Sorption of Pollutants in Wastewater Solids

Abstract

Sorption in wastewater solids is an important removal mechanism for pollutants in biological treatment systems. It is often an overlooked mechanism, since traditionally, excess solids from biological treatment were land filled. However, with the emergence of using wastewater solids as a potential fertilizer, pollutants sorbed into the solids can re-emerge as soil pollutants, with potential uptake by crops, and even transported into groundwater. This is especially applicable for hydrophobic chemicals, like alkyl fluorinated compounds (PFAS, PFOS), which have recently received widespread attention as pollutants in water bodies across the globe. In this chapter, sorption of pollutants in wastewater solids has been presented from both a thermodynamic analysis, involving equilibrium parameters, as well as a kinetic process involving transport to the cell walls and permeation through the cell membranes. Based on experimental data and models it is shown that biodegradation in wastewater systems is actually mass transfer coefficient for diffusive transport across the microbial cell walls.

1. Introduction

Transport of pollutants into wastewater solids (biomass) can occur due to a variety of mechanisms, some of which are surface related, while others involve absorption or sorption into the biomass cells. Uptake of pollutants by the surface of the biomass is defined as “adsorption” driven by several possible mechanisms which includes hydrophobic-hydrophobic interaction, electrostatic interaction and hydrogen bonding. The latter two mechanisms are dominant under basic and acidic conditions, respectively, while hydrophobic-hydrophobic interaction occurs mainly under neutral conditions [1].

Sorption or absorption in biomass involves the transport of the pollutants into the cell, rather than adsorbed on the outside surface of the cells. Sorption in wastewater solids is an important mechanism for removal of organic compounds in biological wastewater treatment systems. Experimental results and theoretical developments related to the sorption process have been reported in our previous work [2, 3]. During isotherm measurements, biological activity in wastewater solids, especially in activated sludge, that contains a substantial amount of active biomass, must be controlled to obtain accurate sorption isotherms. Measurements of varying aqueous phase concentrations could include the effect of biodegradation, resulting in apparent sorption capacities greater than actually achieved.

Sorption in Biomass can be analyzed as an equilibrium process, using isotherms, as well as a kinetic process, involving transport to the biomass cell walls and permeation through the cell membranes.

2. Analysis of equilibrium sorption: surface adsorption vs. partitioning

A dual-process mechanism [4] was postulated for the sorption of lindane and hexachlorocyclohexane on five unidentified bacteria. In this mechanism, sorption was viewed as a combination of rapid surface adsorption and diffusive penetration. A similar mechanism was suggested [5] for the uptake of 2,4-dichlorophenoxyacetic acid by Pseudomonas fluoresces. The result was a combination of the following steps: adsorption onto the cell wall accompanied by passive diffusion into the cytoplasm. Based on the comparable sorption results of organic compounds between live and dead biomass in a Kraft mill generated lagoon, it was suggested that sorption on biomass was mainly a passive diffusion of small molecules into the cell than active or facilitated transport [6].

By comparing the sorption of chloroethanes on different types of microbial biomass, it was speculated [7] that the sorption of organic molecules on microbial biomass was related to the leachable organic carbon which was released from the cell cytoplasm due to the rupture of cells. It was found that the more leachable organic carbon the biomass contained, the higher the uptake capacity of the toxic organic compound it had.

In order to better understand the sorption mechanism on microbial biomass, Bell [8, 9, 10, 11] examined the magnitude of the heats of sorption for diazinon and lindane. The thermodynamic data strongly suggested a physical sorption instead of a chemical sorption. By reviewing the sorption mechanism on biomass in the literature, Bell [9] concluded that firm, general conclusions cannot be reached concerning the mechanism of sorption on biomass. Indeed, the mechanisms may be specific to the particular system of chemicals and biomass. It seems likely that a combination of adsorption and absorption may be responsible for the sorption on biomass and that the relative importance of each mechanism may vary from system to system [12].

Biological activity in wastewater solids, especially in activated sludge which contains a substantial amount of active biomass, must be controlled in order to obtain accurate sorption isotherms. Otherwise, measurements of changing aqueous phase compound concentrations could include the effect of biodegradation, resulting in apparent sorption capacities greater than actually achieved. Despite the difficulties associated with the control of the biological activity in biomass, several attempts have been reported.

In this chapter, sorption in biomass will be modeled as an adsorption partitioning process, in which physical adsorption on the surface and partitioning into the biomass cells occurs simultaneously. Wastewater solids contain high percentage (50–85%) of organic matter, in a relatively loose physical form. It is generally believed that the organic matter is a complex mixture of live and dead microorganisms, which are primarily proteins, fats and carbohydrates, and other organic sediments. While the organic matter is basically solid, it is certainly different from activated carbon. The nature of the organic matter gives the sludge certain characteristics of an organic solvent. Chiou et al. [13, 14, 15] described the sorption of toxic organic compounds on soil organic matter as a partitioning phenomenon. Using the Flory-Huggins theory, they were able to derive an equation relating the partition coefficient of a toxic organic compound between the aqueous phase and the soil organic matter to the molar water solubility of the compound. Essentially, the uptake of toxic organic compounds by sludge through dissolution into cells can be viewed as a partitioning process in which the toxic organic compounds are distributed between two phases: the aqueous solution and the organic matter of the cell.

In the early stage of the sorption process, the cell is basically free of the toxic organic compounds except for the amount adsorbed on the surface. The difference in chemical potential causes the toxic organic compounds to transport from the bulk liquid to the region close to the surface and to be adsorbed onto the surface. In the meantime, the partitioning and subsequent penetration (diffusion) of the toxic organic compounds into cells occurs in parallel with adsorption. When a molecule approaches the site already occupied by another molecule in a process to form a double layer on the sludge surface, unlike in the case of activated carbon adsorption in which the penetration of the adsorbate into the solid wall of carbon normally does not occur, the resulting higher chemical potential on this site is likely to cause the adsorbed molecule to be dissolved in the organic matter of the cell.

To test this hypothesis, isotherm measurements were conducted for the first four compounds in Table 1 using pasteurized sludge to eliminate biodegradation. For the other compounds, listed in Table 1, untreated sludge was used, since these compounds are non-biodegradable within the 6-hour equilibriation time period. The model coefficients obtained for these compounds are also listed in Table 1, along with the average percentage error between the calculated and experimental points. Table 2 lists the contribution of partitioning to the overall sorption amount (q_pi/q) along with the partition coefficient, k_pi and the octanol–water partition coefficient (K_OW).

Pollutant	Partition coefficient (kp) l/g	Maximum adsorption capacity (qa^o) mg/g	Equilibrium adsorption constant (k) l/mg	% Error
Methylene chloride	0.012	0.250	0.30	12.2
Chloroform	0.035	0.149	0.48	6.4
1,1-dichloroethylene	0.140	0.042	0.48	6.4
Carbon tetrachloride	0.210	0.100	1.40	21.5
Chlorobenzene	0.243	0.010	2.60	18.9
Tetrachloroethylene	0.653	0.012	5.29	9.7
Phenanthrene	6.8	0.020	1.29	25.0
Dibutyl phthalate	7.00	0.014	5.30	14.7

Table 1.

Best-fit parameters of the adsorption-partition (A-P) model for sorption of selected pollutants on activated sludge. % error is the average error between the experimental value of pollutant uptake and calculated value.

Pollutant	Partition coefficient (kp) l/g	Octanol–water partition coefficient (KOW)	Total sorption (q) mg/g	qp/q
Methylene chloride	0.012	18	0.07	0.172
Chloroform	0.035	93	0.083	0.420
1,1-dichloroethylene	0.140	134	0.156	0.899
Carbon tetrachloride	0.210	436	0.268	0.783
Chlorobenzene	0.243	690	0.250	0.971
Tetrachloroethylene	0.653	759	0.663	0.985
Phenanthrene	6.8	28,184	6.811	0.998
Dibutyl phthalate	7.00	158,489	7.012	0.998

Table 2.

Partition coefficient, octanol–water partition coefficient, Total sorption and ratio of amount partitioned to the Total sorption amount for selected pollutants in activated sludge. Liquid phase concentration of each pollutant is 1 mg/l.

For the last four compounds in Table 2, adsorption is negligible with over 90% sorption occurring due to partitioning. This is also consistent with the K_OW values for these compounds, which is an indication of the compound’s hydrophobicity, and thus has a higher tendency to partition with the organic matter of the biomass. This shows that a compound’s equilibrium partitioning into biomass due to sorption is correlated directly with its K_OW value, and this correlation (correlation coefficient = 0.97) is given as follows:

$$\mathrm{Log}{k}_{\mathrm{p}}=0.73\mathrm{Log}{K}_{\mathrm{OW}}-2.64$$E1

Experimental studies were conducted to better understand the competition effects in multicomponent systems. it was found that compounds which primarily adsorb on the surface have a strong impact of competitive adsorption, with the adsorption extent of one compound varying greatly with the concentration of the second compound. This is due to the fact that the number of surface adsorption sites on biomass are limited and adsorption of one compound will impact the adsorption capacity of the second compound.

However, for compounds which primarily undergo sorption instead of surface adsorption, there is no competitive sorption between the compounds. The adsorption-partitioning (A-P) model was used to fit the sorption of methylene chloride, chloroform and tetrachloroethylene in the presence of 1,1-dichloroethylene. According to Table 2, the percentage of partitioning in the overall uptake for these compounds are 17.2%, 42% and 98.5%, respectively. Hence, the effect of competition would be most significant for methylene chloride and least significant for tetrachloroethylene. The simulation results are shown in Figures 1–3. For tetrachloroethylene, there is almost no competition effect, as was the case where chlorobenzene was the competing compound. For both methylene chloride and chloroform, the higher the concentration of 1,1-dichloroethylene, the more reduction in total uptake of the key component.

Figure 1.

Effect of concentration of 1,1-dichloroethylene as a competing species for sorption of methylene chloride.

Figure 2.

Effect of the concentration of 1,1-dichloroethylene as a competing species for sorption of chloroform.

Figure 3.

Effect of the concentration of 1,1-dichloroethylene as a competing species for sorption of tetrachloroethylene.

Based on the correlation given by Eq. (1), the degree of domination by either partitioning or surface adsorption depends on the values of K_OW. Table 3 compares the K_OW values and the competition effect in several binary and multicomponent systems, for uptake of compounds by wastewater solids. It is clearly seen that the K_OW value can be qualitatively divided into three ranges: (1) K_OW < 500, there is a clear effect of the presence of a competing compound; (2) 500 < K_OW < 1000, the competition effect is smaller, and depends on the specific compounds being studied; and (3) K_OW > 1000, when competitive surface adsorption can be ignored.

Key pollutant	Competing pollutants	Competing effect	KOW	Reference
Phenol (P)	2-chlorophenol (CP), 2-Nitrophenol (NP)	Yes; Yes	29	[16]
2-Nitrophenol (NP)	2-chlorophenol (CP),; Phenol (P)	Yes; Yes	57	[16]
1,1,2-Trichloroethane (TCE-1)	1,1,2,2-Tetrachloroethane (TCE-2)	Yes	117	[7]
2-Chlorophenol (CP)	Phenol; Nitrophenol (NP)	Yes; Yes	148	[16]
1,1,2,2-Tetrachloroethane (TEC-2)	TCE-1	Yes	363	[7]
Chlorobenzene (CB)	Ethylbenzene (EB)	Slight	690	[16]
Tetrachloroethylene (TCE)	CB	No	759	[2]
Malathion (M)	Diazinon (D)	Yes	776	[9]
Diazinon (D)	Lindane (L); Lindane (L), Pentachlorophenol (PCP), Malathion (M)	No; No	1380; 1380	[9]; [9]
Ethylbenzene (EB)	CB	No	1412	[9]
Lindane (L)	Pentachlorophenol (PCP)	No	5248	[9]
Phenanthrene (PT)	Dibutyl Phthalate (DP)	No	28,000	[2]
Pentachlorophenol (PCP)	L; L,D,M	No; No	44,668; 44,668	[9]; [9]
Dibutyl Phthalate (DP)	PT	No	1.58 x 10^5	[2]

Table 3.

Relationship between K_OW and the competition effect in multicomponent sorption of toxic organic pollutants on wastewater solids.

3. Analysis of sorption kinetics

The rate of partitioning of compounds into biomass depends on the rate of mass transfer of the compound into the cells, and this can be described as occurring in three steps: (1) mass transfer from the bulk water to the surface of the biomass cells; (2) transport through the cell walls; and (3) bonding with the active inter-cellular enzymes followed by biodegradation of the compound within the cell. In this section, these three steps will be quantified and experimental data on biodegradation rates will be used to analyze the extent of each step’s contribution.

Cell membrane permeability has been shown to play an important role in the biodegradation process, when the membrane permeability is increased [17, 18]. The permeability of bilipid membranes can be estimated from the octanol–water partition coefficient and the molecular weight of the compound [13],

$$P=0.003\frac{K_{\mathrm{OW}}}{{\mathit{MW}}^{0.5}}$$E2

where K_ow is the octanol–water partition coefficient and MW is the molecular weight of the organic compound. The permeability coefficient can also be written as [19],

$$P=\frac{k_{\mathrm{p}}{D}_{\text{mean}}}{\lambda }$$E3

Where k_P is the partition coefficient, D_mean is the average diffusion coefficient of the compound through the cell wall membrane, and λ is the thickness of the cell wall membrane. As discussed in the earlier section, the partition coefficient can be determined from the compound’s K_OW value.

The dependance of a compound’s diffusivity through the cell wall, D_mem, on molecular size, represented by molecular volume, is given by the following correlation:

$$\mathrm{Log}{D}_{\mathrm{mem}}=\mathrm{Log}{D}_{\mathrm{mem}}^{V=0}-m_{V}V$$E4

where $D_{\mathrm{mem}}^{V=0}$ is the compound’s diffusion coefficient for a theoretical molecule of infinitely small size, through the membrane. This correlation gives a slope of m_V = −0.0013 molecules/cm³. From Eq. (3) we get the following result:

$$P^{V=0}={10}^{m_{V}V}P$$E5

where P^V = 0 is the cell wall permeability for a molecule of infinitely small size and this limiting permeability values gives a good correlation with the octanol–water partition coefficient, K_OW, as shown in Figure 4.

Figure 4.

Plot of Log(P^V = 0) versus LogK_OW. P^V = 0 is the cell wall permeability for a molecule of infinitely small size.

According to Fick’s first law of diffusion, the flux (J_b) of a compound from bulk liquid to the outside cell wall surface is given by the following equation:

$$J_{\mathrm{b}}=k_{\mathrm{b}}\left(C_{\mathrm{b}}-C_{\mathrm{cm}}\right)$$E6

where k_b is the mass transfer coefficient from the bulk to the cell surface, C_b and C_cm are concentrations of compound in the bulk liquid and at the cell membrane outside surface, respectively.

Flux (J_cm) through the cell membrane can be written as follows:

$$J_{\mathrm{cm}}=P\left(C_{\mathrm{cm}}-C_{\mathrm{i}}\right)$$E7

where P is the compound’s permeability through the cell membrane, C_cm is the compound concentration on the outside surface of the cell membrane and C_i is the intracellular compound concentration. Assuming that the Monod kinetics apply, the rate of substrate biodegradation inside the cell can be given by,

$$J_{\mathrm{i}}=\frac{{\mu }_{\max }{C}_{\mathrm{i}}}{K_{\mathrm{i}}+C_{\mathrm{i}}}\left(\frac{V}{A}\right)$$E8

where J_i is the mass of substrate consumed per unit time per unit surface area of the cell, m_max, K_i are the maximum growth rate and half saturation constants, respectively, V is the volume of a cell and A is the surface area of the cell. For first order Monod kinetics, K_x ≫ C_i so Eq. (8) can be written as:

$$J_{\mathrm{i}}=k_{\mathrm{i}}{C}_{\mathrm{i}}\left(\frac{V}{A}\right)$$E9

where k_i =μ_max/K_i is the first order biodegradation rate constant. Eqs. (6), (7), and (9) can be combined to give the following equation for the flux of the compound into the cell:

$$J_{\mathrm{i}}=J_{\mathrm{cm}}=J_{\mathrm{b}}=J=\frac{C_{\mathrm{b}}}{\left(\frac{1}{k_{\mathrm{b}}}+\frac{1}{P}+\frac{A}{k_{\mathrm{i}}V}\right)}$$E10

The flux of the compound into the cell can also be written as.

$$J=k_{\text{total}}\left(C_{\mathrm{b}}-C_{\mathrm{i}}\right)\left(\frac{V}{A}\right)$$E11

where k_total is the overall mass transfer coefficient. The active intercellular enzymes will significantly reduce the intracellular concentration so that C_i = 0 Combining Eqs. (10) and (11) we get the following result:

$$\frac{1}{k_{\text{total}}}=\frac{1}{k_{\mathrm{b}}}\left(\frac{V}{A}\right)+\frac{1}{P}\left(\frac{V}{A}\right)+\frac{1}{k_{\mathrm{i}}}$$E12

The ratio (V/A) can be determined from the biomass concentration, X, in water, density of mixture of ρ_i, using the following equation, assuming all biomass cells are spherical, with an average diameter of d_i.

$$\frac{V}{A}=\frac{6X}{{\rho }_{\mathrm{i}}{d}_{\mathrm{i}}}=\alpha$$E13

Substituting Eq. (13) into Eq. (12) we get the following result (Figure 5).

Figure 5.

Plot of calculated Log(k_total) vs. Log(α/P) showing that the overall biodegradation rate constant is actually diffusional resistance across the cell membrane for 50 randomly selected toxic organic compounds which were not used in the analysis.

$$\frac{1}{k_{\text{total}}}=\frac{1}{k_{\mathrm{b}}}\alpha +\frac{1}{P}\alpha +\frac{1}{k_{\mathrm{i}}}$$E14

Values for the overall mass transfer coefficient, k_total, were taken from an EPA report [20], the mass transfer coefficient from the bulk water to the outside cell surface, k_b, was estimated from the diffusivity of the compound in water assuming a boundary layer thickness of 4 micrometers [20], the cell permeability, P, was calculated using Eq. (2) assuming a biomass concentration, X, of 2.5 kg/m³ [21], and a liquid density, ρ_i, as 1000 kg/m³ and an average cell diameter, d_i of 1 micrometer [16, 22, 23].

Table 4 shows the calculated values of the bulk phase mass transfer coefficient, k_b, the cell wall permeability, P, calculated from Eq. (2), and the biodegradation kinetic constant, k_i, determined from Eq. (12), using the values of k_total from EPA’s report [20]. The calculated values clearly show that the cell wall permeability is the controlling resistance. It also shows that the measured values of the biodegradation kinetic constant, as given in EPA’s Report [20], are mainly resistance of the compound’s diffusion across the cell wall membrane.

S. No	Compound name	$k_{\text{total}}\left({\mathrm{h}}^{-1}\right)$	$\frac{k_{\mathrm{b}}}{\alpha }\left({\mathrm{h}}^{-1}\right)$	$\frac{P}{\alpha }\left({\mathrm{h}}^{-1}\right)$	$k_{\mathrm{i}}\left({\mathrm{h}}^{-1}\right)$
1	Diisodecyl Pthalate	3.7659	765.8182	3.8827	1495.8965
2	Di-n-Octyl Phthalate	2.5381	706.9091	2.5780	2132.1180
3	Dibenzopyrene1,2,7,8	1.0573	981.8182	1.0727	799.1360
4	Bromacil	1.0087	1060.3636	1.0245	696.2582
5	Indeno (1,2,3-cd)-Pyrene	0.6596	1119.2727	0.6722	364.3080
6	Dimethyl Benz(A)ANT 7,12	0.5522	1197.8182	0.5634	284.7684
7	Dimethylbenz(A)Anthracene (7,12)	0.5522	981.8182	0.5628	300.4840
8	Methyl Cholanthrene 3	0.5394	1060.3636	0.5501	285.2126
9	PPCB’s (Aroclors)	0.4850	1570.9091	0.4955	231.9249
10	Dieldrin	0.3411	922.9091	0.3483	167.9746
11	Benzo(B)Fluoranthene	0.3227	1099.6364	0.3298	153.2084
12	Benzo(K)Fluoranthene	0.3219	1099.6364	0.3289	152.7507
13	Toluene Diisocyanate (2,4)	0.3118	1217.4545	0.3187	145.4517
14	Tetra Chlorodibenzo-p-Dioxin (2,3,7,8)	0.2702	1138.9091	0.2762	124.9391
15	Methoxychlor	0.2546	883.6364	0.2601	120.5382
16	DDT	0.1823	981.8182	0.1864	82.3114
17	ChloroBenzilate	0.1790	1138.9091	0.1831	79.8019
18	Dichlorobenzophenone P,P	0.1608	1335.2727	0.1646	70.5525
19	Benzo(A)Pyrene	0.1517	1767.2727	0.1553	65.5411
20	Pentachlorobenzene	0.1499	1237.0909	0.1534	65.7798
21	Dimethyl Trisulfide	0.1329	1629.8182	0.1361	57.3433
22	Dibenzofurans	0.1183	1178.1818	0.1211	51.4321
23	DDE, p,p′ -	0.1177	1158.5455	0.1205	51.2012
24	Aldrin	0.1156	962.1818	0.1183	50.6902
25	Pentachloronitrobenzene	0.1132	1197.8182	0.1159	49.1063
26	Benzo(A)Anthracene	0.1097	1767.2727	0.1124	46.9333
27	Endrin	0.1088	922.9091	0.1113	47.6631
28	Hexachlorobenzene	0.0971	1158.5455	0.0994	41.9121
29	Tributyl Tin Acetate	0.0965	1138.9091	0.0988	41.6854
30	Tributyl Phosphate	0.0938	1021.0909	0.0960	40.6475
31	Warfarin	0.0903	1060.3636	0.0925	39.0118
32	ChloroBenzylate	0.0891	903.2727	0.0912	38.7346
33	Trifluralin	0.0878	981.8182	0.0899	37.9977
34	Dodecane	0.0860	1158.5455	0.0881	36.9834
35	Triisobutylene	0.0839	1374.5455	0.0859	35.8866
36	Tetrachlorobenzene (1,2,3,4)	0.0771	1453.0909	0.0789	32.8341
37	Tetrachlorobenzene (1,2,3,5)	0.0771	1453.0909	0.0789	32.8330
38	Acifluorfen	0.0674	864.0000	0.0690	29.0357
39	Heptachlor	0.0672	1119.2727	0.0688	28.7305
40	ChloroazoBenzene	0.0659	1453.0909	0.0675	27.9799
41	Triisopropylamine	0.0624	1296.0000	0.0639	26.5454
42	Diisopropyl Benzene (Para)	0.0605	1413.8182	0.0619	25.6515
43	Methylene-Bis (2-Chloroaniline) 4,4′	0.0590	1138.9091	0.0604	25.1252
44	Tributyl Phosphorotrithioate SSS	0.0542	922.9091	0.0555	23.1364
45	Diphenylmethane	0.0539	1531.6364	0.0552	22.8083
46	TetrachloroPhenol (2,3,4,6)	0.0523	1394.1818	0.0535	22.1228
47	TetrachloroPhenol (2,3,5,6)	0.0523	1394.1818	0.0535	22.1223
48	Bisphenol(A)	0.0474	1119.2727	0.0486	20.1181
49	Benzophenone	0.0425	1296.0000	0.0435	17.9528
50	Tetrachlorobenzene (1,2,4,5)	0.0419	1728.0000	0.0429	17.6434
51	Trichlorobenzene 1,2,3	0.0396	1610.1818	0.0406	16.6779
52	Trichlorobenzene 1,3,5	0.0396	1610.1818	0.0406	16.6769
53	Diethylthiophosphatebenzo M Ethyl Pether	0.0357	1080.0000	0.0366	15.0790
54	BIS(1,1,2,2 - Tetrachloropropyl)Ether	0.0356	1040.7273	0.0364	15.0343
55	Biphenyl	0.0339	1610.1818	0.0347	14.2359
56	HexaFluoroacetone	0.0324	1394.1818	0.0331	13.6190
57	ChloroBenzophenone (PARA)	0.0322	1453.0909	0.0330	13.5492
58	Dimethylbenezidine 3,3	0.0311	1217.4545	0.0319	13.1076
59	Cymene, para	0.0308	1433.4545	0.0316	12.9555
60	Diethylbenzene P	0.0308	1590.5455	0.0316	12.9429
61	Methyl Napthalene (1-)	0.0301	1531.6364	0.0308	12.6524
62	Methyl Napthalene (2-)	0.0301	1531.6364	0.0308	12.6527
63	Chloronapthalene, 2-	0.0298	1728.0000	0.0305	12.5058
64	Silvex	0.0286	1138.9091	0.0293	12.0378
65	Chlorophazine	0.0257	1276.3636	0.0263	10.7930
66	Nitrobiphenyl, 4-	0.0256	1374.5455	0.0262	10.7449
67	Pinene (alpha-)	0.0254	1433.4545	0.0260	10.6626
68	Acenapthene	0.0250	1512.0000	0.0256	10.4963
69	Phenylphenol P	0.0230	1335.2727	0.0235	9.6402
70	Diazinon	0.0229	962.1818	0.0235	9.6582
71	Ethylhexylacrylate 2-	0.0220	1197.8182	0.0225	9.2396
72	Ethyl Toluene, 4	0.0220	1531.6364	0.0225	9.2213
73	Tetralin	0.0218	1590.5455	0.0223	9.1447
74	Dichlorobenzonitrile,2,6-	0.0216	1492.3636	0.0221	9.0648
75	Hexachlorobutadiene	0.0214	1217.4545	0.0219	8.9730
76	Dipropylbutral	0.0212	1433.4545	0.0217	8.8953
77	Anthraquinone	0.0212	1492.3636	0.0217	8.8772
78	Phenylcyclohexanone 4	0.0205	1315.6364	0.0210	8.6025
79	Pentachloropheol	0.0204	1197.8182	0.0209	8.5610
80	Diisobutylene	0.0201	1433.4545	0.0206	8.4367
81	Dichlorophenol (2,4)	0.0198	1728.0000	0.0203	8.3269
82	Aminobiphenyl, 4-	0.0190	1492.3636	0.0195	7.9636
83	Octane	0.0188	1394.1818	0.0193	7.8944
84	Propyl (−n) Benzene	0.0188	1531.6364	0.0193	7.8850
85	Dimethyl Phthalate	0.0186	1237.0909	0.0190	8.0786
86	TrimethylPentane 2,2,4	0.0184	1472.7273	0.0188	7.6955
87	Diethyl (N,N) Aniline	0.0183	1158.5455	0.0187	7.6749
88	Endosulfan	0.0181	903.2727	0.0185	7.6105
89	Chlorotoluene-4	0.0179	1708.3636	0.0183	7.4858
90	Bromotoluene 4	0.0179	1669.0909	0.0183	7.4864
91	Dimethyl Amino Azobenzene, 4-	0.0176	1296.0000	0.0181	7.3979
92	Dazomet	0.0176	141.8182	0.0180	7.3761
93	DichloroBenzidine, 3,3′-	0.0175	1315.6364	0.0179	7.3261
94	Cumene	0.0173	1394.1818	0.0177	7.2422
95	Acetylaminofluorene, 2-	0.0170	1178.1818	0.0175	7.1539
96	Alpha Methyl Styrene	0.0168	2238.5455	0.0172	7.0159
97	Methylstyrene (−4)	0.0168	1728.0000	0.0172	7.0224
98	Hexachloroethane	0.0167	1335.2727	0.0171	6.9875
99	Trichloro-1,2,2,- Trifluoroethane, 1,1,2-	0.0167	1590.5455	0.0171	6.9805
100	Acenapthlyene	0.0162	1472.7273	0.0166	6.7824
101	Dimethyl Disulfide	0.0160	1983.2727	0.0164	6.6994
102	Carbendazim	0.0156	1276.3636	0.0160	6.5580
103	Methylene Diphenylamine (MDA)	0.0156	1256.7273	0.0160	6.5331
104	Methylene Diphenyl Diisocyanate	0.0146	1217.4545	0.0150	6.1368
105	Toxaphene	0.0145	844.3636	0.0149	6.1114
106	Toluene	0.0144	1688.7273	0.0148	6.0352
107	Chlorambucil	0.0142	1178.1818	0.0146	5.9616
108	Dichlorophenol (2,6)	0.0138	1728.0000	0.0141	5.7780
108	Dichlorophenol	0.0138	1394.1818	0.0141	5.7826
110	Dichlorophenol 2,5	0.0138	1394.1818	0.0141	5.7841
111	Dichloroethane (1,1) ethylidenedichloride	0.0138	2061.8182	0.0141	5.9160
112	Nitrobenzene	0.0138	1688.7273	0.0141	5.9137
113	DichloroBenzene (1,4) (−p)	0.0138	1551.2727	0.0141	5.7758
114	Bromobenzene	0.0137	1826.1818	0.0140	5.7183
115	Xylene(−m)	0.0133	1531.6364	0.0136	5.5749
116	Anthracene	0.0132	1512.0000	0.0135	5.5204
117	Terpinenol, Alpha	0.0131	1453.0909	0.0134	5.4917
118	Heptane ISO	0.0129	1394.1818	0.0132	5.3957
119	Heptane (−n)	0.0129	1492.3636	0.0132	5.3896
120	Dimethoxy-(3,3′)-Benzidine	0.0128	1080.0000	0.0131	5.3488
121	Xylene(−p)	0.0127	1649.4545	0.0131	5.3348
122	EthylBenzene	0.0126	1527.7091	0.0129	5.2726
123	Nonanol, n	0.0120	1354.9091	0.0123	5.0072
124	Naphthol, alpha	0.0120	1492.3636	0.0122	5.0034
125	Nitro m Xylene, 2	0.0119	1570.9091	0.0121	4.9607
126	Parathion	0.0117	1138.9091	0.0120	4.9201
127	DiphenylHydrazine (1,2)	0.0115	1453.0909	0.0118	4.8052
128	DiChloroAniline 2,3	0.0114	1413.8182	0.0117	4.7824
129	DichloroAniline(2,3)	0.0114	1413.8182	0.0117	4.7832
130	Methyl Cyclohexane	0.0108	1669.0909	0.0111	4.5316
131	Xylene	0.0108	1826.1818	0.0111	4.5150
132	Xylene(−o)	0.0108	1963.6364	0.0111	4.5154
133	Diethylene Glycol Diethyl Ether	0.0106	1335.2727	0.0108	4.4195
134	Captan	0.0105	962.1818	0.0107	4.3904
135	Isodecanol	0.0104	1453.0909	0.0107	4.3643
136	Benzotrichloride	0.0104	1531.6364	0.0107	4.3649
137	Tetrafluoromethane	0.0102	1826.1818	0.0104	4.2524
138	2,4,5 Trichlorophenoxyacetic acid	0.0098	1315.6364	0.0101	4.1248
139	Dinitro-o-Cresol (4,6)	0.0098	1354.9091	0.0100	4.1089
140	Methyl Isocyanate	0.0098	2847.2727	0.0100	4.0764
141	Naphthol, beta-	0.0097	1492.3636	0.0100	4.0679
142	Dichlorophenoxyacetic Acid (2,4)	0.0093	1276.3636	0.0095	3.9000
143	Chlordane	0.0092	864.0000	0.0094	3.8742
144	Carbon Tetrachloride	0.0090	1728.0000	0.0092	3.7650
145	Dichloropropylene 1,2,-(Cis)	0.0089	2160.0000	0.0091	3.7104
146	Hexane(−n)	0.0088	1531.6364	0.0090	3.6858
147	Xylidine Dimethylaniline	0.0088	1649.4545	0.0090	3.6854
148	Pentachloroethane	0.0087	1433.4545	0.0090	3.6556
149	Guthion	0.0087	942.5455	0.0089	3.6368
150	Trifluoroethane (1,1,1)	0.0086	2552.7273	0.0088	3.6057
151	Benzene	0.0084	1924.3636	0.0086	3.5278
152	Dichloropropane 1,2	0.0084	1708.3636	0.0086	3.5210
153	Chrysene	0.0084	1217.4545	0.0086	3.5101
154	Methyl 1-Pentene 2	0.0083	1767.2727	0.0085	3.4883
155	Propyl Ether Iso	0.0083	1826.1818	0.0085	3.4528
156	Styrene Oxide	0.0082	1747.6364	0.0084	3.4277
157	Ehtyl(2)Hexanol	0.0082	1433.4545	0.0084	3.4257
158	Octanol 3	0.0082	1433.4545	0.0084	3.4257
159	Octanol 2	0.0082	1433.4545	0.0084	3.4257
160	Octanol 4	0.0082	1433.4545	0.0084	3.4257
161	Octanol 1	0.0082	1433.4545	0.0084	3.4237
162	MethyleneDianiline 4,4	0.0081	1472.7273	0.0083	3.3975
163	Benzofuran 2,3	0.0081	1767.2727	0.0083	3.3710
164	ChloroNitrobenzene, p	0.0079	1845.8182	0.0081	3.3086
165	Chloronitrobenzene (−o)	0.0079	1845.8182	0.0081	3.3082
166	Chloroacetophnone, 2-	0.0078	1708.3636	0.0080	3.2837
167	Freon 11, Fluorotrichloromethane	0.0077	1963.6364	0.0079	3.2307
168	Dichloropropylene 1,2,- (Trans)	0.0077	2160.0000	0.0079	3.2068
169	ChloroBenzotriFluoride, P	0.0076	1688.7273	0.0078	3.1867
170	ButylIsoButyrate	0.0074	1728.0000	0.0076	3.1139
171	Trichlorofluoromethane	0.0074	1904.7273	0.0076	3.1019
172	Cyclohexane	0.0074	1786.9091	0.0076	3.0974
173	Dimethyl Benzylamine N,N	0.0074	1708.3636	0.0076	3.0938
174	Allyl Ether, diallyl ether	0.0073	1669.0909	0.0075	3.0718
175	Chlorophenol-4	0.0071	1904.7273	0.0073	2.9702
176	Nitrotoluene, o	0.0069	1708.3636	0.0071	2.9057
177	Nitrotoluene, p	0.0069	1688.7273	0.0071	2.9055
178	Nitrotoluene, m	0.0069	1610.1818	0.0071	2.9068
179	ChloroButadiene, 1	0.0069	1963.6364	0.0071	2.9022
180	ChloroBenzyl Alcohol - (m)	0.0068	1865.4545	0.0070	2.8579
181	Triethylene Glycol Dimethyl Ether	0.0068	1315.6364	0.0070	2.8445
182	Freon 12, Dichlorodifluoromethane	0.0066	1669.0909	0.0068	2.7746
183	Ethylphenol,3-	0.0066	1845.8182	0.0068	2.7671
184	Tetraethyl Lead	0.0066	1256.7273	0.0067	2.7591
185	Methyl Benzyl Alcohol 4	0.0065	1688.7273	0.0067	2.7345
186	Carbaryl Sevin	0.0064	1394.1818	0.0065	2.6771
187	Triethylamine	0.0064	1551.2727	0.0065	2.6720
188	Phosphine	0.0063	3573.8182	0.0065	2.6302
189	Proporur (Baygon)	0.0062	1315.6364	0.0063	2.5915
190	Cumeme Hydroperoxide	0.0061	1492.3636	0.0063	2.5584
191	Paraldehyde	0.0061	1570.9091	0.0062	2.5471
192	Bromoform	0.0061	2022.5455	0.0062	2.5417
193	Benzyl Chloride	0.0061	1531.6364	0.0063	2.5349
194	Dibromo-4-HydroxyBenzonitrile,3,5	0.0060	981.8182	0.0062	2.5341
195	Dichloroethane (1,2)	0.0059	1944.0000	0.0060	2.5085
196	Naphthylamine, beta -	0.0058	1649.4545	0.0059	2.4275
197	Acetylmethylphthalate 4	0.0057	1099.6364	0.0058	2.3825
198	Naphthylamine, alpha -	0.0057	1649.4545	0.0058	2.3676
199	Diisopropylamine	0.0056	1531.6364	0.0057	2.3488
200	Dichloroethylene (1,2) Cis	0.0056	2218.9091	0.0057	2.3285
201	Diethylene Glycol Monobutyl Ether	0.0056	1374.5455	0.0057	2.3317
202	Butyl Carbitol	0.0056	1374.5455	0.0057	2.3310
203	TolueneSulfonyl Chloride	0.0055	1276.3636	0.0056	2.3096
204	Thiourea, 1-(o-Chlorophenyl)-	0.0054	1413.8182	0.0055	2.2656
205	Carbon Disulfide	0.0054	1963.6364	0.0055	2.2452
206	Freon 12 Dichlorodifluoromethane	0.0054	2061.8182	0.0055	2.2469
207	Benzal Chloride	0.0053	1865.4545	0.0055	2.2321
208	Chlorophenol-2	0.0053	1865.4545	0.0054	2.2282
209	Trichloroethylene	0.0053	1786.9091	0.0054	2.2093
210	TriPropylene Glycol	0.0052	1413.8182	0.0053	2.1848
211	Toluidine (−0)	0.0052	1786.9091	0.0053	2.1607
212	Toluidine m	0.0052	1806.5455	0.0053	2.1613
213	Dipropylamine	0.0051	2022.5455	0.0053	2.1505
214	Butyl Acrylate	0.0051	1512.0000	0.0052	2.1430
215	Toluic Acid (para-)	0.0051	1531.6364	0.0052	2.1441
216	Pentadiene 1,2	0.0050	2022.5455	0.0051	2.0718
217	Dinitro Toluene 2,6	0.0049	1433.4545	0.0050	2.0460
218	Benzonitrile	0.0049	2002.9091	0.0050	2.0319
219	Methyl Parathion	0.0048	1158.5455	0.0049	2.0302
220	Quinoline	0.0048	1629.8182	0.0049	2.0086
221	Cyclopentadiene	0.0048	2140.3636	0.0049	1.9997
222	DinitroToluene (2,4)	0.0047	1394.1818	0.0048	1.9766
223	Cyclohexylamine	0.0047	2042.1818	0.0048	1.9466
224	Bromoxynil	0.0046	1021.0909	0.0047	1.9477
225	Chloropropylene-2	0.0046	2709.8182	0.0047	1.9276
226	Dichloropropene (1,3)	0.0046	1963.6364	0.0047	1.9226
227	Acrylonitrile	0.0045	2631.2727	0.0046	1.9706
228	Benzoyl Chloride	0.0045	2140.3636	0.0046	1.8869
229	Trichloroethane 1,1,1, Methyl Chloroform	0.0044	1728.0000	0.0045	1.8555
230	Trichloroethane 1,1,2	0.0044	1728.0000	0.0045	1.8590
231	Ethyl Morpholine, Ethyl Diethylene Oxime	0.0044	1728.0000	0.0045	1.8341
232	Methyl Chloride	0.0043	1276.3636	0.0045	1.8212
233	Nitrophenol,4-	0.0043	1885.0909	0.0044	1.8103
234	Methyl-Tertiary-Butyl Ether	0.0043	2061.8182	0.0044	1.7926
235	Ethylene Glycol MonoPhenyl Ether	0.0042	1649.4545	0.0043	1.7791
236	Bromodichloromethane	0.0042	2081.4545	0.0043	1.7656
237	Butadiene - (1,3)	0.0042	2120.7273	0.0043	1.7449
238	Butene	0.0041	2002.9091	0.0042	1.7362
239	Benzoic Acid	0.0041	1570.9091	0.0042	1.7335
240	Butane	0.0041	2199.2727	0.0042	1.7281
241	Furan	0.0041	2395.6364	0.0042	1.7190
242	Tetrachloroethene	0.0041	1610.1818	0.0042	1.7043
243	Tetrachloroethane (1,1,2,2)	0.0041	1551.2727	0.0042	1.7049
244	Dichloromonofluoromethane	0.0040	2258.1818	0.0041	1.6878
245	Benzidine	0.0039	2945.4545	0.0040	1.6619
246	Isobutylene	0.0039	2002.9091	0.0040	1.6351
247	Butyl Acetate (−n)	0.0039	1590.5455	0.0040	1.6334
248	Nitrophenol,2-	0.0039	1669.0909	0.0040	1.6288
249	Diethylene Glycol Dimethyl Ether	0.0039	1354.9091	0.0039	1.6204
250	Hexanol-1	0.0038	1472.7273	0.0039	1.6080
251	Dinitrophenol 2,4	0.0037	1786.9091	0.0038	1.5741
252	Amyl Acetate (−n)	0.0036	235.6364	0.0037	1.5311
253	Dimethyl Sulfide	0.0036	2866.9091	0.0037	1.5114
254	Isophorone	0.0036	1335.2727	0.0037	1.5106
255	Methyl Iodide	0.0036	2042.1818	0.0036	1.4961
256	Benzyl Alcohol	0.0035	1767.2727	0.0036	1.4764
257	Adiponitrile	0.0035	1747.6364	0.0036	1.4764
258	DichloroBenzene (1,2) (−o)	0.0035	1551.2727	0.0036	1.4545
259	Tetraethyldithiopyrophosphate	0.0035	1080.0000	0.0035	1.4628
260	Trichloropropane (1,1,2)	0.0034	1826.1818	0.0035	1.4545
261	Vinyl Acetylene	0.0034	2768.7273	0.0035	1.4435
262	Ethyl Vinyl Ether	0.0034	1924.3636	0.0035	1.4363
263	Diethyl Ether	0.0034	1688.7273	0.0035	1.4284
264	Ethyl Ether	0.0034	1826.1818	0.0035	1.4281
265	Anisidine, o-	0.0033	1747.6364	0.0034	1.3925
266	Ethlene Dibromide	0.0033	2336.7273	0.0034	1.3862
267	Chloramben	0.0033	1669.0909	0.0033	1.3778
268	Hexanoic Acid	0.0033	1649.4545	0.0033	1.3734
269	Acetophenone	0.0032	1708.3636	0.0033	1.3597
270	Bis(2-Chloroethyl)Ether	0.0032	1472.7273	0.0033	1.3628
271	Furfural	0.0032	2042.1818	0.0033	1.3564
272	Cyclohexanol	0.0032	1629.8182	0.0033	1.3543
273	Ethylene Glycol Monobutyl Ether	0.0032	1610.1818	0.0032	1.3295
274	Butyl Cellosolve	0.0032	1590.5455	0.0032	1.3305
275	Dinitrobenzene M	0.0031	1492.3636	0.0031	1.2970
276	Ethyl Acrylate	0.0030	1688.7273	0.0031	1.2703
277	Chloral	0.0030	1904.7273	0.0031	1.2573
278	Ethylene Glycol Monobutyl Ether Acetate	0.0030	1335.2727	0.0030	1.2618
279	Dichloroethene 1,2 trans	0.0030	2336.7273	0.0030	1.2462
280	Benzaldehyde	0.0030	1786.9091	0.0030	1.2472
281	TolueneDiamine (2,6)	0.0029	1806.5455	0.0030	1.2216
282	TolueneDiamine (3,4)	0.0029	1806.5455	0.0030	1.2214
283	Toluene Diamine (2,4)	0.0029	1786.9091	0.0030	1.2225
284	Epoxybutane 1,2	0.0029	2022.5455	0.0029	1.2047
285	tetrahydrofuran	0.0029	2061.8182	0.0029	1.2050
286	Propylene	0.0028	2670.5455	0.0029	1.1914
287	Propene	0.0028	2336.7273	0.0029	1.1923
288	Chloroethane (Ethyl Chloride)	0.0028	2258.1818	0.0029	1.1920
289	Trichloropropane (1,2,2)	0.0028	1826.1818	0.0029	1.1964
290	Propane	0.0028	2592.0000	0.0029	1.1847
291	Chlorophenol-3	0.0028	1845.8182	0.0028	1.1693
292	Toluidine p	0.0027	1845.8182	0.0028	1.1537
293	Methyl Isobutyl Ketone	0.0027	1531.6364	0.0028	1.1408
294	Trinitrotoluene (2,4,6)	0.0027	1256.7273	0.0027	2.0189
295	Propyl Acetate Iso	0.0027	1708.3636	0.0027	1.1239
296	Propyl (−n) Acetate	0.0027	1728.0000	0.0027	1.1234
297	Methyl Morpholine	0.0027	1767.2727	0.0027	1.1224
298	Chloro 2 Butene, 1 Trans	0.0026	1904.7273	0.0027	1.1134
299	Hexen-2-ONE 5	0.0026	1728.0000	0.0027	1.1083
300	Diethylene Glycol Monoethyl Ether	0.0026	1570.9091	0.0027	1.1035
301	Diethylene Glycol Monoethyl Ether	0.0025	1983.2727	0.0026	1.0507
302	Nitropropane 2	0.0025	1413.8182	0.0025	1.0446
303	HexaMethylene 1,6 Diisocyanate	0.0025	1276.3636	0.0025	1.0482
304	Diethylene Glycol Monoethyl Ether Acetate	0.0024	2454.5455	0.0025	1.0167
305	Diethyl Amine	0.0024	2297.4545	0.0025	1.0155
306	Methylene Chloride, Dichloromethane	0.0024	2002.9091	0.0024	0.9926
307	Dioxane (1,4)	0.0023	1158.5455	0.0024	0.9923
308	Ametryn	0.0023	1688.7273	0.0023	0.9700
309	Nitroaniline P	0.0023	216.0000	0.0023	0.9720
310	Phosgene (decomposes)	0.0023	3161.4545	0.0023	0.9536
311	Hydrogen Sulfide	0.0023	2906.1818	0.0023	0.9527
312	Methyl Mercaptan	0.0022	1590.5455	0.0022	0.9365
313Dibromoethane-1,2	0.0022	1845.8182	0.0022	0.9275
314	Ethylene Glycol Dimethyl Ether	0.0022	1983.2727	0.0022	0.9208
315	Butyraldehyde ISO	0.0022	2395.6364	0.0022	0.9204
316	Dimethylethylamine	0.0022	2238.5455	0.0022	0.9202
317	Butyraldehyde	0.0022	2395.6364	0.0022	1.1617
318	Acrolein	0.0022	1826.1818	0.0022	0.9194
319	Ethylene Glycol MonoPropyl Ether	0.0021	2376.0000	0.0022	0.9018
320	Bromomethane	0.0021	2002.9091	0.0022	0.8841
321	Crotonaldehyde	0.0052	1786.9091	0.0053	2.1607
322	Vinyl Bromide	0.0021	2317.0909	0.0021	0.8773
323	Chloropropane-2	0.0020	1983.2727	0.0021	0.8609
324	Dimethyl Carbamoyl Chloride	0.0020	1963.6364	0.0021	0.8621
325	Quinone	0.0020	2101.0909	0.0020	0.8445
326	Ethane	0.0019	3279.2727	0.0020	0.8140
327	Bromochloromethane	0.0019	1963.6364	0.0019	0.8134
328	Allyl Chloride	0.0019	2120.7273	0.0019	0.7973
329	Chloropropene-3	0.0019	2729.4545	0.0019	0.7952
330	Chloropropane-1	0.0019	2022.5455	0.0019	0.7908
331	Catechol	0.0018	1806.5455	0.0019	0.7854
332	Hexachloroxyclohexane (Gamma Isomer)	0.0018	1433.4545	0.0019	0.7904
333	Lindane Hexachlorocyclohexane	0.0018	1217.4545	0.0019	0.7945
334	Dichlorvos	0.0018	1433.4545	0.0019	0.7938
335	Vinyl Acetate	0.0018	1806.5455	0.0019	0.7799
336	EthylAcetate	0.0018	1904.7273	0.0019	0.7758
337	Methyl Isopropyl Ketone	0.0018	1806.5455	0.0018	0.7624
338	Diethylene Glycol Monomethyl Ether	0.0018	1688.7273	0.0018	0.7647
339	Propyl Amine Iso	0.0018	2061.8182	0.0018	0.7534
340	ButylAmine	0.0017	1885.0909	0.0018	0.7466
341	Dichloro-2-Butene, 1,2	0.0017	2022.5455	0.0018	0.7464
342	Dichloro-2-Butene, (1,4)	0.0017	1590.5455	0.0018	0.7465
343	Dichloro-2-Butene, 1,4	0.0017	1826.1818	0.0018	0.7502
344	Thiourea	0.0017	2709.8182	0.0018	0.7349
345	Phenylene Diamine (−o)	0.0017	1944.0000	0.0017	0.7272
346	Phenylene Diamine (−p)	0.0017	1944.0000	0.0017	0.7272
347	Phenylene Diamine (−m)	0.0017	1944.0000	0.0017	0.7251
348	Phthalimide	0.0017	1629.8182	0.0017	0.7302
349	Phthalic Acid	0.0017	1335.2727	0.0017	0.7152
350	Terephthalic Acid	0.0017	1394.1818	0.0017	0.7192
351	Caprolactam	0.0017	1767.2727	0.0017	0.7144
352	Cyclohexanone	0.0016	1688.7273	0.0017	0.7094
353	Cyanogen	0.0016	2690.1818	0.0017	0.7009
354	Acrylamide	0.0016	2081.4545	0.0017	0.6970
355	Resorcinol	0.0016	1708.3636	0.0017	0.6960
356	Butyric Acid	0.0015	1983.2727	0.0016	0.6611
357	Formaldehyde	0.0015	3888.0000	0.0015	0.6257
358	Dibromomethane	0.0015	1649.4545	0.0015	0.6528
359	Propionaldehyde	0.0015	2238.5455	0.0015	0.6351
360	Ethoxyethanol-2	0.0015	1885.0909	0.0015	0.6364
361	Dichloroethyl Ether	0.0015	1865.4545	0.0015	0.6432
362	Methacrylic Acid	0.0014	2061.8182	0.0015	0.6241
363	Pyridine	0.0014	1492.3636	0.0015	0.6139
364	Nitroglycerin	0.0014	1531.6364	0.0015	0.6355
365	Methyl Ether Dimethyl Ether	0.0014	2925.8182	0.0014	0.6034
366	Chloroethylene	0.0014	3024.0000	0.0014	0.6030
367	Diethylhydrazine N,N	0.0014	2022.5455	0.0014	0.6022
368	Ethylene Glycol Monoethyl Ether Acetate	0.0014	1492.3636	0.0014	0.6138
369	Propylenimine 1,22 Methyl Aziridine	0.0014	2847.2727	0.0014	0.5962
370	Methyl Aziridine 2	0.0014	2847.2727	0.0014	0.5946
371	Dimethyl Hydrazine (1,1)	0.0014	2140.3636	0.0014	0.5858
372	Hydroquinone	0.0014	1767.2727	0.0014	0.5909
373	Aminophenol (−o)	0.0013	1688.7273	0.0014	0.5867
374	Aminophenol (−p)	0.0013	471.2727	0.0014	0.5874
375	Chloroprene	0.0013	1963.6364	0.0014	0.5756
376	Tamaron (Methamidiphos)	0.0013	1531.6364	0.0013	0.5692
377	Propanol	0.0012	2238.5455	0.0013	0.5397
378	Propiolactone b	0.0012	2238.5455	0.0013	0.5356
379	Tetranitromethane	0.0012	1374.5455	0.0013	0.5583
380	Methanol	0.0012	3220.3636	0.0012	0.8385
381	Methyl Ethyl Ketone, 2 Butanone	0.0012	1924.3636	0.0012	0.5352
382	Urethane	0.0012	2081.4545	0.0012	0.5202
383	Acetaldehyde	0.0012	2768.7273	0.0012	0.5096
384	Piperazine	0.0012	2042.1818	0.0012	0.5174
385	Chloropropionitrile,3-	0.0012	2454.5455	0.0012	0.5161
386	Chloroallyl Alcohol 2	0.0011	2415.2727	0.0011	0.4933
387	DimethylSulfoxide	0.0011	2179.6364	0.0011	0.4872
388	Neopentyl Glycol	0.0011	1806.5455	0.0011	0.4925
389	Butanedinitrile	0.0011	2317.0909	0.0011	0.4828
390	Dimethyl Sulfate	0.0011	1885.0909	0.0011	0.4803
391	Acrylic Acid	0.0011	2081.4545	0.0011	0.4682
392	Propanoic Acid	0.0010	2199.2727	0.0011	0.4606
393	Aminopyridine, 4-	0.0010	2120.7273	0.0011	0.4630
394	Propyn-1-Ol 2(Proparlgyl)	0.0010	2611.6364	0.0010	0.4468
395	Ethylene Glycol MonoMethyl Ether	0.0010	2199.2727	0.0010	0.4463
396	Ethylene Glycol Monoethyl Ether Cellosol	0.0010	1924.3636	0.0010	0.4505
397	Propylene Oxide	0.0010	1963.6364	0.0010	0.4366
398	Trichloropropane (1,2,3)	0.0010	1552.2727	0.0010	0.4409
399	Trichloropropane 1,1,1	0.0010	1551.2727	0.0010	0.4342
400	Dibromo-3-Chloropropane,1,2	0.0010	1374.5455	0.0010	0.4542
401	Nitroso-N-Methylurea N	0.0010	2002.9091	0.0010	0.4248
402	Ethylene Glycol MonoMethyl Ether Acetate	0.0010	1570.9091	0.0010	0.4406
403	Ethylamine	0.0009	3298.9091	0.0010	0.4190
404	Aziridine ethylene imine	0.0009	3102.5455	0.0010	0.4144
405	Acetaldol	0.0009	2120.7273	0.0010	0.4232
406	Allyl Alcohol	0.0009	2238.5455	0.0010	0.4118
407	Dipropylene Glycol	0.0009	1512.0000	0.0010	0.4185
408	Tetraethylene Pentamine	0.0009	1276.3636	0.0009	0.4169
409	Xylenol(3,4)	0.0009	1629.8182	0.0009	0.4092
410	Methyl Formate	0.0009	2493.8182	0.0009	0.3950
411	Nitromethane	0.0009	2749.0909	0.0009	0.3849
412	Vinyl Chloride	0.0009	2415.2727	0.0009	0.3870
413	Dimethyl Amine	0.0008	3279.2727	0.0009	0.3783
414	DimethylAcetamide	0.0008	2415.2727	0.0009	0.3789
415	DimethylSulfoxide	0.0008	2592.0000	0.0009	0.3753
416	Epichlorohydrin	0.0008	1924.3636	0.0009	0.3753
417	Glutaric Acid	0.0008	1570.9091	0.0008	0.3752
418	HexamethylPhosphoramide	0.0008	1354.9091	0.0008	0.3877
419	Propylene Chlorohydrin	0.0008	2061.8182	0.0008	0.3726
420	Dimethyl Formamide	0.0008	2022.5455	0.0008	0.3564
421	Butylene Glycol - (1,3)	0.0008	2002.9091	0.0008	0.3604
422	Methyl Acetate	0.0007	1963.6364	0.0008	0.3504
423	Diazomethane	0.0007	3436.3636	0.0007	0.3248
424	Adenine	0.0007	1708.3636	0.0007	0.3469
425	Chloromethyl Methyl Ether	0.0007	2631.2727	0.0007	0.3201
426	Chloroacetaldehyde	0.0007	2258.1818	0.0007	0.3168
427	Butanol(S)	0.0007	2199.2727	0.0007	0.2783
428	Butanol-1	0.0007	1826.1818	0.0007	0.2778
429	Butanol Iso	0.0007	1826.1818	0.0007	0.2781
430	DimethylSulfone	0.0006	1944.0000	0.0007	0.3156
431	Ethlene Diamine	0.0006	2768.7273	0.0007	0.2986
432	Dichloro Propanol 2,23	0.0006	1924.3636	0.0007	0.3229
433	Carbonyl Sulfide	0.0006	2552.7273	0.0007	0.2936
434	Diethyl Sulfate	0.0006	1590.5455	0.0006	0.3067
435	Methomyl	0.0006	1413.8182	0.0006	0.3234
436	Acetyl Chloride	0.0006	2258.1818	0.0006	0.3021
437	Acetonitrile	0.0006	3259.6364	0.0006	0.2786
438	Bis(Chloromethyl)Ether	0.0006	1845.8182	0.0006	0.2984
439	Glycidol	0.0006	2395.6364	0.0006	0.2774
440	Succinic Acid	0.0006	1669.0909	0.0006	0.3003
441	Sodium Formate	0.0006	3200.7273	0.0006	0.2680
442	Nitrosomorpholine	0.0006	1963.6364	0.0006	0.2879
443	Maleic Acid	0.0005	2258.1818	0.0006	0.2779
444	Fumaric Acid	0.0005	1688.7273	0.0006	0.2895
445	Ethyl Carbamate	0.0005	2474.1818	0.0006	0.2834
446	Urea	0.0005	2690.1818	0.0005	0.2649
447	Nitrosodimetylamine N	0.0005	2434.9091	0.0005	0.2724
448	Methyl Hydrazine	0.0005	2729.4545	0.0005	0.2567
449	Propylene Glycol	0.0005	2002.9091	0.0005	0.2648
450	Dichloro 2-Propanol 1,3	0.0005	1924.3636	0.0005	0.2671

Table 4.

Values of mass transfer coefficients for overall transport of toxic organic compounds (1/k_total), obtained from Ref. [19], bulk diffusion from bulk water to outside cell surface (α/k_b), across the cell membrane (α/P) and biodegradation rate constant (1/k_i).

To check this surprising finding, 50 organic compounds, listed in Table 5, were randomly selected from EPA’s report [20]. These compounds were not used to correlate the overall degradation rate with the cell wall permeability. Figure 4 shows the plot of the reported Log(k_total) values for these 50 compounds [20] versus the mass transfer resistance for pollutant transport across the cell wall, (α/P). This resulted in an excellent correlation, indicating that cell wall permeability is the rate controlling step for biodegradation, as well as the rate controlling step for sorption, which precedes biodegradation.

S. No	Compound name
1	1,3-Dichloro 2-Propanol
2	Glyphosate
3	Methyl Amine
4	Formamide
5	Phthalic Anhydride
6	Chloroacetic Acid
7	Ethylene Thiourea
8	Acetyl-2-thiourea, 1-
9	Diethanolamine
10	Iso-Propanol
11	Monomethyl Formamide
12	Ethanolamine (mono-)
13	Acetamide
14	N,N-Dimethylaniline
15	Ethylene Glycol
16	Formic Acid
17	Chlorohydrin
18	Morpholine
19	Hydroxyacetic Acid
20	Glyoxal
21	Oxalic Acid
22	Hydrazine
23	Glycerin (Glycerol)
24	Dibromochloromethane
25	Pentaerythritol
26	Nabam
27	Triethanolamine
28	1,3-Propane Sultone
29	Styrene
30	2,4,6-Trichlorophenol
31	Bis(2-Ethylhexyl) Phthalate
32	p-Chloroaniline
33	2-Chloroaniline
34	3-Chloroaniline
35	Ethylene Oxide
36	Aldicarb
37	Vinylidene Chloride
38	Diisopropyl Ketone
39	Ethanol
40	Dichloroethene (1,1) vinylidene chloride
41	Maleic Anhydride
42	Napthalene
43	DibutylPhthalate
44	Acetal
45	Toluic Aldehyde
46	Acetic Acid
47	Phosphine
48	Proporur (Baygon)
49	Cumeme Hydroperoxide
50	Paraldehyde

Table 5.

List of 50 toxic organic compounds selected from the EPA report [19], which were used to test the finding that the biodegradation kinetics, as reported in Ref [19] is actually a measurement of diffusional resistance across the cell membrane.

The kinetics of sorption is the rate of mass transfer to the cell wall followed by permeation of the compound across the cell membrane. Between these two transport steps, permeation across the cell wall is the rate controlling step. This can be written as follows

$$\frac{1}{k_{\text{sorption}}}\approx \alpha \left(\frac{1}{P}\right)$$E15

Table 4 shows that permeation of the compound through the cell membrane is the rate controlling step. The kinetic biodegradation rate constants, as presented in the EPA report [20], also given in Table 4, are actually sorption rate constants, since the cell wall permeability is the dominant rate controlling step.

4. Conclusions

In this chapter, sorption in wastewater solids has been presented both from a thermodynamic viewpoint, with surface adsorption and sorption into the cells represented by an equilibrium isotherm. Experimental data on the equilibrium concentrations of several compounds was analyzed using a multicomponent model. The experimental data shows that for compounds with low K_OW vales (K_OW < 500), competitive surface adsorption occurred, indicating that the multiple compounds were competing for the limited number of surface adsorption sites on the biomass. For compounds with K_OW vales in the 500–1000 range, surface adsorption dominated and there was less competition between the compounds for adsorption. When the K_OW value exceeded 1000, there was insignificant competition between the compounds for surface adsorption and sorption into the cell was dominant. The reason for diminishing competition between the compounds in a multi-component system was due to increasing partitioning of the compounds within the cell, with increases in K_OW above 500. Partitioning of compounds into the cell dominates when the K_OW value exceeds 1000.

Sorption of compounds into biomass has also been presented from a kinetic point of view by detailing the compound’s transport across the cell membrane. The rate of a compounds transfer from bulk water into the biomass cells was sub-divided into three steps: (1) transport from the bulk water to the outside of the cell walls; (2) permeation through the cell membrane walls; and (3) bonding with active intercellular enzymes followed by biodegradation. Each step in the sorption process was further modeled and values of the mass transfer coefficients for each step were calculated using EPA’s data on the overall biodegradation rate for over 500 compounds. This analysis showed that the rate controlling step in sorption was permeation of the compound through the cell walls, and the rate of mass transfer to the cell wall and biodegradation within the cell were not major contributors.

Analysis of sorption kinetics clearly shows that experimental biodegradation rates in the literature, as summarized in EPA report [20] are actual rates of permeation through the cell wall and the use of Monod kinetics, which has been presented as an enzymatic process of biodegradation, is actually a passive diffusive process through the walls of the microbial cells.