L, nominal, and the sodium hydroxide dose was selected to increase water pH and alkalinity so as to optimize raw water turbidity removal. The ozone dose was 6.3 mg/L from Dec. 29,1979 to Feb. 10,1980; it was 2.0 mg/L to Apr. 10,1980, and then was 2.5 mg/L to March 6, 1981; transfer efficiency was 75-85%. The GAC column parameters were 2.0 GPM or 2.5 gal/ft -min, 12 min of E B C T for each column, and downflow mode. As an example of raw water characteristics, the average values for summer and winter periods are given in Table I. 2

Pilot Plant Performance The data obtained from the first 60 weeks of operation of the pilot plant are too extensive to analyze in detail. Therefore, a summary of principal conclusions is given. More detailed discussions and analysis of the data will be published elsewhere (4, 5). Pretreatment. The Neptune-Microfloc "Waterboy" pretreatment unit performed well, giving low turbidity water (

Treatment of Water by Granular Activated Carbon - ACS Publications

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