Fractions of Copper, Chromium and Arsenic during the aerobic composting process of chicken manure and CCA-treated wood

Somjai Karnchanawong Assoc. Prof., Dept. of Environmental Engineering,

Faculty of Engineering/ National Center of Excellence for Environmental and Hazardous

Waste Management (NCE-EHWM), Chiang Mai University, Chiang Mai 50200, Thailand

e-mail:somjai@eng.cmu.ac.th

Neeraya Rattanasatchan Graduate student, National Center of Excellence for

Environmental and Hazardous Waste Management (NCE-EHWM), Chulalongkorn University,

Bangkok 10200, Thailand e-mail: neeraya_385@hotmail.com

Abstract— The change in heavy metal fractions during the aerobic composting process of sawdust from chromated copper arsenate (CCA)-treated wood and chicken manure was determined by sequential extraction procedure. A study was performed in a 1m3 composting unit over a period of 140 d. Four proportions of CCA-treated wood sawdust – 0%, 33%, 66% and 100% by weight – were utilized in creating compost piles. Temperatures were measured daily, while compost characteristics were monitored weekly. The results showed that microorganisms could degrade the organic matter in all compost piles. The compost pile with no CCA-treated wood was found to be more mature, compared with the piles containing CCA-treated wood. The results of sequential extraction showed that during the composting process, arsenic was mainly redistributed into the mobile fraction, whereas copper and chromium had an affinity for the stable fraction.

Keywords- Composting; CCA treated wood; chicken manure; arsenic; copper; chromium; sequential extraction

I. INTRODUCTION Chromated copper arsenate (CCA) is the most common

preservative found in treated wood worldwide [1]. Disposal of decommissioned CCA-treated wood is of increasing concern because of the high concentrations of toxic contaminants present in the treated wood and the large volumes of CCA-treated wood generated. Arsenic (As) and chromium (Cr) are known human carcinogens and can damage the nervous system, while copper (Cu) has a high aquatic toxicity. Composting of the wood waste may be an alternative solution for reducing the toxicity of the waste [2]. Barker and Bryson [3] have revealed that the metallic pollutants can be converted into less bioavailable organic species. In addition, the quantity, mobility and bioavailability of the heavy metals are considered to be important factors for predicting their release into the environment. An approach commonly used for studying partitioning and metal mobility in composting is to use sequential extraction procedure. The objective of this study was therefore to investigate the fractions of Cu, Cr and As throughout the aerobic composting process of CCA-treated wood and chicken manure.

II. MATERIALS AND METHODS

A. Compost mix Four composting 1m3 units made of wood were prepared

(see Fig. 1). One hundred sixty kg of compost mix containing chicken manure and four different proportions of CCA-treated wood (pile 1: 0%; pile 2: 33%; pile 3: 66%; and pile 4: 100% by weight) were composted for 140 d. Mature compost produced from the organic fraction of municipal waste was seeded to a mixture of 5% by weight. Each composting unit was equipped with both vertical and horizontal air-vent pipes, and was manually turned weekly in order to enhance aerobic decomposition. Moisture content of each pile was controlled to be in the range of 55–60% by spraying water.

B. Sampling and analysis Temperature at the central portion of each pile was

measured daily using digital thermometer. Subsamples were randomly collected from three equidistant cross sections and three parts of each pile once a week. Each sample was taken by mixing the subsamples and then analyzed for pH, conductivity (EC), carbon (C), nitrogen (N), volatile solids (VS), and germination index (GI) according to Thai Agriculture Standard method (TAS 9503-2005) [4]. The heavy metal fractions of Cu, Cr and As – water-soluble (F1), exchangeable (F2), carbonate-bound (F3), Fe/Mn oxide-bound (F4), organic matter/sulfide-bound (F5), and residual (F6) – were determined by using sequential extraction procedures [5]. The heavy metal concentration was determined using an atomic absorption spectrophotometer (AAS) (GBC Avanta Model HG3000).

III. RESULTS AND DISCUSSIONS

A. Characterization of compost Fig. 2 presents the changes in characteristics of

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2011 International Conference on Environment Science and Engineering IPCBEE vol.8 (2011) © (2011) IACSIT Press, Singapore

compost mixture during composting. The temperatures of the compost piles gradually increased and reached thermophilic phase (40 ºC to 60 ºC) after 7 d, until around 50 d of the composting period. After that they gradually decreased to room temperature (around 20 ºC) at the end of the composting period. The pH decreased from about 8.6 to 7.9, and then remained constant until the end of experiment. The EC values of composts slightly decreased from 1.5 to 1.9 dS/m and then remained constant at around 1.7 dS/m. The C/N ratio decreased from 25 to approximately 12, 13, 13 and 11 in piles 1 to 4, respectively, after 140 d of composting. The GI values of Brassica campertris var. chinensis seeds increased from 120, 92, 85 and 100 after 30 d of composting to about 217, 156, 132 and 114 in piles 1 to 4, respectively, at the end of composting. Zucconi et al. [6] reported that compost with GI values greater than 80% was phytotoxicity-free and considered as having completed maturity. Similar suggestions were also reported by Tiquia et al. [7].

Considering the overall characteristics of the compost during the composting process, the results illustrated that the raw organic material in every pile could be degraded by microbial activity during the composting process. The finished compost from pile 1 without CCA-treated wood was found to be more mature than the piles with CCA-treated wood added. This might be a result of the presence of preservatives in piles 2 to 4, which enhanced the resistance to degradation and germination.

B. Changes of heavy metal distribution during composting Fig. 3 presents the average total concentration of metal

contents in each compost pile during 140 days. As expected, the composted pile 4 showed the highest total concentration of heavy metals during composting. The total concentration of metals decreased from pile 4 to pile 1 as a result of the different proportions of CCA treated wood added in each

pile. The total concentration of metals in composted piles ranked in the following order: Cr > Cu > As.

Fig. 4 presents the fraction percentages of metal contents in each compost pile. The following results of each metal were obtained.

• Copper

During composting, the variation of the Cu-F1, Cu-F2 and Cu-F3 distribution was trivial, compared to the other fractions. Most of the Cu in all piles (>50%) existed in the Fe/Mn fraction (F4) at the initial phase. The Cu-F5 in pile 1 decreased with time and was redistributed to the residual fraction after 70 d of composting. For piles 2 to 4, Cu was associated with F4 during the initial phase. During the composting process, there was a significant decrease of Cu-F4 in piles 2, 3 and 4 from 67.6%, 65.6% and 67.7% to 33%, 32% and 42%, respectively, while Cu-F5 and Cu-F6 increased. After 70 and 84 d of composting, Cu-F4 appeared to have been transformed into a stable phase in piles 3 and 4. After the maturity period, more than 50% of Cu was found in the stable fractions (F5 and F6). Due to a high affinity for organic matter, Cu was not easily mobilized in the composting process. In addition, some Cu was significantly transferred from mobile fractions to organic-bound fractions during the composting process. Similar results were also found in previous study [8].

• Chromium During the thermophilic phase, the organic fraction (Cr-F5) of Cr in all piles was higher, compared to the other fractions (>50%). An explanation for this is that, in the CCA treating solution, Cr acts as a fixing agent to precipitate As and Cu onto the wood when Cr(VI) is reduced to Cr(III). This function of Cr in the CCA fixation process implies that Cr easily

Figure 1. Composting unit

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Figure 3. Total concentration of metals in the compost piles

forms a complex with wood and thus most Cr isassociated with organic matter [9]. After the thermophilic phase, the percentage of Cr-F5 slightly decreased from 58%, 62%, 64% and 52% to 43%, 39%, 41% and 44% in piles 1 to 4, respectively. These declines were also found in Cr-F4, with a decrease from 41%, 36%, 33% and 39% to 32%, 25.5%, 25.2% and 25.8% in piles 1 to 4, respectively. In contrast, all composted piles showed a significant

increase of the Cr-F6 fraction during composting. Similar to the percentage of Cu, the percentage of Cr fluctuated during composting in pile 1; the variation of Cr-F1, Cr-F2 and Cr-F3 distribution was trivial, compared to the other fractions. Chromium is classified as a low-water-soluble metal (metallic form) and as such is

Figure 2. Changes in characteristics of compost mixture during composting: (a) Temperature, (b) pH, (c) EC, (d) C/N ratio, and (e) GI.

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Figure 4. Fractions of Cu, Cr and As in compost piles

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generally less mobile. However the results obtained from this investigation showed that Cr seems to be redistributed from the reducible fraction and organic fraction to the residual fraction at the end of the maturity period.

• Arsenic The percentage of As was mainly present in the organic fraction (As-F5) at the initial phase, accounting for around 49%, 38.8%, 31.2% and 27.8% of compost piles 1 to 4, respectively. During the composting process, As-F5 dramatically decreased, while As-F1 and As-F2 increased. As-F4 and As-F6 showed less variation and seemed to remain constant. Generally, most As should be fixed in wood after the fixation process, becoming associated with organic matter – in other words, extracted as an organic fraction, resulting in a higher initial percentage of As [9]. During composting, the oxidizable fraction was transformed to soluble and exchangeable fractions, and therefore it can be assumed that fixed As was gradually released from the wood due to changes in the chemical environment during the composting process [10]. Moreover, during the biodegradation of wood mass, these two fractions could also come from the As that failed to fix onto wood, and may have undergone reversed reaction of the fixation process and been converted from insoluble CCA compounds into more soluble compounds [11].

IV. CONCLUSIONS The study showed that CCA-treated wood could be

degraded by microbial activity during the composting process. The results of the sequential extraction showed that during the composting process, As was mainly transformed into the mobile phase, whereas Cu and Cr

had an affinity for the stable fraction. It can be concluded that the composting process is able to reduce the toxicity of Cu and Cr in CCA-treated wood.

REFERENCES

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[2] H. Borazjani,, S. Diehl and H. A. Stewart, “Composting of wood wastes: plywood and sawmill residue.” Research Advances, 2000, 5: 4. Retrieved from http://fwrc.msstate.edu/pubs/composting.pdf

[3] A. V. Barker and G. M. Bryson “Bioremediation of heavy metals and organic toxicants by composting.” Scientific World Journal, 2002, 2: 407–420.

[4] Ministry of Agriculture and Cooperatives. B.E 2548. 2005. Thai Agriculture Standard TAS 9503-2005.

[5] A. Tessier., P. G. C. Campbell, , and M. Bisson,. “Sequential extraction procedure for the speciation of particulate trace metals.” Analytical Chemistry, 1979, 51: 844–851.

[6] F. M. Zucconi, et al.,. “Evaluating toxicity of immature compost.” BioCycle, 1981, 22: 54–57.

[7] S. M. Tiquia, N. F. Y. Tam, I. J. Hodgkiss, “Effects of composting of phytotoxicity of spent pig-manure sawdust litter,” Environmental Pollution. 1996, 93(3): 249–256.

[8] S. Nomeda, P. Valdas, S. Y. Chen, J. G. Lin, “Variations of metal distribution in sewage sludge composting,” Waste management. 2007, 28: 1637-1644.

[9] H. Pan, C. Y. Hse, R. Gambrell, T. F. Shupe, “Fractionation of heavy metals in liquefied chromated copper arsenate (CCA)-treated wood sludge using a modified BCR-sequential extraction procedure,” Chemosphere., 2009, 77: 201–206.

[10] S. Lebow, P. Lebow, D. Foster, “Estimating preservative release from treated wood exposed to precipitation,” Wood Fiber Sci, 2008, 40: 562–571.

[11] S. Kartal, C. A. Clausen, “Leachability and decay resistance of particleboard made from acid extracted and bioremediated CCA-treated wood,” Int. Biodeter. Biodegr, 2001, 47: 183–191.

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