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.

Two-phase anaerobic digestion of the organic fraction of municipal solid waste: estimation of methane production.

Energy generation from methane (CH(4)) is one of the primary targets of the anaerobic digestion process. Consequently, the focus of this study was to investigate the effect on CH(4) production of total solids (TS) loading (measured as % TS) and hydraulic residence time (HRT) during the treatment of the organic fraction of municipal solid waste (OFMSW). Laboratory-scale, two-phase anaerobic digestion systems were employed with each system consisting of an acidogenic reactor and a methanogenic reactor linked in series. The group A runs in the experiment explored the effect on digester performance of four variations in methanogenic HRT (15, 20, 25 and 30 days) at three different feed TS concentrations (8, 12 and 15%). The group B runs compared the actual methane yield (0.14 to 0.45 L g VSfeed−1)) to that predicted by the Chen-Hashimoto model. Results from the group A runs indicated that acidogenesis improved with an increase in % TS and a decrease in HRT; while, methanogenesis behaved inversely, achieving higher yields at the lower % TS and longer HRT values. In comparison with the group B runs, the Chen-Hashimoto model under-predicted (by an average of 16.5 ± 6.6%) the CH(4) yield obtained from the digestion of OFMSW.

Effect of mixture ratio, solids concentration and hydraulic retention time on the anaerobic digestion of the organic fraction of municipal solid waste.

This paper describes how the degradation of the organic fraction of municipal solid waste (OFMSW) is affected through codigestion with varying amounts of return activated sludge (RAS). Solid waste that had its inorganic fraction selectively removed was mixed with RAS in ratios of 100% OFMSW, 50% OFMSW/50% RAS, and 25% OFMSW/75% RAS. The total solids (TS) concentration was held at 8% and three anaerobic digester systems treating the mixtures were held (for the first run) at a total hydraulic retention time (HRT) of 28 days. Increasing amounts of RAS did not however improve the mixture's digestability, as indicated by little change and/or a drop in the main performance indices [including percentage volatile solids (VS) removal and specific gas production]. The optimum ratio in this research therefore appeared to be 100% OFMSW with an associated 85.1 ± 0.6% VS removal and 0.72 ± 0.01 L total gas g(- 1) VS. In the second run, the effect of increasing percentage of TS (8, 12% and 15%) at a system HRT of 28 days was observed to yield no improvement in the main performance indices (i.e. percentage VS removal and specific gas production). Finally, during the third run, variations in the total system HRT were investigated at an 8% TS, again using 100% OFMSW. Of the HRTs explored (23, 28 and 33 days), the longest HRT yielded the best performance overall, particularly in terms of specific gas production (0.77 ± 0.01 L total gas g(-1) VS).

Kinetic rates and mass balance of COD, TKN, and TP using SBR treating domestic and industrial wastewater.

OBJECTIVE: To assess the performance of SBR to treat three different types of wastewater from domestic, hospital, slaughterhouse and investigate the kinetic rates of active biomass. Mass balance calculation of COD, TKN and TP was further performed to explain the mechanisms of the biological nutrient removals processed in the SBR system. The measured kinetic rates were in turn used to evaluate the process performances under different types of wastewater. MATERIAL AND METHOD: Experimental research involving 3 similar SBR lab-scales were installed and operated at the Sanitary Engineering Laboratory. The reactors were seeded with sludge biomass obtained from the Sri-Phraya Domestic Wastewater Treatment Plant in Bangkok. The slaughterhouse, hospital and domestic wastewaters were treated by SBR system for biological organic carbon (COD), nitrogen (TKN) and phosphorus removals. Biological methods for kinetic rates evaluation were conducted in five replicated batch tests. RESULTS: The removal efficiencies of COD and TKN were greater than 90% for all three types of wastewater while the biological phosphorus removal for domestic and hospital wastewaters were less than 60% and phosphorus removal for slaughterhouse exceeded 95%. The kinetic rates of nitrification and denitrification of hospital wastewater was lower than those the domestic and slaughterhouse wastewaters. Phosphorus release and uptake rates of slaughterhouse wastewater were high but domestic and hospital wastewaters were very low. CONCLUSION: The result of system removal efficiency and batch test for kinetic rates confirmed that the domestic and hospital wastewaters were in deficiency of organic carbon with respect to its ability to support successful biological phosphorus removal.

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.