3.3 Biological Bio-augmented Composting and Secondary …
85
For biological treatment process, the NH 3 concentration increased at first and then
reduced with time of biological treatment, and it reached the maximum at the second
day. This was because NH 4
+ was transformed into liquid NH 3 through deprotonation
and further transformed into gaseous NH 3 , which was further diffused into atmosphere. After the biological treatment was ended, the NH 3 concentration accounted
for about 1/3 of that in the early stage of composting. Moreover, the H 2 S concentration also rose at first and then reduced with biological treatment time, reaching the
maximum (0.252 mg/m
3 ) at the fourth day. It was likely related to that in the early
stage of composting, microbial metabolism consumed lots of oxygen, causing the
anaerobic environment to appear at the local area of the pile. The CS 2 concentration
reached the maximum (0.281 mg/m
3 ) at the fourth day of the biological treatment,
which was generally higher than concentrations of the other pollutants. Moreover,
the threshold value of CS 2 is low and therefore people can suffer from acute and
chronic poisoning and even retinopathy when sucking a certain dosage. Therefore,
during the biological treatment, the CS 2 should be considered as an odor pollutant
to be controlled preferentially. The concentrations of styrene, methyl mercaptan and
methyl sulfide were low and gradually decreased with the conduction of biological
treatment.
3.3.4.2 Emission Law of Volatile Organic Compounds During
Mechanical Separation and Biological Pre-treatment
The main pollutants in odorous gas are highly related to the compositions of municipal wastes. The compositions of volatile organic compounds (VOCs) in primary
wastes were analyzed by applying gas chromatography-mass spectrometry (GCMS). As shown in Table 3.7, the VOC composition of primary wastes was complex,
mainly shown as hydrocarbons and benzene series, which involved 12 hydrocarbon
compounds, 9 aromatic compounds, one sulfide, one ketone compound and an ester
compound. The concentration of total VOCs was 8.4606 mg/m
3 .
The results of compositions of odorous gas of municipal wastes during mechanical pre-treatment showed that compared with primary wastes, during primary
separation, the concentrations of various benzene series and ketones (including
benzene, chlorobenzene, trichlorotoluene, m-dichlorobenzene, p-dichlorobenzene,
dichloromethane, tetrachloroethylene, methylbenzene, trimethylbenzene, 1-ethyl4-methylbenzene, ethyl acetate, n-heptane, n-hexane, methyl ethyl ketone, methyl
isobutyl ketone and methyl-n-butyl ketone) generally rose (Table 3.8). Especially, the
concentration of dichloromethane was 6.35 times that of primary wastes, which was
likely related to that mechanical motion during separation speeded up the dispersion
of gases. In industry, dichloromethane shows a great irritation on skin and mucosa
and therefore dichloromethane should be intensively controlled during mechanical
pre-treatment. The concentrations of olefin pollutants generally declined and especially cis-1,3-dichloropropene, hexachlor-1,3-butadiene, trans-1,3-dichloropropene
were not detected during mechanical pre-treatment.
85
For biological treatment process, the NH 3 concentration increased at first and then
reduced with time of biological treatment, and it reached the maximum at the second
day. This was because NH 4
+ was transformed into liquid NH 3 through deprotonation
and further transformed into gaseous NH 3 , which was further diffused into atmosphere. After the biological treatment was ended, the NH 3 concentration accounted
for about 1/3 of that in the early stage of composting. Moreover, the H 2 S concentration also rose at first and then reduced with biological treatment time, reaching the
maximum (0.252 mg/m
3 ) at the fourth day. It was likely related to that in the early
stage of composting, microbial metabolism consumed lots of oxygen, causing the
anaerobic environment to appear at the local area of the pile. The CS 2 concentration
reached the maximum (0.281 mg/m
3 ) at the fourth day of the biological treatment,
which was generally higher than concentrations of the other pollutants. Moreover,
the threshold value of CS 2 is low and therefore people can suffer from acute and
chronic poisoning and even retinopathy when sucking a certain dosage. Therefore,
during the biological treatment, the CS 2 should be considered as an odor pollutant
to be controlled preferentially. The concentrations of styrene, methyl mercaptan and
methyl sulfide were low and gradually decreased with the conduction of biological
treatment.
3.3.4.2 Emission Law of Volatile Organic Compounds During
Mechanical Separation and Biological Pre-treatment
The main pollutants in odorous gas are highly related to the compositions of municipal wastes. The compositions of volatile organic compounds (VOCs) in primary
wastes were analyzed by applying gas chromatography-mass spectrometry (GCMS). As shown in Table 3.7, the VOC composition of primary wastes was complex,
mainly shown as hydrocarbons and benzene series, which involved 12 hydrocarbon
compounds, 9 aromatic compounds, one sulfide, one ketone compound and an ester
compound. The concentration of total VOCs was 8.4606 mg/m
3 .
The results of compositions of odorous gas of municipal wastes during mechanical pre-treatment showed that compared with primary wastes, during primary
separation, the concentrations of various benzene series and ketones (including
benzene, chlorobenzene, trichlorotoluene, m-dichlorobenzene, p-dichlorobenzene,
dichloromethane, tetrachloroethylene, methylbenzene, trimethylbenzene, 1-ethyl4-methylbenzene, ethyl acetate, n-heptane, n-hexane, methyl ethyl ketone, methyl
isobutyl ketone and methyl-n-butyl ketone) generally rose (Table 3.8). Especially, the
concentration of dichloromethane was 6.35 times that of primary wastes, which was
likely related to that mechanical motion during separation speeded up the dispersion
of gases. In industry, dichloromethane shows a great irritation on skin and mucosa
and therefore dichloromethane should be intensively controlled during mechanical
pre-treatment. The concentrations of olefin pollutants generally declined and especially cis-1,3-dichloropropene, hexachlor-1,3-butadiene, trans-1,3-dichloropropene
were not detected during mechanical pre-treatment.