Bismuth dimercaptopropanol (BisBAL) inhibits formation of multispecies wastewater flocs.

AIMS: To determine the ability of a bismuth thiol to control floc formation in a multispecies population of micro-organisms obtained from the activated sludge unit of a wastewater treatment plant. The molecular level mechanisms by which bismuth-2-3-dimercapto-1-propanol (BisBAL) inhibits bioaggregation are also elucidated. METHODS AND RESULTS: Micro-organisms were grown over a 3-day period in a batch system by adding glucose as an electron donor to stimulate short-term heterotrophic activity. Extracellular polymeric substances (EPS) produced by activated sludge micro-organisms during exponential and stationary growth phases in the presence and absence of BisBAL were characterized using colorimetry, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. BisBAL at its minimum inhibitory concentration (MIC, 10 µmol l(-1) ) was most effective in suppressing microbial floc formation. The principal effect of sub-inhibitory concentrations of BisBAL was to decrease total EPS production while largely preserving homology. CONCLUSIONS: Antifouling and bactericidal properties of BisBAL arise from its ability to reduce EPS expression and preferentially suppressing acidic and O-acetylated carbohydrates and certain protein secondary structures viz. ß-structures, random coils, and α-and 3-turn helices. As micro-organisms exhibited a much weaker tendency to aggregate at lower concentrations of these specific EPS components, they also appear to be important for the formation of microbial flocs and bioaggregates. SIGNIFICANCE AND IMPACT OF THE STUDY: BisBAL was shown to be highly effective against multispecies microbial aggregation. Novel bismuth-based biocides could also be potentially employed to control excess sludge production in wastewater treatment systems by inhibiting EPS expression.

Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters.

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.

Simplified analysis of contaminant rejection during ground- and surface water nanofiltration under the information collection rule.

A simple, closed-form analytical expression based on the homogenous solution diffusion model is derived for contaminant removal during nanofiltration (NF) of ground and surface water. Solute permeation and back-diffusion coefficients were used as fitting parameters to model rejection characteristics of four thin-film composite NF membranes under conditions typical of drinking water NF. Nonlinear fits of the model to experimental data suggests that the United States Environmental Protection Agency's (USEPA)'s Information Collection Rule protocol for bench-scale studies could be improved to obtain greater precision of the mass transfer coefficients. The model was found to fit rejection data for several water treatment contaminants including total organic carbon, precursors to total organic halide, four trihalomethanes and nine haloacetic acids containing chlorine and bromine, calcium and total hardness, alkalinity and conductivity. The simplified approach to mass transfer calculations from multisolute systems suggests that feed water recovery has a stronger influence on contaminant rejection than permeate flux. Evidence for coupled transport of divalent inorganic ions is also presented. Even though the model developed does not account for ion coupling and cannot be applied in a purely predictive mode, it can assist in the better design and interpretation of data obtained from site-specific pilot-scale water treatment NF studies conducted in support of plant design.

Peer reviewed: the promise of membrane technology.

An expanded understanding of membrane technology is fostering new environmental applications.