Occurrence of aerobic denitrifying bacteria in integrated fixed film activated sludge system.

Denitrification can be enhanced in the Integrated Fixed Film Activated System (IFAS) system by integrating media into the anoxic or aerobic zone. The simultaneous nitrification and denitrification (SND) in the biofilm layers has been reported in the aerobic zone of the IFAS system. In this study, two IFAS systems with Bioweb® media installed in the anoxic or aerobic reactor were operated in parallel to evaluate both anoxic denitrification or aerobic SND in the biofilm layers enhanced by fixed film media at three different nitrite and nitrate recirculation (NR) ratios of 75%, 100%, and 125%. The results revealed that both IFAS systems achieved the same organic and nitrogen removal efficiencies without statistically significant difference. The NR ratio of 125% enhanced slightly the denitrification in the anoxic zones of both systems. The media increased the anoxic denitrification at the NR ratio of 100%. The SND in the biofilm was found insignificant in both systems. It was evident that suspended-growth microorganisms stored substrates internally in the cells under anoxic conditions due to insufficient retention time. The aerobic denitrifiers including Chryseobacterium sp., Klebsiella pneumonia, and Pseudomonas aeruginosa were abundant in both IFAS systems providing aerobic denitrification with storage products as carbon sources. In summary, the denitrification in the anoxic zone and SND in the biofilm of the aerobic zone, both were enhanced by the fixed film media, did not contribute significantly to the IFAS system for the biological nitrogen removal because of microbial storage products and aerobic denitrification of several aerobic denitrifiers.

Effects of cations on biofilm formation and characteristics in integrated fixed film activated sludge process at different carbon and nitrogen loadings.

Both divalent cations including calcium and magnesium play important roles for microbial aggregates in binding to negatively charged functional groups on bacterial surfaces, in extracellular polymeric substances (EPS), and on inorganic materials in flocs and biofilms. Monovalent cations such as sodium and potassium deteriorate the floc structure and physical properties. The Integrated Fixed Activated Sludge (IFAS) process employs fixed film media in the aerobic zone; therefore, both monovalent and divalent cations are involved in the process performances. In this study, the effects of cations indicated as the monovalent to divalent cations (M/D) ratio on the biofilm formation and characteristics, and on the IFAS performances for carbon and ammonium removals were evaluated. The experiments were conducted in three IFAS systems feeding with the same wastewater but different M/D ratios and two carbon and nitrogen loadings. The findings revealed that high monovalent with low divalent cations at the M/D ratios higher than 2.0 produced excessive polysaccharides in EPS resulting in high viscosity of activated sludge flocs causing viscous bulking with high SVI values, decreasing the biofilm formation, and increasing the biofilm sloughing. Increasing of both monovalent and carbon loading increased more polysaccharides in the EPS leading to the failures of IFAS system. Nitrification failed at higher M/D ratios because of less nitrifiers in flocs and biofilm. The M/D ratio less than 2.0 is suggested to minimize the excessive EPS production in the IFAS system, especially at high organic loading.

Respirometric activities of unacclimatized Enterobacter aerogenes and mixed culture bacteria in sequencing batch reactor systems in response to acrylamide and its biodegradation products.

The acute effects of acrylamide and its biodegradation products on the respiration activities of microbes during wastewater treatment are not well understood. Herein, unacclimatized mixed culture bacteria and Enterobacter aerogenes from two aerobic treatment systems, Activated Sludge (AS) and Integrated Fixed Film Activated Sludge (IFAS) both of which were sequencing batch reactors (SBR), were studied for their response to acrylamide. Respiration activities and biodegradation rates were determined by both the OxiTop respirometer and batch studies. The experimental results revealed that E. aerogenes in the AS system quickly removed both acrylamide and acrylic acid without the need of an acclimation period, but required two hours for removing acrylic acid in the IFAS system. The mixed culture bacteria in both AS and IFAS systems required 2 hours to acclimatize with acrylamide and 1 hour for acrylic acid, respectively. Acrylic acid was initially polymerized to produce acrylic acid polymer or reacted with ammonia to form acrylamide, resulting in the reduced acrylamide biodegradation rate. Both E. aerogenes and mixed culture bacteria from the AS systems could simultaneously biodegrade acrylamide and acrylic acid whereas only acrylamide was biodegraded by both cultures in the IFAS systems due to the limitation of acrylic acid diffusion. The results also indicated that ammonia inhibited the acrylamide biodegradation by both E. aerogenes and mixed culture bacteria from the AS systems. The unacclimatized E. aerogenes and mixed culture bacteria from the AS systems showed superior performances compared to the ones from the IFAS systems.

Evaluation of reusing alum sludge for the coagulation of industrial wastewater containing mixed anionic surfactants.

A coagulation-flocculation process is typically employed to treat the industrial wastewater generated by the consumer products industry manufacturing detergents, soaps, and others. The expenditure of chemicals including coagulants and chemicals for pH adjustment is costly for treating this wastewater. The objective of this study was to evaluate the feasibility of reusing the aluminum sulfate (alum) sludge as a coagulant or as a coagulation aid so that the fresh alum dosage can be minimized or the removal efficiency can be enhanced. The experiments were conducted in a jar-test apparatus simulating the coagulation-flocculation process for simultaneous removals of organic matters, anionic surfactants, suspended solids, and turbidity. At the optimum initial pH value of 10 and the fresh alum concentration of 400 mg/L, the total suspended solids (TSS), total chemical oxygen demand (TCOD), total anionic surfactants, and turbidity removal efficiencies were 71.5%, 76.4%, 95.4%, and 98.2%, respectively. The addition of alum sludge as a coagulant alone without any fresh alum addition could significantly remove the turbidity, TCOD, and anionic surfactants. The TSS was left in the supernatants after the settling period, but would subsequently be removed by adding the fresh alum. The TSS, TCOD, and turbidity removal efficiencies were also enhanced when both the alum sludge and the fresh alum were employed. The TCOD removal efficiency over 80% has been accomplished, which has never fulfilled by using the fresh alum alone. It is concluded that the alum sludge could be reused for the treatment of industrial wastewater generated by the consumer products industry.

Evaluation of waste activated sludge as a coagulant aid for the treatment of industrial wastewater containing mixed surfactants.

Wastewater generated by the industry manufacturing detergents and various kinds of consumer products normally contains very high contents of mixed surfactants, organic matters expressed as chemical oxygen demand (COD), and phosphates that must be treated prior to discharge to the aquatic environment. In this study, jar-test experiments were conducted to evaluate the waste activated sludge (WAS) as a coagulation aid in the coagulation-flocculation process with ferric chloride or aluminum sulfate as a coagulant for the treatment of wastewater collected from the aforementioned industry. The WAS was selected because of its adsorption capability of anionic surfactants and its availability from the wastage stream of biological wastewater treatment process. The effective dosages of both coagulants with and without the WAS additions were determined in this study. Without the WAS addition, the concentrations of 800 mg/L aluminum sulfate at the optimum pH value of 8 and 2208 mg/L ferric chloride at the optimum pH value of 12 were the optimum chemical dosages. It appears that aluminum sulfate was more effective than ferric chloride based on the chemical dosage and removal efficiency. The turbidity, suspended particles, anionic surfactants, COD, and phosphates removal efficiencies of aluminum sulfate and ferric chloride under the optimum dosage were 95.6, 88.2, 78.4, 73.5, 47.3% and 98.8, 92.0, 72.7, 67.5, 53.1%, respectively. The addition of 200 mg/L WAS was sufficient to reduce the optimum dosages of both chemicals by 200 mg/L. The cationic surfactant existing in the wastewater worked as a flocculating agent leading to the flocculation of waste activated sludge resulting in the enmeshment of the suspended particles and colloids on which the COD, anionic surfactants, and phosphates were adsorbed. However, the substances removal efficiencies of ferric chloride and aluminum sulfate were slightly enhanced and reduced, respectively. It is possibly explained that the settling time is insufficient to settle the aluminum hydroxide floc when it is compared to the ferric hydroxide floc because the iron floc is normally heavier than the alum floc.

Stability and capacity enhancements of activated sludge process by IFAS technology.

This research was conducted to evaluate the capacity and stability of the Activated Sludge (AS) process retrofitted to the Integrated Fixed Film Activated Sludge (IFAS) process. Hydraulic retention time (HRT) and solids retention time (SRT) were used as independent variables in this investigation. The IFAS and AS processes were operated in parallel for carbon removal and nitrification at 6, 8, and 10 hours HRTs at which 4, 6, and 8 days SRTs were maintained. The AS system failed to attain steady state conditions at 10 hours HRT with 4 days SRT, 8 hours HRT with 4 and 6 days SRTs, and 6 hours HRT with 4, 6, and 8 days SRTs, whereas the IFAS system was stabilized until the SRT and HRT were at 4 days and 6 hours, respectively. Excessive filamentous microorganisms were observed in the IFAS and AS systems as the results of completely-mixed condition and high readily biodegradable organic content in the wastewater. The filamentous bulking was apparently the cause of system failure and the reduction of nitrification in the AS system. As the HRTs and SRTs were decreased or the system loadings increased, it was clearly demonstrated that the IFAS system was higher in capacity and stability than the AS system. The attached biomass in the IFAS system suppressed the growth of filamentous microorganisms by reducing the amount of substrates in contact with the filamentous microorganisms providing the system stability. Nitrification was completed in the IFAS system and could be independent of the suspended SRT. Both AS and IFAS systems could provide the same performance for COD removal at the experimental conditions.

Effects of dissolved oxygen on biological nitrogen removal in integrated fixed film activated sludge (IFAS) wastewater treatment process.

The objective of this research was to determine the effects of dissolved oxygen on the biological nitrogen removal in the Integrated Fixed Film Activated Sludge (IFAS) and Modified Ludzack-Ettinger (MLE) systems. The carbonaceous and nitrogen removals were investigated at the COD/Nitrogen (C/N) ratios of 4, 6, and 10, and the dissolved oxygen (DO) concentrations of 2, 4, and 6 mg/L. The experimental results indicate that the C/N ratios of 4, 6, and 10 and the DO concentrations of 2, 4, and 6 affected insignificantly on the chemical oxygen demand (COD) removal, but significantly on the nitrogen removal as the consequences of different nitrification and denitrifcation rates in both systems. The COD removal was nearly completed throughout this study because glucose was used as a primary carbon source in the wastewater and both systems were operated at high SRT relative to the minimum SRT requirement for COD removal. The experimental conditions used in this study apparently led to nitrite accumulation in both IFAS and MLE systems. It is suggested that there is no benefit of installing media in the IFAS system at the C/N ratio of 10 because the system was underloaded with the nitrogen. The lower DO concentration, the greater denitrification in the anoxic zone was achieved because nitrite nitrogen was used as an electron acceptor. At the C/N ratios of 4 and 6, the IFAS system was higher in capacity for nitrification as a result of attached biomass on the support media in the aerobic zone. The DO concentration of 6 mg/L is required to maximize the nitrification rates in the systems under these experimental conditions resulting in greater oxidized nitrogen for denitrification in the anoxic zones. The denitrification in the aerobic zone of the IFAS system is not evaluated due to unavailability of nitrite information. The optimal DO concentrations for biological nitrogen removal in the IFAS system at the C/N ratios of 4, 6, and 10 in this study were 6, 6, and 2 mg/L, respectively.