| Abstract
| - The [S,S]-stereoisomer of ethylenediaminedisuccinic acid(EDDS), a biodegradadable strong metal chelant, hassubstituted traditional chelants in a number of consumerproducts. However biodegradability of metal−EDDScomplexes has remained largely undocumented. In thepresent study, activated sludge fed with EDDS as sole Cand N source, was shown to readily biodegrade 1 mM pulsesof Ca−, Cr(III)−, Fe(III)−, Pb−, Al−, Cd−, Mg−, Na−,or ZnEDDS (the latter only after extensive lag phase). Onthe other hand, the Cu−, Ni−, Co−, and Hg−complexesremained essentially undegraded. Only in the case ofHgEDDS was lack of biodegradation due to metal toxicity.Speciation analysis revealed free HEDDS3- concentrationwas higher than 10-5.4 M for all readily biodegradable metal−EDDS complexes and smaller than 10-9.0 M for allrecalcitrant complexes at pseudo-steady-state (i.e. afterinitial rise of aquo metal concentration at onset ofbiodegradation). The rate of metal−EDDS degradationmay be modeled with a Monod expression with HEDDS3-as substrate (half-saturation constant ca. 10-6 M). Thismodel explains the drastic effect of additional metal ligands,e.g. phosphate or iron, on biodegradation rate of severalrecalcitrant metal−EDDS complexes. Continuously fed aeratedbiofilters removed 10 mM Pb− or ZnEDDS at a rate ofca. 0.4 mM h-1.
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