Temperature effects on biological nutrient removal system with weak municipal wastewater

The wastewater characteristics of low organic strength coupled with low temperature would be considerable variables for design and operation of biological nutrient removal (BNR) systems. But temperature studies have mostly been focused on individual process with biological phosphorus removal, nitrification and denitrification, respectively. Overall temperature effects on BNR system may not be fully represented by sum of results of separated studies on biological nutrient removal steps. The operating result of a retrofitted full scale unit along with laboratory-scale BNR unit indicated 90% of nitrification was possible at temperature as low as 8°C. However, the denitrification was turned out to be a key step to regulate the overall nutrient removal efficiencies. When the operating temperature dropped down, a rapid decrease of phosphorus removal efficiencies was observed by the nitrate in return sludge. If nitrification was not well developed, phosphorus removal returned to the normal efficiency even at low temperature of 5°C. The phosphorus removal mechanism was not influenced at this low temperature.     

Re-use of winery wastewaters for biological nutrient removal.

The aim of this study was to evaluate the feasibility of the re-use of the winery wastewater to enhance the biological nutrient removal (BNR) process. In batch experiments it was observed that the addition of winery wastewater mainly enhanced the nitrogen removal process because of the high denitrification potential (DNP), of about 130 mg N/g COD, of the contained substrates. This value is very similar to that obtained by using pure organic substrates such as acetate. The addition of winery wastewater did not significantly affect either phosphorus or COD removal processes. Based on the experimental results obtained, the optimum dosage to remove each mg of N-NO3 was determined, being a value of 6.7 mg COD/mg N-NO3. Because of the good properties of the winery wastewater to enhance the nitrogen removal, the viability of its continuous addition in an activated sludge pilot-scale plant for BNR was studied. Dosing the winery wastewater to the pilot plant a significant increase in the nitrogen removal was detected, from 58 to 75%. The COD removal was slightly increased, from 89 to 95%, and the phosphorus removal remained constant.     

A comparison of BNR activated sludge systems with membrane and settling tank solid-liquid separation.

Installing membranes for solid-liquid separation into biological nutrient removal (BNR) activated sludge (AS) systems makes a profound difference not only to the design of the membrane bio-reactor (MBR) BNR system itself, but also to the design approach for the whole wastewater treatment plant (WWTP). In multi-zone BNR systems with membranes in the aerobic reactor and fixed volumes for the anaerobic, anoxic and aerobic zones (i.e. fixed volume fractions), the mass fractions can be controlled (within a range) with the inter-reactor recycle ratios. This zone mass fraction flexibility is a significant advantage of MBR BNR systems over BNR systems with secondary settling tanks (SSTs), because it allows changing the mass fractions to optimise biological N and P removal in conformity with influent wastewater characteristics and the effluent N and P concentrations required. For PWWF/ADWF ratios (fq) in the upper range (fq approximately 2.0), aerobic mass fractions in the lower range (f(maer) < 0.60) and high (usually raw) wastewater strengths, the indicated mode of operation of MBR BNR systems is as extended aeration WWTPs (no primary settling and long sludge age). However, the volume reduction compared with equivalent BNR systems with SSTs will not be large (40-60%), but the cost of the membranes can be offset against sludge thickening and stabilisation costs. Moving from a flow unbalanced raw wastewater system to a flow balanced (fq = 1) low (usually settled) wastewater strength system can double the ADWF capacity of the biological reactor, but the design approach of the WWTP changes away from extended aeration to include primary sludge stabilisation. The cost of primary sludge treatment then has to be offset against the savings of the increased WWTP capacity.     

Alternate anoxic/aerobic operation for nitrogen removal in a membrane bioreactor for municipal wastewater treatment

A large pilot-scale membrane bioreactor (MBR) with a conventional denitrification/nitrification scheme for municipal wastewater treatment has been run for one year under two different aeration strategies in the oxidation/nitrification compartment. During the first five months air supply was provided according to the dissolved-oxygen set-point and the system run as a conventional predenitrification MBR; then, an intermittent aeration strategy based on effluent ammonia nitrogen was adopted in the aerobic compartment in order to assess the impact on process performances in terms of N and P removal, energy consumption and sludge reduction. The experimental inferences show a significant improvement of the effluent quality as COD and total nitrogen, both due to a better utilization of the denitrification potential which is a function of the available electron donor (biodegradable COD) and electron acceptor (nitric nitrogen); particularly, nitrogen removal increased from 67% to 75%. At the same time, a more effective biological phosphorus removal was observed as a consequence of better selection of denitrifying phosphorus accumulating organisms (dPAO). The longer duration of anoxic phases also reflected in a lower excess sludge production (12% decrease) compared with the standard pre-denitrification operation and in a decrease of energy consumption for oxygen supply (about 50%).     

Impact of different recirculation schemes on nitrogen removal and overall performance of a laboratory scale MBR.

For membrane bioreactors (MBR) with enhanced nutrients removal, rather complex recirculation schemes based on the biological requirements are commonly recommended. The aim of this work was to evaluate other recirculation options. For a laboratory scale MBR, four different recirculation schemes were tested. The MBR was operated with COD degradation, nitrification, post-denitrification without carbon dosing and biological phosphorus removal. For all configurations, efficient COD, nitrogen and phosphorus removal could be achieved. There were no big differences in elimination efficiency between the configurations (COD elimination: 96.6-97.9%, nitrogen removal: 89.7-92.1% and phosphorus removal: 97.4-99.4%). Changes in the degradation, release and uptake rates were levelled out by the changes in contact time and biomass distribution. With relatively constant outflow concentrations, different configurations are still interesting with regard to oxygen consumption, simplicity of plant operation or support of certain degradation pathways such as biological phosphorus removal or denitrification.     

Development of MBR with reduced operational and maintenance costs.

To reduce MBR O&M costs, a new MBR process that conducts efficient simultaneous biological nitrogen and phosphorus removal (BNR) was developed. In the development of this process, various approaches were taken, including reduction of power demand, chemical consumption and sludge disposal costs. To address power demand reductions, air supply requirements for membrane cleaning were reduced. The process adopted an improved membrane that requires less air for cleaning than conventional membranes. It also introduced cyclic aeration, which alternately supplies washing air to the two series of membrane units. Adoption of biological phosphorus removal eliminated chemical costs for phosphorus removal and contributed to the reduction of sludge disposal costs. By combining these technologies, compared to conventional MBR processes, an approximately 27% reduction in O&M costs was achieved.     

Behaviour of activated sludge from a system with anoxic phosphate uptake

Activated sludge from a new activated sludge modification for biological phosphorus and nitrogen removal was studied. Population dynamics and the phenomenon of anoxic phosphate uptake with simultaneous denitrification were investigated.The ability of the process to remove nutrients and to suppress filamentous bulking was studied. The course of phosphate concentrations along the tested system showed an anoxic phosphate uptake with simultaneous denitrification. The mechanism of anoxic phosphate uptake was confirmed using kinetic batch tests. © 1998 IAWQ. Published by Elsevier Science Ltd     

Effects of silver nanoparticles on biological nitrogen removal processes

The effects of silver (Ag) nanoparticles (NPs) on activated sludge in a biological nitrogen removal (BNR) process were investigated under aerobic and anoxic conditions. We show that nitrification was more vulnerable to Ag NPs exposure than denitrification at the same Ag NPs concentration. In continuous operation of the BNR process, a higher inhibitory effect on nitrification was attributed to a smaller size of Ag NPs. About 70-90% of the Ag NPs supplied were embedded in the sludge matrix but 10-30% of the Ag NPs remained in the supernatant. This indicates that significant amounts of Ag NPs could be discharged from wastewater treatment plants and potentially impact on aquatic ecosystems.     

Towards exposure of elusive metabolic mixed-culture processes: the application of metaproteomic analyses to activated sludge.

Protein expression is a direct reflection of specific microbial activities in any ecosystem. In order to assess protein expression in mixed microbial communities, the feasibility of applying proteomic techniques to activated sludge samples has recently been demonstrated. We report the application of metaproteomics to two activated sludges from a laboratory-scale sequencing batch reactor with dissimilar phosphorus removal performances. Fluorescence in situ hybridization (FISH) revealed that the sludge with good enhanced biological phosphorus removal performance (EBPR) was dominated by Betaproteobacteria (65% of EUBMIX binding cells) and gave positive signals for the Rhodocyclus-type PAO specific probe (59%). The non-EBPR sludge was dominated by tetrad-forming Alphaproteobacteria (75%). With regard to the proteomic investigation, 630 individual protein spots were matched across the replicate groups of the anaerobic and aerobic phases of the EBPR sludge with 9.4% of all spots being statistically different between the two phases. The non-EBPR metaproteomic maps exhibited 590 matched spots with 14.7% statistical differences between the two phases. Overall, the non-EBPR sludge expressed around 30% more significant differences than the EBPR sludge. The comparison of protein expression in the two sludges showed that their metaproteomes were substantially different and this was reflected in their microbial community structures and metabolic transformations.     

Sludge-sludge interaction in the enhanced biological phosphorus removal process.

Metabolisms related to enhanced biological phosphorus removal (EBPR) were found to be affected when two activated sludges with different EBPR activities were mixed together. In the present study, two laboratory scale EBPR processes were operated in parallel, one of them with higher and another with lower EBPR activities. The activated sludges from the two reactors were mixed together at different mixing ratios. The supernatant was made the same for all mixing ratios, anaerobic-aerobic batch experiments were performed, and acetate uptake rate and phosphate release rate under anaerobic conditions and phosphate uptake rate under aerobic condition were determined. The metabolic rates measured were expected to be linear to the mixing ratios, as the supernatant was the same for all mixing ratios, whereas the metabolic rates were either promoted or inhibited by mixing of sludges. As an indicator for the sludge mixing effect on the metabolic rates, mixing effect intensity (MEI) was introduced. Chemical substances that are produced by microorganisms in activated sludge are proposed to be one of the possible causes of the sludge mixing effect.     

Design and performance of BNR activated sludge systems with flat sheet membranes for solid-liquid separation.

The use of immersed membranes for solid-liquid separation in biological nutrient removal activated sludge (BNRAS) systems was investigated at lab scale. Two laboratory-scale BNR activated sludge systems were run in parallel, one a MBR system and the other a conventional system with secondary settling tanks. Both systems were in 3 reactor anaerobic, anoxic, aerobic UCT configurations. The systems were set up to have, as far as possible, identical design parameters such as reactor mass fractions, recycles and sludge age. Differences were the influent flow and total reactor volumes, and the higher reactor concentrations in the MBR system. The performances of the two systems were extensively monitored and compared to identify and quantify the influence of the membranes on system response.The MBR UCT system exhibited COD, FSA, TKN, TP and TSS removals that were consistently equivalent or superior to the conventional system. Better P removal in the MBR was attributed to lower observed P uptake in the anoxic zone. High nitrate loads to the anoxic reactor appeared to be the determining factor in stimulating P uptake.The MBR UCT system had a greater sludge production than the conventional system. This was partly attributable to the retention of all solids in the MBR reactor. For steady state design this increase is accommodated by increasing the influent unbiodegradable particulate COD fraction. Additionally an attempt was made to determine the Alpha values in the oxygen transfer rate.This paper briefly summarises and compares the results from both systems, and the conclusions that can be drawn from these results.     

Enhanced nutrient removal MBR system with chemical addition for low effluent TP

A pilot study was conducted to test an membrane bioreactor (MBR) process for combined biological and chemical P removal to achieve a very low effluent total phosphorus (TP) concentration of 0.025 mg P/L. With the data from the pilot test, a simulation study was performed to demonstrate that: (1) the pilot system behaviour (effluent quality, MLSS, etc.) can be modelled accurately with an activated sludge model combined with a chemical precipitation model; and (2) with the calibrated model, simulation scenarios can be performed to further understand the pilot MBR process, and provide information for optimizing design and operation when applied at full-scale. Results from the pilot test indicated that the system could achieve very low effluent TP concentration through biological P removal with a limited chemical addition, and chemical addition to remove P to very low level did not affect other biological processes, i.e., organic and nitrogen removal. Simulation studies indicate that the process behaviour can be modelled accurately with an activated sludge model combined with a chemical precipitation model, and the calibrated model can be used to provide information to optimize system design and operation, e.g., chemical addition control under dynamic loading conditions is important for maintaining biological P removal.     

Experimental and model-based evaluation of the role of denitrifying polyphosphate accumulating organisms at two large scale WWTPs in northern Poland.

The capabilities of denitrifying Polyphosphate Accumulating Organisms (DPAOs) in two large-scale plants in northern Poland performing enhanced biological phosphorus removal (EBPR) were evaluated in this study. A series of batch tests with the process biomass aimed at the measurements of phosphate release (with artificial substrate and real wastewater) and subsequent phosphate uptake under anoxic/aerobic conditions. The process kinetics were predicted using ASM2d implemented in the GPS-X ver. 4.0.2 simulation package. The results from one experimental series (summer) were used for the model calibration, whereas the results from another series (spring) were used for the model validation. The model parameters were also accurately confirmed by predictions of the accompanying field measurements in the full-scale bioreactors. The experimental and simulation results revealed that a relatively small fraction of PAO could denitrify (eta(NO3,PAO) = 0.32). The denitrification rates associated with the anoxic storage of PP and the anoxic growth of PAO only constituted 16.0-21.0% of the denitrification rates associated with the anoxic activity of "ordinary" heterotrophs.     

Comparison of sequentially combined carbon with sole carbon in denitrification and biological phosphorus removal.

The sequentially combined carbon (SCC) of methanol and acetic acid was used for the biological nutrient removal (BNR). Its BNR performance was compared with methanol or acetic acid as a sole carbon substrate. Compared to the sole carbon substrate, the use of SCC demonstrated the highest overall TIN removal of 98.3% at a COD ratio of 30 mg COD/l of methanol/50 mg CDO/l of acetic acid. Furthermore, denitrification was more enhanced when methanol was used as one of the SCC, rather than as a sole carbon source. Complete phosphorus removal was accomplished with a non-detectable o-P concentration when SCC was added. This research also showed that aerobic denitrifiers appear to prefer acetic acid to methanol, and the amount of poly-beta-hydroxybutyrate (PHB) stored by P accumulating organisms (PAOs) using acetic acid in the anoxic zone could be another important factor in improving the aerobic denitrification. The SCC was a very favorable carbon source for the aerobic denitrification since acetic acid was utilized more efficiently for P-release in accordance with increase of PHB stored in the cell of PAOs by removing nitrogen first using methanol.     

Comparison of nutrient removal efficiency between pre- and post-denitrification wastewater treatments.

A shortage of organic substances (COD) may cause problems for biological nutrient removal, that is, lower influent COD concentration leads to lower nutrient removal rates. Biological phosphorus removal and denitrification are reactions in which COD is indispensable. As for biological simultaneous nitrogen and phosphorus removal systems, a competition problem of COD utilisation between polyphosphate accumulating organisms (PAOs) and non-polyphosphate-accumulating denitrifiers is not avoided. From the viewpoint of effective utilisation of limited influent COD, denitrifying phosphorus-removing organisms (DN-PAOs) can be effective. In this study, DN-PAOs activities in modified UCT (pre-denitrification process) and DEPHANOX (post-denitrification process) wastewater treatments were compared. In conclusion, the post-denitrification systems can use influent COD more effectively and have higher nutrient removal efficiencies than the conventional pre-denitrification systems.     

Outcomes of a 2-year investigation on enhanced biological nutrients removal and trace organics elimination in membrane bioreactor (MBR).

Two configurations of membrane bioreactors were identified to achieve enhanced biological phosphorus and nitrogen removal, and assessed over more than two years with two parallel pilot plants of 2m3 each. Both configurations included an anaerobic zone ahead of the biological reactor, and differed by the position of the anoxic zone: standard pre-denitrification, or post-denitrification without dosing of carbon source. Both configurations achieved improved phosphorus removal. The goal of 50 microgP/L in the effluent could be consistently achieved with two types of municipal wastewater, the second site requiring a low dose of ferric salt ferric salt < 3 mgFe/L. The full potential of biological phosphorus removal could be demonstrated during phosphate spiking trials, where up to 1 mg of phosphorus was biologically eliminated for 10 mg BOD5 in the influent. The post-denitrification configuration enabled a very good elimination of nitrogen. Daily nitrate concentration as low as 1 mgN/L could be monitored in the effluent in some periods. The denitrification rates, greater than those expected for endogenous denitrification, could be accounted for by the use of the glycogene pool, internally stored by the denitrifying microorganisms in the anaerobic zone. Pharmaceuticals residues and steroids were regularly monitored on the two parallel MBR pilot plants during the length of the trials, and compared with the performance of the Berlin-Ruhleben WWTP. Although some compounds such as carbamazepine were persistent through all the systems, most of the compounds could be better removed by the MBR plants. The influence of temperature, sludge age and compound concentration could be shown, as well as the significance of biological mechanisms in the removal of trace organic compounds.     

Performances of a hybrid adsorption/submerged membrane biological process for toxic waste removal.

This study focuses on a hybrid process, which combines adsorption on powdered activated carbon (PAC), membrane separation using immersed hollow fibers and biological activity. The first part shows that PAC addition in a complex system (containing dissolved molecules and biological particles) can reduce membrane fouling. In that system, DMP removal is function of the activated carbon concentration. Then, respirometric experiments allowed comparison of toxic sensitivity and biological degradation of different bioreactors (membrane bioreactor (MBR), adsorptive membrane bioreactor (PAC-MBR) and classical activated sludge bioreactor (AS)). Results point out that MBR sludge is less sensitive to the toxic than the AS. For high toxic concentration, PAC addition in the MBR decreases rapidly the toxic concentration under the EC50 in the bioreactor, which allows a better biodegradation of the toxic compound. DMP assimilation is completed more rapidly with the PAC-MBR than the MBR.     

A novel wastewater treatment process: simultaneous nitrification, denitrification and phosphorus removal.

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen concentration (DO, 0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHA), accompanied with phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to less than 0.5 mg/L at the end of the cycle. Ammonia was also oxidised during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis found that the final denitrification product was mainly nitrous oxide (N2O) not N2. Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen-accumulating organisms rather than denitrifying polyphosphate-accumulating organisms were responsible for the denitrification activity.     

泥龄对反硝化除磷脱氮系统效率的影响分析

反硝化除磷脱氮系统中,生物脱氮与生物除磷是两个相互独立、相互竞争又相互交叉的生理反应过程,存在着硝化菌与聚磷菌的不同泥龄之争。应用数学模式分析了泥龄对氮、磷去除效率的影响,并就反硝化除磷脱氮工艺的单、双级污泥系统的泥龄进行了探讨。推导出以下结论:缩短泥龄可以提高系统的同化除磷能力;长泥龄的生物除磷系统单靠生物作用以期达到完全除磷是几乎不可能的。