Restructuring anaerobic hydrolysis kinetics in plant-wide models for accurate prediction of biogas production.

In this study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. A linear correlation was determined between the percentage of primary sludge mass in the total sludge fed to the digester and the overall anaerobic hydrolysis rate. The anaerobic hydrolysis rate of primary sludge was determined to be three times higher than that of biological sludge. The reduction factors for anaerobic hydrolysis (ηHYD,ana) were identified in the range of 0.11-0.30 which is lower compared to the recommended range (0.30-0.50) given in the literature. This study proposes a new model approach where anaerobic degradation kinetics of influent originated (XB) and decay originated (XB,E) particulate biodegradable organics are separated. Current plant-wide models with a single kinetic expression required recalibration of the model for calculating biogas flowrate for each treatment facility with different primary and secondary sludge ratios fed to the digesters. The new model structure is able to predict biogas production of all wastewater treatment plants without any recalibration effort by segregating degradation kinetics of two particulate biodegradable organic fractions (XB, XB,E).

Model-based evaluation of simultaneous nitrification and denitrification in aerobic granular sludge systems.

A lab-scale granular sludge sequencing batch reactor (G-SBR) system was operated using synthetic wastewater. The total nitrogen removal efficiency of 85% was obtained together with the achievement of complete total phosphorus removal with average granule diameter of 400 µm. Dual-step nitrification and denitrification model with fixed biofilm thickness was used for performance analysis. The denitrification mode only contributed to TN removal with 25% which can be calculated with process stoichiometry. The remaining nitrogen removal could be explained by simulating simultaneous nitrification and denitrification which was responsible for 75% denitrification during aerobic period. In addition, low NO3- concentration at the beginning of the fill period provided advantage for securing a prolonged anaerobic period for enhanced biological phosphorus removal (EBPR). The model parameters of boundary layer thickness (zBL = 50 µm) and half-saturation of O2 for nitrite-oxidizing bacteria (KO2,NOB = 0.5 gO2/m3) were tuned to fit NO2 and NO3 profiles in SBR cycle.

A comprehensive evaluation of process kinetics: A plant-wide approach for nutrient removal and biogas production.

The present study investigated the deviations of operational parameters of a large-scale wastewater treatment plant (WWTP) from design basis through combining dedicated batch experiments with full-scale dynamic modeling results. The long-term process performance of a full-scale biological nutrient removal (BNR) plant equipped with anaerobic sludge digestion system was monitored to evaluate the process kinetics of both carbon and nutrient removal and anaerobic sludge digestion. In this respect, plant-specific characterization; chemical oxygen demand (COD) fractionation, batch kinetic studies and sludge settling velocity tests were performed together with plant-wide SUMO model simulation. Results showed that nitrification and anaerobic hydrolysis were found to be 30% and 70% lower than literature values, respectively. The anaerobic digestion test coupled with plant-wide model calibration showed that anaerobic hydrolysis was the bottleneck in biogas production. Correspondingly, performance of the anaerobic digestion in the full-scale plant was poor as low biogas production yields were observed. In addition, the degradation rate via anaerobic hydrolysis of primary sludge was found to be higher (∼2-2.5) compared to anaerobic hydrolysis of biological sludge. The results of this study provide insight into model-based experimental characterization as well as plant-wide modeling approach. Coupling model-based batch experiments with full-scale modeling enabled to reduce the number of kinetic parameters to be fine-tuned. Moreover, the information gathered from kinetic batch tests to the simulation platform yielded a satisfying prediction of long-term performance of the plant operation.

A New Activated Sludge Model with Membrane Separation-Implications for Sewage and Textile Effluent.

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.

Insights into the acute effect of anti-inflammatory drugs on activated sludge systems with high solids retention time.

The increase in the occurrence of the pharmaceuticals in the environmental compartments is becoming emerging concern as it reflects their inefficient treatment in the wastewater treatment plants which are the main sources of these micropollutants. Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the most commonly prescribed and frequently detected pain medications in wastewater treatment plants. A lab scale sequencing batch reactor (SBR) was operated for seven months and acute inhibitory effect of NSAIDs on activated sludge was tested with respirometry. Culture amendment with different concentrations of NSAIDs in the presence as well as absence of nitrification inhibitor resulted in considerable variation in the oxygen uptake rate (OUR) profiles. The decrease in OUR and nitrate production rate governed with reduced heterotrophic and nitrification activity. The kinetics of half saturation for growth and maximum autotrophic growth rates are determined to be affected negatively by the acute impact of anti-inflammatory pharmaceuticals even at the environmentally relevant concentrations. High removal of tested NSAIDs was observed even for the first time introduce with these compounds.

Determination of the potential of pickle wastewater as feedstock for biopolymer production.

Food industry wastewater (FIWW) streams with high organic content are among the most suitable and inexpensive candidates for polyhydroxyalkanoate (PHA) biopolymer production. Due to its high organic acid content, pickle industry wastewater (PIWW), can be considered as one of the prospective alternatives to petroleum-based polymers for PHA production. In this context, this study aimed to investigate the production of PHA with enriched microbial culture using PIWW. Two laboratory scale sequencing batch reactors (SBRs) were operated under aerobic dynamic feeding conditions at a sludge retention time of 8 days, with a total cycle duration of 24 hours. SBRs were fed with peptone mixture and PIWW. In-cycle analysis and batch respirometric tests were performed to evaluate PHA storage together with biodegradation kinetics. In-cycle analysis showed that maximum PHA content was 1,820 mgCOD/L, corresponding to 44% in the biomass (ratio of chemical oxygen demand (COD) to volatile suspended solids) for PIWW. Experimental results were also confirmed with activated sludge model simulations. As for the PHA composition, hydroxybutyrate was the major fraction. Model simulations proposed a unique conversion-degradation-storage pathway for the organic acid mixture. This paper presents a novel insight for better understanding of PHA biopolymer production using high saline FIWW.

Membrane integrated process for advanced treatment of high strength Opium Alkaloid wastewaters.

In this study, an integrated aerobic membrane bioreactor (MBR)-nanofiltration (NF) system has been applied for advanced treatment of Opium processing wastewaters to comply with strict discharge limits. Aerobic MBR treatment was successfully applied to high strength industrial wastewater. In aerobic MBR treatment, a non-fouling unique slot aeration system was designed using computational fluid dynamics techniques. The MBR was used to separate treated effluent from dispersed and non-settleable biomass. Respirometric modeling using MBR sludge indicated that the biomass exhibited similar kinetic parameters to that of municipal activated sludge systems. Aerobic MBR/NF treatment reduced chemical oxygen demand (COD) from 32,000 down to 2,500 and 130 mg/L, respectively. The MBR system provided complete removal of total inorganic nitrogen; however, nearly 50 mgN/L organic nitrogen remained in the permeate. Post NF treatment after MBR permeate reduced nitrogen below 20 mgN/L, providing nearly total color removal. In addition, a 90% removal in the conductivity parameter was reached with an integrated MBR/NF system. Finally, post NF application to MBR permeate was found not to be practical at higher pH due to low flux (3-4 L/m2/hour) with low recovery rates (30-40%). As the permeate pH lowered to 5.5, 75% of NF recovery was achieved at a flux of 15 L/m2/hour.

Impact of paint shop decanter effluents on biological treatability of automotive industry wastewater.

A lab-scale Sequencing Batch Reactor (SBR) was implemented to investigate biological treatability and kinetic characteristics of paint shop wastewater (PSW) together with main stream wastewater (MSW) of a bus production factory. Readily biodegradable and slowly biodegradable COD fractions of MWS were determined by respirometric analysis: 4.2% (SS), 10.4% (SH) and 59.3% (XS). Carbon and nitrogen removal performance of the SBR feeding with MSW alone were obtained as 89% and 58%, respectively. When PSW was introduced to MSW, both carbon and nitrogen removal were deteriorated. Model simulation indicated that maximum heterotrophic growth rate decreased from 7.2 to 5.7day-1, maximum hydrolysis rates were reduced from 6 to 4day-1 (khS) and 4 to 1day-1 (khX). Based on the dynamic model simulation for the evaluation of nitrogen removal, a maximum specific nitrifier growth rate was obtained as 0.45day-1 for MSW feeding alone. When PSW was introduced, nitrification was completely inhibited and following the termination of PSW addition, nitrogen removal performance was recovered in about 100 days, however with a much lower nitrifier growth rate (0.1day-1), possibly due to accumulation of toxic compounds in the sludge. Obviously, a longer recovery period is required to ensure an active nitrifier community.

Effect of simultaneous nitrification and denitrification on nitrogen removal performance and filamentous microorganism diversity of a full-scale MBR plant.

The nutrient removal performance of a membrane bioreactor (MBR) plant treating the wastewater of 10,000 PE was investigated with dynamic simulations. The average process performance with respect to chemical oxygen demand and total nitrogen were reported to be 97 and 81%, respectively. The modeling study showed that low dissolved oxygen (DO) levels (0.2-0.3 mgO2/L) due to limited aeration capacity within aeration tank that provided additional total nitrogen removal of 15-20 mgN/L. Simultaneous nitrification and denitrification process was found to be the reason of performance increase. However, low DO levels <0.3 mgO2/L in the aeration tank triggered the proliferation of filamentous microorganisms within one month as a side effect. In this respect, the morphotypes of Type 0092 and Nocardia (Gordonia) amarae were found to be excessively abundant in the MBR system. Overflow of foam layer covering the tanks was frequently reported during bulking period. A hypochloride dosing of 4.5 gCL/kgMLSS/day was applied to get over filamentous bulking problem as a short term action.

Biological NOx removal by denitrification process in a jet-loop bioreactor: system performance and model development.

Nitrogen monoxide (NO) and nitrogen dioxide referred as NOx are one of the most important air pollutants in the atmosphere. Biological NOx removal technologies have been developing to reach a cost-effective control method for upcoming stringent NOx emission standards. The BioDeNOx system was seen as a promising biological NOx control technology which is composed of two reactors, one for absorbing of NO in an aqueous Fe(II)EDTA2- solution and the other for subsequent reduction to N2 gas in a biological reactor by the denitrification process. In this study, instead of two discrete reactors, only one jet-loop bioreactor (JLBR) was utilized as both absorption and denitrification unit and no chelate-forming chemicals were added. In other words, the advantage of better mass transfer conditions of jet bioreactor was used instead of Fe(II)EDTA2-. The process was named as Jet-BioDeNOx. The JLBR was operated for the removal of NOx from air streams containing 500-3000 ppm NOx and the results showed that the removal efficiency was between 81% and 94%. The air to liquid flow ratio (Q(G)/Q(RAS)) varied in the range of 0.07-0.12. Mathematical modelling of the system demonstrated that the removal efficiency strongly depends on this ratio. The high mass transfer conditions prevailed in the reactor provided a competitive advantage on removing NO gas without any requirement of chelating chemicals.

Biodegradation characteristics and size fractionation of landfill leachate for integrated membrane treatment.

The fate of organics and nitrogen during the biological treatment with MBR and subsequent membrane filtration processes (nano filtration, NF; reverse osmosis, RO) were investigated for a landfill leachate. The chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal performances of membrane bioreactor (MBR) were obtained to be around 89% and 85%, respectively. The effluent COD of MBR was measured to be 1935 mg/L (30 kDa) which is much lower than experimentally determined soluble inert COD of 3200 mg/L using 0.45 µm filter. The readily and slowly biodegradable COD fractions were estimated to be 17% and 52% of raw influent COD, respectively. The respirometry based modeling test performed on raw leachate exhibited much slower degradation kinetics compared to municipal wastewater. A unique subset of model parameters was extracted from batch respirometry by using acclimated MBR sludge. The sequential ultrafiltration (UF) experiments (particle size distribution, PSD) revealed that most of the organics was below 2 nm filter mesh size. In addition, NF/RO post treatment after MBR system was required to increase COD and total nitrogen (TN) removal performances up to 99%. Relatively lower salt rejection rates around 94% was obtained for RO system as a post treatment of MBR system.

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.

Modeling of simultaneous growth and storage kinetics variation under unsteady feast conditions for aerobic heterotrophic biomass.

The heterotrophic biomass has the capacity of utilizing substrate predominantly for growth or storage processes under steady-state conditions. In this study, the short-term variations in growth and storage kinetics of activated sludge under disturbed feeding conditions were analyzed using a multi-component biodegradation model. The variations in growth and storage kinetics were investigated with the aid of multi-response modeling and identifiability analysis. It was found that the heterotrophic biomass is able to increase its direct growth activity together with reducing the substrate storage capability under the availability of external substrate. Reducing the sludge age (SRT) from 10 to 2 days increased the maximum specific growth rate, µ (OHO,Max) from 3.9 to 7.0 day(-1), but did not considerably affected the maximum storage rate, k (Stor,OHO). The alteration of sludge age also elevated the half-saturation constant for growth (K (S,OHO)) from 5 to 25 mg COD/L. The increase in primary growth metabolism together with reduced storage rate was validated by model for two different sludge ages in the availability of external substrate. Aside from having a lower storage capability, the biomass had fast adaptation ability to direct growth process at low SRTs. The alteration of feed conditions was found to have different impacts on storage and growth kinetics. These results are significant and advance the field of activated sludge modeling under dynamic conditions by incorporation of short-term effects. Appropriate modifications including short-term effects in model structure may also reduce dynamic model recalibration efforts in the future.

Acute effect of benzo[a]anthracene on the biodegradation of peptone under aerobic conditions.

BACKGROUND: This study investigated the acute effect of benzo[a]anthracene, a significant compound among polycyclic aromatic hydrocarbons, on the biodegradation of a synthetic organic substrate-a peptone/meat extract mixture-under aerobic conditions. METHODS: A laboratory-scale sequencing batch reactor was sustained at steady state at a sludge age of 10 days with substrate feeding. Inhibition tests involved running a series of batch reactors initially seeded with the biomass obtained from the parent reactor. After the biomass seeding, the reactors were started with the peptone mixture and a range of initial benzo[a]anthracene concentrations between 0.5 and 88 mg/L. Experimental profiles of oxygen uptake rates and polyhydroxyalkanoates were evaluated by calibration of a selected model. RESULTS: Lower doses of benzo[a]anthracene had no effect on process kinetics. The noticeable acute impact was only observed with the addition of 88 mg/L of benzo[a]anthracene, but it was limited with the storage mechanism: the amount of organic substrate diverted to polyhydroxyalkanoates was significantly reduced with a corresponding decrease in the maximum storage rate, k (STO), from 2.7 down to 0.6 day(-1). Similarly, the maximum growth rate from internally stored polyhydroxyalkanoates was lowered from 2.3 to 1.0 day(-1). CONCLUSION: Among the mechanisms for direct substrate utilization, only the hydrolysis rate was slightly reduced, but otherwise, the overall COD removal efficiency was not affected.

Respirometric evaluation and modelling of acetate utilization in sequencing batch reactor under pulse and continuous feeding.

The study investigated the effect of feeding regime and sludge age on acetate utilization. Parallel sequencing batch reactors (SBRs) were operated at steady-state with pulse and continuous feeding of acetate at sludge ages of 8 and 2 days. Acetate was always partially converted to poly-ß-hydroxybutyrate (PHB). The adopted model remained equally applicable to oxygen uptake rate and PHB profiles reflecting different feeding regimes and culture history. Sludge age was significant on the rate parameters of storage and direct growth (k(STO), µ(H1)), while the feeding regime affected half saturation coefficients (K(STO), K(S1)). Changing the sludge age from 8 days to 2 days reduced the k(STO) value from 8.0 day(-1) to 6.5 day(-1) and increased the corresponding µ(H1) value from 1.5 day(-1) to 2.5 day(-1), regardless of the feeding regime; conversely, changing from pulse to continuous feeding reduced K(STO) while increasing K(S) for the SBR operation at the same sludge age.

Effect of stabilization on biomass activity.

The study aimed to compare aerobic and aerobic/anoxic stabilization processes in terms of organic matter and the biomass removal efficiencies using a municipal sludge sample. The efficiency of stabilization process was assessed monitoring suspended solids (SS), volatile suspended solids (VSS), total and dissolved organic carbon (TOC, DOC), nitrate, nitrite, and phosphate parameters. The oxygen uptake rate (OUR) measurements were conducted to determine active biomass concentration. On the 30th day of the aerobic stabilization, the SS, VSS and TOC removal efficiencies were 22%, 28% and 55%, respectively. Under aerobic/anoxic conditions, removal efficiencies for SS, VSS and TOC were 25%, 27% and 67%. On the 17th day of the stabilization, SS and VSS removal rates were 60 mg SS/L day and 47 mg VSS/L day for aerobic and 102 mg SS/L day and 63 mg VSS/L day for aerobic/anoxic conditions, respectively. These findings reflected the higher stabilization performance of the aerobic/anoxic conditions. Based on respirometric results, the ratios of the active biomass were decreased to 30% and 24% for the 17th and 30th day of the aerobic stabilization, respectively. Such results have significant implications relative to the activity decrease quantification of the biomass as well as its further application potentials after aerobic or aerobic/anoxic sludge stabilization.

Respirometric assessment of substrate binding by antibiotics in peptone biodegradation.

The study evaluated the inhibitory impact of antibiotics on the biodegradation of peptone mixture by an acclimated microbial culture under aerobic conditions. A fill and draw reactor fed with the peptone mixture defined in the ISO 8192 procedure and sustained at steady state at a sludge age of 10 days was used as the biomass pool with a well-defined culture history. Acute inhibition experiments involved running six parallel batch reactors seeded with biomass from the fill and draw reactor and the same peptone mixture together with pulse feeding of 50 mg/L and 200 mg/L of Sulfamethoxazole, Erythromycin and Tetracycline. Substrate utilization was evaluated by observing the respective oxygen uptake rate profiles and compared with a control reactor, which was started with no antibiotic addition. While all available external substrate was removed from solution, addition of antibiotics induced a significant decrease in the amount of oxygen consumed, indicating that a varying fraction of peptone mixture was blocked by the antibiotic and did not participate to the on-going microbial growth mechanism. This observation was also compatible with the concept of the uncompetitive inhibition mechanism, which defines a similar substrate blockage through formation of an enzyme- inhibitor complex.

Mechanism and design of intermittent aeration activated sludge process for nitrogen removal.

The paper provided a comprehensive evaluation of the mechanism and design of intermittent aeration activated sludge process for nitrogen removal. Based on the specific character of the process the total cycle time, (T(C)), the aerated fraction, (AF), and the cycle time ratio, (CTR) were defined as major design parameters, aside from the sludge age of the system. Their impact on system performance was evaluated by means of process simulation. A rational design procedure was developed on the basis of basic stochiometry and mass balance related to the oxidation and removal of nitrogen under aerobic and anoxic conditions, which enabled selected of operation parameters of optimum performance. The simulation results indicated that the total nitrogen level could be reduced to a minimum level by appropriate manipulation of the aerated fraction and cycle time ratio. They also showed that the effluent total nitrogen could be lowered to around 4.0 mgN/L by adjusting the dissolved oxygen set-point to 0.5 mg/L, a level which promotes simultaneous nitrification and denitrification.

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

This study evaluated the kinetics of simultaneous biodegradation of peptone mixture and 2,6-dihydroxybenzoic acid (2,6-DHBA) by an acclimated dual microbial culture under aerobic conditions. A laboratory-scale sequencing batch reactor was sustained at steady-state with peptone mixture feeding. During the study period, peptone mixture feeding was continuously supplemented with 2,6-DHBA. Related experimental data were derived from three sets of parallel batch reactors, the first fed with the peptone mixture, the second with 2,6-DHBA and the third one with the two substrates, after acclimation of microbial culture and simultaneous biodegradation of both organics. A mechanistic model was developed for this purpose including the necessary model components and process kinetics for the model calibration of relevant experimental data. Model evaluation provided all biodegradation characteristics and kinetics for both peptone mixture and 2,6-DHBA. It also supported the development of a dual microbial community through acclimation, with the selective growth of a second group of microorganisms specifically capable of metabolizing 2,6-DHBA as an organic carbon source.

Biodegradation kinetics of 2,6-dihydroxybenzoic acid and peptone mixture by acclimated microbial culture at low sludge age.

This study evaluated the kinetics of 2,6-dihydroxybenozic acid and peptone biodegradation at low sludge age by acclimated culture under aerobic conditions. A laboratory-scale sequencing batch reactor was set and fed with peptone mixture. The system was operated at steady-state at a sludge age of 2 days. In order to assess biodegradation kinetics of 2,6-dihydroxybenozic acid and its impact on peptone utilization, a mixture of 2,6-dihydroxybenzoic acid and peptone was fed to mixed culture. After a period of four days, the system became acclimated to simultaneously remove both 2,6-dihydroxybenzoic acid and peptone mixture. A mechanistic model was developed involving model components and kinetic parameters for both substrates. This model was calibrated with related experimental data such as oxygen uptake rate and COD. Biodegradation characteristics and kinetics of peptone and 2,6-dihydroxybenzoic acid was estimated. The evaluation of calibrated model indicated that a group of microorganisms adjusted their enzymatic tools for the utilization of 2,6-dihydroxybenzoic acid resulting in dual microbial community development at low sludge age.