Modified Ludzack-Ettinger Process Research Articles

Greenhouse gas production from an intermittently dosed cold-climate wastewater treatment wetland

This study explores the greenhouse gas (GHG) fluxes of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) from a two-stage, cold-climate vertical-flow treatment wetland (TW) treating ski area wastewater at 3 °C average water temperature. The system is designed like a modified Ludzack-Ettinger process with the first stage a partially saturated, denitrifying TW followed by an unsaturated nitrifying TW and recycle of nitrified effluent. An intermittent wastewater dosing scheme was established for both stages, with alternating carbon-rich wastewater and nitrate-rich recycle to the first stage. The system has demonstrated effective chemical oxygen demand (COD) and total inorganic nitrogen (TIN) removal in high-strength wastewater over seven years of winter operation. Following two closed-loop, intensive GHG winter sampling campaigns at the TW, the magnitude of N2O flux was 2.2 times higher for denitrification than nitrification. CH4 and N2O emissions were strongly correlated with hydraulic loading, whereas CO2 was correlated with surface temperature. GHG fluxes from each stage were related to both microbial activity and off-gassing of dissolved species during wastewater dosing, thus the time of sampling relative to dosing strongly influenced observed fluxes. These results suggest that estimates of GHG fluxes from TWs may be biased if mass transfer and mechanisms of wastewater application are not considered. Emission factors for N2O and CH4 were 0.27 % as kg-N2O-N/kg-TINremoved and 0.04 % kg-CH4-C/kg-CODremoved, respectively. The system had observed seasonal emissions of 600.5 kg CO2 equivalent of GHGs estimated over 130-days of operation. These results indicate a need for wastewater treatment processes to mitigate GHGs.

Effects of Nitrate Recycle on the Sludge Densification in Plug-Flow Bioreactors Fed with Real Domestic Wastewater

The impact of adding a modified Ludzack–Ettinger (MLE) configuration with Nitrate Recycle (NRCY) on continuous-flow aerobic granulation has yet to be explored. The potential negative effects of MLE on sludge densification include that: (1) bioflocs brought by NRCY could compete with granules in feast zones; and (2) carbon addition to anoxic zones could increase the system organic loading rates and lead to higher feast-to-famine ratios. Two pilot-scale plug flow reactor (PFR) systems fed with real domestic wastewater were set up onsite to test these hypotheses. The results showed that MLE configuration with NRCY could hinder the sludge granulation, but the hindrance could be alleviated by the NRCY location change which to some extent also compensates for the negative effect of higher feast-to-famine ratios due to carbon addition in MLE. This NRCY location change can be advantageous to drive sludge densification without a radical washout of the sludge inventory, and had no effects on the chemical oxygen demand (COD) and nitrogen removal efficiencies. The PFR pilot design for the MLE process with a modified NRCY location tested in this study could be developed as an alternative to hydrocyclones for full-scale, greenfield, continuous sludge densification applications.

Optimizing dissolved oxygen requirement and energy consumption in wastewater treatment plant aeration tanks using machine learning

Most aeration tanks in wastewater treatment plants (WWTPs) operate at fixed dissolved oxygen (DO) concentrations of 2.0 mg/L. Such control systems do not consider various influent loadings. Thus, it does not respond effectively to fluctuating influent behavior, resulting in energy and cost wastage. This paper proposes a dynamic supervised machine-learning model dependent on real-time influent biochemical oxygen demand predictions and biological treatment oxygen constraints that have not been considered in previous studies for optimizing air-blower operation in WWTP aeration tanks. The model is tested against WWTP operating based on the modified Ludzack–Ettinger process. The dataset covers three years and two months of operation, containing 1155 daily readings. The Random Forest and Gradient Boost models predicted the optimum DO concentration by achieving a 1.00 coefficient of determination and 0.01 mean absolute error. The optimization led to a 23 % reduction in energy consumption. Such an intelligence framework can be extended to other air-blower applications and generalized nationwide to optimize energy consumption and cost savings for intelligent WWTPs. The proposed system is distinguished by being automated, intelligent, and following quality assurance and risk management approaches to predict the optimum DO setpoint, suppress the treated effluent quality violation risks, and enhance environmental protection.

Control parameters in three-stage deammonification process for a mature leachate treatment based on a traditional Modified Ludzack-Ettinger process

This study evaluated a three-stage deammonification process consisting of a sequentially Modified Ludzack-Ettinger (denitritation (DN) and partial nitritation (PN)) and anaerobic ammonium oxidation (ANAMMOX) for the treatment of mature leachate. In the initial stage, the nitrogen removal performance by two-stage deammonification was evaluated without an internal recycle (IR). The results showed that the ANAMMOX activity was severely inhibited from 0.19 to 0.03 gN/gVSS/d despite the stable partial nitritation. As inhibitors of ANAMMOX activity, the toxic effects of Refractory organic matter (ROM) and nitrite were found to deteriorate the stability of the process, and in particular, the ROM severely inhibited the activity. A three-stage deammonification process with the IR was implemented to alleviate the inhibition effects. As the IR was increased from 0 to 2Q, the ROM and nitrogen loads decreased by 35.3% and 27.8%, respectively. In addition, improved DN efficiency with external carbon sources allowed the ROM to serve as a potential electron donor for denitritation. With stabilization of ANAMMOX activity, the nitrogen removal performance rapidly stabilized. A nitrogen removal rate of 0.49 ± 0.02 kg/m3/d could be achieved with a nitrogen removal efficiency of 92.1 ± 2.1%.

How elevation dictates technology selection in biological wastewater treatment

Most wastewater treatment facilities are built using procedures from previous designs which are predominantly from sites and regions not located at high elevation. Recognizing this limitation, we assessed the effects of elevation above sea level on the suitability of process configurations and technologies as well as their associated energy costs. Using the International Water Association (IWA) benchmark simulation model No. 2 (modified Ludzack-Ettinger process layout) as a reference, we simulated scenarios including different activated sludge process configurations, operating under different environmental and process conditions. In order to include a wide sample of environmental conditions, data on atmospheric pressure, wastewater temperature, air temperature, and relative humidity (for average, warmest, and coldest months) were collected from municipal wastewater treatment plants located at different latitudes and elevations. The results confirm that elevation is a driver against the selection of diffused aeration technologies. Aeration costs for aerobic wastewater treatment are highly influenced by local project conditions, particularly by elevation and wastewater temperature, which together influence the driving force for oxygen transfer into water. When the driving force is low, operating costs are high. Recommendations for designing treatment processes effectively, including diffused aeration systems operating at high elevations above sea level, are proposed.

Enhancing nitrogen removal and reducing aeration energy for wastewater treatment with intermittent Modified Ludzack-Ettinger process: A field demonstration

Previously an enhanced nitrogen removal process, i.e., intermittent Modified Ludzack-Ettinger (iMLE), was developed by incorporating intermittent aeration into the MLE process. In this research, a field demonstration of iMLE process on enhancing nitrogen removal was conducted in Shenzhen Guangming Wastewater Treatment Plant (WWTP) at a daily treatment capacity of 25,000 m3/d. Results indicated that, when operating the iMLE process with dissolved oxygen (DO) based control mode, its effluent chemical oxygen demand (COD) and ammonia concentrations were consistently less than 30 mg/L and 1.5 mg/L, respectively, similar to the original two-stage Anoxic/Oxic (A/O) process with continuous aeration. Even though the influent had insufficient organic matter (BOD5/TN = 2.5), the effluent TN concentration in the iMLE was still consistently below the new limit of 10 mg-N/L, with an average and removal rate of 6.1 ± 1.0 mg-N/L and 78%, respectively. This performance was similar to that in the two-stage A/O process equipped with step feed and external carbon addition. Without the addition of external carbon in the iMLE process, it saved approximately 0.16 Chinese yuan for one cubic meter of wastewater treated. In addition to eliminating external carbon addition, the iMLE process decreased the air consumption by 20–30%, which would also reduce operation cost. Therefore, the iMLE process operated with appropriate DO control could reduce chemical cost and aeration energy use synergistically, which provides a cost-effective approach for WWTP upgrade.

Excess Sludge Reduction Using a High-pressure Jet Device via a Modified Ludzack-Ettinger Process: Performance and Microbial Communities

Excess Sludge Reduction Using a High-pressure Jet Device via a Modified Ludzack-Ettinger Process: Performance and Microbial Communities

Upgrading of Tafresh municipal wastewater treatment plant (TMWTP) using the Modified Ludzack-Ettinger (MLE) process

The present study aimed to evaluate the treatment efficiency of the modified Ludzack-Ettinger (MLE) process using the conventional activated sludge (CAS) in Tafresh city, located in Iran during October-December 2016 (before upgrading) and October-December 2017 (after upgrading to the MLE process). The measured parameters in the study included chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), nitrate-nitrogen, total suspended solids, phosphate, dissolved oxygen, ammonium-nitrogen, and pH. According to the obtained results, the treatment efficiency of the MLE process based on the BOD5 and COD was 92.11% and 91.20%, respectively. On the other hand, the treatment efficiency of the CAS process (before upgrading) based on the BOD5 and COD removal was 48.55% and 56.76%, respectively. Therefore, it could be concluded that the MLE process was able to successfully upgrade wastewater treatment services.

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.

Enhanced removal of total nitrogen and total phosphorus by applying intermittent aeration to the Modified Ludzack-Ettinger (MLE) process

In the conventional preanoxic Modified Ludzack-Ettinger (MLE) process, the nitrified mixed liquor cannot be completely returned to the preanoxic zone for denitrification. In this study, we applied intermittent aeration to the MLE process to enhance denitrification and total phosphorus (TP) removal. Pilot-scale test results indicated that, when treating municipal wastewater with a carbon (represented by five-day biological oxygen demand) to total nitrogen (TN) ratio (e.g. C/N ratio) of 2.4 or greater, the effluent ammonia, TN, and TP were generally less than 0.5 mg-N/L, 5 mg-N/L, and 0.5 mg-P/L, respectively. The removal efficiencies of both TN and TP were approximately 90%. Under extremely low temperature of 9.3 °C and low C/N ratio of 1.6 conditions, this process still removed 76% of TN and 56% of TP. Compared to the conventional MLE process, the implementation of intermittent aeration significantly improved TN and TP removal and also saved aeration energy by 10%. Existing MLE plants can be easily upgraded to this intermittent aeration mode to achieve enhanced nutrient removal while saving energy.

Effects of recirculation rate of nitrified liquor and temperature on biological nitrification–denitrification process using a trickling filter

AbstractIn the modified Ludzack–Ettinger process, high‐energy input is required in a nitrification tank. To address this issue, a new biological nitrification–denitrification system was constructed with a trickling filter for nitrification. The effects of recirculation rate of nitrified liquor and temperature through the treatment of municipal wastewater were evaluated. The highest DN removal efficiency was observed at 6.5 h of hydraulic retention in the denitrification tank and 350% of recirculation rate of nitrified liquid against the influent flow rate. The DN removal efficiencies did not reach theoretical values for all conditions tested because the COD/N ratios in the influent often decreased to less than 5 g‐COD/g‐N and temperatures dropped to less than 15°C in winter. The former inhibited the denitrification process and the latter significantly decreased the bioactivity of nitrifying bacteria. As such, this system is suitable in tropical and subtropical areas with annual minimum temperatures of over 15°C.

Comprehensive Numerical Modeling of Greenhouse Gas Emissions from Water Resource Recovery Facilities.

A numerical model was developed to comprehensively predict greenhouse gas (GHG) emissions from water resource recovery facilities. An existing activated sludge model was extended to include a nitrifier-denitrification process and carbon dioxide (CO₂) as a state variable. The bioreactor model was coupled to a process-based digester model and an empirical model of indirect CO₂emissions. Direct emissions were approximately 90% of total GHG emissions for a plantwide simulation using the Modified Ludzack-Ettinger process. Biogenic CO₂, nitrous oxide (N₂O), and methane (CH₄) represented 10, 43, and 34% of total emissions. Simulating a dissolved oxygen controlled closed-loop system reduced both sensitivity and uncertainty of GHG emissions. Nitrous oxide emissions were much more sensitive under different design and operating conditions compared to CH₄and CO₂, indicating a significant mitigation potential. An uncertainty analysis found that the uncertainty in GHGs emissions estimates could be significant. Nitrous oxide emissions dominated in both magnitude and uncertainty.

Levels of Norovirus and <i>E. coli</i> in Untreated, Biologically Treated and UV-Disinfected Sewage Effluent Discharged to a Shellfish Water

The efficacy of an activated sludge (modified Ludzack-Ettinger (MLE)) UV disinfection processes in removing human noroviruses and E. coli from sewage were compared with the prevalence of these microorganisms in a settled storm discharge from the same sewage treatment works. Both discharges impacted a designated oyster production area. The treatment process delivered average NoV and E. coli reductions of 2.9log10 and 5.2log10, respectively. Most E. coli reductions occurred during the UV disinfection process whereas the MLE process was comparatively more important in reducing NoV levels. A positive relationship was found between NoV removal and measured applied UV dose. The average levels of total NoV in the settled storm tank were of the same order of magnitude of those in screened raw influent at the works. These results highlight the importance of measures to reduce the impact of stormwater discharges to minimise the risk of NoV gastroenteritis associated with the consumption of oysters.

Performance of Self-Manufactured Ion Selective Microelectrode (ISME) for Continuous Monitoring of Ammonia and Nitrate Ions

The ion selective microelectrodes (ISME) have been applied to observe the continuous profiles of NO3-N and NH4-N in bulk solutions or biofilms. In order to evaluate the performance and applicability of ion concentration measuring system, the characteristics, such as slope of calibration curve, detection limit and potentiometric selectivity coefficient were investigated. The slopes of calibration curve showed high degree of correspondence for each target ion concentrations. And the detection limits of nitrate and ammonia ion selective microelectrode were 10-4.7 M and 10-4.4 M, respectively. These ion selective microelectrodes were proved that their own performance could be maintained for 16 days after making. NO3-N and NH4-N selective microelectrodes were also adapted to detect the continuous ion profiles of cilia media packed MLE (Modified Ludzack-Ettinger) process. And the monitored nitrate and ammonia ion profiles with the ion selective microelectrode were stable and well corresponded to the results with conventional ion chromatograph. However, the electric potential was unstable until 8 hr because of the unknown noise. The tip shape and performance of the ion selective microelectrode was stably kept over 2 days continuous monitoring.

Assessment and selection of best available technology (BAT) for wastewater facilities in the leather tanning and finishing industry

Determining the best available technology (BAT) that is economically viable is indispensable in managing industrial wastewater discharging facilities. In this study, a BAT evaluation tool was applied to a case study of the leather tanning and finishing industry in South Korea. In examining the evaluation, the following factors and flows were considered: (1) information on source characterization, (2) selection of candidate technology, (3) analysis of regulatory compliance, (4) assessment of environmental factors (non water quality factors), (5) assessment of economic feasibility, (6) assessment of technical factors, and (7) selection of the BAT.Wastewater discharge from the leather tanning and finishing industry contains high concentrations of organic compounds, chromate, nitrogen, and sulfide, of which nitrogen is concerning, being significantly higher than the other factors in general. Six treatment technologies were evaluated for the industry. Based on the results, technology option F (chemical precipitation+modified Ludzack–Ettinger process+fenton process) was selected as the BAT for wastewater facilities in the leather tanning and finishing industry. The methods and results of this study can be used guide the development of policies for industrial wastewater management facilities.

Advanced Treatment of Wastewater from Food Waste Disposer in Modified Ludzack-Ettinger Type Membrane Bioreactor

This paper proposes a modified Ludzack-Ettinger (MLE) type membrane bioreactor (MBR) as a method of treatment for wastewater from food waste disposer. Micro-membrane filtration allows for an extremely low concentration of suspended solids in the effluent. The effluent of the reactor in question is characterized by a relatively high level of non-biodegradable organics, containing a substantial amount of soluble microbial products and biomass. Results obtained in this paper by measurement of membrane fouling are consistent with biomass concentration in the reactor, as opposed to chemical oxygen demand (COD). The MLE process is shown to be effective for the treatment of wastewater with a high COD/N ratio of 20, resulting in are markedly high total nitrogen removal efficiency. Denitrification could be improved at a higher internal recycle ratio. Despite the low concentration of influent phosphorus, the phosphorus concentration of the outflow is seen to be relatively high. This is because outflow phosphorous concentration is related to COD consumption, and the process operates at along solids retention time.

The community analysis of ammonia-oxidizing bacteria in wastewater treatment plants revealed by the combination of double labeled T-RFLP and sequencing

The functional gene of amoA, which produces the α-subunit of ammonia monooxygenase (AMO), has been analyzed to reveal the microbial community structure of ammonia-oxidizing bacteria (AOB) by culture-independent methods. In this study, the distribution of the amoA gene in 10 wastewater treatment plants (WWTPs) was revealed by the fingerprinting method of terminal restriction fragment length polymorphism (T-RFLP) and comparative sequencing. T-RFLP showed diverse communities of AOB in the modified Ludzack-Ettinger process, in the anaerobic-anoxic-oxic processes, in the hanging biological contactor, and in the sequencing batch reactor. In all of these environments, long solid retention time (SRT) was expected to be the critical factor for maintaining the diverse AOB community structure. Because T-RFLP does not offer sufficient information to confirm the phylogenetic information of AOB, the microbial community structures were analyzed by comparative sequencing for seven samples that were selected by the statistical categorization using principal component analysis (PCA) among 14 samples. The phylogenetic tree of 21 operational taxonomic units (OTUs) among 88 clones obtained in this study revealed that AOB of Nitrosomonas oligotropha and europaea lineages were predominant in WWTPs. Double labeled T-RFLP produced group-specific terminal restriction fragments (T-RFs) representing several groups of AOB and offered advanced resolution comparing with the single labeled T-RFLP.

Microbial community analysis in the autotrophic denitrification process using spent sulfidic caustic by denaturing gradient gel electrophoresis of PCR-amplified genes

Spent sulfidic caustic (SSC) produced from petrochemical plants contains a high concentration of hydrogen sulfide and alkalinity, and some almost non-biodegradable organic compounds such as benzene, toluene, ethylbenzene and xylenes (BTEX). SSC is mainly incinerated with auxiliary fuel, leading to secondary pollution problems. The reuse of this waste is becoming increasingly important from economic and environmental viewpoints. To denitrify wastewater with low COD/N ratio, additional carbon sources are required. Thus, autotrophic denitrification has attracted increasing attention. In this study, SSC was injected as an electron donor for sulfur-based autotrophic denitrification in the modified Ludzack-Ettinger (MLE) process. The efficiencies of nitrification, COD, and total nitrogen (TN) removal were evaluated with varying SSC dosage. Adequate SSC injection exhibited stable autotrophic denitrification. No BTEX were detected in the monitored BTEX concentrations of the effluent. To analyse the microbial community of the MLE process, PCR-DGGE based on 16 S rDNA with EUB primers, TD primers and nirK gene with nirK primers was performed in order to elucidate the application of the MLE process to SSC.

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.

Comparison of 4-Stage Biological Aerated Filter (BAF) with MLE Process in Nitrogen Removal from Low Carbon-to-Nitrogen Wastewater

Performance of a 4-stage biological aerated filter (BAF) system was evaluated with low TCOD/TKN ratio municipal wastewater, focusing on nitrogen removal. To evaluate the BAF system, a modified Ludzack-Ettinger (MLE) process was set up and compared to the BAF system. Laboratory experiments were conducted to examine the effect of hydraulic retention time (HRT). Results of the long-term operation of both systems showed that overall NH4 -N removal efficiency of the MLE was drastically reduced (from 98% to 17%) as hydraulic retention time decreased from 6 h to 3 h, whereas that of the BAF was stable with the removal efficiency of 95–96% on average, regardless of HRT applied. The effectiveness of the proposed BAF was observed in denitrification performance. Effluent NOx-N concentrations of the BAF system were lower than MLE (average of 5 mg/L) within 95% confidence level at the HRT of 6 h. At a total chemical oxygen demand (TCOD) to total kjeldahl nitrogen (TKN) ratio of 3.6, the effluent NO3-N concentration of...