A novel system and method for biodegradation

Patent Survey

161 30, 418-425.

Table 1. Dissolved oxygen concentration

Methylmecarptan (mg/litre)

Methyl sulphide (mg/litre)

0.0012 0.0076

0-009 1.1

>/2 mg/litre < 2 mg/litre

Gonzalez, G. et al., A kinetic model for pretreated wheat straw saccharification by cellulase. J. Chem. Tech. Biotechnol., 1989, 275. Noike, T. et al., Characteristics of carbohydrate degradation and the ratelimiting step in anaerobic digestion. Biotechnology and Bioengineering, 1985, 27, 1482-1489. 9 US patent publications. 2 European patent publications. 1 International patent publication.

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A novel system and method for biodegradation

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Fig. 4. An element (11), which may consist of a duct or channel, connects reactor I l) with a separating device (4), in which dissolved and undissolved sub~tances are separated and the former ,ire removed as a liquid fraction via element (20) into reactor (3) and the latter are removed via element (14) into reactor (2). Reactor (1) is directly connected with reactor (2) via element (12), thus substances located in reactor (1) can be directly fed to reactor (2). Element (13) connects reactor (2)with element (11) with the result that dissolved and undissolved substances are removed from reactor (2) and fed into the separating device (4), the undissolved organic substances being supplied to reactor (3). In contrast to the apparatus used for performing the PAOUES method, the apparatus described here has no duet for the return of the solids into reactor

(1). Reactor (3) is connected via a further element (22) with reactor (2) directly or, alternatively and additionally, with element (14) with the result that substances present in reactor (3) are fed into reactor (2). Reactor (3) has an outlet (23) suitable for the controlled removal of water. Reactors 2 and 3 are also provided with outlets for the removal of gas, such as methane, and they have suitable connections to further ducts for such removal. In this system, which is preferably utilized for continuous charging of the solids hydrolysis stage, reactor (2) is

connected by element (15) with a separating device (5) (FFF5) for the separation of dissolved and undissolved materials to give a solids fraction and a liquid fraction. The separation device is connected by means of a further element (21) with element (20) so that dissolved substances removed from reactor (2) can be supplied to reactor (3). Via an outlet (16) provided on the separating device (5) or via a communicating element (16) residues are removed from the separating device (5).

References Buchholz, K. et al., Untersuchungen zur Bildung yon Biogas aus Rubenprebschnitzeln. Zuckerindustrie, 1986, 837-844. Gijzen, H. et al., High-rate two-phase process for the anaerobic degradation of cellulose, employing rumen microorganisms for an efficient acidogenesis. Biotechnology and Bioengineering, 1988,

George Pierce, Cristopher Smith and Carolyn English, biochemists assigned to the above company, have designed a method and system for the aerobic reaction of compounds such as aromatic, nitro-aromatic and haloaromatic, aliphatic and halo-aliphatic compounds with the aid of a microorganism of the group with ATCC accession nos 55641-55649 and 572255727. The degradation of organic compounds may occur in fluid or solid phase. The researchers provided novel isolated microorganisms in pure or mixed culture which appeared useful for the aerobic degradation of the aforementioned compounds when contained in elastomer and/or tarry solids, sludges or soils, as well as when contained in nonelastomeric compositions. Figure 5 is a schematic illustration of a slurry phase formation from an elastomeric solid, sludge or soil and Fig. 6 shows the correlation between decreasing levels of hydrocarbon compounds and increasing levels of CO2 evolved. An elastomeric sludge containing a mixture of high levels of aromatic, nitro-aromatic, halo-aromatic, halo-

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Patent Survey

162

nitro-aromatic, aliphatic and halo-aliphatic compounds was fluidized by mixing the elastomeric sludge with water. Table 2 shows the average concentration (in ppm) for selected compounds found in the original elasto-

meric sludge. After mixing, the slurry was decanted away from the residual elastomeric sludge to form an approximately 30% (w/w) slurry and was placed in a conventional stirred tank vessel (B. Braun, Allentown, PA). The slurry was

Q, Naphthalene Q, Toluene O, Benzene

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Fig. 6. Table 2. Average concentration (ppm)

Compound

Chloroform Benzene Toluene Chlorobenzene Ethylbenzene o-Xylene Aniline Nitrobenzene Naphthalene 2-Methylnaphthalene 2-Chloronaphthalene m~o-Xylene

680 720 3000 130 240 680 630 720 42 000 2800 < 100 2300

Table 3. Compound Chloroform Benzene Toluene Chlorobenzene Ethylbenzene o-Xylene Aniline Nitrobenzene Naphthalene

TCLP untreated a

TCLP treated"

TCLP limits

314 94 509 18 15 61 114 39 3249

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neutralized to approximately pH 7 by the addition to NaOH (2 r~) and inoculated with a 10% (v/v) mixed culture of induced microorganisms. The hydrocarbon compounds present in the elastomeric sludge were the only source of carbon and energy for the microorganisms. A 4 iitre vessel containing the inoculated neutralized slurry was stirred at about 400 rpm and aerated with pure oxygen at about 15 Psi (250 ml/min) at room temperature for 24 h. The slurry was sampled before and after biological treatment of 24 h to determine the concentration of compounds present in the slurry. The slurry was extracted using the toxicity characteristic leaching protocol (TCLP), and analysed by gasliquid chromatography as outlined by EPA SW-846. As shown in Tabl9 3, the compounds present in slurry that were analysed were successfully bioremediated. Effluent gas, containing stripped VOC and CO2 was collected in two granular activated carbon traps and in two alkali (2N KOH), traps, respectively. Over the 24 h incubation period, less than 2% of the total volatile organic compounds present were lost due to stripping. Furthermore, Fig. 6 shows a correlation between decreasing amounts of compounds present and an increasing amount of CO2 produced by the microorganisms. Because the vessel was aerated with pure oxygen, any CO2 production was a direct result of microbial aerobic utilization of the compounds present in the slurry. Therefore, Fig. 6 also indicates that the microorganisms were able to utilize the compounds present in the original sludge as the sole source of carbon and energy and that these compounds were degraded to CO2 and H2.

References Funk et al., A two-step in situ treatment process for soils contaminated with 2,4,6-trinitrotoluene, hexahydro1,3,5-trinitro- 1,3,5,-triazine. Applied Environmental Microbiology, 1993, 59, 2171-2177. Heitkamp et al., Controlled microcosms studies. Applied Environmental Microbiology, 1987, 53, 129-136. OItmanns et al., Bacteria enriched from nature which can be constructed and being capable of degrading 1,4-dichlorobenzene via a modified orthopathway, not present in the wild-type strains. Applied Microbiology and Biotechnology, 1988, 23, 609-616. Speitel, et al., The degradation of phenols. Environmental Science Technology, 1989, 68-74. 9 US patent publications.