Enhancement of nutrient removal performance of activated sludge with a novel hybrid biofilm process.

The aim of this study was to investigate the efficacy of a hybrid biofilm pilot-scale treatment plant, designed with a novel configuration by the integration of a fixed-film system, to improve nitrogen removal. The pilot-scale system was established at a wastewater treatment plant in Istanbul and operated based on stream separation following a process consisting of Bio-P and primary sedimentation units in which carbonaceous compounds were entrapped/incorporated in settled biomass. The ammonia-rich supernatant was directed to a moving bed biofilm (MBBR) nitrification tank to obtain an efficient nitrification with the reduced organic loading after the primary sedimentation. The conventional activated sludge process, for which the net specific growth rate ([Formula: see text]) was measured to be 0.26 day-1 at 15 °C, exhibited a low nitrification capacity. However, the pilot-scale hybrid biofilm system secured nitrification performance up to 1.8 gN/m2/day ammonia loading, providing a competitive advantage over the conventional single sludge systems. The proposed hybrid configuration enables removal efficiencies of 80% and 85% for total nitrogen and phosphorus. It was possible to entrap organic matter by mixing 30% of return activated sludge (RAS) with raw wastewater. Simulation-based design study showed that the use of the hybrid biofilm system reduces the environmental footprint and aeration requirement of the nutrient removal by about 50% and 19%, respectively. Economic analyses highlighting the benefit of hybrid biofilm over conventional BNR system are illustrated.

Microbial endogenous response to acute inhibitory impact of antibiotics.

Enhanced endogenous respiration was observed as the significant/main response of the aerobic microbial culture under pulse exposure to antibiotics: sulfamethoxazole, tetracycline and erythromycin. Peptone mixture and acetate were selected as organic substrates to compare the effect of complex and simple substrates. Experiments were conducted with microbial cultures acclimated to different sludge ages of 10 and 2 days, to visualize the effect of culture history. Evaluation relied on modeling of oxygen uptake rate profiles, reflecting the effect of all biochemical reactions associated with substrate utilization. Model calibration exhibited significant increase in values of endogenous respiration rate coefficient with all antibiotic doses. Enhancement of endogenous respiration was different with antibiotic type and initial dose. Results showed that both peptone mixture and acetate cultures harbored resistance genes against the tested antibiotics, which suggests that biomass spends cellular maintenance energy for activating the required antibiotic resistance mechanisms to survive, supporting higher endogenous decay rates. ABBREVIATIONS: [Formula: see text]: maximum growth rate for XH (day-1); KS: half saturation constant for growth of XH (mg COD/L); bH: endogenous decay rate for XH (day-1); kh: maximum hydrolysis rate for SH1 (day-1); KX: hydrolysis half saturation constant for SH1(mg COD/L); khx: maximum hydrolysis rate for XS1 (day-1); KXX: hydrolysis half saturation constant for XS1 (mg COD/L); kSTO: maximum storage rate of PHA by XH (day-1); [Formula: see text]: maximum growth rate on PHA for XH (day-1); KSTO: half saturation constant for storage of PHA by XH (mg COD/L); XH1: initial active biomass (mg COD/L).

Dynamic modeling of nutrient removal by a MBR operated at elevated temperatures.

The process performance of a MBR operated on municipal sewage at elevated temperatures was evaluated by dynamic modeling. The enhanced biological phosphorus removal (EBPR) performance varied from 40% to 95% with process temperature ranging from 24 to 38 °C. The respective maximum substrate uptake rate (qPHA) was estimated at 1.5 gCODS/gCODX.day-1 for Glycogen Accumulating Organisms (GAO) and 4.7 gCODS/gCODX.day-1 for Phosphate Accumulating Organisms (PAO) with Arrhenius coefficients (θ) for GAOs and PAOs of 1.06 and 1.04 respectively. With these parameters the effluent PO4 levels of the MBR operated for 450 days could be well described. In addition, the impact of mesophilic conditions and low influent P/VFA levels on GAO proliferation was evaluated under dynamic process conditions. Nitrification process was temporarily impaired at high temperatures around 38 °C. Simulations revealed that the contribution of the anoxic reactor to the total overall denitrification was limited to 40%The contribution of simultaneous nitrification and denitrification (SNdN) process to the denitrification was around 40-50% depending upon dissolved oxygen levels in aerobic and MBR tanks. The large contribution of SNdN was due to gas/liquid mass transfer limitation conditions mediated by high mixed liquor viscosities (20-35 mPa.S) in MBR system. The membrane flux was 43 L/m2/h corresponding to the specific permeability (K) of 413 L/m2/h/bar at 38 °C.

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.

Acute impact of tetracycline on the utilization of acetate by activated sludge sustained under different growth conditions.

The study evaluated acute impact of tetracycline on the biodegradation of acetate by microbial cultures acclimated to different growth conditions. Two fill/draw reactors were operated to obtain acclimated cultures at sludge ages of 2 and 10 days. Acclimated biomass seeding was used in two series of batch experiments. The first run served as control and others were started with tetracycline doses of 100mg/L and 400mg/L. Parallel batch reactors were also operated for oxygen uptake rate (OUR) measurements. Acute impact was evaluated by model calibration of OUR, chemical oxygen demand (COD) and intracellular storage profiles. Exposure to tetracycline did not impair COD removal but induced a shift in acetate utilization toward polyhydroxybutyrate (PHB) storage. This shift was more pronounced for fast growing biomass; it identified itself both in related process kinetics and the modified stoichiometry between the magnitude of acetate directly used for microbial growth and converted to PHB.

Long-term study on the impact of temperature on enhanced biological phosphorus and nitrogen removal in membrane bioreactor.

The study involved experimental observation and performance evaluation of a membrane bioreactor system treating municipal wastewater for nutrient removal for a period 500 days, emphasizing the impact of high temperature on enhanced biological phosphorus removal (EBPR). The MBR system was operated at relatively high temperatures (24-41 °C). During the operational period, the total phosphorus (TP) removal gradually increased from 50% up to 95% while the temperature descended from 41 to 24 °C. At high temperatures, anaerobic volatile fatty acid (VFA) uptake occurred with low phosphorus release implying the competition of glycogen accumulating organisms (GAOs) with polyphosphate accumulating organisms (PAOs). Low dissolved oxygen conditions associated with high wastewater temperatures did not appreciable affected nitrification but enhanced nitrogen removal. Dissolved oxygen levels around 1.0 mgO2/L in membrane tank provided additional denitrification capacity of 6-7 mgN/L by activating simultaneous nitrification and denitrification. As a result, nearly complete removal of nitrogen could be achieved in the MBR system, generating a permeate with no appreciable nitrogen content. The gross membrane flux was 43 LMH corresponding to the specific permeability (K) of 413 LMH/bar at 39 °C in the MBR tank. The specific permeability increased by the factor of 43% at 39 °C compared to that of 25 °C during long-term operation.

Effect of extended aeration on the fate of particulate components in sludge stabilization.

The study investigated the effect of extended aeration on the fate of particulate components of biological sludge in aerobic stabilization. Biological sludge was generated in a fill and draw reactor fed with domestic sewage and sustained at steady state, at a sludge age of 20 days. Particulate fractions of sludge were determined by model evaluation of the corresponding oxygen uptake rate profile. Extended aeration could not produce a mineralized biomass. External aerobic stabilization of the thickened sludge achieved a volatile suspended solids reduction of 68% after 60 days. High reduction could be attributed to the relatively higher rate for the hydrolysis of accumulated particulate metabolic products, compared to conventional activated sludge. Model evaluation based on death-regeneration mechanism indicated a gradually decreasing decay rate for solids; the first phase could be associated with the inactivation/death of the viable biomass and the second controlled by the slower breakdown of particulate metabolic products.

Scientific basis of dissolved organic carbon limitation for landfilling of municipal treatment sludge--is it attainable and justifiable?

This study evaluated the scientific and technical basis of the dissolved organic carbon (DOC) limitation imposed on municipal sludge for landfilling, mainly for assessing the attainability of the implemented numerical level. For this purpose, related conceptual framework was analyzed, covering related sewage characteristics, soluble microbial products generation, and substrate solubilization and leakage due to hydrolysis. Soluble COD footprint was experimentally established for a selected treatment plant, including all the key steps in the sequence of wastewater treatment and sludge handling. Observed results were compared with reported DOCs in other treatment configurations. None of the leakage tests performed or considered in the study could even come close to the prescribed limitation. All observed results reflected 10-20 fold higher DOC levels than the numerical limit of 800 mg/kg (80 mg/L), providing conclusive evidence that the DOC limitation imposed on municipal treatment sludge for landfilling is not attainable, and therefore not justifiable on the basis of currently available technology.

Chronic impact of sulfamethoxazole on acetate utilization kinetics and population dynamics of fast growing microbial culture.

The study evaluated the chronic impact of sulfamethoxazole on metabolic activities of fast growing microbial culture. It focused on changes induced on utilization kinetics of acetate and composition of the microbial community. The experiments involved a fill and draw reactor, fed with acetate and continuous sulfamethoxazole dosing of 50 mg/L. The evaluation relied on model evaluation of the oxygen uptake rate profiles, with parallel assessment of microbial community structure by 454-pyrosequencing. Continuous sulfamethoxazole dosing inflicted a retardation effect on acetate utilization in a way commonly interpreted as competitive inhibition, blocked substrate storage and accelerated endogenous respiration. A fraction of acetate was utilized at a much lower rate with partial biodegradation of sulfamethoxazole. Results of pyrosequencing with a replacement mechanism within a richer more diversified microbial culture, through inactivation of vulnerable fractions in favor of species resistant to antibiotic, which made them capable of surviving and competing even with a slower metabolic response.

Modeling the fate of particulate components in aerobic sludge stabilization--performance limitations.

The study investigated the effect of sludge composition on the limitations of aerobic stabilization. It was designed with the foresight that the stabilization mechanism could only be elucidated if the observed volatile suspended solids reduction were correlated with the fate of particulate components in sludge. Biomass sustained at sludge ages of 2 and 10 days were used in the stabilization reactors. Particulate components were determined by model evaluation of corresponding oxygen uptake rate profiles. Interpretation of the experimental data by modeling, based on death-regeneration mechanism without external substrate, could simulate the fate and evolution of major components in sludge during stabilization. It showed that both microbial decay and hydrolysis of non viable cellular material proceeded at much slower rates as compared with biological systems sustained with substrate feeding. Modeling also indicated that particulate metabolic products generated by sludge acclimated to high sludge age undergo slow biodegradation under prolonged stabilization.

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.

Are standard wastewater treatment plant design methods suitable for any municipal wastewater?

The design and operational parameters of an activated sludge system were analyzed treating the municipal wastewaters in Istanbul. The design methods of ATV131, Metcalf & Eddy together with model simulations were compared with actual plant operational data. The activated sludge model parameters were determined using 3-month dynamic data for the biological nutrient removal plant. The ATV131 method yielded closer sludge production, total oxygen requirement and effluent nitrogen levels to the real plant after adopting correct influent chemical oxygen demand (COD) fractionation. The enhanced biological phosphorus removal (EBPR) could not easily be predicted with ATV131 method due to low volatile fatty acids (VFA) potential.

Pollution profile and biodegradation characteristics of fur-suede processing effluents.

This study investigated the effect of stream segregation on the biodegradation characteristics of wastewaters generated by fur-suede processing. It was conducted on a plant located in an organized industrial district in Turkey. A detailed in-plant analysis of the process profile and the resulting pollution profile in terms of significant parameters indicated the characteristics of a strong wastewater with a maximum total COD of 4285 mg L(-1), despite the excessive wastewater generation of 205 m3 (ton skin)(-1). Respirometric analysis by model calibration yielded slow biodegradation kinetics and showed that around 50% of the particulate organics were utilized at a rate similar to that of endogenous respiration. A similar analysis on the segregated wastewater streams suggested that biodegradation of the plant effluent is controlled largely by the initial washing/pickling operations. The effect of other effluent streams was not significant due to their relatively low contribution to the overall organic load. The respirometric tests showed that the biodegradation kinetics of the joint treatment plant influent of the district were substantially improved and exhibited typical levels reported for tannery wastewater, so that the inhibitory impact was suppressed to a great extent by dilution and mixing with effluents of the other plants. The chemical treatment step in the joint treatment plant removed the majority of the particulate organics so that 80% of the available COD was utilized in the oxygen uptake rate (OUR) test, a ratio quite compatible with the biodegradable COD fractions of tannery wastewater. Consequently, process kinetics and especially the hydrolysis rate appeared to be significantly improved.

Effect of sludge age on simultaneous nitrification and denitrification in membrane bioreactor.

This study evaluated the effect of sludge age on simultaneous nitrification and denitrification in a membrane bioreactor treating black water. A membrane bioreactor with no separate anoxic volume was operated at a sludge age of 20 days under low dissolved oxygen concentration of 0.1-0.2mg/L. Its performance was compared with the period when the sludge age was adjusted to 60 days. Floc size distribution, apparent viscosity, and nitrogen removal differed significantly, together with different biomass concentrations: nitrification was reduced to 40% while denitrification was almost complete. Modelling indicated that both nitrification and denitrification kinetics varied as a function of the sludge age. Calibrated values of half saturation coefficients were reduced when the sludge age was lowered to 20 days. Model simulation confirmed the validity of variable process kinetics for nitrogen removal, specifically set by the selected sludge age.

Is the naphthalene sulfonate H-acid biodegradable in mixed microbial cultures under aerobic conditions?

Synthetically prepared wastewater originating from the H-acid (4-Amino-5-hydroxy-2,7-naphthalene disulfonic acid) manufacturing process was subjected to respirometric analysis for evaluating the level of achievable biodegradation in the presence of this commercially important azo dye precursor. For this purpose, H-acid was mixed with synthetic substrate having the same characteristics as sewage at a concentration and composition being typical for H-acid manufacturing wastewater. Experimental results indicated that H-acid was not biodegradable under activated sludge treatment conditions even after prolonged acclimation periods. The results were also confirmed by model evaluation of oxygen uptake rate profiles. H-acid also did not inhibit the biodegradation of synthetic sewage but accumulated as soluble inert COD in the treated wastewater.

Effect of low dissolved oxygen on simultaneous nitrification and denitrification in a membrane bioreactor treating black water.

Effect of low dissolved oxygen on simultaneous nitrification and denitrification was evaluated in a membrane bioreactor treating black water. A fully aerobic membrane bioreactor was operated at a sludge age of 60 days under three low dissolved oxygen (DO) levels below 0.5mg/L. It sustained effective simultaneous nitrification/denitrification for the entire observation period. Nitrification was incomplete due to adverse effects of a number of factors such as low DO level, SMPs inhibition, alkalinity limitation, etc. DO impact was more significant on denitrification: Nitrate was fully removed at low DO level but the removal was gradually reduced as DO was increased to 0.5mg/L. Nitrogen removal remained optimal within the DO range of 0.15-0.35 mg/L. Experimental results were calibrated and simulated by model evaluation with the same model coefficients. The model defined improved mass transfer with lower affinity coefficients for oxygen and nitrate as compared to conventional activated sludge.

Respirometric evaluation of biodegradation characteristics of dairy wastewater for organic carbon removal.

This study evaluates the biodegradation kinetics of an integrated dairy wastewater, with the main purpose of defining the experimental basis for modelling of the activated sludge process. Besides conventional characterization, the experiments involved detailed chemical oxygen demand (COD) fractionation and assessment of major kinetic and stoichiometric coefficients, by using respirometric methods. A multi-component model based on the endogenous decay concept was used for the kinetic interpretation. The results of conventional analyses and respirometric evaluations together with the assessment of residual components showed that the organic carbon content of the dairy wastewater was mostly soluble and biodegradable. The soluble, slowly biodegradable COD was the major COD fraction, representing around 50% of the total COD. Model calibration of the oxygen uptake rate profiles were consistent and revealed the existence of dual hydrolysis kinetics for soluble and particulate COD components. The hydrolysis rate associated with the main COD component--the soluble, slowly biodegradable COD fraction--was found to be 1.2 d(-1), which is quite low and underlines the role of this COD fraction as the rate-limiting factor for effluent quality. Simulation of process efficiency by the adopted model, calibrated with the experimentally determined parameters, indicated that effective control of the biodegradation of the soluble biodegradable COD components could be done by selection of appropriate values for the sludge age and hydraulic retention time. In this way, the total effluent soluble COD level could be lowered to 30-40 mg L(-1) range, in conformity with effluent limitations.

Respirometric assessment of biodegradation for acrylic fibre-based carpet finishing wastewaters.

The paper evaluates biodegradation characteristics of wastewaters generated from acrylic fibre-based carpet processing and manufacturing. It involves detailed characterisation, respirometric modelling and kinetic description of dyeing and softening wastewater streams and the composite effluent. The wastewaters exhibit different COD content and fractionation. The resulting composite effluent has a total COD of 775 mgL(-1), predominantly soluble and with a biodegradable fraction of 86%. In respirometric studies, the OUR profiles can only be calibrated with a dual hydrolysis model with rates significantly slower compared to domestic sewage and other textile plant effluents. Kinetic information derived from the experiments is applied for the conceptual evaluation of the treatability of the composite wastewater using two different continuous-flow activated sludge configurations.

Effect of photochemical pre-treatment on COD fractionation of a non-ionic textile surfactant.

The work presented in this paper is focused on the effect of photochemical (H2O2/UV-C) pretreatment on COD fractionation and degradation kinetics of a non-ionic textile surfactant. In the first part of the study, the COD of non-ionic surfactant was adjusted to 1000 mg/L in order to simulate real effluent originating from the textile preparation stage featuring desizing, scouring, washing and rinsing operations. The surfactant was subjected to H2O2/UV-C pretreatment for up to 120 min at a dose of 30 mM (980 mg/L) H2O2. The biodegradability studies for untreated and photochemically treated samples were evaluated on the basis of modeling of oxygen uptake rate (OUR) profiles. Modelling of OUR profiles conducted for untreated sample showed that single complex substrate was subjected to enzymatic breakdown and disintegrated into one readily and two types of slowly biodegradable substrates. After modelling the biodegradation of photochemically pretreated sample, the readily biodegradable COD fraction was reduced, on the other hand, more slowly biodegradable organics were generated. A higher disintegration rate was obtained for chemically pretreated samples. However, other kinetic constants of growth and hydrolysis processes were not affected considerably.

Critical appraisal of respirometric methods for metal inhibition on activated sludge.

This paper evaluates the merit of oxygen uptake rate measurements for the assessment of metal inhibition on activated sludge. For this purpose, experiments are conducted to calculate EC50 levels of nickel and hexavalent chromium using the ISO 8192 procedure, yielding results that are highly variable and difficult to correlate, depending on the type of substrate and the initial food to microorganism ratio. Similar experiments based on continuous respirometric measurements to give the entire oxygen uptake rate profile provide a much better insight on the impact of inhibition on different biochemical processes taking place in the reactor. The results indicate that percent reduction of the amount of dissolved oxygen utilized after an appropriate reaction time is a much better index for the assessment of the inhibitory effects.