Metabolism of Organic Sulfonates by
Activated Sludge
JAMES M. SYMONS, Assistant Professor of Sanitary Engineering
Massachusetts Institute of Technology
Cambridge, Massachusetts
and
LUIS A. DEL VALLE-RIVERA, Assistant Professor of Civil Engineering
University of Puerto Rico
Rio Piedras, Puerto Rico
This study was undertaken with the hope that information gained concerning the mechanisms of biological removal of simple aromatic sulfonates
by activated sludge might be useful to investigators concerning themselves
with the continuing problem of the removal of synthetic detergents from waste
waters. Reports of the lack of complete degradability of the commercial
alkyl benzene sulfonate in use in the U. S. at this time are widespread (1)(2)
(3)(4)(5)(6). This commercial alkyl benzene sulfonate is a mixture of widely
varying structures, long and short alkyl chains, straight and branched alkyl
chains, and secondary and tertiary attachment of the benzene ring to the alkyl
side chain. All of these structural variations affect the ease of biological
degradability.
Ryckman (4) showed that the attachment of the benzene ring greatly affected the metabolism of alkyl benzene sulfonate. Straight chain alkyl
benzene sulfonates of varying chain lengths with a primary ring attachment
were readily degraded by activated sludge, similar compounds with a secondary ring attachment were also degraded by activated sludge, although the
shorter chain length compounds were more difficult to acclimate. Similar
compounds with a tertiary ring attachment were very resistant to biological
removal.   Branched chain compounds were not studied by Ryckman.
Recently, Nelson, et al., (7) have reported on the successful degradation
of a straight chain alkyl benzene sulfonate containing a tertiary attachment
of the benzene ring. They also studied branched chain alkyl henzene sulfonates and found that the presence of quaternary carbon near the end of the
chain prevented successful degradation. Alkyl chains other than straight
chains caused reduced metabolism by activated sludge. Mohanrao (8) has also
shown recently the ability of activated sludge to metabolize organic molecules
containing quaternary carbon atoms. Therefore, as such, the quaternary carbon in some of the alkyl benzene sulfonates in the commercial mixture cannot
be considered an absolute metabolic block.
The sulfonate group in an alkyl benzene sulfonate does not present a
problem if the material is degradable (Ryckman (4) showed greater than 90
per cent release of sulfate ion during metabolism), nor does it seem to be the
cause of the inhibition in the molecules which are undegradable. The latter
statement stems from the agreement of most investigators that the metabolism
of alkyl benzene sulfonates begins from the methyl or hydrophobic end of the
molecule which dissolves into the lipid portion of the bacterial cell wall.
Metabolism then proceeds as far as possible along the alkyl chain and, if
complete, into the benzene ring.
McKinney and Donovan (3) and McGauhey and Klein (6) have indicated
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