Odor composition analysis and odor indicator selection during sewage sludge composting

Figures & data

Table 1. Aeration parameters of the experiment.

Composting stages	Hours (hr)	On/off (min)	Frequency (HZ)	Volume (m^3/hr)
First stage	72	6/32	30	4,800
Second stage	360	10/30	40	5,900

Table 2. Properties of the raw materials and initial mixtures.

	MC (%)^a	TOC (g/kg)^b	TN (g/kg)^b	TS (g/kg)^b	VS (%)^b
Sewage sludge	80.34	390.1	57.6	20.1	73.62
Sawdust	13.27	497.7	5.2	1.9	98.34
Mature compost	51.23	400.3	27.2	11.2	83.72
Mixture	62.96	434.5	28.3	10.6	85.21

^aWet weight basis.

^bDry weight basis.

Figure 1. (a) Schematic of sewage sludge composting. (b) Structure of the composting system.

Figure 2. (a) Dynamic changes in temperature and MC during sewage sludge composting. (b) Dynamic changes in pH during sewage sludge composting.

Figure 3. Dynamic changes in odor concentration during sewage sludge composting.

Table 3. Odor composition during sewage sludge composting.

	Species	Pollutants
Volatile inorganic compounds	2	Hydrogen sulfide, ammonia
Sulfur organic compounds	4	Methyl mercaptan, dimethyl sulfide, dimethyl disulfide, carbon disulfide
Benzenes	16	Benzene, toluene, ethylbenzene, dimethylbenzene, p-xylene, isopropylbenzene, propylbenzene, m-ethyltoluene, m-xylene, 1,3,5-trimethylbenzene, o-ethyltoluene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, 1,2-diethylbenzene, 1,4-diethylbenzene, styrene
Alkanes	27	Isobutane, butane, isopentane, pentane, 2,2-dimethyl-butane, cyclopentane, 2,3-dimethyl-butane, 2-methyl-pentane, 3-methyl-pentane, n-hexane, methyl-cyclopentane, 2,4-dimethyl-pentane, cyclohexane, 2-methyl-hexane, 2,3-dimethyl-pentane, 3-methyl-hexane, 2,2.4-trimethyl-pentane, heptane, methyl-cyclohexane, 2,3,4-trimethyl-pentane, 2-methyl-heptane, 3-methyl-heptane, n-octane, nonane, decane, undecane, dodecane
Alkenes	15	1-Butene, 1,3-butadiene, t-2-butene, c-2-butene, 3-methyl-1-butene, 1-pentene, isoprene, t-2-pentene, c-2-pentene, 2-methy-2-butene, cyclopentene, 4-methyl-1-pentene, 1-hexene, t-2-hexene, c-2-hexene
Halogenated compounds	19	Freon-12, dichloromethane, Freon-114, vinyl-chloridev, chloroethane, freon 11, 1,1-dichloro-ethene, 1,1-dichloroethane, Freon-113, 1,1-dichloro-ethane, 1,2-dichloro-ethene (E), chloroform, 1,2-dichloroethane, carbon tetrachloride, 1,2-dichloro-propane, trichloroethane, chlorobenzene, 1,2-dichloro-benzene, 1,3-dichloro-benzene

Table 4. Concentration range of typical odor gas during sewage sludge composting.

	Critical odor pollutants	Concentration range (mg/m^3)
Volatile inorganic compounds	Ammonia	10 – 150
	Hydrogen sulfide	2 – 40
	Carbon disulfide	0 – 15
Sulfur organic compounds	Dimethyl disulfide	0 – 12
	Dimethyl sulfide	0 – 13
	Methyl mercaptan	0 – 0.2
Benzenes	Toluene	0 – 10
	Ethylbenzene	0 – 1.5
	Dimethylbenzene	0 – 5
Alkanes	Isopentane	0 – 0.7
	Undecane	0 – 0.2
	Butane	0 – 0.4
Alkenes	1-Butene	0 – 1.3
	t-2-Butene	0 – 8
	1-Pentene	0 – 1.6
Halogenated compounds	Freon-11	0 – 0.1
	Carbon tetrachloride	0 – 0.1
	Trichloroethylene	0 – 0.8

Table 5. Concentration of each compound class at different stages (unit: µg/m³).

	Day 2		Day 5		Day 18
	Internal	Surface	Internal	Surface	Internal	Surface
Volatile inorganic compounds	123,688	53,793	97,799	96,476	13,063	1,258
Sulfur organic compounds	35,142	515	3,420	6,095	574	272
Benzenes	3,611	609	1,159	1,371	1,031	552
Alkanes	3,107	787	932	687	1,396	694
Alkenes	23,365	403	125	187	61	448
Halogenated compounds	98	116	136	77	86	60
Total	189,010	56,222	103,572	104,893	16,211	3,283
Odor concentration	524.2	112.7	379.1	130.9	89	76

Figure 4. Percentage of each class of compounds in relation to odor concentration.

Table 6. Correlation analysis between odor concentration and emission of each class.

	Odor concentration	VICs	Sulfur organic compounds	Benzenes	Alkanes	Alkenes	Halogenated compounds	Total
Odor concentration	1	0.804	0.828*	0.841*	0.768	0.795	0.502	0.881*
Volatile inorganic compounds		1	0.690	0.719	0.487	0.579	0.449	0.961*
Sulfur organic compounds			1	0.987**	0.931**	0.985**	0.052	0.863*
Benzenes				1	0.936*	0.956*	0.082	0.878*
Alkanes					1	0.956**	0.079	0.699
Alkenes						1	0.033	0.782
Halogenated compounds							1	0.379
Total								1

*Denotes p < 0.05 significant relation.

**Denotes p < 0.01 extremely significantly correlation.

Table 7. Odor threshold values of different compounds during sewage sludge composting (unit: ppm).

Pollutants	Molecular formula	Odor thresholds	Pollutants	Molecular formula	Odor thresholds
Ammonia	NH3	1.5	Benzene	C6H6	2.7
Hydrogen sulfide	H2S	0.00041	Toluene	C6H5CH3	0.33
Methyl mercaptan	(CH3)SH	0.00007	Ethylbenzene	C6H5CH2CH3	0.17
Carbon disulfide	CS2	0.21	Styrene	C6H3CH=CH2	0.035
Dimethyl disulfide	(CH3)2S2	0.0022	1,3,5-Trimethylbenzene	C6H3(CH3)3	0.17
Propylene	CH2=CHCH3	13	1,2,4-Trimethylbenzene	C6H3(CH3)3	0.12
Isobutene	C4H8	10	p-Xylene	C6H4(CH3)2	0.058
Cyclohexane	C6H12	2.5	Isopropylbenzene	C6H5CH(CH3)2	0.0084
Heptane	C7H16	0.67	Undecane	C11H24	0.87
n-Hexane	C6H14	1.5	Dodecane	C12H26	0.11
n-Octane	C8H18	1.7

Note. During calculation, volume concentration should be converted to mass concentration with the formula of mass concentration (µg/m³) = volume concentration (ppb) × relative molecular mass/22.4.

Table 8. Core, concentration, and health indicators during sewage sludge composting.

	Core indicators	Concentration indicators	Health indicators
1	Hydrogen sulfide	Ammonia	Benzene
2	Methyl mercaptan	Hydrogen sulfide	m-Xylene
3	Dimethyl disulfide	Carbon disulfide	p-Xylene
4	Dimethyl sulfide	Dimethyl disulfide	Dimethylbenzene
5	Ammonia	Methyl mercaptan	Dichloromethane
6	Carbon disulfide	Toluene	Toluene
7		Dimethylbenzene	Chlorobenzene
8		Propylbenzene	Trichloromethane
9		Isopentane	Carbon tetrachloride
10			Ethylbenzene

Note. The table shows that the contribution degree of the core indicators and the production concentration of the concentration indicators decreased.

Table 9. Correlation analysis for dimethyl sulfide, carbon disulfide, and dimethyl disulfide inside the pile.

	Dimethyl sulfide	Carbon disulfide	Dimethyl disulfide
Dimethyl sulfide	1	0.568	0.932*
Carbon disulfide		1	0.808*
Dimethyl disulfide			1

*Denotes p < 0.05 significant relation.

Table 10. Correlation analysis for dimethyl sulfide, carbon disulfide, and dimethyl disulfide on the surface of the pile.

	Dimethyl sulfide	Carbon disulfide	Dimethyl disulfide
Dimethyl sulfide	1	0.906	0.788*
Carbon disulfide		1	0.973*
Dimethyl disulfide			1

*Denotes p < 0.05 significant relation.

Figure 5. Dynamic changes of the dimethyl disulfide during sewage sludge composting.