Use of immobilised bacteria for the wastewater treatment--examples from the sugar industry.

This work focuses on the implementation of high performance systems to the wastewater treatment of sugar factories. For this purpose, systems with immobilised bacteria were studied. For the hydrolysis of organic matter and denitrification, fluidized bed reactors were used. The nitrification was studied with an airlift reactor system. Both hydrolysis and nitrogen elimination were investigated on laboratory and pilot scales in sugar factories. Although with porous materials higher biomass concentrations are attainable for the hydrolysis (up to 55 kg/m3), for economical reasons sand was used (22.5 kg/m3) for the pilot scale-study. With a pilot-scale reactor (volume 1 m3) the maximum sucrose conversion rate achieved with sand in the first campaign was 52 kg/(m3 d). For the nitrogen elimination on the pilot scale, a system with denitrification and nitrification was combined. The highest performance for the nitrification (reactor volume: 0.68 m3) with pumice as support material was 1.2 kg NH4-N/(m3 d), limiting the whole system. The denitrification rate (reactor volume: 0.12 m3) was four times higher (3.5-5 kg NO3-N/(m3 d). Rules of the modelling of the system are discussed.     

Automatic control strategy for biological nitrogen removal of low C/N wastewater in a sequencing batch reactor.

To establish an automatic control system of external carbon addition in biological nitrogen removal, a bench-scale sequencing batch reactor with real-time control strategy was designed in this study. An oxidation-reduction potential (ORP) profile was used for automatic control of external carbon addition. The mean removal efficiency of total organic carbon was over 98%. Complete denitrification in an anoxic phase and complete denitrification and nitrification in anoxic and oxic phases were accomplished, respectively, because the oxic and anoxic periods were also appropriately controlled with ORP and pH profiles, respectively. Mean removal efficiency of total nitrogen was over 95%. When concentration of influent wastewater was changed, volume of additional carbon was automatically changed with the influent fluctuation, and flexible hydraulic retention time was achieved in this system.     

High strength nitrogen removal from nightsoil and piggery wastes.

Nightsoil and piggery wastes generally present high strength organics and nitrogen. This study evaluated the nitrogen removal characteristics with the existing and modified nightsoil and piggery waste treatment plants. The existing conventional plants showed 20 to 40% nitrogen removal, but the modification with SBR or MLE process could remove effectively both nitrogen and organics with the minimum COD/TN and alkalinity/TN ratios of 6 and 3.6, respectively. Nitrite nitrification and denitrification rates obtainable at higher nitrogen loads were faster than the rates of nitrate nitrification and denitrification resulting in less reactor volume requirement. However, the higher nitrogen loads increased the organic loads resulting in the reactor temperature inhibiting nitrification. Thus, a combined treatment with anaerobic digestion with the adjustment of influent bypass rates was proposed to reduce the reactor temperature and the external carbon requirement. The biological treatment could discharge about 1,100 mg/L soluble COD and 50 mg/L soluble nitrogen, respectively.     

Total nitrogen removal from high-strength ammonia recycle stream using a single submerged attached growth bioreactor.

An experimental study investigating the nitrogen removal efficiency from the recycle stream generated in the dewatering facility of the anaerobically digested sludge at the Deer Island wastewater treatment plant (WWTP) in Boston was conducted using a single submerged attached growth bioreactor (SAGB), designed for simultaneous nitrification and denitrification. The applied nitrogen loading to the reactor ranged from 0.7 to 2.27 kg-N/m3xd, and the corresponding total nitrogen (TN) removal rate ranged from 0.38 to 1.8 kg-N/m(3)xd. The observed nitrification rates varied from 0.42 kg-N/m3-d to 1.45 kg-N/m(3) xd with an ammonia load of 0.5 kg-N/m3-d and 1.8 kg-N/m(3)xd, respectively. An average nitrification efficiency of 91% was achieved throughout the experiment. Denitrification efficiency varied from 55%/o, obtained without any addition of carbon source, to 95% when methanol was added in order to obtain a methanol/nitrate ratio of about 3 kg methanol/kg NO3- -N.     

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.     

Enhanced nitrogen removal using C/N load adjustment and real-time control strategy in sequencing batch reactors for swine wastewater treatment.

The laboratory-scale sequencing batch reactor (SBR) was used to study the effectiveness of an integrated strategy of real time control with C/N ratio adjustment for practical swine wastewater treatment. Swine waste was used as the external carbon source for continuous treatment in the SBR reactors. Oxidation-reduction potential and pH were used as parameters to control the continuous denitrification and nitrification process, respectively. A constant effluent quality could be obtained, despite drastic variations in the characteristics of influent wastewater. Also, a relatively complete removal of nutrients was always ensured, since the optimum quantity of the external carbon source could be provided for complete denitrification, and a flexible hydraulic retention time was achieved by the successful real-time control strategy. The average removal efficiencies of total organic carbon and nitrogen were over 94% and 95%, respectively.     

Treatment of landfill leachate by a pilot-scale modified Ludzack-Ettinger and sulfur-utilizing denitrification process.

Nitrogen removal efficiency of a pilot-scale system consisted of Modified Ludzack-Ettinger (MLE) followed by sulfur-utilizing denitrification (SUDNR) process was evaluated with a landfill leachate. For SUDNR, a down-flow mode sulfur packed bed reactor (SPBR) filled with sulfur and limestone particles was used. Although total nitrogen removal efficiency of the MLE process was about 80% at the recycle ratio of 4, effluent contained 350-450 mg/L NO(3-)-N. Up to a loading rate of 1.2 kg NO(3-)-N/m3-day, the SPBR could achieve complete removal of nitrate, and nitrate removal rate was kept to that level even at higher loading rate. When a COD/N ratio of MLE process was maintained at 2 instead of 4, more organics with molecular weight less than 500 were utilized for heterotrophic denitrification although denitrification was not complete with the lack of electron donors. Clogging in the SPBR, mainly by the accumulation of nitrogen gas in the pores, could easily be removed by introducing the effluent in an upward direction for 1 min at 1 hr intervals. The proposed treatment system could achieve nitrate free effluent with a slight increase in chemical cost. Furthermore, depending on further COD removal requirement after biological treatment, the proposed treatment system can be an economical solution.     

Nitrogen removal rates at a technical-scale pilot plant with the one-stage partial nitritation/Anammox process.

Traditional nitrification/denitrification is not suitable for nitrogen removal when wastewater contains high concentrations of ammonium nitrogen and low concentrations of biodegradable carbon. Recently, a deammonification process was developed and proposed as a new technology for treatment of such streams. This process relies on a stable interaction between aerobic bacteria Nitrosomonas, that accomplish partial nitritation and anaerobic bacteria Planctomycetales, which conduct the Anammox reaction. Simultaneous performance of these two processes can lead to a complete autotrophic nitrogen removal in one single reactor. The experiments where nitrogen was removed in one reactor were performed at a technical-scale moving-bed pilot plant, filled with Kaldnes rings and supplied with supernatant after dewatering of digested sludge. It was found that a nitrogen removal rate obtained at the pilot plant was 1.9 g m(-2) d(-1). Parallel to the pilot plant run, a series of batch tests were carried out under anoxic and aerobic conditions. Within the batch tests, where the pilot plant's conditions were simulated, removal rates reached up to 3 g N m(-2)d(-1). Moreover, the batch tests with inhibition of Nitrosomonas showed that only the Anammox bacteria (not anoxic removal by Nitrosomonas) are responsible for nitrogen removal.     

Achieving and maintaining of short-cut nitrification in a cyclic activated sludge system

A lab-scale Cyclic Activated Sludge Technology (CAST) system was operated more than 5 months to evaluate the effects of the operation mode on nitrogen removal performance and investigate a feasible method for achieving short-cut nitrification in the system. Results showed that nitrogen was removed by conventional biological nitrification and denitrification in traditional operation mode (fill/aeration 2 h, settle 1 h, decant 1 h), whereas short-cut nitrification and denitrification was the main nitrogen removal pathway in modified operation mode and the nitrogen removal performance was enhanced. Short-cut nitrification was successfully achieved in CAST system at 17 ± 1 °C by adjusting operation conditions and the average total nitrogen removal efficiency increased by 11.4% compared to traditional mode. It was assumed that low dissolved oxygen (<1.0 mg/L) limitation combined with free ammonia (0.28-0.34 mg/L) inhibition on nitrite-oxidizing bacteria caused nitrite accumulation in modified mode. During maintaining period of short-cut nitrification, preset aeration time enhanced ammonium-oxidizing bacteria dominance. It was also found that low DO could result in overgrowth of filamentous microorganisms and poor sludge settleability. The pH variation could provide effective information for controlling aeration duration in modified mode. However, no evident breakpoint appeared on pH and DO profiles in traditional mode.     

Comparative studies on the differently operated trains of the North-Budapest Wastewater Treatment Plant

In order to reduce the pollution load of the Danube, the North-Budapest Wastewater Treatment Plant has been upgraded to enhanced nitrogen removal by establishing a new activated sludge treatment line and modifying the existing unit for nitrification and denitrification. As both the influent flow rate and the influent chemical oxygen demand (COD), biological oxygen demand (BOD(5)) and total suspended solids (TSS) concentration levels remained far below the design values, setting one fourth of the reactor volume out of operation in the Old Line, and operating the nitrification reactor of the New Line with part-time aeration proved to be possible. Analytical data as well as simulation studies supported the advantage of the intermittent-aeration process in efficient N-removal. However, the lengths of the aerated periods have to be increased with decreasing temperature, and thereby effluent total nitrogen (TN) concentration can increase due to decreasing denitrification efficiency. Potential occurrence of low-dissolved oxygen (DO) bulking should be hindered through applying an efficient anoxic selector system.     

Nitrogen removal from sludge digester liquids by nitrification/denitrification or partial nitritation/anammox: environmental and economical considerations.

In wastewater treatment plants with anaerobic sludge digestion, 15-20% of the nitrogen load is recirculated to the main stream with the return liquors from dewatering. Separate treatment of this ammonium-rich digester supernatant significantly reduces the nitrogen load of the activated sludge system. Two biological applications are considered for nitrogen elimination: (i) classical autotrophic nitrification/heterotrophic denitrification and (ii) partial nitritation/autotrophic anaerobic ammonium oxidation (anammox). With both applications 85-90% nitrogen removal can be achieved, but there are considerable differences in terms of sustainability and costs. The final gaseous products for heterotrophic denitrification are generally not measured and are assumed to be nitrogen gas (N2). However, significant nitrous oxide (N2O) production can occur at elevated nitrite concentrations in the reactor. Denitrification via nitrite instead of nitrate has been promoted in recent years in order to reduce the oxygen and the organic carbon requirements. Obviously this "achievement" turns out to be rather disadvantageous from an overall environmental point of view. On the other hand no unfavorable intermediates are emitted during anaerobic ammonium oxidation. A cost estimate for both applications demonstrates that partial nitritation/anammox is also more economical than classical nitrification/denitrification. Therefore autotrophic nitrogen elimination should be used in future to treat ammonium-rich sludge liquors.     

Full-scale applications for both COD and nutrient removal in a CIRCOX airlift reactor.

The airlift reactor technology has been successfully applied at full scale for both COD and nitrogen removal. In this study, the results of the biofilm development and biological performance of two full scale reactors are discussed. At Paulaner Brewery in Munich, the airlift reactor was applied for COD and ammonia removal of anaerobically treated wastewater. In the other case the airlift reactor was applied as a pretreatment of nitrogen removal by the Anammox process. Water from a Tannery company in Lichtenvoorde in the Netherlands, The Hulshof Royal Dutch Tanneries, was pretreated anaerobically for COD removal and aerobically to remove the sulphides as sulphur. In an airlift reactor the ammonia was partially oxidised to nitrite. In both cases the granular biomass developed well; the concentrations amounted to 250 microl/L and 500 ml/L respectively. In the first case, 4 kg/m(3)/day of COD was removed, the soluble concentration of COD was less than 250 mg/L. The nitrification to nitrate was nearly complete and amounted to 0.5 kg NH4-N/m(3)/day. In the second application, 50% of the ammonia (on average 0.45 kg N/m3/d) was nitrified to nitrite. This process was easily controlled by regulating the amount of air according to the nitrite and ammonia concentrations in the effluent. It can be concluded that in both cases the particular processes were very stable and easy to operate.     

Application of a sponge media (BioCube) process for upgrading and expansion of existing caprolactam wastewater treatment plant for nitrogen removal.

For the upgrade and expansion of an existing caprolactam wastewater treatment plant, a freely floating sponge media (BioCube) process was selected based on extensive pilot-plant tests, due to extreme space constraints. In order to protect nitrifier inhibition caused by high strength organics in caprolactam wastewater, the pilot plant consisted of an organics removal reactor, which functioned as a pretreatment for nitrification, and followed the nitrogen removal reactor. The suspended MLSS was 1,800-4,000 and the media attached MLSS was maintained at 22,000-26,000 mg/L. The final effluent COD was noticeably low, around 20.4-37 mg/L, even with fairly large fluctuations in the feed levels, between 1,400-6,770 mg/L. The removal of total nitrogen with the system, when denitrification was close to completion, was approximately 97.6%. For the entire run, complete nitrification of 99.6% was achieved, which might have been due to well-acclimatized nitrifiers attached in the BioCube media. Specifically, after adaptation, the nitrification continuously increased in the organics removal reactor, even under high residual organics conditions. From the numerous experimental results, the BioCube process seemed to be an effective method for the upgrading and expansion of the existing wastewater treatment plant, with minimum reactor enlargement.     

Optimizing sequencing batch reactor (SBR) reactor operation for treatment of dairy wastewater with aerobic granular sludge

The biological wastewater treatment using aerobic granular sludge is a new and very promising method, which is predominantly used in SBR reactors which have higher volumetric conversion rates than methods with flocculent sludge. With suitable reactor operation, flocculent biomass will accumulate into globular aggregates, due to the creation of increased substrate gradients and high shearing power degrees. In the research project described in this paper dairy wastewater with a high particle load was treated with aerobic granular sludge in an SBR reactor. A dynamic mathematical model was developed describing COD and nitrogen removal as well as typical biofilm processes such as diffusion or substrate limitation in greater detail. The calibrated model was excellently able to reproduce the measuring data despite of strongly varying wastewater composition. In this paper scenario calculations with a calibrated biokinetic model were executed to evaluate the effect of different operation strategies for the granular SBR. Modeling results showed that the granules with an average diameter of 2.5 mm had an aerobic layer in between 65-95 microm. Density of the granules was 40 kgVSS/m3. Results revealed amongst others optimal operation conditions for nitrogen removal with oxygen concentrations below 5 gO2/m3. Lower oxygen concentrations led to thinner aerobic but thicker anoxic granular layers with higher nitrate removal efficiencies. Total SBR-cycle times should be in between 360-480 minutes. Reduction of the cycle time from 480 to 360 minutes with a 50% higher throughput resulted in an increase of peak nitrogen effluent concentrations by 40%. Considering biochemical processes the volumetric loading rate for dairy wastewater should be higher than 4.5 kgCOD/(m3*d). Higher COD input load with a COD-based volumetric loading rate of 9.0 kgCOD/(m3*d) nearly led to complete nitrogen removal. Under different operational conditions average nitrification rates up to 5 gNH/(m3*h) and denitrification rates up to 3.7 gNO/(m3*h) were achieved.     

External carbon feeding strategy for enhancing nitrogen removal in SBR.

Effective method for feeding an external carbon source (ECS) in SBR was investigated to enhance denitrification based on modifying the anoxic/aerobic sub-cycle for swine wastewater treatment. The wastewater discharged from the scraper-type barns contains relatively low readily biodegradable organic. Therefore NOx-N was accumulated during repeating sub-cycle in SBR operation. When acetic acid was fed as ECS during the final sub-cycle, the maximum nitrogen removal rate was 0.22 kg N/m3/d. This was due to both less denitrification rate during the sub-cycle period and inhibition of denitrification by pH drop during the final cycle. The pH drop was caused by a large amount of ECS feeding to remove high concentration of NOx-N in the final period. To overcome these limitations and achieve higher nitrogen removal rate, the intermittent ECS feeding method with raw wastewater at every anoxic period was developed. Using the modifying ECS feeding method, the removal rate was increased to 0.45 kg N/m3/d without NOx-N accumulation.     

Nitrite accumulation followed by denitrification using sequencing batch reactor.

Biological ammonia-nitrogen removal utilizes two distinct processes, nitrification and denitrification. In nitrification, ammonia oxidizes to nitrite then to nitrate. In this study, elimination of nitrite oxidation to nitrate step was attempted in order to directly remove nitrite to nitrogen gas by denitrification. For this study the supernatant from an anaerobic digester was used as an ammonia source and a sequencing batch reactor (SBR) was employed. Emphasis was given to the evaluation of the operational factors affecting nitrite accumulation and the elucidation of kinetics for biological nitrification and denitrification. Accumulation of nitrite in the nitrification process was achieved by suppressing the growth of Nitrobacter, a nitrite oxidizer, by loading high concentration ammonia supernatant immediately after all ammonia in the previous loading was oxidized to nitrite. Nitrite oxidation was taking place as the solid retention time (SRT) was increased from 2.5 days to 3.0 days in a continuously aerated SBR mode with daily feeding. However, nitrite accumulation was achieved even at longer SRT of 5 days when the aeration and non-aeration periods were appropriately combined and the non-aeration period can be used for denitrification of the accumulated nitrite with a carbon source supplied.     

Biological nitrogen removal in SBR bypassing nitrate generation accomplished by chlorination and aeration time control.

A novel control strategy for biological nitrogen removal with high nitrite built-up through chlorine dosage was studied. In the biological nitrogen removal process operated in a bench-scale sequencing batch reactor, dose of chlorine of 0.2 mg/l in the form of sodium hypochlorite was applied after the COD was depleted. The aerobic phase switched to an anoxic phase shortly after the ammonium was completely biotically oxidized. Nitrite accumulation was stably achieved which was attributed to the chlorination and the lag-time of nitrification. With the time control, stable 100% conversion of nitrite could also be sustained even under the absence of chlorine for at least 20 days. The nitrite oxidizer should have been killed rather than been suppressed in this study. For engineering applications, the advantages of the nitrification/denitrification via nitrite can compensate the cost of chlorine dosage. Combined with the aeration time control, it is feasible to apply chlorination in a biological nitrogen removal process in SBRs.     

好氧颗粒污泥反应器快速启动及除碳脱氮试验

为快速启动好氧颗粒污泥反应器,在SBR反应器中同时接种硝化污泥和厌氧颗粒污泥,控制反应条件,温度23~25℃,pH值7.5~8.5,DO质量浓度1.5 mg/L左右,15 d即完成反应器快速启动。形成的好氧颗粒污泥粒径1.5~2.5 mm,SVI值54 mL/g。颗粒污泥结构紧密,沉降性能良好。反应器连续运行40多天,改变进水COD及NH4+-N浓度,COD和NH4+-N去除率均能稳定在80%以上,反应器内发生了同步硝化反硝化过程。     

Nitrogen removal from pharmaceutical manufacturing wastewater with high concentration of ammonia and free ammonia via partial nitrification and denitrification.

In this study, laboratory-scale experiments were conducted applying a Sequencing Batch Reactor (SBR) activated sludge process to a wastewater stream from a pharmaceutical factory. Nitrogen removal can be achieved via partial nitrification and denitrification and the efficiency was above 99% at 23 degrees C+/-1. The experimental results indicated that the nitrite oxidizers were more sensitive than ammonia oxidizers to the free ammonia in the wastewater. The average accumulation rate of nitrite was much higher than that of nitrate. During nitrogen removal via the nitrite pathway, the end of nitrification and denitrification can be exactly decided by monitoring the variation of pH. Consequently, on-line control for nitrogen removal from the pharmaceutical manufacturing wastewater can be achieved and the cost of operation can be reduced.