bioremediation of contaminated soil and sediment by composting

109

REMEDIATION Autumn 2006

There are many well-established bioremediation technologies applied commercially at contami-

nated sites. One such technology is the use of compost material. Composting matrices and com-

posts are rich sources of microorganisms, which can degrade contaminants to innocuous com-

pounds such as carbon dioxide and water. In this article, composting of contaminated soil and

sediment was performed on a laboratory bench-scale pile. Fertilizer was added to increase the

nutrient content, and the addition of commercial compost provided a rich source of microorgan-

isms. After maintaining proper composting conditions, the feasibility of composting was assessed

by monitoring pH, total volatile solids, total microbial count, temperature, and organic contami-

nant concentration. The entire composting process occurred over a period of five weeks and re-

sulted in the degradation of contaminants and production of compost with a high nutritional con-

tent that could be further used as inocula for the treatment of hazardous waste sites. © 2006 Wiley

Periodicals, Inc.

INTRODUCTION

According to Hogos et al. (2002), composting is a biochemical process in which or-ganic materials are biologically degraded (Eq. 1), resulting in the production of organicor inorganic by-products and energy in the form of heat. Heat is trapped within thecomposting mass, leading to the phenomenon of self-heating that is characteristic of thecomposting process (Semple et al., 2001).

organic biodegradable stabilized organic residue � microbial residue � O2 biomass � CO2 �H2O � heat (1)

As applied to nonhazardous materials, the main objectives of composting are:

(1) To stabilize and oxidize organic materials;(2) To reduce the volume of waste;(3) To reduce the moisture content of waste; and(4) To initiate pathogen destruction.

These objectives are also applicable to remediation projects that use composting todegrade hazardous substances into innocuous end products.The process of compost biore-mediation is similar to what occurs biologically in soil; however, composting may acceler-ate the destruction of contaminants (Buyuksonmez et al., 1999; Rao et al., 1996;Williams

microbes→

© 2006 Wiley Periodicals, Inc.Published online in Wiley Interscience (www.interscience.wiley.com). DOI: 10.1002/rem.20105

Zareen Khan

Y. Anjaneyulu

Bioremediation of Contaminated Soiland Sediment by Composting

& Keehan, 1993).The composting process is primarily facilitated by a high concentrationof biodegradable organic material in the compost matrix and an active microbial popula-tion. Such compost offers a good nutrient source for microbes (Laine & Jorgensen, 1996).The bulky structures of the organic material in compost open and stabilize the structure ofcontaminated soil in most cases (Laine et al., 1997). Secondary enhancers of microbialactivity include moisture, inorganic nutrients, and oxygen.The nature of the organic con-taminant, composting conditions and procedures, microbial communities, and time allaffect mechanisms or conversions in composts or soils (Weed et al., 1999).

In this study, the application of composting as a bioremediation technology wastested in the laboratory on soil and sediment contaminated with phenols, chloro/nitrophenols, and benzenes.

MATERIALS AND METHODS

Sample Collection

Soil and sediment samples were collected from the Patancheru industrial area located inHyderabad, A.P, India.The samples were characterized following standard procedures(American Public Health Association [APHA], 1998). Organic carbon was analyzed usingthe wet digestion method (Walkey & Black, 1934).The physicochemical characteristics areprovided in Exhibit 1. Phenol, p-nitrophenol, 4-chloro-2-nitrophenol, 2,4-dichlorophenol,

Bioremediation of Contaminated Soil and Sediment by Composting

Remediation DOI: 10.1002.rem © 2006 Wiley Periodicals, Inc. 110

Exhibit 1. Physicochemical characteristics of soil and sediment

Parameter Sediment SoilpH 6.7 7.5Electrical conductivity, dS/m 0.872 0.1TKN (total kjeldahl nitrogen), mg/g 6 0.056% organic carbon 26.1 0.93Calcium, mg/g 0.5 0.8Magnesium, mg/g 0.07 0.469Nitrates, mg/g 0.8 0.1Sulfates, mg/g 2.1 0.15Chloride, mg/g 0.85 0.379Sodium, mg/g 1.5 0.04Potassium, mg/g 0.6 0.145Phosphates, mg/g 1.2 0.2Arsenic, mg/kg 2.5 � dlCadmium, mg/kg 4.8 � dlChromium, mg/kg 3 � dlMercury, mg/kg 0.09 � dlNickel, mg/kg 4.1 � dlLead, mg/kg 0.048 � dlZinc, mg/kg 150 0.1

� dl—below detectable limit

and benzene were the hazardous organic compounds identified in the samples. Phenolswere present in the range of 16–24 mg/kg in both the soil and sediment, and the concen-tration of benzene was 7.3 mg/kg in soil and 3.4 mg/kg in sediment.

Nutrient Amendments

Commercially available mixed fertilizer was procured and characterized per standard pro-cedures (APHA, 1998).The physicochemical characteristics of the fertilizer are presentedin Exhibit 2.To increase the biodegradability of contaminants, commercial compost wasalso obtained and characterized per standard procedures (APHA, 1998).The physicochem-ical characteristics of the compost are also shown in Exhibit 2. About 10 kg of a soil/sedi-ment mixture were prepared with 0.5 percent fertilizer and 50 percent compost.

Piling

The mixed compost/soil/sediment material was then deposited on a bed of wire meshat an altitude of 30 cm.The experimental setup used for the composting studies isshown in Exhibit 3.The material was collected on a layer of gravel, forming a triangularsection of pile measuring 1.5 m in diameter at the base, 0.15 m high, and with a surfaceof 4 m.Wood chips were added as a supporting and aerating material to enhance theconditions for microbial growth. Four piles were formed, and two were used as experi-mental controls for soil and sediment.


© 2006 Wiley Periodicals, Inc. Remediation DOI: 10.1002.rem 111

Exhibit 2. Physicochemical characteristics of fertilizer and compost

Parameter Fertilizer CompostpH 7.5 6.9Electrical conductivity, dS/m 0.69 0.592Moisture (%) 3 10TKN (total kjeldahl nitrogen), mg/g 4.2 2.9Nitrate (ppm) 560 420Ammonium (ppm) 110 35Organic carbon (%) — 49Total phosphorus (%) 2.8 1.1P2O5 (%) 0.5 0.187Total potassium (%) 3.1 1.5K2O (%) 1.5 0.324Calcium (%) — 2.8Magnesium (%) — 0.5Sodium (%) 0.05 0.2Iron (%) — 0.5Manganese (ppm) — 150Copper (ppm) — 110Zinc (ppm) — 85Boron (ppm) — 52

Conditions of Composting Operation

Savage et al. (1985) presented the principal engineering parameters for optimal haz-ardous waste composting as the following:

• aeration,• moisture,• temperature,• pH, and• carbon/nitrogen (C/N) ratio.

These are the principal environmental factors that affect the compost process.Thesignificance of these factors with respect to the compost process is the fact that individu-ally and collectively they determine the rate and extent of decomposition. Aeration wascarried out through natural ventilation and by turning over the piles, and the moisturelevel was maintained between 40 and 70 percent by spraying water over the piles.

The feasibility of composting was assessed by monitoring pH, total volatile solids(TVS), total microbial count, temperature, and hazardous organic concentration in thesoil and sediment piles. For the purpose of analysis, samples were collected from 10 to20 different points in each pile, mixed by shaking, and sieved through an 8-mm sieve.The samples were stored at 4°C prior to chemical and microbiological analysis.

Analysis

Total Microbial Count

Ten grams of the composite sample were oven-dried at 105°C to a constant mass.The differ-ence in mass before and after drying was used to determine the dry mass of the compost



Exhibit 3. Experimental setup used for the composting studies

sample.A compost suspension was made by adding 10 g of compost to 90 mL of sterilesodium pyrophosphate (0.1 percent w/v, pH 7.0).The suspension was shaken vigorously for20 minutes at ambient temperature.A series of dilutions (10–1, 10–4, 10–6, 10–8, 10–10, 10–12)of the suspension was then made.This dilution series was appropriate for enumeration of vi-able colony forming units (CFUs) in compost.Aliquots (0.1 mL) of each of the three dilu-tions were pour plated in triplicate onto the nutrient agar plates.All of the plates were incu-bated at 37°C for a period of 24 hours. CFUs were counted by using a colony counter.Thoseplates containing 20–200 CFUs were used for the calculation of microbial concentrations.

Estimation of Contaminant Concentration

Soil and sediment samples were extracted with acetone, filtered, and re-extracted indichloromethane for good distribution and separation.The dichloromethane layer wasevaporated in a rotavapor.The residual was collected using methanol and injected in aShimadzu HPLC (C18 column, mobile phase: methanol [60 percent]: water [40 percent]:acetic acid [0.1 percent]) for analysis.The peaks were identified by injecting the standardsof phenol, p-nitrophenol, 4-chloro-2-nitrophenol, 2,4-dichlorophenol, and benzene.

The frequency of analysis was as follows:

a) pH: one or more times per turnover period;b) Total volatile solids: three times a week;c) Humidity: three or four times a week;d) C/N: three times a week;e) Microbial count: three times a week;f) Nitrogen and phosphorous: twice a week; andg) High-performance liquid chromatography (HPLC) analysis for hazardous organ-

ics: before composting and for the final composted product.

RESULTS AND DISCUSSION

The Composting Process

The parameter changes for the soil and sediment piles are presented in Exhibits 4–12.Initially, the C/N ratio was 1:2 for soil and 4:3 for sediment, and after mixing with thecompost, the C/N ratio increased. Between days 1 and 4, the temperature and humiditydecreased due to an increase in moisture and acclimatization of the microorganisms.Although some bacteria readily degraded the materials following exposure, bacteria oftenrequires a period of acclimation on adaptation before effective degradation can occur.Theacclimatization stage lasted for five days for soil and sediment piles.The pH varied be-tween 6.7 and 7.1 due to the bacterial catabolism of hazardous organics and other carbonsources to organic acids, carbon dioxide (CO2), and hydrochloric acid (HCl).

Between days 6 and 18, the thermophillic phase started.The mesophillic organismsresponsible for initial warming were substituted by the thermophillic organisms raisingthe temperature to an average of 66°C in the two piles.The thermophillic phase lastedfor 12 days. At the beginning of the thermophillic phase, alkaline pH was observed dueto the microorganism-induced hydrolysis of protein and organic nitrogen producing am-monia.The bacterial population rose to the highest level during this period, declined,



Although some bacteriareadily degraded thematerials following expo-sure, bacteria oftenrequires a period of accli-mation on adaptationbefore effective degrada-tion can occur.

and peaked again toward the end of the thermophillic stage. On day 5, the piles werecovered with black plastic to favor the increase of temperature characteristic of the ther-mophillic phase. On day 9, the C/N ratio was determined, and 0.5 kg of urea wereadded to maintain the C/N ratio in the two piles.

The composting rate is generally measured by the rate of organic matter decomposi-tion.The process of composting includes four main phases, which are the initial phase,the thermophillic phase, the mesophillic phase, and the maturation phase.The organicmatter in the six piles started decreasing, with the decrease more intense during the ther-mophillic phase (66°C).This may be attributed to the greater activity of the microorgan-isms, which had a large quantity of easily available degradable substances. All of the pileswere turned frequently to ensure that all parts were exposed to high temperatures.

The mesophillic phase started from day 18 and lasted until day 32.The bacterialpopulation rose to its highest level within one week of the construction of the piles,then declined and peaked again toward the end of the thermophillic stage. Since bacteriaare the most important decomposers during the most active phase of composting, theirnumbers are expected to increase at the start of the process, when nutrient levels arethe highest. Falcon et al. (1987) and Hardy and Sivasithamparam (1989) reported simi-lar trends.The temperature remained constant during the mesophillic stage.The stabi-lization phase started between days 32 and 35.The humidity went up because of the de-composition of microorganisms, and low temperatures were registered.The maturingphase was from day 35 to day 40.The temperature further decreased, humidity dimin-ished to 40 percent, and the microbial count was low for all piles.

pH

The variation of pH for the two piles is provided in Exhibit 4.The initial pH was neu-tral. During the first phase of composting, the pH varied from 6.8 to 7.0 due to the ac-tivity of acid-forming bacteria, which broke down the complex organic substances to or-ganic acid fermentation intermediates. In the latter phases, as the temperatures rose to66°C, so did the pH (~9.5), and then stabilized due to ammoniac production.With thisbehavior of pH, it can be deduced that during the first few days there was a rapid acido-genesis, resulting in an intense production of carbonic acid and organic acids. At the



Exhibit 4. Variation of pH with time during composting of soil pile

beginning of the thermophillic phase, alkalization occurred due to the hydrolysis of pro-teins by microorganisms producing ammonia.

Humidity

The humidity in all the experiments was near the optimum values of 60–70 percent(Hogos et al., 2002).The variation of humidity with time is shown in Exhibit 5.

Organic Matter

The organic matter values are expressed as TVS, and the variation is given in Exhibit 6.Rapid consumption of organic matter occurred during the thermophillic phase.

Temperature

The temperature increase that occurs during composting is the result of the oxidation oforganic matter by bacteria. During the initial phase of composting (four days), the



Exhibit 5. Variation of humidity during composting

Exhibit 6. Variation of organic matter (as TVS) during composting

temperature decreased due to the different microbial activities taking place during com-posting.The thermophillic phase started between 6 and 18 days and raised the tempera-ture of the piles to 66°C.The thermophillic phase lasted for 12 days, during which rapiddegradation of organic matter in all the piles occurred (Exhibit 7).

During composting, the temperature rises, because energy that is generated fromthe microbial metabolism but not utilized for further growth is retained by the insulat-ing effect of the compost heap.The consequent fall in the temperature marks the start ofthe maturation phase.This enables growth for those mesophillic bacteria that have sur-vived the thermophillic stage to resume and others that have been subsequently intro-duced through the activities of worms and insects to develop.

Microbial Status During Composting

The increase in the microbial count after the additions of initial fertilizer and compost isshown in Exhibit 8. Initially, between days 1 and 4, the mesophillic organisms increasedin number and were slowly substituted by thermophillic microorganisms, which raisedthe temperature of all piles and were responsible for rapid degradation of organic mat-ter. During the organic matter decomposition, thermophillic microorganisms started todecrease and were substituted by mesophillic microbes (Exhibit 9).The overall popula-tion of bacteria declined as the concentration of readily available nutrients, moisturecontent, and the temperature of the compost pile declined with maturity.



Exhibit 7. Variation of temperature during composting

Exhibit 8. Microbial counts during enrichments

Days Bacterial Count Bacterial Count(CFU/g soil) (CFU/g sediment)

0th Day (dry count) 34 � 104 42 � 104

2nd Day (fertilizer addition) 50 � 107 76 � 108

3rd Day (compost addition) 27 � 1010 30 � 1010

Nutrients

The amounts of total phosphorus and nitrogen remained at the same level during com-posting, although the amounts of the available form of nutrients (i.e., soluble phospho-rus, ammonium, and nitrate) were rapidly used by the microbes (Exhibits 10 and 11).

Variation of C/N with Time

The C/N changes during the composting are given in Exhibit 12.The initial C/N waslow then rose due to the addition of compost. As the carbonaceous material starts get-ting oxidized to CO2, which escapes out, the total content of the organic carbon getsreduced continuously.The amount of nitrogen will be getting incorporated into thebiomass being produced and does not change in concentration.There is no way of itescaping, and, as a consequence, the C/N ratio keeps on getting reduced as more and



Exhibit 9. Variation of microbial count during composting

Exhibit 10. Variation of soluble phosphorus during composting

more organic matter is oxidized. As a consequence of this oxidation, the temperaturewithin the heap increased till the heap was turned over.

Hazardous Organic Analysis

The chromatographic analysis of the soil and sediment for the estimation of hazardousorganic concentration in the two piles before composting is given in Exhibit 13. Peakshaving the retention times at 5.1 min, 17.2 min, 11.2 min, 14.8 min, and 23 min wereidentified for phenol, p-nitrophenol, 4-chloro-2-nitrophenol, 2,4-dichlorophenol, andbenzene, which disappeared at the end of the composting period (Exhibit 13).

Odor Production

During the composting processes, odors were produced as a by-product of the microbialdegradation. At the beginning, a foul smell was detected, characteristic of waste sludge.Later, the odor had an ammonia-type characteristic, as expected from the microbialtransformation of nitrogen-containing compounds.



Exhibit 11. Variation of soluble nitrogen during composting

Exhibit 12. Relation of C/N against time

Experimental Controls

Control soil and sediment piles were maintained to demonstrate that biological pro-cesses were responsible for removal of the compounds from the contaminated soil.Thecontrols allowed the biological effects to be assessed independently from other factorssuch as hydrolysis, volatilization, photodegradation, and organic complexing.The pileswere poisoned with HgCl2 (0.2/10 g of soil/sediment), incubated (Joyce et al., 1998),watered, and composted.The HgCl2-poisoned controls maintained the greenish hue(i.e., did not turn into a brown color, which is reminiscent of decaying organic matter)throughout the entire composting procedure, indicating biodegradation had occurred.No microbial growth or other discernible changes in the composition or volume of thecontrol samples were observed throughout the entire experiment.

Quality of Compost

The characteristics of the final compost obtained in all the experiments are given inExhibit 14. In Exhibit 15, the nutritional content of common manure from differentsources is compared with the compost product obtained from the two piles.The mineral



Exhibit 13. Chromatograms

content in the final compost was low compared with the optimum requirement, whichis: phosphorous: 0.22–0.3 percent for phosphorus, 0.24–0.6 percent for potassium,0.25 percent for magnesium, and 7 percent for calcium (Hogos et al., 2002).

CONCLUSION

The application of composting as a treatment alternative for the industrially contaminatedsoils and sediments seems to be a viable option. Operating parameters like aeration, mois-ture, temperature, pH, and C/N ratio for effective degradation of contaminants were opti-mized.The thermophillic phase lasted for a very short period where there was maximumreduction of contaminants.The obtained compost could be a good substratum for fertilizingbecause the final characteristics were satisfactory. Good control over the process parameterswill yield good-quality compost, which can be used as manure for surrounding fields or asinocula to further treat other hazardous organic contaminated soil/sediment. Compostingcan be carried out on site, thus making the decontamination process cost-effective.



Exhibit 14. Characteristics of the final compost obtained

Parameter Soil Pile Sediment PilepH 7.7 8.5Moisture 45 51.5Organic carbon, % 41.1 53TKN (total kjeldahl nitrogen), mg/g 4 4.1Nitrates, % 0.05 0.12Phosphates, % 0.29 0.15Phosphorus, % 0.2 0.02Potassium, % 0.056 0.1Calcium, % 0.5 2.8Magnesium, % 0.011 0.1

Exhibit 15. Comparison of nutritional content between common manure and compost of dif-

ferent piles

Manure from Soil Sediment

Parameter Cattle Chicken Pig Sheep Pile Pile

pH 8.7 7.8 7.2 9.00 7.7 8.5Organic carbon, % 48.2 29.4 46.9 48.2 41.1 53TKN (total kjeldahl nitrogen), mg/g 2.1 5.1 3.1 2.3 4 4.1

Phosphates, % 0.58 2.06 0.64 0.72 0.29 0.15Potassium, % 3.1 2.2 1.83 4.36 0.056 0.1Calcium, % 3.39 20.1 1.68 2.91 0.5 2.8Magnesium, % 0.97 0.88 0.93 0.57 0.011 0.1

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cides during composting: Composting, pesticides and pesticide degradation. Compost Science and

Utilization, 7(4), 66–82.

Falcon, M. A., Corominas, E., Perez, M. L., & Perestelo, F. (1987). Aerobic bacterial populations and envi-

ronmental factors involved in the composting of agricultural and forest wastes of the Canary Islands.

Biological Wastes, 20(2), 89–99.

Hardy, G. E., & Sivasithamparam, K. (1989). Microbial, chemical and physical changes during the compost-

ing of a eucalyptus (Eucalyptus calopyhila and Eucalyptus diversicolor) bark mix. Biology and Fertility of

Soils, 8, 260–270.

Hogos, S. E. G., Juarez, J. V., Ramonet, C. A., Lopez, J. G., Rios, A. A., & Uribe, E. G. (2002). Aerobic ther-

mophilic composting of waste sludge from gelatin-grenetine industry. Resources Conservation &

Recycling, 34, 161–173.

Joyce, J. F., Sato, C., Cardenas, R., & Surampalli, R. Y. (1998). Composting of polycyclic aromatic hydrocar-

bons in simulated municipal solid waste. Water Environment Research, 70, 356–361.

Laine, M. M., Haario, H., & Jorgensen, K. S. (1997). Microbial functional activity during composting of

chlorophenol contaminated sawmill soil. Journal of Microbiological Methods, 30, 21–32.

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diation of chlorophenol contaminated soil. Applied and Environmental Microbiology, 65, 1507–1513.

Rao, N., Grethlain, H. E., & Reddy, C. A. (1996). Effect of temperature on composting of atrazine-amended

lignocellulosic substrates. Compost Science and Utilization, 4(3), 83–88.

Savage, G. M., Diaz, L. F., & Golueke, C. G. (1985). Disposing of organic hazardous wastes by composting.

Biocycle, 26, 1–31.

Semple, K. T., Reid, B. J., & Fermor, T. R. (2001). Impact of composting strategies on the treatment of soils

contaminated with organic pollutants. Environmental Pollution, 112, 269–283.

Walkey, A., & Black, I. A. (1934). An examination of the Degtjareff method for determining soil organic mat-

ter, and a proposed modification of the chromic acid titration method. Soil Science, 37, 29–38.

Weed, D. A. J., Kanwar, R. S., & Salvador, R. J. (1999). A simple model of alachlor dissipation. Journal of

Environmental Quality, 28, 1406–1412.

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Zareen Khan, PhD, is a former lecturer at the Institute of Science & Technology, Jawaharlal Nehru

Technological University, in India. Dr. Khan has postdoctoral research experience from Blaise Pascal

University in France. Her areas of expertise include bioremediation and phytoremediation of contaminated

soils, sediments, and groundwater. She has a master’s degree and graduated in the top of her class.



Y. Anjaneyulu, PhD, is the former director at the Institute of Science & Technology, Jawaharlal Nehru

Technological University, in India. Dr. Anjaneyulu has extensive experience in the corporate, academic, and gov-

ernment sectors with a focus in the past ten years on several environmental issues, particularly air pollution,

hazardous waste management, reclamation of polluted rivers, and environmental impact assessment technolo-

gies. He has received the “Best Teacher Award” and has also authored several books on the environment.



bioremediation of contaminated soil and sediment by composting

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