Biodegradation kinetics of peptone and 2,6-dihydroxybenzoic acid by acclimated dual microbial culture

Co-metabolism of nonylphenol ethoxylate in sequencing batch reactor under aerobic conditions

The study evaluated the co-metabolism of nonylphenol polyethoxylate (NPEO) within a main substrate stream subjected to biodegradation in an activated sludge system. Peptone mixture simulating sewage was selected as the synthetic substrate. As a novel approach, the NPEO concentration was magnified to match the COD level of the peptone mixture, so that co-metabolism could be evaluated by respirometry and modeling. A sequencing batch reactor (SBR) set-up at high sludge age to also allow nitrification was operated for this purpose. A long acclimation phase was necessary to start NPEO biodegradation, which was completed with 15% residual by-products. Modeling of respirometric data could identify COD fractions of NPEO with corresponding process kinetics for the first time, where the biodegradation of by-products could be interpreted numerically as a hydrolysis mechanism. Nonylphenol diethoxylate (NP2EO) was observed as the major by-product affecting the biodegradation of NPEO, because NPEO and NP2EO accounted for 60 to 70% of the total soluble COD in the solution during the course of biological reactions. The co-metabolism characteristics basically defined NPEO as a substrate, with no appreciable inhibitory action on the microbial culture both in terms of heterotrophic and autotrophic activities.

Interdependence between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge in semi-continuous reactors

The objective of the present work was to analyze the interrelationship between the aerobic degradation of BPA and readily biodegradable substrates by activated sludge (AS) in semi-continuous reactors (SCRs). AS were obtained from three SCRs fed with glucose, acetate or peptone. AS from these reactors were used as inocula for three SCRs that were fed with each biogenic substrate, and for three SCRs that were fed with the biogenic substrate and BPA. In all cases, dissolved organic carbon (DOC), BPA, total suspended solids (TSS) and respirometric measurements were performed. Although BPA could be removed in the presence of all the tested substrates, AS grown on acetate exhibited the longest acclimation to BPA. Reactors fed with peptone attained the lowest TSS concentration; however, these AS had the highest specific BPA degradation rate. Specific DOC removal rates and respirometric measurements demonstrated that the presence of BPA had a negligible effect on the removal of the tested substrates. A mathematical model was developed to represent the evolution of TSS and DOC in the SCRs as a function of the operation cycle. Results suggest that the main effect of BPA on AS was to increase the generation of microbial soluble products. This work helps to understand the relationship between the biodegradation of BPA and readily biodegradable substrates.

Kinetic evaluation of nitrification performance in an immobilized cell membrane bioreactor

High rate membrane bioreactor (MBR) systems operated at extremely low sludge ages (superfast membrane bioreactors (SFMBRs)) are inefficient to achieve nitrogen removal, due to insufficient retention time for nitrifiers. Moreover, frequent chemical cleaning is required due to high biomass flux. This study aims to satisfy the nitrification in SFMBRs by using sponge as carriers, leading to the extension of the residence time of microorganisms. In order to test the limits of nitrification, bioreactor was run under 52, 5 and 2 days of carrier residence time (CRT), with a hydraulic retention time of 6 h. Different degrees of nitrification were obtained for different CRTs. Sponge immobilized SFMBR operation with short CRT resulted in partial nitrification indicating selective dominancy of ammonia oxidizers. At higher CRT, simultaneous nitrification-denitrification was achieved when accompanying with oxygen limitation. Process kinetics was determined through evaluation of the results by a modeling study. Nitrifier partition in the reactor was also identified by model calibration.

Modelling aerobic stabilization of domestic and industrial sludge using a multi-component biomass model

The objective of the study was to investigate the achievable limits of aerobic sludge stabilization applied on waste-activated sludge generated in domestic, tannery, and pharmaceutical wastewater treatment plants. Stabilization study involved monitoring of conventional parameters and model evaluation of oxygen uptake rate and particulate components of waste sludge. Multi-component biomass approach was adopted based on death-regeneration mechanism. The results showed that sludge stabilization efficiency ranged between 25% and 30%, which was closely related to the fate of different particulate fractions of biomass, that is, viable biomass, hydrolysable particulates, and microbial metabolic products. Model calibration exercises yield in rate coefficient ranges of 0.18-0.32/day for biomass decay and 0.60-0.65/day for hydrolysis of non-biomass components. Degradation rates of particulate metabolic products were estimated as 0.035, 0.04, and 0.01/day for domestic, tannery, and pharmaceutical sludge, respectively. Relatively low degradation rates compared to conventional biological treatment processes confirmed reduced microbial activity in the course of aerobic stabilization.

Chronic impact of tetracycline on nitrification kinetics and the activity of enriched nitrifying microbial culture

This study evaluated the chronic impact of tetracycline on biomass with enriched nitrifying community sustained in a lab-scale activated sludge system. For this purpose, a fill and draw reactor fed with 100 mg COD/L of peptone mixture and 50 mg N/L of ammonia was sustained at a sludge age of 15 days. At steady-state, the reactor operation was continued with a daily tetracycline dosing of 50 mg/L for more than 40 days, with periodic monitoring of the microbial composition, the nitrifying bacteria abundance, as well as the amoA and 16S rRNA gene activity, using molecular techniques. Changes in the kinetics of nitrification were quantified by modelling concentration profiles of major nitrogen fractions and oxygen uptake rate profiles derived from parallel batch experiments. Activated sludge modeling results indicated inhibitory impact of tetracycline on the growth of nitrifiers with a significant increase of the half saturation coefficients in corresponding rate equations. Tetracycline also inactivated biomass components of the enriched culture at a gradually increasing rate with time of exposure, leading to total collapse of nitrification. Molecular analyses revealed significant changes in the composition of the microbial community throughout the observation period. They also showed that continuous exposure to tetracycline inflicted significant reduction in amoA mRNA and 16S rRNA levels directly affecting nitrification. The chronic impact was much more pronounced on the ammonia oxidizing bacteria (AOB) community. These observations explained the basis of numerical changes identified in the growth kinetics of nitrifiers under stress conditions.

Effect of high loading on substrate utilization kinetics and microbial community structure in super fast submerged membrane bioreactor

The study investigated the effect of high substrate loading on substrate utilization kinetics, and changes inflicted on the composition of the microbial community in a superfast submerged membrane bioreactor. Submerged MBR was sequentially fed with a substrate mixture and acetate; its performance was monitored at steady-state, at extremely low sludge age values of 2.0, 1.0 and 0.5d, all adjusted to a single hydraulic retention time of 8.0 h. Each MBR run was repeated when substrate feeding was increased from 200 mg COD/L to 1000 mg COD/L. Substrate utilization kinetics was altered to significantly lower levels when the MBR was adjusted to higher substrate loadings. Molecular analysis of the biomass revealed that variable process kinetics could be correlated with parallel changes in the composition of the microbial community, mainly by a replacement mechanism, where newer species, better adapted to the new growth conditions, substituted others that are washed out from the system.

Impact of aerobic stabilization on the characteristics of treatment sludge in the leather tanning industry

The efficiency of aerobic stabilization on the treatment sludge generated from the leather industry was investigated to meet the expected characteristics and conditions of sludge prior to landfill. The sludge types subjected to aerobic stabilization were chemical treatment sludge, biological excess sludge, and the mixture of both chemical and biological sludges. At the end of 23 days of stabilization, suspended solids, volatile suspended solids and total organic carbon removal efficiencies were determined as 17%, 19% and 23% for biological sludge 31%, 35% and 54% for chemical sludge, and 32%, 34% and 63% for the mixture of both chemical and biological sludges, respectively. Model simulations of the respirometric oxygen uptake rate measurements showed that the ratio of active biomass remained the same at the end of the stabilization for all the sludge samples. Although mixing the chemical and biological sludges resulted in a relatively effective organic carbon and solids removal, the level of stabilization achieved remained clearly below the required level of organic carbon content for landfill. These findings indicate the potential risk of setting numerical restrictions without referring to proper scientific support.

Acute impact of erythromycin and tetracycline on the kinetics of nitrification and organic carbon removal in mixed microbial culture

The study evaluated acute impact of erythromycin and tetracycline on nitrification and organic carbon removal kinetics in mixed microbial culture. Acclimated biomass was obtained from a fill and draw reactor fed with peptone mixture selected as synthetic substrate and operated at a sludge age of 10 days. Acute inhibition was tested in batch reactors involving a control unit started solely with substrate and the others with additional doses of each antibiotic. Modeling indicated that both steps of nitrification were totally blocked by erythromycin. Tetracycline inhibited and retarded nitrification kinetics at 50 mg/L and stopped nitrite oxidation at 200 mg/L, leading to nitrite accumulation. Both antibiotics also affected organic carbon removal by inducing partial inactivation of the heterotrophic community in the culture, increased substrate storage and accelerated endogenous respiration, with a relatively slight impact on heterotrophic growth. Major inhibitory effect was on process stoichiometry, leading to partial utilization of organic substrate.

Model evaluation of starch utilization by acclimated biomass with different culture history under pulse and continuous feeding

The study involved model evaluation of the fate and utilization of starch by microbial culture acclimated to different growth conditions and feeding regimes. For this purpose, parallel sequencing batch reactors were operated with pulse and continuous feeding of soluble starch at sludge ages of 8 and 2 days. High-rate adsorption was identified as the initial process for starch utilization under all operating conditions. Hydrolysis mechanism acted as the rate limiting mechanism for different substrate removal/storage modes sustained under pulse and continuous feeding at different sludge ages. Together with variable growth kinetics, faster growth conditions also triggered high-rate hydrolysis and relatively slower storage kinetics to ensure the level of substrate supply for faster microbial growth. Model evaluation indicated the presence of particulate sugar adsorbed, especially under continuous feeding. It enabled accurate interpretation of observed particulate sugar values and this way, differentiating glycogen from the adsorbed starch remaining on the biomass.

Potential of ultrafiltration for organic matter removal in the polymer industry effluent based on particle size distribution analysis

The purpose of the study was the experimental evaluation of ultrafiltration as a potential innovative technology for the removal of organic matter of around 15,000 mg chemical oxygen demand (COD) per liter in the polymer industry wastewater. Particle size distribution (PSD) analysis served as the major experimental instrument along with conventional chemical settling. Biodegradation characteristics of the remaining COD after ultrafiltration were determined by model interpretation of the corresponding oxygen uptake rate (OUR) profile. The study first involved a detailed characterization of the polymer wastewater including PSD analysis of the COD content. Chemical treatability was investigated using lime alone and with ferric chloride as coagulants followed with a PSD assessment of the chemically settled effluent. Modeling of the OUR profile generated by the ultrafiltration effluent defined related biodegradation kinetics and provided information on the overall COD removal potential. PSD analysis indicated that more than 70 % of the total COD accumulated in the 220- to 450-nm size range. It indicated that ultrafiltration was potentially capable of removing more than 90 % of the COD with an effluent lower than 1,500 mg COD/L. Chemical settling with 750 mg/L of FeCl(3) dosing at a pH of 7.0 provided a similar performance. The ultrafiltration effluent included mainly hydrolysable COD and proved to be biodegradable, with the process kinetics compatible with domestic sewage. PSD evaluation proved to be a valuable scientific instrument for underlining the merit of ultrafiltration as the appropriate innovative technology for polymer wastewater, removing the major portion of the COD in a way that is suitable for recovery and reuse and producing a totally biodegradable effluent.

Intracellular storage of acetate/starch mixture by fast growing microbial culture in sequencing batch reactor under continuous feeding

The paper evaluated intracellular storage formation in fast growing microbial culture fed with acetate/starch mixture under continuous feeding. Three parallel laboratory-scale sequencing batch reactors (SBRs) were operated at a sludge age of 2 days: one of the SBRs was fed with acetate/starch mixture and the other two with acetate and starch, respectively, for comparing the results with single substrate systems. Despite continuous feeding, both acetate and starch components in the substrate mixture were partially converted to storage biopolymers. Poly-hydroxybutyrate (PHB) and glycogen pools were formed during SBR operation at steady state. Only a limited fraction of 12% of the acetate fed during each cycle generated PHB storage while the rest was directly utilized for microbial growth. Around half of the starch fraction of the substrate mixture was converted to glycogen. Increasing the sludge age to 8 days did not affect storage stoichiometry both for acetate and starch in the mixture.

Fate and effect of xenobiotics on biodegradation processes: basis for respirometric appraisal

The paper mainly focused on illustrating the merit of respirometric analysis in assessing the inhibitory/toxic impact of xenobiotics on substrate biodegradation. It also evaluated biodegradation characteristics of these chemicals at continuous exposure through acclimation ofthe microbial culture. The nature and role ofoxygen uptake rate (OUR) profiles were discussed in conjunction with appropriate modelling, which should incorporate dissolved oxygen as an indispensable component for respirometric evaluation. Emphasis was placed upon differentiating acute effects from chronic impact, which may be totally different as it involves biodegradation of the chemical due biomass acclimation. Three case studies, each involving OUR measurements and process modelling, were presented for this purpose. The first one related to the inhibitory action of pharmaceutical effluent when mixed with plain-settled tannery wastewater. The second investigated the fate of H-acid, a commercially important naphthalene sulfonate, which exerted no adverse effect on substrate biodegradation, while remaining intact before and after a long acclimation period. The third one involved 2,6-dihydroxybenzoic acid, a naturally occurring organic compound in olive oil wastewater, which became biodegradable after acclimation by the development ofa specific microbial biomass fraction, while it heavily inhibited substrate biodegradation at first exposure. Model evaluation of the experimental data could provide related information on process stoichiometry and kinetics in all studies.

Is ammonification the rate limiting step for nitrification kinetics?

This study investigated relative magnitude of hydrolysis and ammonification by separate analysis of ammonia release and nitrification mechanisms. A peptone mixture was used as substrate in two parallel experiments seeded with nitrifying biomass conducted with and without nitrification inhibitor. Results were evaluated by means of model analysis of the ammonia and the oxygen uptake rate (OUR) profiles. A dual hydrolysis mechanism with maximum rate coefficients of 6.3 and 0.5/day characterized the peptone mixture and a kinetic balance was established for the ammonia release mechanism with a corresponding ammonification rate of 0.08 m(3)/g COD day. The experiments also showed a low soluble ammonia nitrogen generation that was rapidly depleted, confirming the existence of ammonification. These rate coefficients were verified using model calibration of the OUR profile related to simultaneous carbon removal and nitrification. Results indicated that ammonification would not be rate limiting for wastewaters such as domestic sewage, with lower hydrolysis kinetics.