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PubMed2006

Aeration control for simultaneous nitrification-denitrification in a biological aerated filter using internal model approach.

Experience has shown that simultaneous nitrification/denitrification in a biological aerated filter is possible. However these systems react very sensitively to the aeration control strategies applied. Poorly adapted control strategies induce a strong decrease in treatment efficiency. A new control strategy for simultaneous N/DN is developed. The strategy proposed makes use of ammonia measurements and the inlet and outlet: a Feedback/Feedforward block. Passing by a calculation of the load to be eliminated, an estimation of the air flow velocity to be applied is carried out dynamically. A retroactive loop corrects this prediction in order to reach exactly the desired set point. This control approach has been implemented and tested at pilot plant scale for a period of 18 months. The pilot plant consists of two coupled BAF cells, reflecting closely industrial scale situations. Comparative studies reveal clearly the improved performance of the developed FF/FB control strategy compared to classical controllers. The benefits include 5% increase in nitrogen removal performance and a reduction of 15 to 20% in air requirement, offering a rapid return of investment costs.

Algorithms↗
PubMedDate not supplied

Linking nitrifying biofilm structure and function through fluorescent in situ hybridization and evaluation of nitrification capacity.

Fluorescent in situ hybridization (FISH) was used to quantify the ammonia-oxidizing populations within intact biofilm samples collected from a full-scale nitrifying trickling filter (NTF). Ammonia, nitrite, and nitrate concentrations were measured for aqueous samples taken in conjunction with biofilm samples at multiple filter depths. The ammonia removal capability of collected biofilms was evaluated by transferring the biofilms to laboratory batch reactors. Nitrate plus nitrite generation rates were calculated for the full-scale NTF and for the bench-scale reactors. Correlation coefficients for individual sampling events, calculated by simple linear regression of FISH signal area and nitrate plus nitrite generation rates for the full-scale NTF, ranged from -0.882 to 0.984. Correlation coefficients obtained for FISH signal area and nitrate plus nitrite generation rates for the bench-scale reactors ranged from 0.853 to 0.994 when using probe Nso190 and from 0.919 to 0.986 when using probe Neu23a. Occasional differences between the number of ammonia-oxidizing bacteria quantified by the probe Nso190 versus the NEU23a probe with depth suggest that genera other than Nitrosomonas are present in the NTF.

Ammonia↗
PubMed2001

Real-time control strategies for predenitrification-nitrification activated sludge plants biodegradation control.

This paper presents the real-time control strategies developed to regulate both the ammonia and nitrate concentration in the effluent of the new Vitoria WWTP (Spain). Nitrate control aims at the optimal use of the denitrification potential at any moment. For this purpose, the proposed control algorithm continuously adapts the internal recycle flow in order to maintain a desired nitrate set-point in the anoxic zone. Ammonia control aims at maintaining the required average concentration of ammonia in the effluent by manipulating the Dissolved Oxygen (DO) set-point. The control strategies have been based on a hierarchical structure where a high-level or supervisory control selects the set-point of the low-level or conventional controllers. The design of the controllers was carried out using the Quantitative Feedback Theory QFT for the design of robust control systems. Moving average values of some variables have been introduced in order to eliminate the perturbations associated with the daily 24-hour profiles. The controllers have been verified using long-time dynamic simulations based on a mathematical model previously calibrated in pilot plant. Influent load and temperature used in the simulations correspond to the real values measured in the full-scale WWTP during 12 months. The results obtained in the simulations show the good performance and stability of the control strategies independently from external disturbances. A short-time experimental verification of the controllers in pilot plant with real wastewater is also presented.

Ammonia↗
PubMed2001

Nitrification in sequencing biofilm batch reactors: lessons from molecular approaches.

The nitrifying microbial diversity and population structure of a sequencing biofilm batch reactor receiving sewage with high ammonia and salt concentrations (SBBR 1) was analyzed by the full-cycle rRNA approach. The diversity of ammonia-oxidizers in this reactor was additionally investigated using comparative sequence analysis of a gene fragment of the ammonia monooxygenase (amoA), which represents a key enzyme of all ammonia-oxidizers. Despite the "extreme" conditions in the reactor, a surprisingly high diversity of ammonia- and nitrite-oxidizers was observed to occur within the biofilm. In addition, molecular evidence for the existence of novel ammonia-oxidizers is presented. Quantification of ammonia- and nitrite-oxidizers in the biofilm by Fluorescent In situ Hybridization (FISH) and digital image analysis revealed that ammonia-oxidizers occurred in higher cell numbers and occupied a considerably larger share of the total biovolume than nitrite-oxidizing bacteria. In addition, ammonia oxidation rates per cell were calculated for different WWTPs following the quantification of ammonia-oxidizers by competitive PCR of an amoA gene fragment. The morphology of nitrite-oxidizing, unculturable Nitrospira-like bacteria was studied using FISH, confocal laser scanning microscopy (CLSM) and three-dimensional visualization. Thereby, a complex network of microchannels and cavities was detected within microcolonies of Nitrospira-like bacteria. Microautoradiography combined with FISH was applied to investigate the ability of these organisms to use CO2 as carbon source and to take up other organic substrates under varying conditions. Implications of the obtained results for fundamental understanding of the microbial ecology of nitrifiers as well as for future improvement of nutrient removal in wastewater treatment plants (WWTPs) are discussed.

Ammonia↗
PubMed2002

Simulation of a nitrification control concept considering influent ammonium load.

Buchenhofen wastewater treatment plant of Wupperverband (650,000 p.e.) is currently being expanded for targeted nitrogen elimination. In view of the limited space available for extension, an optimized control concept is to be used in order to minimize the number of additional tanks required. This concept was investigated by dynamic simulation based on Activated Sludge Model No. 1. The investigations included a pure feedback control configuration and a configuration combining feedback und feedforward control, considering the influent ammonium load, for aeration. The results show that combined feedforward/feedback control has significant advantages over pure feedback control. In particular, this configuration allows a reduction in the effluent NH4-N peaks, which is especially important because of the low NH4-N limit of 5 mg NH4-N/L in a grab sample.

Computer Simulation↗
PubMed2003

Biological nitrification and denitrification of opto-electronic industrial wastewater.

Development and application of biological nutrient removal processes accelerated significantly over the past decade due to more stringent nutrients (nitrogen and phosphorus) discharge limits being imposed on wastewater treatment plants. The opto-electronic industry has developed very fast over the past decade in the world. The wastewater often contains a significant quantity of organic nitrogen compounds and has a ratio of over 95% in organic nitrogen (Org-N) to total nitrogen (T-N). In this study, a 2-stage Anoxic/Aerobic pre-denitrification process was established and the efficiency of wastewater treatment was evaluated. Wastewater from an actual LCD-plant was obtained as the sample for looking into the feasibility of opto-electronic industrial wastewater treatment. Hydraulic retention time (HRT) and mixed liquor recycle rate (MLR) were controlled independently to distinguish between the effects of these two factors. Under suitable HRT and mixed liquor recycle ratio, effluents of NH4-N, NOx-N and COD can fall below 20 mg/l, 30 mg/l and 80 mg/l.

Bioreactors↗
PubMed2004

Nitrogen removal from sludge reject water by a two-stage oxygen-limited autotrophic nitrification denitrification process.

Nitrogen removal from sludge reject water was obtained by oxygen-limited partial nitritation resulting in nitrite accumulation in a first stage, followed by autotrophic denitrification of nitrite with ammonium as electron donor (similar to anaerobic ammonium oxidation) in a second stage. Two membrane-assisted bioreactors (MBRs) were used in series to operate with high sludge ages and subsequent high volumetric loading rates, achieving 1.45 kg N m(-3) day(-1) for the partial nitritation MBR and 1.1 kg N m(-3) day(-1) for the anaerobic ammonium oxidation MBR. Biomass retention in the nitritation stage ensured flexibility towards loading rate and operating temperature. Nitrite oxidisers were out-competed at low oxygen and high free ammonia concentration. Biomass retention in the second MBR prevented wash-out of the slowly growing bacteria. Nitrite and ammonium were converted to dinitrogen gas in a reaction ratio of 1.05, thereby maintaining nitrite limitation to assure process stability. The anoxic consortium catalysing the autotrophic denitrification process consisted of Nitrosomonas-like aerobic ammonium oxidizers and anaerobic ammonium oxidizing bacteria closely related to Kuenenia stuttgartiensis. The overall removal efficiency of the combined process was 82% of the incoming ammonium according to a total nitrogen removal rate of 0.55 kg N m(-3) day(-1), without adding extra carbon source.

Bacteria, Anaerobic↗
PubMed2004

The stability of nitrite nitrification with strong nitrogenous wastewater: effects of organic concentration and microbial diversity.

A stable achievement of nitritation with strong nitrogenous wastewaters is considered as a difficult task in practice, probably due to the fate of interaction between dominating heterotrophs and nitrifier species. An experimental study was carried out to examine the organic effects in lab-scale biofilm nitritation reactors. The control unit without organic addition showed a stable nitritation performance for more than 220 days of operating period. The nitritation activity gradually failed at the reactors with an organic addition, but the nitritation activity eventually recovered with a prolonged aeration. It was not possible to explain the nitritation recovery with neither free ammonia inhibition concept nor DO competition hypothesis in these cases. The results suggest that the nitritation with organic requires a long start-up period for acclimation. In addition, the results of quinone profile analysis were in agreement with nitritation activity in reactors. The diversity of microbial community in the nitritation reactors could be described by the quinone profiles.

Biofilms↗
PubMed2004

Alternating shortcut nitrification-denitrification for nitrogen removal from soybean wastewater by SBR with real-time control.

A novel treating technology for nitrogen removal from soybean wastewater was studied. The process for nitrogen removal was achieved by alternating aeration and mixing, combined with real-time control strategies. Results showed that the COD and total nitrogen removal rates are more than 90% and 92% at COD and total nitrogen loads of 1.0 - 1.2 kg COD/(kgMLSS x d) and 0.20 - 0.27 kg TN/(kgMLSS x d), respectively. In addition, it could improve sludge settling property. SVI value is less than 70 g/ml during the whole cycles. The method not only may be adapted to treat soybean wastewater with high nitrogen, but also may be applied to treat other high nitrogen wastewater.

Automation↗
PubMed2006

[Effects of hydraulic retention time (HRT) on nitrification performance and microbial community of conventional activated sludge (CAS)].

A conventional activated sludge system was used to treat the ammonium-bearing inorganic wastewater for 260 days under decreased HRTs. When treating 500 mg x L(-1) NH4+ -N wastewater, over 98% ammonia removal could be obtained at HRT > or =20 h. Sharp washout of biomass occurred when HRT was further decreased, resulting in the accumulation of ammonium and nitrite. Changes in the community structure were monitored by microbial quinone and conventional analytical methods. Quinone profiles indicated that ammonia-oxidizing bacteria (AOB) in beta-Protevbacteria and Nitrobacteria in alpha-Proteobacteria were the predominant species to oxidize ammonia and nitrite, respectively. The number of AOB decreased with the reduction of biomass in bioreactor, while that of nitrite-oxidizing bacteria (NOB) changed little and fluctuated at 10(5) CFU x L(-1)

Biodiversity↗