Formation Of Soluble Microbial Products Research Articles

Characterization, Transformation, and Bioavailability of Dissolved Organic Nitrogen in Biofilters Treating Domestic Onsite Wastewater

This study investigated the transformation, bioavailability, and seasonal changes of dissolved organic nitrogen (DON) in nitrogen removing biofilters (NRBs) treating domestic onsite wastewater. The results demonstrated that NRBs were able to remove 92.6–94.3% DON from septic tank effluent with low effluent DON concentrations (0–5.8 mg N L–1), comparable to the levels detected in the tertiary municipal wastewater treatment plant. Both hydrophilic and hydrophobic DON were efficiently removed by the sand filters, while additional hydrophilic DON (0.8–1.8 mg N L–1) was produced in the lignocellulose/sand layer due to soluble microbial product formation. Seasonal change (i.e., temperature variation) did not impact the effluent DON composition or its removal efficiency by NRBs, while higher concentrations of hydrophilic DON (1.7–2.5 mg N L–1) were detected in the final effluent during the summer months (16.4–22.9 °C). DON in the NRB effluent had a higher potential to stimulate algal growth than other nitrogen forms (NH4+ and NOx–), confirmed by higher chlorophyll-a concentrations observed in the bioassay tests. The results suggest the DON levels in the final effluent of an onsite wastewater treatment system shall also be considered in onsite wastewater quality management and the effluent discharge regulations.

Characterization and modelling of soluble microbial products in activated sludge systems treating municipal wastewater with special emphasis on temperature effect.

Soluble microbial products (SMP) classified as utilization-associated products (UAP) and biomass-associated products (BAP) are the predominant foulants determining fouling in tertiary filtration. However, the exact mechanisms of BAP and UAP generation when treating real wastewaters under cold temperatures remain unrevealed. This paper presents the first study linking biological processes and SMP formation when treating real wastewaters through a combination of bioprocess modelling and advanced SMP characterization. Further, the impact of low operating temperatures on SMP production which has received relatively little attention was studied in detail. The use of liquid chromatography-organic carbon detection (LC-OCD) revealed a significant increase in protein and polysaccharide concentrations in the treated effluents as temperature decreased with a more sensitive impact on polysaccharides. The generation of SMP from biomass decay (BAP) and substrate utilization (UAP) was derived from the LC-OCD data on the basis of protein and polysaccharide mass balances. UAP and BAP yields were estimated as the ratios of the observed generation rates to the rates of substrate utilization and endogenous decay respectively, which both declined as temperature increased. A strong correlation was observed between temperature and BAP/UAP yields whereas the generation of BAP was more temperature sensitive than UAP. Such process modelling can be employed to assist with the optimization of the design and operation of membrane processes when treating wastewaters under challenging conditions like low temperature.

Formation of microbial products by activated sludge in the presence of a metabolic uncoupler o-chlorophenol in long-term operated sequencing batch reactors

Metabolic uncouplers are widely used for reducing excess sludge in biological wastewater treatment systems. However, the formation of microbial products, such as extracellular polymeric substances, polyhydroxyalkanoate and soluble microbial products by activated sludge in the presence of metabolic uncouplers remains unrevealed. In this study, the impacts of a metabolic uncoupler o-chlorophenol (oCP) on the reduction of activated sludge yield and formation of microbial products in laboratory-scale sequencing batch reactors (SBRs) were evaluated for a long-term operation. The results show the average reduction of sludge yield in the four reactors was 17.40%, 25.80%, 33.02% and 39.50%, respectively, when dosing 5, 10, 15, and 20 mg/L oCP. The oCP addition slightly reduced the pollutant removal efficiency and decreased the formation of soluble microbial products in the SBRs, but stimulated the productions of extracellular polymeric substances and polyhydroxyalkanoate in activated sludge. Furthermore, the significant reduction of electronic transport system activity occurred after the oCP addition. Microbial community analysis of the activated sludge indicates dosing oCP resulted in a decrease of sludge richness and diversity in the SBRs. Hopefully, this study would provide useful information for reducing sludge yield in biological wastewater treatment systems and behaviors of activated sludge in the presence of uncouplers.

Surface crystallization behavior of calcium carbonate in the presence of SMPs secreted by SRB

Surface crystallization of insoluble carbonate poses a serious problem for marine equipment industries which can be seriously influenced by soluble microbial products (SMPs). In Here, the effects of SMPs secreted by sulfate-reducing bacteria on the formation of CaCO3 were investigated by monitoring the crystallization rates and crystal polymorphs and morphologies. When 8.95 mg/L of SMP was added, vaterite and calcite were formed at the initial stage. This could be partly attributed to the formation of SMP and Ca2+ complexes, which provided a nucleation site for calcite. Simultaneously, crystallization by particle attachment promoted the increase of the crystallization mass density in the early stage of crystallization. As the concentration increased to 17.90 mg/L, a larger proportion of vaterite was stabilized. However, a further increase of SMP concentration to 44.76 mg/L did not enhance the proportion of vaterite and a different morphology of elongated calcite was formed. All investigated concentrations of experiments indicate that lower concentrations of SMP promotes calcite nucleation, and higher concentrations inhibit the formation of vaterite. However, an inverse relationship still exists between the concentration of SMP and the amount of surface crystallization of calcium carbonate.

Importance of nutrient availability for soluble microbial products formation during a famine period of activated sludge: Evidence from multiple analyses

Much remains unknown about compositional variations in soluble microbial products (SMP) with the shift of the substrate condition from a feast to a famine phase in biological treatment systems. This study demonstrated that the formation of SMP could be suppressed by up to 75% during the famine phase with the addition of essential nutrients. In contrast, presence of electron acceptor did not play any significant role during the stress condition, showing the similar amounts of SMP (r = 0.98, p < 0.05) formation between the bioreactors supplied with air and N2. The SMP formed in the famine phase was more bio-refractory in the famine versus the feast phase with a linear correlation shown between the production and their aromatic structures in the composition (R2 > 0.95). The fluorescence excitation–emission matrix coupled with parallel factor analysis (EEM-PARAFAC) revealed the presence of four different fluorescent components, including two protein-like (C1 and C4), fulvic-like (C2), and humic-like (C3) components, in the SMP and bEPS formed at different conditions. Both C1 and C4 showed increasing trends (R2 > 0.95) with the length of starvation in the bioreactors without essential nutrients. Nutrient availability was found to be a key factor to quench the production of large-sized biopolymers. This study provides a wealth of information on operation conditions of activated sludge treatment systems to minimize large sized SMP molecules (particularly proteins), which typically exert many environmental concerns to effluent organic matter quality.

Bioactivities and formation/utilization of soluble microbial products (SMP) in the biological sulfate reduction under different conditions

The biological sulfate reduction (BSR) plays a critical role in the organic compound removal in the sulfur bioconversion-associated sewage treatment process. The soluble microbial products (SMP) are the major components of residual organic compounds in the secondary treatment effluent and its presence directly affects treatment capacity. In addition, the SMP could be one of the available organic substrates and be utilized as an electron donor in the bioreactions. However, the SMP formation and utilization in the BSR are poorly understood. Herein, the BSR activities and SMP generation/utilization were simultaneously investigated under different conditions, i.e. pH, temperature and ratio of organic carbon (C) to sulfur (S). The role of SMP as the electron donor for BSR was also identified. The higher BSR activities and rapid SMP synthesis were found under neutral and alkaline conditions, but the SMP utilization as the electron donor is not favorable at pH 7.0. The BSR activity became higher and more SMP was synthesized by raising the temperature. The ratio of C to S rarely affected the sulfidogenic activity but has an effect on the net SMP generation (total SMP generation – SMP consumption by SBR as the electron donor). The lower ratio of C/S could result in the low residual SMP level in the reactor. And the SMP-induced BSR activity was higher under the acid and alkaline conditions compared with the neutral condition.

Calibration and validation of an activated sludge model for membrane bioreactor wastewater treatment plants

ABSTRACTA mathematical model to simulate the biological processes occurring in a membrane bioreactor (MBR) is presented. The model accounts for different MBR technical features by introducing specific permeability parameters for the applied membrane system. The model considers for the heterotrophic storage process and the formation of soluble microbial products. The introduction of an inhibition coefficient influencing the anoxic kinetics enables the model to simulate the particular operating conditions of the plant, such as a high or low dissolved oxygen concentration in the denitrification tank. The model was applied at the MBR wastewater treatment plant of Vila Nova do Ceira (Portugal) which uses a classic pre-denitrification cycle. Data for calibration and validation were sampled at the same wastewater treatment plant. Calibration was achieved by varying the kinetic parameters of the model to match the simulation results to the experimental data. The values of the kinetic parameters were similar to those found in the literature. The validation was performed by two different methodologies to analyse the model response to diverse operating conditions, and to evaluate the resilience of the MBR. Calibration and validation results were evaluated with mean average error, root mean square error and fractional mean bias as performance indexes. In most cases, these indexes confirmed the high accuracy of the model. Overall, the results of the calibration and validation steps enriched the proposed model by providing an effective biological description of the processes characterizing the MBR. Thus, the model is a reliable tool for the management and designing of MBR.

Qualitative and quantitative spectrometric evaluation of soluble microbial products formation in aerobic granular sludge system treating nitrate wastewater.

In present study, the characteristics of soluble microbial products (SMP) were evaluated in aerobic granular sludge system during denitrification process under different chemical oxygen demand/nitrogen (C/N) ratios. Batch experiment showed that the effluent nitrate (NO3--N) concentration were 15.24 ± 1.83 and 1.72 ± 1.53mg/L at C/N ratio of 1 and 6, respectively. For the release of SMP, the protein (PN) and polysaccharide contents increased from 1.23 ± 0.38 and 7.46 ± 1.13mg/L to 1.80 ± 0.76 and 10.53 ± 1.24mg/L with increasing C/N ratios, respectively. Excitation-emission matrix identified four peaks in SMP, including aromatic PN-like, tryptophan PN-like, fulvic acid-like and humic acid-like substances. Fluorescence regional integration suggested that biodegradable PN-like substances occupied the percentage between 53.0 and 61.7% in SMP. Synchronous fluorescence spectra coupled with two-dimensional correlation spectroscopy indicated that the release of SMP fractions in the early stage (0-150min) changed in the following sequences: PN-like fraction > fulvic acid-like fraction.

Characterization Composition of Soluble Microbial Products in an Aerobic Granular Sludge System

Using flocculent activated sludge as seed sludge to cultivate aerobic granular sludge in a SBR, the main objective of this study was focused on the accumulation, relative molecular mass distribution, and composition of soluble microbial products (SMP) in an aerobic granular sludge (AGS) system. SMP were predominant (71-85 mg·L-1) in the effluent of the AGS system. The formation of SMP was related to substrate utilization, biomass decay, and EPS hydrolysis. A relative molecular mass distribution analysis indicated that the majority of SMP, accounting for about 54.8%-71.7%, had Mr<3×103; whereas, the Mr>100×103 formed a small fraction, constituting only 9.3%-14.5%. Three-dimensional excitation emission matrix fluorescence spectra (3D-EEM) identified four peaks in SMP, belonging to aromatic protein-like, tryptophan protein-like, humic acid-like, and fulvic acid-like substances. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that esters (39.0%), short chain alkanes (14.9%), alkenes (11.7%), and alcohols (7.6%) were the main compounds in SMP. Most notably, bis(2-ethylhexyl) phthalate, as one kind of ester, accounted for 32% of the identified SMP.

Effect of acetate and propionate on the production and characterization of soluble microbial products (SMP) in aerobic granular sludge system

It is well known that soluble microbial products (SMP) derived from biological systems found in wastewater treatment plant effluent are responsible for chemical oxygen demand (COD). Aerobic granular sludge (AGS) is recognized as an efficient and innovative approach for wastewater treatment. Acetate and propionate as two dominant organic substances in wastewater need to be effectively removed before discharge. The aim of this study was to investigate the effectiveness of acetate and propionate to interfere with the accumulation, molecular weight (MW) distribution and composition of SMP in aerobic granular sludge (AGS) system using two identical sequencing batch reactors (SBR) named R1 and R2, respectively, thus reducing the COD. The results demonstrated that more SMP accumulated in R1 in presence of acetate compared to R2 treated with propionate. A positive correlation for SMP formation was detected as evidenced by aeration rates, but a negative correlation with hydraulic retention time (HRT). The MW distribution analysis suggested that small molecules (MW <3 kDa) were the dominant fraction of SMP in R1 and R2, accounting for 57–79% and 39–61%, respectively. In addition, gas chromatography-mass spectrometry (GC-MS) demonstrated that esters, alkanes, alkenes and alcohols were the predominant low-MW SMP in R1 and R2. More peaks were present in R2 (61) than R1 (46). Esters were the predominant SMP (39%) in R1, while alkanes were the predominant SMP (31%) in R2. Further, microbial community analysis indicated that more α- and γ-Proteobacteria groups which readily utilize low-MW SMP were found in R2 compared to R1-granules which may have contributed to less SMP accumulated in R2. The abundant genera in the granules were Zoogloea and Azoarcus, in particular, a greater quantity of Azoarcus was detected in R2 than R1-granules, which may be associated with higher degradation of aromatics in SMP.

Changes in spectroscopic signatures in soluble microbial products of activated sludge under different osmotic stress conditions

Spectroscopic techniques were used to examine the subtle changes in soluble microbial products (SMP) of batch activated sludge bioreactors working at different salinities (i.e., 0%, 1%, 3%, and 5% NaCl). The changes in different fluorescent constituent were tracked by excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC), and the sequential production was further identified by two-dimensional correlation spectroscopy (2D-COS). Greater enrichment of tryptophan-like component and large-sized biopolymer were found in SMP for higher saline bioreactors, suggesting the SMP sources from bound extracellular polymeric substances and excreted intercellular constituents. 2D-COS revealed the opposite sequences of the fluorescence changes in SMP between the low and the high saline bioreactors, following the order of “tyrosine-like > tryptophan-like > humic-like fluorescence” for the latter. This study clarified the dominant mechanisms involved in SMP formation during elevating salinity, which were well supported by the changes in SMP spectroscopic features, microbial activity, and organic degradation rates.

Formation of soluble microbial products and their contribution as electron donors for denitrification

Soluble microbial products (SMP) cause major soluble chemical oxygen demands (sCOD) in secondary effluent and significantly affect effluent quality. However, SMP can be also treated as new organic carbon resource, which can provide electrons for denitrification under anoxic conditions. This work investigated contribution of SMP as electron donors during denitrification under different conditions (feast, feast–famine, and famine). Only fraction of utilization-associated products could be adopted as electron donors for denitrification in feast condition because of sufficient organic carbon supply. Most biomass-associated products remained in water. In feast-famine condition, the nitrogen (nitrate and nitrite) reduction using influent TOC and SMP as electron donors were 86.4 and 55.2mgN/L respectively. SMP accounted for 33.6% and 39.0% of total nitrogen (TN) removal and total nitrogen (nitrate and nitrite) reduction, respectively. Only SMP can be adopted as sole electron donors in famine condition. Approximately 128.7mgN/L of nitrogen (nitrate and nitrite) reduction was calculated. Nitrate and TN removal were 91.4% and 51.7%, respectively. As electron acceptors under anoxic conditions, nitrate or nitrite can stimulate SMP generation from hydrolysis of extracellular polymeric substances.

Response of methane production and microbial community to the enrichment of soluble microbial products in goethite-dosed anaerobic reactors

Iron oxide facilitated methane production process has recently attracted more and more attention in the worldwide. On the other hand, soluble microbial products (SMPs) was found to play an important role in the wastewater treatment systems. The purpose of this study was to investigate the role of SMPs in the goethite (a typical iron oxide mineral) facilitated methanogenic process, where a dialysis bag was used to enrich the SMPs in the aqueous system. Results showed that both methane yield and production rate were enhanced significantly using the dialysis bag with a molecular weight of 2000Da compared to the controlled goethite-dosed reactors. Chemical analysis indicated that the increase in contacting time between goethite and microorganisms had insignificant impact on SMPs formation and methane production. It was also found that SMPs especially Flavins secreted from microorganisms could play an important role in the goethite facilitated methane production process. Additionally, enrichment of SMPs not only improved the abundance of electroactive bacteria and but also promoted the growth of aceticlastic methanogenesis.

A Fluorescence Approach to Assess the Production of Soluble Microbial Products from Aerobic Granular Sludge Under the Stress of 2,4-Dichlorophenol.

In this study, a fluorescence approach was used to evaluate the production of soluble microbial products (SMP) in aerobic granular sludge system under the stress of 2,4-dichlorophenol (2,4-DCP). A combined use of three-dimension excitation emission matrix fluorescence spectroscopy (3D-EEM), Parallel factor analysis (PARAFAC), synchronous fluorescence and two-dimensional correlation spectroscopy (2D-COS) were explored to respect the SMP formation in the exposure of different doses of 2,4-DCP. Data implied that the presence of 2,4-DCP had an obvious inhibition on biological nitrogen removal. According to EEM-PARAFAC, two fluorescent components were derived and represented to the presence of fulvic-like substances and humic-like substances in Component 1 and protein-like substances in Component 2. It was found from synchronous fluorescence that protein-like peak presented slightly higher intensity than that of fulvic-like peak. 2D-COS further revealed that fluorescence change took place sequentially in the following order: protein-like fraction > fulvic-like fraction. The obtained results could provide a potential application of fluorescence spectra in the released SMP assessment in the exposure of toxic compound during wastewater treatment.

Quantification and kinetic characterization of soluble microbial products from municipal wastewater treatment plants

Soluble microbial products (SMP) formed by microorganisms in wastewater treatment plants (WWTPs) adversely affect final effluent quality and treatment efficiency. It is difficult to distinguish SMP from residual proteins, lipids and carbohydrates present in the influent that may persist during treatment. No method is currently available to determine quantitatively the extent to which SMP contribute to organic discharges from municipal WWTPs. In this work a modeling approach is presented which allows the SMP fraction of the effluent of a municipal WWTP to be quantified and described. The model is validated, in terms of utilization-associated products, biomass-associated products and extracellular polymeric substances, using influent from a municipal WWTP. SMP was found to account for, on average, 27 mg/L of chemical oxygen demand (COD), or 61% of the total COD in the WWTP effluent. Over 90% of the SMP was comprised of biomass-associated products. Five main factors influencing SMP formation in WWTP were evaluated. Neither wastewater composition nor mixed liquor suspended solids concentration was found to affect SMP production. On the other hand, a positive correlation was observed for SMP formation with both solids retention time and influent COD concentration, and a negative correlation with hydraulic retention time. Thus, operating or designing WWTPs with short solids retention and long hydraulic retention times could be considered as solutions for minimizing SMP production.

Simultaneous in-situ sludge reduction and nutrient removal in an A2MO-M system: Performances, mechanisms, and modeling with an extended ASM2d model

Among the existing in-situ sludge reduction processes, the oxic-settling-anaerobic (OSA) process is of particular interest because it has shown significant sludge reduction with several advantages. However, an ideal process for practical application must simultaneously incorporate effluent quality with sludge reduction. In this study, an improved OSA system, the stage-aerated anaerobic, anoxic, micro-aerobic, and oxic system combining a micro-aerobic starvation tank (abbreviated as A2MO-M system) was developed. Compared with OSA3# (hydraulic retention time (HRT) of 12 h), the A2MO-M2# system with optimized HRT of 9 h yielded almost 16.3% less sludge. The average total nitrogen (87.3%) and total phosphorus (91.9%) removal efficiencies in A2MO-M2# were 20.6 and 42.2% higher than those in OSA3#. Investigation of the mechanisms of sludge reduction revealed that, except for the main factors of energy uncoupling metabolism (16.7%) and sludge decay (21.2%), enrichment of slow-growing bacteria and lysis-cryptic growth metabolism analyzed by high-throughput 454 pyrosequencing were shown to contribute to sludge reduction in the A2MO-M system. On the basis of effluent organic matters (EfOM) measurements, soluble microbial products (SMP) were the major components in EfOM; and different reduction-oxidation (redox) potentials controlled in the OSA and A2MO-M systems led to different SMP formation mechanisms. To explore the mechanism and kinetics of SMP formation under different redox potentials, three new components (SUAP, SBAP, and XEPS) were integrated in an extended ASM2d model. Experimental and modeling results revealed that biomass-associated products (BAP) supported a substantial population of SMP that were quite sensitive to different redox potentials. The extended ASM2d model further illustrated that more BAP produced in the alternating anaerobic and aerobic conditions in the OSA system adversely affected its effluent quality.

Fractionation, characterization and C-, N-disinfection byproduct formation of soluble microbial products in MBR processes

Soluble microbial products are heterogeneous organic materials generated during microbial growth and decay, which are the major soluble organic matters in MBR effluents and are the primary precursors forming disinfection by-products (DBPs). In this study, biomass associated products (BAP) and utilization associated products (UAP) were separately produced to investigate their physical chemical characteristics and disinfection byproduct (DBP) formation during chlorination in the presence of ammonia. BAP had higher formation reactivity of halogenated carbonaceous and nitrogenous DBPs including trihalomethanes, haloketones, haloacetonitriles and trichloronitromethane due to their higher percentage of large molecular weight (MW) materials and humic substances compared with UAP. However, the nonhalogenated species N-nitrosodimethylamine (NDMA) yield of UAP was twice higher than that of BAP because UAP contained more nitrogenous organic matters with MW<500Da including aromatic polypeptide/amino acid-like materials and secondary amines, which have been proved to have high NDMA formation potential.

Relationship between soluble microbial products (SMP) and effluent organic matter (EfOM): Characterized by fluorescence excitation emission matrix coupled with parallel factor analysis

Effluent organic matter (EfOM) originating from wastewater treatment plant (WWTP) is of significant concern, as it not only influences the discharge quality of WWTP but also exerts a significant effect on the efficiency of the downstream advanced treatment facilities. Soluble microbial products (SMP) is a major part of EfOM. In order to further understand the relationship between soluble microbial products (SMP) and EfOM, and in turn, to propose measures for EfOM control, the formation of SMP and EfOM in identical activated sludge sequencing batch reactors (SBR) with different feed water was investigated using fluorescence excitation and emission spectroscopy matrix coupled with parallel factor analysis (EEM–PARAFAC) as well as other organic matter quantification tools. Results showed that EfOM contained not only SMP but also a considerable amount of allochthonous organic matter that derived not merely from natural organic matter (NOM). Four components in EfOM/SMP were identified by EEM–PARAFAC. Tyrosine-like substances in EfOM (Component 3, λex/em=270/316nm) were mainly originated from utilization associated products (UAP) of SMP. Tryptophan-like substances (Component 2, λex/em=280/336nm) as well as fulvic-like and humic-like substances in EfOM (Component 1, λex/em=240(290)/392nm and Component 4, λex/em=260(365)/444nm) were majorly derived from the refractory substances introduced along with the influent, among which Component 2 was stemmed from sources other than NOM. As solid retention time (SRT) increased, Component 2 and polysaccharides in SMP/EfOM decreased, while Component 4 in SMP increased.

Evaluation of a MBR pilot treating industrial wastewater with a high COD/N ratio

BACKGROUND In this study the performance of a membrane bioreactor (MBR) pilot plant treating industrial wastewater at the Heraklion Industrial Park, at three different sludge retention times (SRTs), was investigated. Membrane fouling in the MBR was monitored through the transmembrane pressure build up and by measuring accumulation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). The effect of hydraulic residence time (HRT) on effluent quality and membrane fouling was examined as well. RESULTS The highest removal efficiencies (COD, TN, P) of the order of 99.2%, 94.3% and 89.3%, respectively, as well as moderate formation of EPS and SMPs were observed at a SRT of 20 days. Changes in HRT had a small effect on carbon and ammonium removal, but a strong impact on denitrification and phosphate removal. Total EPS and SMP were higher at higher SRTs in contrast to reported common observations. However, the shorter SRT of 15 days led to a more rapid increase of TMP. CONCLUSION The system's performance regarding COD, TN and P removal was very good despite the high COD/N input ratio and the huge variations in influent quality. The observed membrane fouling behavior reflects the complexity of the biological process. © 2014 Society of Chemical Industry

Soluble Microbial Products Decrease Pyrite Oxidation by Ferric Iron at pH &lt; 2

Research on microbial activity in acid mine drainage (AMD) has focused on transformations of iron and sulfur. However, carbon cycling, including formation of soluble microbial products (SMP) from cell growth and decay, is an important biogeochemical component of the AMD environment. Experiments were conducted to study the interaction of SMP with soluble ferric iron in acidic conditions, particularly the formation of complexes that inhibit its effectiveness as the primary oxidant of pyrite during AMD generation. The rate of pyrite oxidation by ferric iron in sterile suspensions at pH 1.8 was reduced by 87% in the presence of SMP produced from autoclaved cells at a ratio of 0.3 mg DOC per mg total soluble ferric iron. Inhibition of pyrite oxidation by SMP was shown to be comparable to, but weaker than, the effect of a chelating synthetic siderophore, DFAM. Two computational models incorporating SMP complexation were fitted to experimental results. Results suggest that bacterially produced organic matter can play a role in slowing pyrite oxidation.