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Letters in Applied Microbiology 2001, 33, 256±263 Co-composting of pharmaceutical wastes in soil T.F. GuerinShell Engineering Pty Ltd, Granville, NSW, Australia 2001/139: received 9 May 2001, revised 28 June 2001 and 16 July 2001 T. F . GU ER IN . 2001.
Aims: Soils at a commercial facility had become contaminated with the pharmaceutical chemical residues, Probenecid and Methaqualone, and required remediation.
Methods and Results: Soil composting was investigated as an alternative to incineration for treatment. In laboratory trials, a factorial experimental design was used to evaluate organic matter amendment type and concentration, and incubation temperature. In pilot scale trials, Probenecid was reduced from 5100 mg kg±1 to < 10 mg kg±1 within 20 weeks in mesophilic treatments. An 8 tonne pilot scale treatment con®rmed that thermophilic composting was effective under ®eld conditions. In the full-scale treatment, 180 tonnes of soil were composted.
Initial concentrations of the major contaminants in the full-scale compost treatment were 1160 mg kg±1 and 210 mg kg±1, for Probenecid and Methaqualone, respectively. Probenecid concentration reached the target level of 100 mg kg±1 in 6 weeks, and removal of Methaqualone to < 100 mg kg±1 was achieved after 14 weeks.
Conclusions: Co-composting was effective in reducing soil concentrations of Probenecid and Methaqualone residues to acceptable values.
Signi®cance and Impact of the Study: Co-composting is a technology that has application in the remediation of pharmaceutical contaminants in soil.
process conditions: matrix moisture content, pH, tem- perature, oxygen supply and elemental ratios. The major Composting has been used for many years for disposal of difference between the two processes is in the ratio agricultural, municipal and domestic wastes. However, of biodegradable materials to soil matter. In bioremediation composting has only relatively recently been investigated of soil, the organics of concern occur typically in the range of for treatment of soils contaminated with polycyclic aromatic 0á001 to 1á0% but in composting, organic matter concen- hydrocarbons (PAHs) (Guerin 2000; Semple et al. 2001), trations would be more typically in the range 20 to 80% nitroaromatic explosives (Williams et al. 1992; Griest et al.
(Rhodes et al. 1994a,b). In some cases where the standard 1993; Emery and Faessler 1997; Tuomi et al. 1997) and approaches to bioremediation are not effective, the higher other hazardous wastes (Kamnikar 1992; Betts 1993; Bennet rates of biodegradation activities and more diverse popula- and Barriuso 1997; Cook et al. 1997; Lewandowski and tions of micro-organisms found in compost (with therefore a DeFilippi 1998; Semple et al. 2001). The type of organic much wider range of metabolic capabilities), in combination amendments used and the ratio of contaminated soil to with physical and chemical effects, may be able to achieve organic amendment are crucial parameters in making this degradation of the contaminants (Rhodes et al. 1994a,b).
technique cost-competitive with other disposal and treat- Examples of bioremediation processes, including compo- The principles and concepts of bioremediation of con- Composting is an engineered process in which organic taminated soils are similar in many respects to composting.
waste materials are degraded by micro-organisms, in the Both aim to maximize microbial activities through control of presence of air, to produce inorganic products (carbon dioxide, water, various salts) and stabilized organic matter, i.e. compost. Many different composting system designs have been used (Huang 1993). Mixed compost piles or Correspondence to: Dr T.F. Guerin, Shell Engineering Pty Ltd, NSW State Of®ce, PO Box 26, Granville 2142 NSW, Australia windrows (long narrow piles) are mechanically turned to (e-mail: [email protected]).
provide aeration. Static piles, on the other hand, may be ã 2001 The Society for Applied Microbiology CO-COMPOSTING OF PHARMACEUTICAL WASTES 257 Table 1 Bioremediation technologies for contaminated soil and The US Army has been evaluating composting treatments for soils contaminated with explosives such as TNT for some years. Bench and ®eld studies showed the technical capability of the technique in reducing explosive concen- trations to acceptable levels. They identi®ed two process parameters crucial to making this approach cost-competitive with incineration as a disposal route. These were the type of organic amendments used, and the ratio of contaminated soil to organic amendment (Griest et al. 1993; Emery and In the current study, soil contaminated with the pharma- ceutical compounds Probenecid and Methaqualone was composted in an effort to treat these residues so that the soil *No longer recognized as an industry best practice.
could be re-used for landscaping purposes. The pharma- ceutical residues were expected to be relatively non-toxic but built over ventilation pipes. More highly engineered reactor are, by their nature, biologically-active compounds (Israili vessels provide means for greater process control and et al. 1972; Fernandez Gomez et al. 1984); they are described environmental controls (e.g. for odour management) (Huang in Table 2. While the metabolism of these compounds is 1993). The high loading of biodegradable organic matter in well understood, their fate in the environment has not been composting processes normally results in the temperature of compost heaps gradually rising as microbial decomposition The principal objective of the study was to apply proceeds, releasing heat. Typically, composting materials are composting technology to soil contaminated with pharma- poor thermal conductors and as a result, the compost pile is ceutical wastes to reduce its phytotoxicity and allow its usually self-insulating. Temperatures may reach 55±60°C.
re-use. The composting of pharmaceutical wastes is This heat is crucial to the usefulness of composting in discussed, presenting the results of laboratory-, pilot- and decontaminating sewage sludge, which contains pathogenic micro-organisms. The higher temperatures also increase the rates of both biological and chemical reactions in the Recent developments for the treatment of some industrial organic wastes have included the use of more moderate Expansion of facilities at a pharmaceutical manufacturing (mesophilic) temperature processes (Guerin 1999a). Typic- facility in south-eastern Australia required the excavation ally, contaminated or waste materials are mixed with organic of an area previously used as land®ll. Out of date, waste or matter, mineral nutrients and a bulking agent, and the `off-spec' product was previously land®lled on the site.
composting process allowed to proceed. With lower organic Other materials, including some laboratory wastes, were matter content, and appropriate process management, also placed in the land®ll. A portion of the excavated soil mesophilic temperatures are maintained. In well managed was found to be contaminated with pharmaceutical compost systems, a succession of complex and active process wastes and these residues included Probenecid microbial populations occurs. These can include bacteria, (4-[(dipropylamino) sulphonyl] benzoic acid) and Metha- actinomycetes, fungi and higher organisms such as protozoa.
(2-methyl-3-(2-methylphenyl)-4(3H)-quinazoli- The types and numbers of individual strains, and the none or Methaqualone hydrochloride (Fig. 1). A quantity dynamics of the microbial succession, are dependent on the of ®llers and binders (e.g. lactose) was also present.
nature of the organic materials used, moisture content, pH, Solvents such as xylene, aniline, dichlorobenzene, temperature, oxygen supply and elemental ratios. The fatty acids and fatty acid esters, including volatile fatty micro-organisms tend to be nutritionally and metabolically acids, were also detected at low concentrations in some diverse. This is because of the wide range of microsites within the compost with very different physicochemical parameters. The activity of these populations leads to inter- active effects where, for example, the product of one meta- bolic pathway can act as a substrate and lead into a second The contaminated soil was a silty clay. It contained a large pathway, thereby allowing a more complete degradation of amount of pharmaceutical contaminants present in forms the organic compounds in the compost (Huang 1993).
ranging from extremely large lumps through small nodules ã 2001 The Society for Applied Microbiology, Letters in Applied Microbiology, 33, 256±263 2-Methyl-3-(2-methylphenyl)-4(3H)-quinazolinone Benacen; Benemid; Benemide; Benn; Probalan; Quaalude; Mandrax; Parest; Sopor; Melsedin Probecid; Proben; Probenid; Robenecid; Uricocid Used as a uricosuric agent in the treatment of gout.
Hypnotic, sedative; was commonly abused as a Because of its inhibitory effects on renal tubule transport processes, probenecid is also used as a therapeutic adjunct to enhance blood levels of In 14 day tests with rats, doses of 3200 mg kg)1 A serum concentration higher than 8 mg l)1 is life Sample selection and preparationThe excavated material was extremely heterogeneous. Sam- ples were collected for the laboratory study after the material was removed from the waste bins and placed in a single large pile in the warehouse building. These 21 samples were sieved to remove large `non-soil' items such as broken glass, plastic etc., and thoroughly mixed to prepare a soil composite which was then split into portions for the experimental treatments.
This initial composite was found to contain 8400 mg kg±1 Probenecid and 75 mg kg±1 Methaqualone, with lower con- centrations of various organic acids.
Laboratory feasibility studyWhile the metabolism of these compounds is well under- stood in mammals (Israili et al. 1972; Fernandez Gomez et al. 1984), their fate in the environment has not been Fig. 1 Chemical structures of the speciality chemicals treated by previously investigated. Hence, an appropriate treatment of the soil was seen to be desirable before disposal. A feasibility study was therefore undertaken to determine whether soil composting could degrade concentrations of the pharma- of white chalky material to powder form. The soil also ceutical residues. Treatments were carried out to simulate contained waste materials including bottles, glass and either a mesophilic process (incubation at 25°C) (Treat- plastic, tablets, pipettes, rubber teats and bungs, and other ments 1, 2, 5 and 6) or a moderately thermophilic process assorted waste. All of these gross contaminants were (48°C). Soil was mixed with either horse manure (HM) or removed prior to treatment. Physical properties of the soil partially composted plant material (PM) at 30% by weight suggested that some pre-processing operation would be of the total ®nal wet weight. In addition, two controls were required to break up large soil and residue aggregates, as run, one unamended soil and one poisoned with mercuric well as to distribute the contaminants for effective compo- chloride (HgCl2) to eliminate microbiological activity. The sting. It was evident at the time of the soil excavation that an mercuric chloride was added to the soil mixture at a rate of organic amendment would need to be selected to provide 1 g to 100 g soil (1% w/w basis). These were incubated at some bulking to the soil and to improve its structural 25°C and mixed weekly as per the treatments. Two controls included one unamended soil and one soil poisoned.
ã 2001 The Society for Applied Microbiology, Letters in Applied Microbiology, 33, 256±263 CO-COMPOSTING OF PHARMACEUTICAL WASTES 259 of the composting soil was collected and recycled back into the process. Odours and potential movement of spores and Following presentation of these preliminary results to the particulate matter from the composting was contained since appropriate regulatory body, an interim criterion for a the process was conducted in an enclosed warehouse. All pilot scale treatment was established at 100 mg kg±1 for mixing of the soil was conducted using a bobcat with a Probenecid. A pilot-scale treatment was carried out to enable assessment of the following design requirements for · the physical processing requirements of the contaminated Chemical analysis. The pharmaceutical residues were · materials handling and compost mixing, volumes and analysed by gas chromatography following extraction by dichloromethane:acetone (3 : 1) (1 g 100 ml±1). For com- · the suitability of the available local raw materials for pounds identi®ed by GC-MS, the sample concentration of the corresponding GC-FID peak areas was reported as · the effectiveness and rate of composting, i.e. the time mg kg±1 dry matter. Probenecid and Methaqualone concen- required to reduce contaminant levels to target concen- trations were measured by GC-MS. Total petroleum hydrocarbons were measured by USEPA method EO-82.
· the heat generation characteristics of the compost, and Moisture content was determined by drying at 105°C requirements for temperature control, including effect of overnight. Organic matter content was determined by ashing (550°C, 4±5 h). Volatile organics were analysed by GC-MS · odour and leachate control requirements.
using USEPA method 8260B. All results are reported on a The composting operations were conducted within a large warehouse, which had a concrete ¯oor with a useable area of Microbiology. Microbiological populations were deter- the ¯oor slab, including those areas taken up by the stockpile mined in the pilot-scale trial only and were conducted using of soil, of approximately 400 m2. Approximately 8 tonnes of plate count methods. Speci®cally, total mesophilic, hetero- the contaminated soil were removed from the stockpile. This trophic organisms were determined on Tryptone Soy Agar was mixed with approximately 30% by weight of organic (TSA) (Oxoid) (Guerin 1999b) at 28°C. Mesophilic popu- material (commercially-available mulch consisting of lations were incubated at 28°C and thermophilic populations chipped wood waste and leaf, horse manure and site grass by incubation of the same plates at 60°C. Fungi were clippings) to form a composting mixture. The chosen enumerated using Rose Bengal Chloramphenical Agar.
composition re¯ected the requirements to provide suf®cient Presumptive coliforms were enumerated using MacConkey organic material to promote composting, to break up the clay Agar for total coliforms. These were monitored because the soil, but with an acceptable volume of low bulk density proposed end-use would require site workers to handle the organic material which would be needed for the large-scale compost which included manure. Pseudomonads were operation. The pharmaceutical contaminants were present as enumerated on Psuedomonas Selective Media. The micro- agglomerates, some extremely large, and ®ne powder. Pre- biological methods are described in Dindal (1991).
processing was required to break up large soil and residue aggregates, and to distribute the contaminants for effective Temperature. All temperature measurements in the pilot- composting. Ventilated piles were constructed, which were and full-scale processes were measured using ®eld monitoring subjected to a regular mixing (weekly). All mixing of the soil probes (Model DT 50 by DataTaker, Sydney, Australia).
was conducted using a bobcat with a 0á25 m3 bucket.
Temperature measurements in the laboratory-scale treat- ments were measured using a mercury thermometer.
Full-scale treatmentThis was commenced after reporting of the effectiveness of the pilot-scale process and was conducted in a large, enclosed warehouse at the facility. Approximately 110 m3 (180 tonnes) of the contaminated soil was mixed with Initial samples from the microcosms contained between approximately 30% by weight of commercially-available leaf 3500 mg kg±1 and 7700 mg kg±1 Probenecid on a dry soil mulch and horse manure to form the composting mixture.
basis (with a mean of 5100 mg kg±1). Signi®cant decreases The volume of the pile when freshly mixed was 280 m3 in Probenecid concentration were noted after 19 weeks, (15 m ´ 11 m ´ 1á7 m high). Any drainage from irrigation with four treatments containing no detectable Probenecid ã 2001 The Society for Applied Microbiology, Letters in Applied Microbiology, 33, 256±263 Table 3 Probenecid degradation in soil in * Variation in the analyses ranged from 8 to 15%.
  PM = plant material (green tree waste).
(Table 3). The most effective treatments were those main- degradable material was decomposed. The soil rapidly tained at 25°C. Probenecid removal in the thermophilic changed from a light grey±brown clay containing obvious treatments ranged from 75 to 100%. Over the ranges tested, white powdery residues, to a dark, organic appearance soon no signi®cant effects were seen from either the type or the concentration of organic amendments. No decrease was Probenecid concentrations were reduced to below the observed in the poisoned control, but the unamended target concentration (100 mg kg±1) in a period of 2±3 weeks.
control also showed a substantial reduction in Probenecid The initial compost microbial populations after amend- concentration (78%). This probably re¯ected the biostimu- ment of the soil were 109 g±1 compost, i.e. about 10 times lation effect of mineral nutrients, moisture, mixing/aeration, higher than for the contaminated soil. The microbial and the presence of `compostable' organics in the wastes numbers increased over the ®rst 3 weeks of treatment, then added to the land®ll, such as sugar-based binders and ®llers, steadily declined as the compost `matured'. Characteriza- used in pharmaceutical formulations. Various organic acids, tion of signi®cant sub-populations of organisms (pseudo- mainly fatty acids, sterols, hydrocarbons and cineole (a sub- monads, coliforms, yeasts and fungi, and thermophiles) stituted aromatic compound found in eucalyptus oils), were showed that except for pseudomonads, these constituted also detected (data not shown). These were derived from the 2% or less of the total mesophilic heterotrophic population organic matter added to the soil, or from the biomass (Table 4). The number of yeasts and fungi increased, and produced during the composting process. Over the course of pseudomonads decreased slightly. A substantial decrease the treatments the concentrations of these decreased. The was measured in the number of coliforms (from more than most effective treatments were those maintained at 25°C.
107 to 105 g±1). These changes are a response to the changing conditions of substrate availability, temperature, pH and other parameters in the compost as it matures.
There were no detectable thermophilic organisms in the A pilot-scale treatment was carried out to assess: soil soil compost mix. Addition of organic matter (OM) raised processing requirements prior to compost blending; mate- the numbers of each type, especially the thermophiles and rials handling, bulking and space requirements; the suit- coliforms. This most likely re¯ects the biologically-active ability of the available local organic materials; the rate of state of the organic materials as delivered to the site. The contaminant removal in a large-scale operation; and the heat manure in particular was warm and steaming as a result of generation characteristics of the compost.
its natural composting process, and the leaf mulch showed In the pilot study, initial concentrations of the major evidence of high temperatures in the centre of the contaminant (Probenecid) in the compost, directly after stockpile. No signi®cant effects were apparent on degra- blending operations, was measured at 1200 mg kg±1. The dation rate or ef®ciency from the type or the concentration temperature of the compost piles rose rapidly after mixing of organic amendment used, over the range tested. The (with a 0.25 m3 bucket excavator) and peaked at 57°C after rate of Probenecid degradation was signi®cantly enhanced 30 h. The temperature then declined slowly as the bio- ã 2001 The Society for Applied Microbiology, Letters in Applied Microbiology, 33, 256±263 CO-COMPOSTING OF PHARMACEUTICAL WASTES 261 Table 4 Selected microbial populations in Micro-organisms g)1 compost (dry weight basis) à Rose-Bengal Chloramphenicol Agar (Oxoid).
§ Pseudomonas Selective Isolation Agar.
± MacConkey Agar (Oxoid). The media listed in foot notes 1±5 are described elsewhere Presumptive coliforms in the soil-OM mixture were two microbial numbers increased over the ®rst 3 weeks of orders of magnitude greater than those populations in the treatment, then steadily declined as the compost matured.
soil unamended with organic matter. These higher popula- Characterization of signi®cant sub-populations of organisms tions (2á3 ´ 107 colony-forming units (cfu) or cfu g±1 (thermophiles, yeasts and fungi, pseudomonads and coli- soil-OM mixture) decreased to numbers lower than those forms) showed that addition of organic matter raised the measured in the unamended soil (i.e. to 1á1 ´ 105 cfu g±1) numbers of each type, especially the thermophiles and after 4 days of composting. These results showed that any coliforms (Table 4). This increase most likely re¯ects the presumptive coliforms present in the compost soil mixture origin and biologically-active state of the organic materials as would be signi®cantly reduced in the full-scale process.
delivered to the site. During soil composting, the thermo- The composting treatment resulted in changes to the philic population declined slightly and was never more than physical appearance of the soil, so that no wastes or residues 3% of the total mesophilic population. A substantial were visible. No objectionable odours were generated from decrease was measured in the number of coliforms (from the process, or were noticeable in the treated soil. Moisture more than 107 g±1 to about 105 g±1) (Table 4).
additions were managed so that leachate was minimized.
The pilot-scale composting resulted in the soil changing All soil-processing and composting operations were from a light grey±brown clay, containing obvious white conducted within a large warehouse building. Approxi- powdery residues, to a dark organic appearance soon after mately 5 m3 (8 tonnes) of the contaminated soil were mixed the composting commenced, so that no wastes or residues with 16 m3 of organic material (commercially-available were visible. No objectionable odours were generated from mulch consisting of chipped wood waste and leaf, horse the process or were noticeable in the treated soil. Moisture additions were managed so that leachate generation was The compost pile temperatures rose rapidly after mixing minimized, and the ®nal product was found to be suitable to peak at 57°C after 30 h. The temperatures then declined slowly as the biodegradable material was decomposed. The piles were regularly mixed to provide aeration using mobile The initial concentrations of Probenecid and Metha- The entire remaining volume of contaminated soil was qualone directly after the blending operations were treated in a similar manner to the pilot-scale treatment. This 1200 mg kg±1 and 60 mg kg±1, respectively. Probenecid was commenced after reporting of the effectiveness of the concentrations were reduced to below the target level (100 mg kg±1) in 2±3 weeks, and to < 10 mg kg±1 after Initial concentrations of the major contaminants (Pro- 5 weeks. Methaqualone concentrations declined at a slower benecid and Methaqualone) in the compost directly after rate, reaching < 10 mg kg±1 at the completion of the pilot blending operations were measured at 1160 ppm and 210 ppm, respectively. The target concentrations for the After amendment of the soil with organic matter, the total principal contaminant (Probenecid) were achieved after microbial populations were 109 g±1 compost, i.e. approxi- 6 weeks of treatment. Extension of the composting treat- mately 10 times higher than for the contaminated soil. The ment was required to reduce the concentrations of the ã 2001 The Society for Applied Microbiology, Letters in Applied Microbiology, 33, 256±263 Fig. 2 Pharmaceutical residues in full scale soil compost. (h), Probenecid; (j), Methaqualone; ( ), organic acids and terpenes; ( ), hydrocarbons secondary contaminant (Methaqualone), found to be present subsequently been used for landscaping purposes across in the compost, to regulatory requirements. Results of the analysis of replicate samples are presented in Fig. 2.
Methaqualone had not previously been measured, while testing soil or compost, at concentrations above 65 ppm, and had not been considered to be a major contaminant prior to Stuart Rhodes (Rio Tinto Technical Services, Sydney, the start of the full-scale works. Removal of Methaqualone Australia) for technical support and project management, to below target concentrations (100 mg kg±1) and ®nal clean- Philip Peck (formerly Minenco, Sydney) for technical up validation of the soil was achieved after 20 weeks. The support and project management, and John Leeder compost was allowed to mature further, without processing, (Leeder Consulting, Melbourne) for analytical support.
until 30 weeks, at which time the average Methaqualone The work reported in this study are the opinions of the concentration had fallen to 23 mg kg±1. Temperatures author and do not necessarily re¯ect those of Shell reached 60°C in the full-scale treatment windrows.
As far as is known, no other studies conducting a similar composting process on these or related pharmaceuticals have been reported in the literature. Other co-composting studies reporting the composting of other organic Bennet, P. and Barriuso, E. (1997) Fate of 14C-ring labelled 2,4-D, contaminants have, however, shown similar heating pro®les 2,4-dichlorophenol and 4-chlorophenol during straw composting.
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