WASTE RECOVERY: Removing Refractory Compounds

Transcription

1 WASTE RECOVERY: Removing Refractory Compounds Activated carbon adsorption is being used to process waste from a synthesized terpene plant that uses isoprene as raw material. S. Wiseman, Rhodia, Inc., Freeport, Tex., and B. T. Bawden, Calgon Corp., Pittsburgh, Pa. The Freeport, Tex., plant of Rhodia, Inc., manufactures chemicals for the perfume and pharmaceutical industries. Starting with isoprene as a basic feed stock, the final products include dehydrolinalool, citral, pseudo ionone, methyl pseudo ionone, and citronellal. The plant is operated in two campaigns. In the first, isoprene is reacted with hydrochloric acid to form isoprene hydrochloride, which is reacted with acetone to form methyl heptenone. That, in turn, is reacted with acetylene to produce dehydrolinalool. Major waste streams are hydrochloric acid waste, steam condensate from the vacuum jets, and aqueous waste from the use of sparge steam in distillation. Because of the nature of the process, the aqueous waste contains a high percentage of caustic soda, which poses a ph control problem. In the second campaign, dehydrolinalool is rearranged to form citral, which is then reacted with acetone to form pseudo ionone, or reacted with methyl ethyl ketone to form methyl pseudo ionone, or hydrogenated to form citronellal. Waste from this operation includes sodium salts, steam condensate from vacuum jets, and aqueous waste from the use of sparge steam in distillation. Other wastes include sanitary, utility, rain run-off, and process decontamination streams. Treated waste water is discharged to the DOW Canal, which conveys treated waste waters from various industries in the area. The canal discharges to the Brazos River, which empties into the Brazos River Tidal Basin, and from there into the Gulf of Mexico. Effluent quality of waters discharged to the canal is intended to allow contact and non-contact recreation and propagation of fish and wildlife. Because a large portion of the organic material in Rhodia s waste water is biodegradable, biological oxidation was considered to be the most economical and reliable treatment process. Performance of the initial wastewater treatment system was poor and inconsistent, however, due to fluctuations in influent BOD,, COD, and ph. It was decided, therefore, to investigate further possible approaches toward improving the effluent quality to comply with Texas Water Quality Control Board discharge requirements. Studies were conducted under the supervision of Bernard Johnson, Inc., consulting engineers. Highly alkaline waste water Waste waters generated in the manufacturing process usually exhibit a ph greater than 1 and contain high concentrations of chloride and dissolved organics. Table 1 shows the analyses on an equalized composite sample of waste water obtained in late September, This sample was highly alkaline with a ph of The total organic carbon (TOC) content was 1,65 mg./l., with the fraction 6 of organics in the true dissolved state, as measured by the difference of TOC vs. soluble organic carbon (SOC), at 96%. The chemical oxidation demand (COD)-to-TOC ratio was 2.58 and is typical of many industrial waste waters. This ratio also indicates that there is some oxidizable material that is not organic in nature. The suspended solids level was quite low at 15 mg./l. Based on an average flow of 5,4 gal./day, the average daily suspended solids load was approximately 1 lb. Oils and greases, measured as ether extractable material, were very low at 2 mg./l. The measured chloride conoentratipn of 1,25 mg./1. did not merit special materials of construction, Initial pilot studies began in late February, 1 continued until mid-august of that year. In these studies, biological treatment systems consisting of aerated lagoons of five; 1, and 15 days retention times, and activated sludge units of five, 1, and 25 hr. retention times were operated on unequalized process waste mixed with utility blowdown and sanitary waste. All the biological units suffered from extreme fluctuations in influent BOD, COD, and ph. Performance of the activated sludge units was inconsistent and generally poor, with removal of COD and BOD running usually less than 3%. The three aerated lagoons, at times, performed well providing BOD and COD removals of 5 to 6%. However, fluctuations in the influent BOD and COD concentrations caused periodic major upsets from which the biological units did not recover. Initial adsorption isotherm tests on this waste water showed that activated carbon adsorption provided good COD removal, but also indicated that large amounts of carbon might be required. Calgon Corp. was contacted to aid in conducting additional adsorption feasibility tests. A validation study, undertaken to determine the applicability of granular activated carbon for the,treatment of the effluent, included the following specific objectives: 1. Determine the feasibility of granular activated carbon to reduce the organic content of the waste water. 2. Determine the effluent quality produced by an operating adsorption system. 3. Determine the; carbon exhaustion rate required to treat the waste to a practically attainable effluent TOC objective. 4. Determine possible pretreatment requirements prior to carbon adsorption. 5. Determine the most economic orientation of an adsorption system and the overall process required to produce the degree of treatment required with operational stability. Batch adsorption isotherms were conducted to determine the feasibility of adsorption to remove dissolved organics, Figures 1 and 2. Since the ph of the waste water CEP May 1977

2 , and 2.1.?he tests demonffective carbon utilization was ter was subjected to adsorption tion isotherms at ph 11.4,7., and 2.1. o the range of 1 mg./l. or less, rate was over 16 lb./ 1, gal. sample was used for further es column study was conducted on the pilot equalnd effluent to determine the effect of contact imal. The single fixed 13% of the influent or- hat removal of the highly adefficient subsequent treatment at this laboratory validation study d to affect the

3 Figure 3. Carbon adsorption followed by biological treatment, effect 1,2 1, COD WON EFFLUENT 1 UNIT NO. 6 1 UNIT NO. 7 h -\ NOV+-, DEC.1974 JAN FE. Figure 4. Carbon adsorption followed by biological treatment, effect on COD. 19 Based on studies conducted on the validation sample, the ability of a combination carbon-biological system to remove 9% of the soluble organics, measured as TOC, was predicted to be achieved at a carbon usage rate of 72 lb./ 1, gal. of waste water treated. pilot work Because of the lack of success with straight biological treatment of the process waste, it was decided to try biological treatment in conjunction with equalization and

4 studies, which began in late Noo equalization tanks, two aerated stam4 and pilot scale activated carbon columns. of the carbon adnt types of waste, Table 2. Comparison of raw waste water characteristics. September, 1974 June, 1976 ph BOD, (mg./l.) COD (mg./ 1.)...4,26...1,55 TOC (mg./l.)... 1, Oil and Grease (mg./l.) Chlorides (mg./l.)...1, ,8 1. to 11,5 mg./l. ranged from 39 to that of the un- typical of the waste owing January 12, carbon column was aign I1 the effluent To determine the effects of carbon adsorption on biological treatment the carbon treated process waste was mixed with utility blowdown and sanitary waste and then fed to a five day aerated lagoon. As in the case of biological treatment after equalization, carbon treated process waste and utility and sanitary waste were mixed in the ratio of one-third process waste to two-thirds utility and sanitary waste to aimulate future conditions. Duplicate aerated lagoons were also operated during this study. Effluent BOD and COD concentrations from these two biological units are plotted in Figures 3 and 4. Influent. COD values range from 1 mg./l. to 1,7 mg./l. and filtered effluent COD values ranged from 4 mg./l. to 4 mg./l. Influent BOD values ranged from 3 mg./l. to 78 mg./l. and filtered effluent BOD values ranged from 3 mg./l. to 45 mg./l., if we do not count the single high BOD value recorded in January, when an upset occurred in the bio-units. The variations in influent COD and BOD values can be explained by the fact that, as previously mentioned, the waste from Campaign I1 is such that it exhibits an almost immediate leakage of approximately 1, mg./l. COD through the carbon columns. In spite of this rather high COD concentration in the effluent from the carbon column, the performance of the bio-system did not suffer UTILITY BLOWOWfl i- I I I I SANITARY r WASTE

5 1976 BOD January-February , March ,843, April-May , June-July , Average ,29... Maximum Discharge Limits ,... during the period corresponding to Campaign 11. Much of the apparent fluctuation in effluent COD and BOD concentrations is due to the fact that the first three weeks were spent trying to determine the optimum carbon cycle time. During this time, the carbon column was occasionally operated longer than the optimum cycle time. Thus, the resulting influent to the aerated lagoon and consequently the effluent was high in COD and BOD. After the optimum carbon cycle time was determined and after the system was given time to equilibrate, the filtered effluent COD values ranged from 4 mg./l. to 18 mg./l. over a period of approximately 75 days. The addition of the activated carbon pretreatment provided lower effluent BOD and COD values and more consistency in the effluent quality of the aerated lagoon system. These results, plus the fact that carbon adsorption ahead of the bio system offered better protection against upsets, were the deciding factors upon which a decision was made to install a combination granular carbon/ aerated lagoon system. Final design of the waste water treatment system is shown schematically in Figure 5. The process waste water is collected in a 3 day equalization pond and from there is directly applied to the activated carbon adsorption system. The carbon effluent is first adjusted to near neutral ph and then combined with sanitary and utility waste waters in an 865, gal. aerated lagoon. The aeration lagoon contains four, 1 h.p. floating aerators and provides five days detention. The aerated effluent is then processed through three polishing lagoons in series with a total of 2.5 days retention before being discharged. Based on the successful results of the adsorption tests, Rhodia accepted a proposal by Calgon for an adsorption service contract using the criteria established in the validation and pilot studies. Under the terms of the contract, Calgon supplied all equipment and installation of the adsorption system and routinely replaces spent activated carbon with fresh carbon. The waste water, following equalization, is pumped at a controlled rate downflow through the adsorption system. Equipment for the adsorption system consists of two lined carbon steel adsorbers and one carbon transfer tank with associated piping for two stage operation. The adsorbers are rated for 74 lb./ SQ. in. gauge at 15"F, and are designed to contain 2, lb. of granular activated carbon. The waste water contacts the lead adsorber of the adsorption train, following which it moves to the second adsorber, also downflow, as a polishing stage. When the lead adsorber becomes exhausted, the spent carbon in the lead adsorber is replaced with fresh activated carbqn; and by manually resetting the valves, it is placed in the polishing position. The other adsorber then assumes the lead position. Spent carbon is conveyed from the lead adsorber to a transfer tank, utilizing plant air or nitrogen as the motive force. Fresh activated carbon is transferred as a slurry 64 from the Calgon trailer to the appropriate adsorber by pressurizing the trailer w&h plant air or nitrogen. Spent carbon in the transfer tank is then transferred under pressure to the empty trailer for return to Calgon for reactivation. Performance The original design of the adsorption system was based on removal of 83 lb./day of organics (i.e., 1,6 mg./l. to 1,4 mg./l. at 5,4 gal./day). In actual performance over 16 months of operation the carbon system has been removing 14 lb./day of organics based on 5,4 gal./day flow. This is primarily due to changes in the influent organic mix and concentration. A comparison of the original waste water characterization and one taken 18 months later is shown in Table 2. The level of organics in the waste water has dropped to about one-fourth its 1974 level. It appears, however, that this drop was mainly in the poorly adsorbable fraction because the carbon is now able to remqve more organic material from this lower concentration. Average performance of the activated carbon system over 16 months shows an influent TOC of 67 mg./l. and an effluent of 268 mg./l, Overall performance of the total system is indicated by a final discharge representing over 9% removal of BQD, TOC, and COD. Data from the first seven months of 1976 show quite good performance, as illustrated in Table 3. The levels of TOC, BOD, and TSS of 48 mg./l., 24.9 mg./l., and 69 mg./l. show a high quality of treatment and are well within discharge specifications also shown in Table 3. The COD level has been omitted since erratic results were obtained due to chloride interference. Initially, chlorides were under 1,3 mg./l. while chlorides now average about 7, mg./l., as shown in Table 2. # S. L. Wiseman, process engweer for Rhodia, Inc.'s Freeport, Tex. plant, earned his B3Ch.E. from tbe Univ. of Kansas. B. T. Bawden. suoervisor. customer services for CEP May 1977