Online monitoring of volatile organic compound production and emission during sewage sludge composting

Bioresource Technology 123 (2012) 463–470

Contents lists available at SciVerse ScienceDirect

Bioresource Technology journal homepage: www.elsevier.com/locate/biortech

Online monitoring of volatile organic compound production and emission during sewage sludge composting Yujun Shen a,b, Tong-Bin Chen a, Ding Gao a,⇑, Guodi Zheng a, Hongtao Liu a, Qiwei Yang a,b a b

Center for Environmental Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, PR China Graduate University of the Chinese Academy of Sciences, Beijing 100049, PR China

h i g h l i g h t s " The production and emission of VOCs were evaluated using online monitoring method. " Total VOCs production was 2.3 times as high as its emission. " Maximum production and emission masses occurred in the mesophilic phase. " Relation of production rates and time can be expressed as a quadratic equation. " Relation of emission rates and time can be expressed as a linear equation.

a r t i c l e

i n f o

a b s t r a c t

Article history: Received 5 March 2012 Received in revised form 27 April 2012 Accepted 1 May 2012 Available online 22 May 2012

The production and emission of volatile organic compounds (VOCs) were studied using an online monitoring method in a well-operated sludge composting plant. Results indicated that VOC production within the pile was different from emission at the pile surface. The total mass of VOC production was 1.09 g C kg DM1, which was 2.3 times as high as the total mass of emission. The maximum production and emission masses occurred in the mesophilic phase of composting and were 444 and 202 mg kg DM1 d1, respectively. VOC production and emission rates also varied rapidly at different times. The relationship of VOC production rates and time in an on/off aeration cycle at different periods could be expressed as a quadratic equation, while the emission rate could be expressed as a linear equation. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Composting Volatile organic compounds Online monitoring Production Emission

1. Introduction Composting is widely considered to be a low-cost and environmental friendly method to manage and treat organic solid wastes. However, the intense microbial activity during composting may produce and release volatile organic compounds (VOCs). The potential environmental consequences, such as odor and hazardous pollution, have not been taken seriously until recently. The term VOCs usually refers to organic compounds with melting points lower than room temperature and boiling points between 50– 260 °C (WHO, 1989). The VOCs produced from composting typically include nitrogen-based compounds, sulfur-based compounds,

Abbreviation: VOC, volatile organic compound.

⇑ Corresponding author. Tel./fax: +86 010 64889303. E-mail addresses: [email protected] [email protected] (D. Gao).

(Y.

Shen),

[email protected],

0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2012.05.006

volatile fatty acids, hydrocarbons, trepans, esters, ethers, alcohols, and aldehydes/ketones (Smet et al., 1999). Compost-generated VOCs can be evaluated in terms of two processes: the production within the pile due to organic matter degradation, and emission at the pile surface after gas convection within the pile. Most studies on VOCs from composting have concentrated on their emission and effects. Kumar et al. (2011) reported that the emission rate of VOCs in the early stage of green waste composting was five times higher than in the late stage. According to Eitzer (1995), who investigated VOC emissions from eight municipal solid-waste composting facilities, most VOCs were emitted in the initial composting period, with the maximum emission being 100 mg m3, which was 1.5–2 times the concentration in a later period. Turan et al. (2007) stated that the concentrations of VOCs emitted from the pile could exceed 14,000 mg m3 in the early stage of composting. Therefore, the initial period of composting is key to VOC emission.

464

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470

The scale of the composting system is a factor that influences VOC emission. Total VOC emission was 0.282 kg Mg1 dry matter when organic waste was composted in an 8 L reactor (Staley et al., 2006). Smet et al. (1999) reported a cumulative VOC emission of 1.51 kg Mg1 dry matter while composting food waste at a pilot scale volume of 224 L. Martínez-Blanco et al. (2010) found that the total VOC emission was approximately 1.80 kg Mg1 dry matter when composting in a reactor, while it was about 3.90 kg Mg1 dry matter when composting in a plant. Compared with reactor composting, composting plants generally use higher-frequency blowers for aeration and consequently accelerate VOC emission. Therefore, ventilation substantially impacts the emission of VOCs. Muller et al., 2004 found that excessive aeration sped up VOC emission from a compost pile. However, insufficient aeration can also result in higher VOC emission (Homans and Fischer, 1992), which may be attributed to anaerobic conditions within the pile that can increase VOC production and are not conducive to timely diffusion after emission. VOC emission is the process by which VOCs are discharged from the pile surface after their convection through the pile, whereas VOC production is the process by which VOCs are formed by microbial decomposition of organic matter. The process of VOC production is not clear and requires further study. Most previous studies monitored VOC concentrations indirectly (Pagans et al., 2006b; Eitzer, 1995), for example by chromatographic analyses of vacuum-sampled gases. It is easy for the gas samples to become chemically modified during transport to the lab; therefore, accurate and instantaneous VOC concentrations in the media are difficult to assess. In addition, the sampling intervals in most studies have varied from 20 h to 10 days (Pagans et al., 2006b; Turan et al., 2007), so the dynamics of VOC concentrations could not be accurately traced. Furthermore, the gas emission rate during composting changes quickly (Delgado-Rodriguez et al., 2011), so VOC emission rates that are measured indirectly represent an average over the sampling period rather than an instantaneous value. Real-time online monitoring can reduce measurement errors by sampling VOCs in situ and instantaneously. Based on these considerations, the objective of this work was to evaluate VOC production and emission in a large-scale sludge composting facility using a real-time online monitoring method. Another important objective was to establish dynamic models of VOC production and emission rates for different composting stages. 2. Methods 2.1. Composting procedures The experiment was carried out in the Lvgang Municipal Sewage Sludge Treatment Plant in the city of Qinhuangdao, China;

the composting system is pictured in Fig. 1. The compost pile was 30  5  1.6 m (L  W  H). Air was supplied (from bottom to top of the pile) by an air blower with a mass flow of 140 m3 min1. The aeration strategy was auto-controlled using an innovative static forced-aeration process called Control Technology of Bio-composting (CTB). This control technology is based on combined feedback data from temperature and oxygen-concentration sensors, and the composting process was controlled by CompsoftÒ V3.0 software (Chen et al., 2011). The specific aeration parameters were as follows: The aeration period was 13 min (3 min aerated, 10 min unaerated) in the early mesophilic phase; 16 min (3 min aerated, 13 min unaerated) in the late mesophilic phase; 29 min (9 min aerated, 20 min unaerated) in the thermophilic phase; and 35 min (15 min aerated, 20 min unaerated) in the curing phase. Temperature was measured using a PT100 sensor connected to the CTB auto-control system. VOC concentrations were detected with a custom-made device with a PID-A1 sensor (Alphasense, UK) connected to the CTB auto-control system. The pile was turned over on days 11, 14, and 16 using turning equipment (BLFP-540) made in China. The turning equipment included a turning drum, elevator, a 134.5 kW walking motor, control system, and cooling system. During processing, the turning equipment faced the pile head-on. After the turning drum started and the elevator was in place (at a depth of 1.5 m below the pile surface), the walking motor began the turning operation. The turning drum had a 5300 ± 5 mm span and a maximum walking speed of 5.2 m min1. On day 20, the compost materials were removed from the compartment. 2.2. Composting materials Sewage sludge (SS) was taken from the No. 4 Municipal Wastewater Treatment Plant in Qinhuangdao. Mature compost (MC) and wood chips (WC) collected from the Lvgang Sewage Sludge Treatment Facility were used as composting mixtures. The mass ratio of sludge, compost, and wood chips was 8:3:1 to adjust the moisture level of the initial composting materials to around 65%. The physicochemical properties of the raw materials are shown in Table 1. 2.3. Compost sampling and analytical methods The sampling points were in the center of the compost pile to minimize edge and wall effects. An iron cubic structure (1.6  1.6  1.6 m) with no cover or bottom was inserted into the compost pile to prevent disturbance to the probes. Three equallyspaced probes connected to the custom-made detectors were inserted into the pile at a depth of 0.8 m (middle layer); the middle layer most representative of instantaneous VOC concentrations in the pile (Akdeniz et al., 2010). A plastic cubic structure with no

Fig. 1. Structure of the composting system.

465

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470 Table 1 Properties of the compost materials. Materials

Moisture (%)

Density (g cm3)

Volatile solids (% dry basis)

TOC (%)

Sewage sludge Mature compost Wood chips

83.0 ± 0.3 39.4 ± 2.7 10.3 ± 2.7

1 0.30 0.20

68.6 ± 1.2 65.1 ± 2.6 96.1 ± 2.3

34.2 ± 0.3 26.9 ± 0.9 46.3 ± 1.7

bottom and two small holes (about 0.5 cm in diameter) in the lid covered a portion of the emitting surface (2.56 m2), thus creating an airtight chamber (1.6 m  1.6 m  0.5 m) above the iron cubic structure. The plastic structure was pressed into the composting material to a depth of approximately 0.05 m and used to measure VOC emissions. Three additional probes were equally-spaced in the center of the plastic chamber to capture the VOC fluxes from the pile. The detectors switched on automatically to monitor the VOC concentrations every 0.5 min, allowing monitoring of the constantly-changing gas production and emissions (Chen et al., 2011). We measured VOC concentrations in and outside the pile every 0.5 min over 20 days, through all different phases of composting. The compost pile was assumed to be uniform. Considering the experimental area (1.6  1.6  1.6 m) as a compost unit, the instantaneous concentration of VOCs in any given moment represented the instantaneous concentration in the previous moment and the production concentration between the previous moment and the sampling time, minus diffusion from the compost unit. The relationship is shown in Fig. 2. The variation of VOC concentrations over a period of time follows the following equation (Fig. 2):

C t1 ¼ C t0  C d þ C p

ð2Þ

In an aerated static pile, the patterns of gas convection between the pile and outside include both forced and free convection. Romain et al., 2005) reported that the velocity at the pile surface in a forced aeration system was 0.3 ± 0.1 m/s, which was about 150 times as high as that of a static system (Szanto et al., 2007). Therefore, forced convection is the main pattern of gas convection, occurring at a far greater rate than free convection, in an aerated static pile (Zhang et al., 2010). Consequently, free convection was ignored in this study. The pile was static (Cd@0) when it was unaerated, so

ð4Þ 3

1

Rp is the VOC production rate between t0 and t1 (mg m min ). Volatile organic compounds mainly come from the degradation of organic matter, but the degradation of organic matter in an on/ off aeration cycle that varies between 13 and 35 min is not obvious (Cai et al., 2012); therefore, the variation in VOC production rate was considered to follow the same rules during the aerated and unaerated phases in the on/off aeration cycle. The VOC production rate (mg m3 min1), measured every 0.5 min, during the unaerated phase in an on/off aeration cycle can be calculated from Eq. (4). Furthermore, the equation describing the relationship between VOC production rate and time during this phase can represent the VOC production characteristics in an on/off aeration cycle. The VOC production mass during the aerated phase can be obtained by integrating the product of the VOC production rate (mg m3 min1) and gas flux (m3) over this period, while the VOC production mass during the unaerated phase can be obtained by integrating the product of the VOC production rate (mg m3 min1) and gas volume of the experimental unit (m3) over this period. The formula is as follows:

Fp ¼ v

Z

t1

f ðtÞdt þ V

t0

Z

t2

f ðtÞdt

ð5Þ

t1

Where Fp is the VOC production mass during an on/off aeration cycle; f(t) is the function describing VOC production rates in an on/off aeration cycle; v is the gas flux in the experimental unit during an aerated phase (m3); V is the gas volume in the experimental unit during an unaerated phase (m3); t0 is the time that aeration starts in an on/off aeration cycle; t1 is the time aeration ends in an on/ off aeration cycle; and t2 is the time an on/off aeration cycle ends. The instantaneous concentration of VOCs monitored inside the dynamic chamber above the pile surface represents the instantaneous concentration in the previous moment and the emission concentration during that moment. Therefore, the relationship between the emission concentration and instantaneous concentration is:

C e ¼ C 0t1  C 0t0

ð6Þ

Where C t1 ’ is the instantaneous concentration at the pile surface at moment t1 (mg m3); C t0 ’ is the instantaneous concentration at the pile surface at moment t0 (mg m3); and Ce is the emission concentration of VOCs from t0 to t1 (mg m3). So,

Re ¼ C e =ðt1  t 0 Þ

Fig. 2. Relationships among the instantaneous, production, and diffusion concentrations of volatile organic compounds. Represents the instantaneous concentration at time t0 (C t0 , mg m3); Represents the production concentration from 3 t0 to t1 (Cp, mg m ); s Represents the concentration over the whole the compost unit from t0 to t1 (Cd, mg m3).

ð3Þ

Rp ¼ C p =ðt 1  t 0 Þ

ð1Þ

Where C t1 is the instantaneous concentration in the pile at moment t1 (mg m3); C t0 is the instantaneous concentration in the pile at moment t0 (mg m3); Cd is the concentration that diffuses from the compost unit between t0 and t1 (mg m3); and Cp is the production concentration from t0 to t1 (mg m3). Therefore,

C p ¼ C t1  C t0 þ C d

C p ¼ C t 1  C t0

ð7Þ

where Re is the emission rate of VOCs between t0 and t1 (mg m3 min1). The forced convection was far greater than free convection in the aerated pile, so the pile was considered static during the unaerated phase, and no emissions were released from the pile surface. Therefore, VOC emission only occurred in the aerated phase. The formula is as follows:

Fe ¼ v

Z

t1

t0

gðtÞdt

ð8Þ

466

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470

Where Fe is the VOC emission mass of an on/off aeration cycle; g(t) is the function describing VOC emission rates in an on/off aeration cycle; v is the gas flux in the experimental unit during the aerated phase (m3); t0 is the time aeration begins in an on/off aeration cycle; and t1 is the time aeration ends in an on/off aeration cycle. The total masses of VOC production and emission during the whole composting process can be obtained by summing the respective masses during each on/off aeration cycle. Nine solid samples were taken from the pile at the beginning and the end of the composting process. These were each bulked to form single samples for the two time periods, from which three sub-samples (about 200 g fresh mass each) were analyzed in the laboratory. Moisture, volatile solids (VS), and total organic carbon (TOC) were determined as recommended by the US Department of Agriculture and the US Composting Council (2002). The integration was performed using Maplesoft Maple v13.0 software.

3. Results and discussion 3.1. Dynamics of the instantaneous concentrations of VOCs during composting The maximum instantaneous concentrations of VOCs in the pile and on the pile surface every 12 h are shown in Fig. 3. According to temperature variations monitored in the pile (data not shown), the early mesophilic phase of composting occurred in days 0–1, the late mesophilic phase occurred in days 1–3, the thermophilic phase occurred in days 3–14, and the curing phase occurred in days 14– 20. The maximum instantaneous concentrations of VOCs were very high in the mesophilic phase and decreased thereafter. The VOC concentrations peaked on the second day at 3275 mg m3 in the pile and 1197 mg m3 at the pile surface. Concentrations decreased to below 100 mg m3 and remained at relatively low levels when entering into the thermophilic phase. In the late thermophilic phase and curing phase, the VOC concentrations increased once more, because the pile was turned over on days 11, 14, and 16; the second peaks occurred on day 12, with 462 mg m3 in the pile and 198 mg m3 at the pile surface. Obviously, the mesophilic phase of composting was the critical period in which VOCs are produced and emitted, and turning could accelerate these processes.

In pile Pile surface

3500

VOCs concentrations (mg

-3

cm )

4000

3000 2500 2000

Turning

1500 1000 500 0 0

2

4

6

8

10

12

14

16

18

20

Time(d) Fig. 3. Dynamics of the volatile organic compound concentrations during composting.

3.2. VOC production and emission rates during composting VOC production rates over time, as calculated by Eq. (4), at different composting stages are shown in Fig. 4. The statistical relationship between VOC production rate and time could be expressed as a quadratic equation. The general relationship can be expressed as follows:

f ðtÞ ¼ expðat 2 þ bt þ cÞ

ð9Þ

where f(t) is the function describing VOC production rate and time; t is time; and a, b, and c are constants. Rp = exp(c) is the initial VOC production rate during an on/off aeration cycle at different composting phases. Rp = (4ac  b2)/4a determined the peak value, which was the maximum production rate during an on/off aeration cycle. The initial and maximum VOC production rates occurred after 30 h (Fig. 4b) and 40 h (Fig. 4c) and decreased significantly during the thermophilic and curing stages of composting. The constant a determined the shape of the fitted curves. The greater the value of |a|, the smaller the fitted curve opening. The value of |a| decreased as the composting process progressed, so the variation in the VOC production rate declined gradually. The value of b/2a determined the time at which VOC production rate peaked. The greater the value of b/2a, the later the VOC production rate peaked. The value of b/2a increased from 4.32 after 16 h (Fig. 4a) to 11.25 after 15 days (Fig. 4e). Thus, the curve of the VOC production rate gradually flattened as composting proceeded. Fig. 5 shows the relationship between VOC emission rate and time, as calculated by Eq. (7), during different on/off aeration cycles. The relationship could be expressed as a linear equation. The general relationship can be expressed as:

gðtÞ ¼ kt þ m

ð10Þ

where g(t) is the function describing VOC emission rates over time; t is time; and k and m are constants. The constant k determined the slope of the curves. When k > 0, the VOC emission rate increased with time. The higher the constant k, the higher the slope of the curve and the faster the VOC emission rate increased; when k < 0, the VOCs emission rate decreased with time. The VOC emission rates increased with aeration time in the mesophilic stage of composting, while they decreased with aeration time in the thermophilic and curing stages of composting due to the reduction of microbial activity and the degradation of organic matter (Fig. 5). The constant m determined the intercept of the curves, indicating the initial VOC emission rate at the start of an on/off aeration cycle. The maximum initial emission rate (with 76 mg m3 min1) occurred after 30 h, and the rate decreased to below 10 mg m3 min1 as the composting proceeded (Fig. 5). As indicated in Figs. 4 and 5, VOC production and emission rates changed rapidly during different composting stages, even in an on/ off cycle. However, in most prior research, the sampling intervals at which concentrations were determined varied from 20 h to 10 days (Pagans et al., 2006b; Turan et al., 2007). Sampling intervals that are too long are certain to ignore some important VOC emissions and lead to inaccurate dynamics. On the contrary, VOC production and emission during different composting stages can be accurately traced by variations in the VOC production rate using online monitoring. Furthermore, VOC production and emission also vary spatially as well as temporally because of nonuniformities in the composting substrates. Cadena et al. (2009) obtained the total mass of VOC emission using a spatial interpolation over 15 sampling points on the pile surface. Unfortunately, they did not consider temporal variability. In this study, the composting substrates were assumed to be uniform, therefore, only temporal

467

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470 5

10

(a) 16h 2 lnf(t)=-0.11t +0.95t+1.02

4

(b) 30h 2 lnf(t)=-0.05t +0.53t+4.22

8

R =0.80 p<0.01

R =0.79 p<0.01

-1

lnf(t) (mg·cm ·min )

2

3

6

-3

-3

-1

lnf(t) (mg·cm ·min )

2

2

1

4

2

0 0 0

2

4

6

8

10

12

14

16

18

20

0

2

4

6

8

10

10

14

16

18

20

3

(c) 40h 2 lnf(t)=-0.04t +0.36t+3.61

8

(d) 7d 2 lnf(t)=-0.01t +0.23t-0.38

2

2

2

R =0.92 p<0.01 -1

lnf(t) (mg·cm ·min )

R =0.87 p<0.01

-1

lnf(t) (mg·cm ·min )

12

Time after aeration stopped (min)

Time after aeration stopped (min)

1

-3

-3

6

4

2

0

-1

0

-2 0

2

4

6

8

10

12

14

16

18

20

0

2

4

Time after aeration stopped (min)

6

8

10

12

14

16

18

20

Time after aeration stopped (min)

2

(e) 15d 2 lnf(t)=-0.008t +0.18t-0.29

1

-3

-1

lnf(t) (mg·cm ·min )

2

R =0.67 p<0.01

0

-1 0

2

4

6

8

10

12

14

16

18

20

Time after aeration stopped (min) Fig. 4. VOC production rates over time during different composting stages. (a) VOC production rates over time during the 16th hour of composting. (b) VOC production rates over time during the 30th hour of composting. (c) VOC production rates over time during the 40th hour of composting. (d) VOC production rates over time during the 7th day of composting. (e) VOC production rates over time during the 15th day of composting.

variability was considered. In the future, a much more realistic dynamic for VOC production and emission through the pile will be obtained by considering both spatial and temporal variability. 3.3. VOC production and emission masses The VOC production and emission masses for one day at different composting stages were calculated using Maplesoft 13.0 by substituting formulas (10) and (9) into formulas (5) and (8), respectively. Maximum VOC production and emission masses occurred in the late mesophilic phase and were 444 and 202 mg kg DM1 d1, respectively (Fig. 6). The minimum values

were 16.7 and 2.37 mg kg DM1 d1, respectively, in the thermophilic phase. The VOC production and emission masses in the curing phase increased slightly compared with the thermophilic phase because the pile was turned. Our results showed that VOC production was significantly correlated with organic matter degradation, a pattern similar to that reported by Kulikowska and Klimiuk (2011) (R2 = 0.98, p < 0.01) (data not shown). According to Cai et al. (2012), intense degradation of organic matter occurred during the mesophilic phase, while the rate of decay was greatly reduced later. Therefore, VOC production and emission mainly occurred during the mesophilic phase and declined thereafter. In essence, VOC production was related to microbial activity. The

468

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470 60

200

150

-1

-1 -3

g(t) (mg·cm ·min )

40

-3

g(t) (mg·cm ·min )

(a) 16h g(t)=4.17t+19.70 2 R =0.97 p<0.01

20

0

100

(b) 30h g(t)=31.2t+76.0 2 R =0.86 p<0.01

50

0 0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5

1.0

1.5

Aeration time (min)

2.0

2.5

60

(d) 7d g(t)=-1.68t+4.73 2 R =0.78 p<0.01

-1

6

-3

-1

g(t) (mg·cm ·min )

50

-3

3.5

10

8

g(t) (mg·cm ·min )

3.0

Aeration time (min)

40

(c) 40h g(t)=2.40t+40..0 2 R =0.87 p<0.01

30

4

2

0 20 0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.5

1.0

Aeration time (min)

1.5

2.0

2.5

3.0

Aeration time (min)

10

(e) 15d g(t)=-2.25t+7.35 2 R =0.97 p<0.01

6

-3

-1

g(t) (mg·cm ·min )

8

4

2

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Aeration time (min) Fig. 5. Relationship between VOC emission rate and time during different composting stages. (a) VOC emission rates over time during the 16th hour of composting. (b) VOC emission rates over time during the 30th hour of composting. (c) VOC emission rates over time during the 40th hour of composting. (d) VOC emission rates over time during the 7th day of composting. (e) VOC emission rates over time during the 15th day of composting.

quantity of microorganisms increased rapidly in the mesophilic phase, leading to organic matter degradation and increased VOC production. Microorganism biodiversity is highest in the mesophilic phase (Mayrhofer et al., 2006). Previous work has shown that proteobacteria and lactic acid bacteria mainly appeared in the mesophilic phase and could accelerate the degradation of organic matter (Tang et al., 2007) and increase VOC production further. After the mesophilic phase, many kinds of microorganism died as the temperature increased. The quantities and varieties of microorganism decreased substantially, impeding the organic matter degradation and VOC production. In addition, the predominant bacteria in the thermophilic phase was Bacillus cereus (Schloss

et al., 2003), which can decompose some VOCs, such as organic sulfur and nitrogen compounds, while degrading organic matter (Conde et al., 2001). Therefore, the VOC concentrations in this stage were low. We conclude that the quantities and varieties of microorganisms in different composting stages determined the organic matter degradation rate and resulted in different VOC masses. The mesophilic phase is the critical period of VOC production and emission and should be followed closely. The total masses of VOC production and emission over the entire procedure are shown in Table 2. The total masses were 1.09 and 0.47 g C kg DM1, respectively, accounting for 3.74% and 1.62% of C loss, which was mainly distributed in the neutral

VOCs production and emission masses (mg kg dry matter-1 d-1 )

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470 600 500

Production Emission

400

469

production and emission masses occurred in the mesophilic phase, with 444 and 202 mg kg DM1 d1, respectively. Therefore, the mesophilic phase is the critical period for VOC control.

300

Acknowledgements

200

The project was financially supported by the National HighTech R&D Program of China (863 Program) (No. 2009AA064703), the state environmental protection public welfare professional program (No. 201209022), and the National Key Technology R&D Program of China (No. 2011BAZ03160). The authors wish to acknowledge with thanks the help received from Dr. Leah Larkin in correcting the English text.

80 60 40 20 0

Early stage of Late stage of Thermophilic phase Curing phase mesophilic phase mesophilic phase Composting stages Fig. 6. VOC production and emission masses for one day during different composting stages.

Table 2 Total masses of VOC production and emission. VOCs-C

Production Emission

Mass (g C kg DM1)

% of the initial carbon

% of the C loss

1.09 ± 0.26 0.47 ± 0.14

0.31 ± 0.07 0.13 ± 0.04

3.74 ± 0.89 1.62 ± 0.48

detergent soluble and water insoluble fractions (Zhao et al., 2011). Actually, the total mass of VOC production was 2.3 times as high as the mass of emission. This phenomenon is related not only to the difficulty of gas convection in porous media (Veeken et al., 2002), but also to VOC adsorption and degradation by composting materials. Anfruns et al. (2011), Vandurme et al. (1992), and Baltrenas and Zagorskis (2010) all proved that sludge, mature compost, and wood chips can adsorb VOCs to some extent, but VOC levels are primarily reduced by microbial degradation in the substrate (Oh et al., 2009; Singh et al., 2010). Therefore, the total mass of VOC emission on the pile surface was lower than that of production in the pile. Most previous studies used instantaneous concentrations at the sampling times to represent an average over the sampling period to calculate VOC emission masses; VOC emission masses reported for composting facilities were 0.82 g kg DM1 (Cadena et al., 2009) and 3.90 g kg DM1 (Martínez-Blanco et al., 2010). The total VOC emission mass in this work was 0.47 g kg DM1, which was lower than in previous studies. The differences in VOC emission attributed to C loss were related to composting materials (Antil et al., 2011). More important, the instantaneous concentration of VOCs includes the instantaneous concentration in the previous moment and the production concentration at the time of sampling. Therefore, substituting the instantaneous concentration for the production concentration can result in an overestimation of the emission mass.

4. Conclusions VOC production and emission, and curves describing their rates during different composting stages were obtained using an online monitoring method. The relationship of production rates and time in an on/off aeration cycle could be expressed as a quadratic equation, while the emission rate could be expressed as a linear equation. The total mass of VOC production was 1.09 g C kg DM1, which was 2.3 times as high as the emission mass. The maximum

References Anfruns, A., Martin, M.J., Montes-Moran, M.A., 2011. Removal of odourous VOCs using sludge-based adsorbents. Chem. Eng. J. 166, 1022–1031. Antil, R.S., Bar-Tal, A., Fine, P., Hadas, A., 2011. Predicting nitrogen and carbon mineralization of composted manure and sewage sludge in soil. Compos. Sci. Util. 19 (1), 33–43. Akdeniz, N., Koziel, J.A., Ahn, H.K., Glanville, T.D., Crawford, B.P., 2010. Field scale evaluation of volatile organic compound production inside biosecure swine mortality composts. Waste Manage. (Oxford) 30, 1981–1988. Baltrenas, P., Zagorskis, A., 2010. Investigation into the air treatment efficiency of different structures. J. Environ. Eng. Landsc. 18, 23–31. Cadena, E., Colon, J., Sanchez, A., Font, X., Artola, A., 2009. A methodology to determine gaseous emissions in a composting plant. Waste Manage. (Oxford) 29, 2799–2807. Cai, L., Gao, D., Chen, T.-B., Liu, H.-T., Zheng, G.-D., Yang, Q.-W., 2012. Moisture variation associated with water input and evaporation during sewage sludge bio-drying. Bioresour. Technol.. http://dx.doi.org/10.1016/j.biortech.2012.03. 092. Chen, J., Chen, T.B., Gao, D., Lei, M., Zheng, G.D., Liu, H.T., Guo, S.L., Cai, L., 2011. Reducing H2S production by O2 feedback control during large-scale sewage sludge composting. Waste Manage. (Oxford) 31, 65–70. Conde E, Alba J, Lopez E, Perez-Guevara, F., 2001. Removal of complex mixtures of VOC (thinner) from waste air and establishment of the evolution of microbial consortium during biofiltration process//LATINI G, BREBBIA C A. Air Pollution Ix. Southampton; in Press. 355–364. Delgado-Rodriguez, M., Ruiz-Montoya, M., Giraldez, I., Lopez, R., Madejon, E., Diaz, M.J., 2011. Influence of control parameters in VOCs evolution during MSW trimming residues composting. J. Agric. Food Chem. 59, 13035–13042. Eitzer, B.D., 1995. Emissions of volatile organic-chemicals from municipal solidwaste composting facilities. Environ. Sci. Technol. 29 (4), 896–902. Homans, W.J., Fischer, K., 1992. A composting plant as an odour source, compost as an odour killer. Acta Horticul. 302, 37–44. Kulikowska, D., Klimiuk, E., 2011. Organic matter transformations and kinetics during sewage sludge composting in a two-stage system. Bioresour. Technol. 102, 10951–10958. Kumar, A., Alaimo, C.P., Horowitz, R., Mitloehner, F.M., Kleeman, M.J., Green, P.G., 2011. Volatile organic compound emissions from green waste composting: Characterization and ozone formation. Atmos. Environ. 45 (10), 1841–1848. Martínez-Blanco, J., Colón, J., Gabarrell, X., Font, X., Sánchez, A., Artola, A., Rieradevall, J., 2010. The use of life cycle assessment for the comparison of biowaste composting at home and full scale. Waste Manage. (Oxford) 30 (6), 983–994. Mayrhofer, S., Mikoviny, T., Waldhuber, S., Wagner, A.O., Innerebner, G., FrankeWhittle, I.H., Mark, T.D., Hansel, A., Insam, H., 2006. Microbial community related to volatile organic compound (VOC) mission in household biowaste. Environ. Microbiol. 8, 1960–1974. Muller, T., Thissen, R., Braun, S., Dott, W., Fischer, G., 2004. (M) VOC and composting facilities. Part 1: (M) VOC emissions from municipal biowaste and plant refuse. Environ. Sci. Pollut. R 11, 91–97. Oh, D.I., Song, J., Hwang, S.J., Kim, J.Y., 2009. Effects of adsorptive properties of biofilter packing materials on toluene removal. J. Hazard. Mater. 170, 144–150. Pagans, E., Font, X., Sanchez, A., 2006. Emission of volatile organic compounds from composting of different solid wastes: Abatement by biofiltration. J. Hazard. Mater. 131, 179–186. Romain, A.C., Godefroid, D., Kuske, M., Nicolas, J., 2005. Monitoring the exhaust air of a compost pile as a process variable with an e-nose. Sens. Actuators B-Chem. 106, 29–35. Schloss, P.D., Hay, A.G., Wilson, D.B., Walker, L.P., 2003. Tracking temporal changes of bacterial community fingerprints during the initial stages of composting. FEMS Microbiol. Ecol. 46, 1–9. Singh, K., Singh, R.S., Rai, B.N., Upadhyay, S.N., 2010. Biofiltration of toluene using wood charcoal as the biofilter media. Bioresour. Technol. 101, 3947–3951. Smet, E., Van Langenhove, H., De Bo, I., 1999. The emission of volatile compounds during the aerobic and the combined anaerobic/aerobic composting of biowaste. Atmos. Environ. 33, 1295–1303.

470

Y. Shen et al. / Bioresource Technology 123 (2012) 463–470

Staley, B.F., Xu, F., Cowie, S.J., Barlaz, M.A., Hater, G.R., 2006. Release of trace organic compounds during the decomposition of municipal solid waste components. Environ. Sci. Technol. 40, 5984–5991. Szanto, G.L., Hamelers, H.V.M., Rulkens, W.H., Veeken, A.H.M., 2007. NH3, N2O and CH4 emissions during passively aerated composting of straw-rich pig manure. Bioresour. Technol. 98, 2659–2670. Tang, J.C., Shibata, A., Zhou, Q.X., Katayama, A., 2007. Effect of temperature on reaction rate and microbial community in composting of cattle manure with rice straw. J. Biosci. Bioeng. 104, 321–328. The US Department of Agriculture and The US Composting Council, 2002. Test Methods for the Examination of Composting and Compost(TMECC). Edaphos International, Houston, USA.

Turan, N.G., Akdemir, A., Ergun, O.N., 2007. Emission of volatile organic compounds during composting of poultry litter. Water Air Soil Pollut. 184, 177–182. Vandurme, G.P., McNamara, B.F., McGinley, C.M., 1992. Bench-scale organiccompounds at a composting facility. Water Environ. Res. 64, 19–27. Veeken, A., de Wilde, V., Hamelers, B., 2002. Passively aerated composting of strawrich pig manure: Effect of compost bed porosity. Compos. Sci. Util. 10 (2), 114–128. Zhang, J., Gao, D., Chen, T.B., Zheng, G.D., Chen, J., Ma, C., Guo, S.L., Du, W., 2010. Simulation of substrate degradation in composting of sewage sludge. Waste Manage. 30 (10), 1931–1938. Zhao, L., Wang, X.Y., Gu, W.M., Shao, L.M., He, P.J., 2011. Distribution of C and N in soluble fractionations for characterizing the respective biodegradation of sludge and bulking agents. Bioresour. Technol. 102, 10745–10749.