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).

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.

The effect of temperature and sludge age on COD removal and nitrification in a moving bed sequencing batch biofilm reactor.

This study investigates the effect of temperature and the sludge age on the performance of a moving bed sequencing batch biofilm reactor (MBSBBR) for COD removal and nitrification. The experiments are conducted in a lab-scale MBSBBR operated at three different temperatures (20, 15 and 10 degrees C) with a synthetic feed simulating domestic sewage characteristics. Evaluation of the results revealed that removal of organic matter at high rates and with efficiencies over 90% was secured at all operation conditions applied. The nitrification rate was significantly influenced by changes in temperature but complete nitrification occurred at each temperature. The nitrification rates observed at 20 and 15 degrees C were very close (0.241 mg NO(x)-N/m2d, 0.252 mg NO(x)-N/m2 d, respectively), but at 10 degrees C, it decreased to 0.178 mg NO(x)-N/m2d. On the other hand, the biomass concentration and sludge age increased while the VSS/TSS ratios that can be accepted as an indicator of active biomass fraction decreased with time. It is considered that, increasing biofilm thickness and diffusion limitation affected the treatment efficiency, especially nitrification rate, negatively.

Biological treatability of raw and ozonated synthetic penicillin formulation effluent.

Chemical pre-treatment of synthetic Procaine Penicillin G (PPG) effluent with ozone (applied dose = 1440 mg/h; treatment duration = 60 min) at pH = 7 was investigated. Successive biological treatability studies were performed with raw, ozonated penicillin formulation effluent and synthetic readily biodegradable substrate as simulated domestic wastewater. The PPG effluent additions were adjusted to constitute approximately 30% of the total COD in the reactor. Ozonation of PPG effluent resulted in practically complete removal of the parent pollutant accompanied by 40% COD abatement. Speaking for the raw PPG effluent, prolonged acclimation periods were necessary to obtain significant COD removal efficiencies. Batch activated sludge treatment experiments and respirometric studies have demonstrated that the selection of true retention time is extremely crucial for having high amount of slowly hydrolysable substrate or complex wastewater, like pharmaceutical effluent. The effect of ozonation time on biological treatability performance of PPG has been evaluated in the study. Pre-ozonation of PPG effluent did not improve its ultimate biodegradability.

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.

Characterization and COD fractionation of domestic wastewaters.

Results of a comprehensive study are reported for wastewater characterization in relation to modelling and design of biological nutrient removal systems for the Metropolitan Area of Istanbul. Domestic sewage quality was experimentally assessed in terms of major polluting parameters. Size distribution and calculation of significant ratios such as BOD5:COD and COD:N were used to evaluate the merit of candidate physical, chemical and biological treatment alternatives. COD fractionation was effected to assess biological treatability and to yield the necessary process components to the recent modelling approaches.

Alternatives for upgrading the Wilderness Wastewater Treatment Plant for biological nutrient removal.

The Wilderness Wastewater Treatment Plant (WWTP) located in Orange County, Virginia is a four concentric ring oxidation ditch activated sludge system with a rated capacity of 1,935 m3/day. The three outer rings are used for wastewater treatment and the inner ring is used as an aerobic digester. The flow capacity has been increased from 1,935 to 3,760 m3/d, however, the desired design capacity has since been increased to 3,870 m3/d, and there are plans to eventually expand to approximately 4,840 m3/d with improved nitrogen removal. The design goal for the planned upgrade is to discharge an effluent that contains less than 10 mg/l total nitrogen (TN) at all times, with an annual average of 8 mg/l or less. In this study, the pre-upgrade performance of the Wilderness Wastewater Treatment Plant was evaluated and several modifications were recommended for the incorporation of biological nutrient removal (BNR).

Modification and expansion of a pure oxygen WWTP for biological nutrient removal (BNR).

A pure oxygen activated sludge system was converted to a VIP configuration BNR (biological nutrient removal) system wherein three of the five pure oxygen sections were retained, and performance was compared to that of a side-by-side air aeration MUCT (modified UCT) system. Because the pure oxygen BNR system could not obtain good nitrification, its treatment capacity had to be downgraded from 113,550 m3/d to a flow of only 60,000 m3/d. At the lesser flow, it was determined that adequate nitrification and improved denitrification could be accomplished in the pure oxygen system by continuously seeding it with 100% of the WAS from the MUCT system. Fortunately, while the capacity of the pure oxygen system had to be downgraded, it was determined that the capacity of the MUCT system was substantially greater than its design flow, and the combined system is capable of treating the entire design flow. However, this requires increasing the operating sludge age of the MUCT system. The pure oxygen BNR system performed better phosphorus removal than the MUCT system, both before and after seeding with the MUCT WAS. Apparently this was because the MUCT system was operated at a substantially higher sludge age than the pure oxygen system. However, both systems have consistently discharged effluent phosphorus concentrations of less than 2.0 mg/L TP, which is the Chesapeake Bay standard. Even with improved nitrification and denitrification in the pure oxygen BNR system, neither it nor the MUCT system have proven to be capable of meeting the Virginia Chesapeake Bay goal of 10 mg/L total nitrogen in the effluent.

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 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.

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.

The effects of diquat dibromide on biological wastewater treatment plants.

The objective of the study was to investigate the fate and effects of diquat dibromide which is the active ingredient in formulations used to control the growth of roots into sewers when applied as Razorooter and mixed with raw sewage, settled sewage, and activated sludge, and when introduced into activated sludge wastewater treatment systems. Both fully aerobic and biological nutrient removal (BNR) activated sludge systems were used for experimental purpose, and both continuous flow and batch reactors were used. The sorption of diquat by both raw sewage particles and activated sludge suspended solids was determined. Diquat dibromide concentrations ranged from 0.93 to 12.6 mg/L in the influent flow. Both the fully aerobic and two full biological nutrient removal systems were fed municipal sewage spiked with diquat dibromide, and operated at a mixed liquor temperature of 10 degrees C and an MCRT of 10 days. One of the BNR systems was a control system. The results showed that only about 20% of the diquat in raw sewage flow was removed by adsorptions to the sewage solids, but 80% or more of the diquat was removed in activated sludge systems. When the influent diquat dibromide concentration was approximately 1mg/L, over 99% of the diquat dibromide was removed by the activated sludge process. Some of the removal was believed to be by biodegradation. The diquat dibromide used in this study had no observable detrimental effects on any of the biological processes of the continuous flow fully aerobic and BNR activated systems.

Effects of pH and substrate on the competition between glycogen and phosphorus accumulating organisms.

This article evaluates effects of pH and substrate on the competition between glycogen (GAOs) and phosphorus accumulating organisms (PAOs). A sequencing batch reactor system was operated for enhanced biological phosphorus removal (EBPR) with acetate as the sole carbon source and acetate added domestic wastewater at different influent acetate/phosphate ratios. Some batch tests were performed using acetate added domestic wastewater at different influent acetate, phosphate ratios, with different initial pH values of acetate and domestic wastewater mixture. The resulting experimental data supported the presence of GAOs for all tested HAC P ratios, especially under P limiting conditions for acetate as sole carbon source. Strong evidence is observed that acetate added domestic wastewater system had higher PAOs fraction than acetate system as sole source carbon, with using model components, namely substrate uptake, glycogen utilization and P release.