Modified Ludzack Ettinger System Research Articles

Impact of Influent Composition and Operating Conditions on Carbon and Nitrogen Removal from Urban Wastewater in a Continuous-Upflow (Micro)Aerobic Granular Sludge Blanket Reactor

Aerobic granular sludge is an interesting alternative to the conventional activated sludge (CAS) system and modified-Ludzack–Ettinger (MLE) process for biological wastewater treatment, as it allows a more cost-effective and simultaneous removal of carbon (C) and nitrogen (N) compounds in a single stage. In this study, (micro)aerobic C and N removal from synthetic urban wastewater was investigated in a continuous-double-column-upflow aerobic granular sludge blanket (UAGSB) system. The UAGSB reactor was operated under different dissolved oxygen (DO) ranges (0.01–6.00 mg∙L−1), feed C/N ratios (4.7–13.6), and hydraulic retention times (HRTs) (6–24 h). At a DO range of 0.01–0.30 mg∙L−1, feed C/N ratio of 13.6, and HRT of 24 h, the UAGSB achieved the highest chemical oxygen demand (COD), N-NH4+, and total inorganic nitrogen (TIN) removal efficiencies of 86, 99, and 84%, respectively. A preliminary assessment of the energy and economic savings associated with the process investigated was also carried out. The impact of capital and operating costs mainly related to the energy consumption of the aeration was taken into account. The assessment reveals that the capital and energy expenses of the UAGSB reactor would result in cost savings of around 14 and 7%, respectively, compared with a MLE system.

Modified Ludzack–Ettinger system role in efficient nitrogen removal from swine manure under high total suspended solids concentration

The current scenario requires treatment systems with high efficiency, easy operation and low cost. The solid–liquid separation process as a pre-treatment of swine manure is an efficient strategy improving the wastewater management and treatment. In this sense, the aim of this study was to establish for the first time a condition in which swine manure treatment could be successfully performed using a simple solid-liquid separation, combined with nitrification and denitrification process in a modified Ludzack–Ettinger system. The solids separation was done with a brush-roller screen (2 mm mesh) followed by a settling unit. The nitrogen removal unit was composed of a modified Ludzack–Ettinger process, operated in three phases, according to different sedimentation times in the solid–liquid separation process. The modified Ludzack–Ettinger system showed good performance for treatment of swine wastewater with total suspend solids concentration higher than 14 g L−1, reaching removal efficiency of 88.3% for nitrogen and 86.3% for total organic carbon removal. The results obtained in this study confirm that it is possible to operate the modified Ludzack–Ettinger system at high total solids concentration using a simple solid–liquid separation process keeping a high nitrogen removal efficiency.

Methane and nitrous oxide emission from different treatment units of municipal wastewater treatment plants in Southwest Germany.

We measured the atmospheric emission rates of methane (CH4) and nitrous oxide (N2O) in two wastewater treatment plants in Southwest Germany, which apply different treatment technologies. Dissolved gas concentrations and fluxes were measured during all processing steps as well as in the discharge receiving streams. N2O isotopocule analysis revealed that NH2OH oxidation during nitrification contributed 86–96% of the N2O production in the nitrification tank, whereas microbial denitrification was the main production pathway in the denitrification tank in a conventional activated sludge (CAS) system. During wastewater treatment using a modified Ludzack-Ettinger system (MLE) with energy recovery, N2O was predominantly produced by the NO2- reduction by nitrifier-denitrification process. For both systems, N2O emissions were low, with emission factors of 0.008% and 0.001% for the MLE and the CAS system, respectively. In the effluent-receiving streams, bacterial denitrification and nitrification contributed nearly equally to N2O production. The CH4 emission from the MLE system was estimated as 118.1 g-C d-1, which corresponds to an emission factor of 0.004%, and was three times lower than the emission from the CAS system with 0.01%.

English

Activated sludge samples were used to analyse microbial community structures from the anoxic and aerobic zones of a labora­tory-scale modified Ludzack-Ettinger system. Fluorescent in situ hybridization and denaturing gradient gel electrophoresis were applied for analysis. With the help of DNA specific fluorochrome DAPI, approximately 75 to 80% of total cells were detected, hybridised with a specific eubacterial probe for the anoxic and aerobic zones. Results corroborate the dominance of the alpha and gamma subclasses of the Proteobacteria in the anoxic zone whilst the aerobic zone was dominated with the beta subclass of the Proteobacteria. Genetic diversity of the microbial community present in each of the anoxic and aerobic zones was employed by the DGGE technique. Results were obtained from the application of fluorescent in situ hybridisation (FISH) and PCR-DGGE yields a more precise understanding of the microbial community structure and genetic diversity present in domestic wastewater of a laboratory scale treatment process. Nitrogen mass balances indicated an upset in the nitrogen levels for wastewater batches two and seven. The carbon mass balance fell in the range of 92.4 and 105.9% and the nitrogen mass balance fell in the range of 98.4 and 160.0%. Key words: Fluorescent in situ hybridisation (FISH), denaturing gradient gel electrophoresis (DGGE), COD and nitrogen mass balances.

Influence of anoxic to aerobic volume ratio on sludge settleability and bacterial community structure in a denitrifying–nitrifying activated sludge system

Biological treatment processes under nitrifying and denitrifying conditions are complex systems, in which different kinds of microbes dynamically cultivate and interact. The sludge bulking in these systems can be controlled by understanding the relationship between reactor performance and microbial diversity. In this study, sludge settleability and bacterial community structure were investigated in a modified Ludzack–Ettinger system as anoxic to aerobic volume ratio increased from 1:3 to 1:2 and finally to 2:1. Results indicated that settleability significantly improved as the anoxic to aerobic volume ratio increased (p < 0.01), accompanied by the increase in nitrogen removal efficiency and the change in filamentous bacteria. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis revealed that the diversity and richness of bacterial species increased with a small volume ratio but decreased as the volume ratio increased, because of the low energy obtained from anoxic respiration. Proteobacteria were the predominant group, followed by Bacteroidetes. The influence of the anoxic condition on bacterial community structure was evaluated through correspondence analysis. The changes in bacterial community structure concurred with the reactor performance in terms of nitrogen removal efficiency and settleability. Samples with different settleability values were inclined to cluster into different groups.

Biodegradability of wastewater and activated sludge organics in anaerobic digestion

The investigation provides experimental evidence that the unbiodegradable particulate organics fractions of primary sludge and waste activated sludge calculated from activated sludge models remain essentially unbiodegradable in anaerobic digestion. This was tested by feeding the waste activated sludge (WAS) from three different laboratory activated sludge (AS) systems to three separate anaerobic digesters (AD). Two of the AS systems were Modified Ludzack – Ettinger (MLE) nitrification-denitrification (ND) systems and the third was a membrane University of Cape Town (UCT) ND and enhanced biological P removal system. One of the MLE systems and the UCT system were fed the same real settled wastewater. The other MLE system was fed raw wastewater which was made by adding a measured constant flux (gCOD/d) of macerated primary sludge (PS) to the real settled wastewater. This PS was also fed to a fourth AD and a blend of PS and WAS from settled wastewater MLE system was fed to a fifth AD. The five ADs were each operated at five different sludge ages (10–60d). From the measured performance results of the AS systems, the unbiodegradable particulate organic (UPO) COD fractions of the raw and settled wastewaters, the PS and the WAS from the three AS systems were calculated with AS models. These AS model based UPO fractions of the PS and WAS were compared with the UPO fractions calculated from the performance results of the ADs fed these sludges. For the PS, the UPO fraction calculated from the AS and AD models matched closely, i.e. 0.30 and 0.31. Provided the UPO of heterotrophic (OHO, fE_OHO) and phosphorus accumulating (PAO, fE_PAO) biomass were accepted to be those associated with the death regeneration model of organism “decay”, the UPO of the WAS calculated from the AS and AD models also matched well - if the steady state AS model fE_OHO = 0.20 and fE_PAO = 0.25 values were used, then the UPO fraction of the WAS calculated from the AS models deviated significantly from those calculated with the AD models. Therefore in plant wide wastewater treatment models the characterization of PS and WAS as defined by the AS models can be applied without modification in AD models. The observed rate limiting hydrolysis/acidogenesis rates of the sludges are listed.

Fate and toxicity of melamine in activated sludge treatment systems after a long-term sludge adaptation

Melamine is a nitrogen-rich (67% nitrogen by mass) heterocyclic aromatic compound that could significantly increase effluent total nitrogen concentrations. In this study, we investigated the degradation of melamine and its impact on activated sludge operations by employing two common activated sludge processes, namely the Modified Ludzack-Ettinger (MLE) process and the continuous stirred tank reactor (CSTR) process. Melamine was dosed continuously from day 125 in both activated sludge treatment systems at an influent concentration of 3 mg/L for about 100 days. Even after such a long period of sludge adaptation, melamine appeared not to be easily biodegradable. The average melamine removal efficiencies in the CSTR and MLE systems were 14 ± 10% and 20 ± 15%, respectively. There was no significant difference in melamine removal between the two different activated sludge processes. The long-term input of melamine resulted in a decrease in the nitrifying bacterial activities (by 82 ± 8%) and population in both systems. Short-term microtiter assay results also showed that melamine reduced activated sludge growth by 80% when supplied at a concentration of 75.6 mg/L. These results suggest that sludge adaptation plays a minimal role in melamine degradation, as the enzymes responsible for hydrolytic deamination of melamine in activated sludge are not easily induced. The insignificant biodegradation of melamine is also attributed to bacterial growth inhibition under long-term dosing conditions with melamine, resulting in a significant decrease in effluent water quality.

Pushing the hydraulic retention time envelope in Modified Ludzack Ettinger systems

This study demonstrated the feasibility of operating a biological nutrient-removal employing Modified Ludzack Ettinger (MLE), at a reduced hydraulic retention time (HRT) of 5.5 h. The MLE process not only achieved full nitrification and 75–80% total nitrogen removal, at temperatures as low as 12 °C but also reduced the net observed biomass yield by 28% relative to the full-scale plant to 0.31 g VSS g −1 COD r. Biomass settleability drastically improved relative to the conventional activated sludge (CAS) full-scale plant as reflected by sludge volume index (SVI) of 97 mL g −1 versus 202 mL g −1. Respirometric studies indicated that the heterotrophic biokinetic coefficients for the conventional activated sludge and the MLE systems were very similar and consistent with literature values for primary effluent. However, biomass-specific nitrification rates in the MLE system of 0.14 g NH 4-N g −1 VSS d −1 at 20 °C were 55% higher than in the CAS, with both systems having comparable nitrification temperature correction coefficients of 1.084 for (CAS) and 1.092 in (MLE). This study confirmed through both pilot testing and modeling that biological nutrient removal (BNR) systems treating low strength municipal wastewater can be designed for overall HRT as low as 5 h in cold climates. Furthermore, the process achieved significant biomass yield reduction due to anoxic consumption of organic matter.

Bacterial response to a shock load of nanosilver in an activated sludge treatment system

The growing release of nanosilver into sewage systems has increased the concerns on the potential adverse impacts of silver nanoparticles (AgNPs) in wastewater treatment plants. The inhibitory effects of nanosilver on wastewater treatment and the response of activated sludge bacteria to the shock loading of AgNPs were evaluated in a Modified Ludzack–Ettinger (MLE) activated sludge treatment system. Before shock-loading experiments, batch extant respirometric assays determined that at 1 mg/L of total Ag, nitrification inhibitions by AgNPs (average size = 1–29 nm) and Ag + ions were 41.4% and 13.5%, respectively, indicating that nanosilver was more toxic to nitrifying bacteria in activated sludge than silver ions. After a 12-h period of nanosilver shock loading to reach a final peak silver concentration of 0.75 mg/L in the MLE system, the total silver concentration in the mixed liquor decreased exponentially. A continuous flow-through model predicted that the silver in the activated sludge system would be washed out 25 days after the shock loading. Meanwhile, a prolonged period of nitrification inhibition (>1 month, the highest degree of inhibition = 46.5%) and increase of ammonia/nitrite concentration in wastewater effluent were observed. However, nanosilver exposure did not affect the growth of heterotrophs responsible for organic matter removal. Microbial community structure analysis indicated that the ammonium-oxidizing bacteria and nitrite-oxidizing bacteria, Nitrospira, had experienced population decrease while Nitrobacter was washed out after the shock loading.

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.

Performance evaluation of hybrid and conventional sequencing batch reactor and continuous processes

Bench-scale systems, using conventional and compact hybrid activated sludge configurations, were set up to evaluate the systems' nitrification-denitrification performance, operating sludge age/MLSS concentration and sludge settleability at a Hong Kong municipal STW. Configurations tested were the continuous clarifier modified Ludzack Ettinger (MLE) and the sequencing batch reactor (SBR) with and without hybrid suspended biofilm carriers. Results demonstrated that the hybrid SBR and MLE systems consistently achieved close to complete nitrification (effluent NH4-N = 2.4 and 6.9 mg/L) and 75% and 67% removal of nitrogen (N) (effluent NO3-N < 10 mg/L) with an overall hydraulic retention time of only 7.5 hours, operating sludge age as short as 5.2 days, and mixed liquor suspended solids concentration of approximately 1,300 mg/L with a sludge volume index of 109 and 229 mL/g, respectively. The most sensitive and slowest growing nitrifiers attached to the hybrid biofilm carriers. This allowed the hybrid processes to be operated at a sludge age shorter than the critical nitrifying sludge age while still retaining near complete nitrification. In contrast, to achieve complete nitrification, the conventional MLE system needed to be operated at 1.5 to 2.5 times the critical sludge age. These results indicate that the hybrid MLE configuration is a suitable process for use in upgrading existing conventional works for N removal and for increasing hydraulic capacity of existing N removal works, without major civil works modifications, in Hong Kong. For new works, consideration might be given to the use of the hybrid SBR, which shows a more stable N removal performance than the MLE process due to its inherent in-basin equalization capacity and better reaction conditions for nitrification in terms of higher initial NH4-N level. It was also observed that the conventional SBR produced better nitrification performance than the hybrid MLE process tested. Design parameters and operating conditions of the hybrid systems should be subjected to further full-scale trial for higher hydraulic capacity and N removal performance.

Pre-denitrification and pre- and post-denitrification treatment of high-ammonia landfill leachate

This bench-scale study investigated the nitrogen-removal capabilities of two different biological process configurations treating methanogenic-state landfill leachate containing up to 1200 mg N/L of ammonia. The first configuration was a pre-denitrification system known as the modified Ludzack-Ettinger (MLE) process. Large clarifier sludge recycle flows, set to yield clarifier recycle ratios of 7:1 and 8:1, were evaluated as a means to reduce effluent NOx concentrations. A pre- and post-denitrification system, known as the four-stage Bardenpho process, was the second configuration evaluated. The MLE systems (20 day aerobic solids retention time (SRT)) were capable of producing effluent containing about 50 mg N/L of ammonia and 200-235 mg N/L of total inorganic nitrogen (ammonia + NOx) when treating leachate containing approximately 1200 mg N/L of ammonia. In contrast, effluent from the four-stage Bardenpho system contained less than 1 mg N/L of ammonia and 15 mg N/L of NOx, when treating 1100 mg N/L ammonia leachate. An aerobic number 1 SRT of 20 days (total aerobic SRT approximately equal to 40 days) was used with aerobic number 1 and clarifier sludge recycle ratios of 4:1 and 3:1, respectively. The ammonia-removal potential of both systems was clearly demonstrated but each system also showed certain disadvantages, characteristic of each process.Key words: ammonia-N, anoxic denitrification, leachate treatment, nitrification, pre-denitrification.