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Effects of Organic Chemicals in Sludge Applied to Soil

2. Organic contaminants in wastewater sludge

A previous monitoring study was conducted in Denmark in 1995 and included analyses of more than 100 specific organic contaminants in 20 sludge samples from 19 different wastewater treatment plants (WWTPs) (Tørsløv et al. 1997). The analyses performed during this study showed that surfactant-derived substances and phthalates were normally present at high mg per kg levels (on dry weight basis). Typical organic contaminants and their concentrations in Danish sludges are shown in Table 2.1.

Table 2.1
Typical organic contaminants in Danish wastewater sludges
Typiske, organiske, miljøfremmede stoffer i dansk spildevandsslam

  Range
m g/kg d.w.1		 Average
m g/kg d.w.1		 Median
m g/kg d.w.1		 Number of
positive
identifications2
Hydrocarbons and PAHs
Toluene (mg/kg d.w.) <2-370 21 0,29 15
Naphthalene <10-380 88 50 13
Methylnaphtalenes <10-2,500 305 93 13
Dimethylnaphthalenes <10-9,700 1,205 375 19
Trimethylnaphthalenes <10-10,000 1,166 325 17
Acenaphthylene <10-160 30 20 9
Acenaphthene <10-110 36 25 12
Fluorene <10-320 71 23 10
Phenanthrene <10-1,800 307 134 18
Fluoranthene <10-3,300 323 102 17
Benz(a)anthracene <10-600 82 39 20
Chrysene <10-710 105 77 19
Pyrene <10-3,800 310 35 11
Benzo(a)pyrene <10-1,400 152 72 19
Benzo(b,j,k)fluoranthene 12-2,400 291 130 20
Benzo(g,h,i)perylene <10-1,400 118 10 10
Indeno(1,2,3,-cd)pyrene <10-630 67 23 14
Dibenz(a,h)anthracene <10-79 33 24 11
PCB congeners, sum
PCB: #28, #52, #101, #118, #138, #153,#180 <27-186 48 32 10
Chlorinated aliphatics
Chloroform <0.4-3 0.81 0.50 11
Trichloroethylene <0.4-32 2.9 0.50 8
Tetrachlorethylene <0.5-290 18 0.50 9
Surfactants (mg/kg d.w.)
Nonylphenol + ethoxylates3 0.3-67 15 8.0 20
LAS 11-16,100 2,700 530 19
Phthalates (mg/kg d.w.)
Butylbenzylphthalate <0.02-0.74 0.18 0.10 13
Di(2-ethylhexyl)phthalate 3.9-170 38 25 20
Di-n-octyl phthalate <0.02-2.8 0.61 0.34 20
Di-n-butylphthalate <0.02-26 3.9 0.30 7
P-triesters
Tri-n-butylphosphate <20-2,400 252 59 11
Triphenylphosphate <20-1,900 284 66 11
Tricresylphosphate <20-2,400 175 99 13
Pesticides
Dieldrin <15-1,200 247 120 74
Isophoron <5-83 23 6.0 74
Miscellaneous
AOX (mg C1/kg d.w.) 75-890 244 180 19

1) Concentrations are m g/kg dry weight unless otherwise indicated
2) Results above analytical detection limits out of 20 analyses
3) Nonylphenol + nonylphenol ethoxylates with 1-2 ethoxylate units
4) Results above analytical detection limits out of 11 analyses

The concentrations of specific organic contaminants in the sludges depend of the type of the WWTP. Aerobic or anaerobic treatment conditions, as in activated and digested sludge respectively, have significant influence on the biodegradation of many organic compounds. This is evident when the data of the previous monitoring study are related to one of two main sludge types: (i) activated sludge and (ii) mixed activated and anaerobically digested sludge. Table 2.2 shows that the concentrations of LAS, nonylphenol ethoxylates (NPEs) and nonylphenol (NP) were significantly lower in activated sludge compared to mixed activated and digested sludge (according to Student’s t test with p < 0.005). A straight forward explanation exists for LAS as these compounds are not degraded in the absence of molecular oxygen while substantial biodegradation of LAS is normally seen in activated sludge systems. Differences in the biodegradation under anaerobic and aerobic conditions may also explain the observed levels of NP and NPEs in the two sludge types as NP is the major product from anaerobic transformation of NPEs. The major degradation products from the biotransformation of NPEs under aerobic conditions are nonylphenoxy carboxylates while NP is formed in smaller amounts (Ball et al. 1989). The nonylphenoxy carboxylates were not included in the previous monitoring programme (Tørsløv et al. 1997). The data in Table 2.2 do thus not document that aerobic conditions during activated sludge treatment will lead to extensive elimination of all nonylphenolic compounds.

Table 2.2
Concentrations of LAS and nonylphenol ethoxylates in activated sludge samples and in samples partly composed of activated and anaerobically digested sludge
Koncentrationer af LAS og nonylphenolethoxylater i prøver med aktivt slam og i prøver sammensat af aktiveret og anaerobt udrådnet slam

  LAS
[mg/kg dry weight ± SD2]		 NP + NPE1
[mg/kg dry weight ± SD]
  Average Median Average Median
Activated sludge
(11 samples)		 101 ± 183 20 4.0 ± 4.7 1.0
Mixtures of activated and anaerobically
digested sludges
(9 samples)		 5,519 ± 6,654 940 29 ± 22 20

1) nonylphenols and nonylphenol ethoxylates with 1 and 2 ethoxylate units
2) standard deviation

No differences between the sludge types were seen for DEHP and the sum of the PAHs specified in the Danish regulation of the application of waste products, i.e. acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, benzo(b,j,k)fluoranthene, benzo(a)pyrene, benzo(g,h,i)perylene, and indeno(1,2,3-cd)pyrene (Ministry of Environment and Energy 1996).

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