Post-denitrification Process Research Articles

Modeling generation of microorganism-derived dissolved organic nitrogen (mDON) under different carbon-to-nitrogen ratios in post-denitrification process

Quantifying microorganism-derived dissolved organic nitrogen (mDON) formed from microbial activities is a prerequisite for reducing effluent nitrogen. In this work, a new model based on activated sludge model for nitrogen (ASMN) is proposed for determining mDON formation together with its dynamics in post-denitrification under different carbon-to-nitrogen (C/N) ratios of 3, 4, 5, and 6. This model incorporates mDON as a separate component among four-step denitrification and introduces three new mDON-related parameters (i.e., fH,mDON, KH,mDON, and KI4SS) to develop mDON production and utilization equations. The model was calibrated and established with data from an experiment using synthetic wastewater, demonstrating its capability of accurately simulating mDON generation (R2 = 0.909–0.986). Accordingly, the simulated results successfully captured the experimental trends, suggesting that higher C/N ratios were preferred for mitigating mDON generation. The model applicability was further tested by predicting mDON generation in real wastewater, producing reasonable predicted results of formed mDON (1.16–1.63 mg/L). These predicted results were also indirectly confirmed by newly produced nitrogenous molecules (i.e., lipid-, carbohydrates-, and protein/amino sugars-like molecules). Overall, this work offers a tool to quantify mDON which benefits controlling mDON toward minimizing the adverse impacts of effluent organic nitrogen on receiving waters.

Hydraulic retention time optimization achieved unexpectedly high nitrogen removal rate in pilot-scale anaerobic/aerobic/anoxic system for low-strength municipal wastewater treatment

Applications of post-denitrification processes are subjected to low reaction rates caused by a lack of carbon resources. To offer a solution for reaction rate promotion, this research found a pilot-scale anaerobic/aerobic/anoxic bioreactor treating 55–120 m3/d low-strength municipal wastewater for 273 days. A short hydraulic retention time (HRT, 5–6 h) and a high nitrogen removal rate (63.2 ± 9.3 g-N/m3·d) were achieved using HRT optimization. The effluent total nitrogen concentration was maintained at 5.8 ± 1.4 mg/L while operating at a high nitrogen loading rate of 86.2 ± 12.8 g-N/m3·d. The short aeration (1.25–1.5 h) minimized the Glycogen loss. The endogenous denitrification rate increased to above 1.0 mg/(g-VSS·h). The functional genus Ca. Competibacter enriched to 2.3 %, guaranteeing the efficient post-denitrification process. Dechloromonas rose to 1.1 %, aiding in the synchronous phosphorus removal. These findings offered fresh insights into AOA processes to achieve energy/cost-saving wastewater treatment.

Enhancing simultaneous nitrate and phosphate removal in sulfur‑iron (II) autotrophic denitrification biofilters by endogenous magnetic fields: Performance and mechanism

The sulfur‑iron (II) autotrophic denitrification (SIAD) technology can achieve simultaneous nitrogen and phosphorus removal from wastewater with a low C/N ratio without an organic carbon source. However, the low nutrient removal load limits its large-scale application. To enhance N removal load and decrease the effluent SO42− concentration, we propose a novel bioaugmentation technology by adding magnetite to a sulfur‑iron (II) biofilter to generate an endogenous magnetic field (EMF). The treatment characteristics of two biofilters with sulfur‑iron (II) (S1) and sulfur‑iron (II)-magnetite (S2) were comparatively studied in long-term experiments. The maximum nitrate removal load of the S2 system was 1.02 ± 0.04 kg N/(m3·d), 1.27 times higher than that of S1. The S2 system also showed a 40 % higher PO43− removal efficiency compared to S1. The production of SO42− was reduced by >12.34 % in S2 with 5.40 g SO42−/g N. The EMF significantly increased nitrate reductase activity by 3.50 times and enhanced the size of the attached microbial bacterial population by 30 %–50 %. Functional gene prediction indicated that amino acid metabolism, cell activity, N/S metabolism were improved under the EMF, and the genera Ferritrophicum and Thiobacillus were the predominant autotrophic bacteria, forming a symbiotic relationship. Our study demonstrates a novel solution to resolve the limits of high sulfate byproduct and low nutrient removal load in SIAD biofilters, which could promote large-scale application of SIAD process as a highly efficient and low-cost postdenitrification process.

Potential of food waste-derived volatile fatty acids as alternative carbon source for denitrifying moving bed biofilm reactors

Fossil-based materials such as methanol are frequently used in the denitrification process of advanced biological wastewater treatment as external carbon source. Volatile fatty acids (VFAs) produced by anaerobic digestion of food waste, are sustainable compounds with the potential to act as carbon sources for denitrification, reducing carbon footprint and material costs. In this study, the effectiveness of food waste-derived VFAs (AD-VFA) was investigated in the post-denitrification process in comparison with synthetic VFA and methanol as carbon sources. Acetic acid had the highest rate of disappearance among single tested VFAs with a denitrification rate of 0.44 g NOx-N removed/m2/day, indicating a preferential utilization pattern. While AD-VFA had a denitrification rate of 0.61 mg NOx-N removed/m2/day, sVFA had a rate of 0.57 mg NOx-N removed/m2/day, indicating that impurities in AD-VFA did not play substantial role in denitrification. AD-VFA proved to be promising carbon source alternative for denitrification in wastewater treatment plants.

Coupled sulfur and electrode-driven autotrophic denitrification for significantly enhanced nitrate removal

Elemental sulfur (S0)-based autotrophic denitrification (SAD) has gained intensive attention in the treatment of secondary effluent for its low cost, high efficiency, and good stability. However, in practice, the supplementary addition of limestone is necessary to balance the alkalinity consumption during SAD operation, which increases water hardness and reduces the effective reaction volume. In this study, a coupled sulfur and electrode-driven autotrophic denitrification (SEAD) process was proposed with superior nitrate removal performance, less accumulation of sulfate, and self-balance of acidity-alkalinity capacity by regulating the applied voltage. The dual-channel electron supply from S0 and electrodes made the nitrate removal rate constant k in the SEAD process 3.7-5.1 and 1.4-3.5 times higher than that of the single electrode- and sulfur-driven systems, respectively. The S° contributed to 75.3%-83.1% of nitrate removal and the sulfate yield during SEAD (5.67-6.26 mg SO42−/mg NO3−-N) was decreased by 17%-25% compared with SAD. The S0 particle and electrode both as active bio-carriers constructed collaborative denitrification communities and functional genes. Pseudomonas, Ralstonia and Brevundimonas were the dominant denitrifying genera in S0 particle biofilm, while Pseudomonas, Chryseobacterium, Pantoea and Comamonas became dominant denitrifying genera in the cathode biofilm. The narG/Z/H/Y/I/V, nxrA/B, napA/B, nirS/K, norB/C and nosZ were potential functional genes for efficient nitrate reduction during the SEAD process. Metagenomic sequencing indicated that S0 as an electron donor has greater potential for complete denitrification than the electrode. These findings revealed the potential of SEAD for acting as a highly efficient post denitrification process.

Influence of additional methanol on both pre- and post-denitrification processes in treating municipal wastewater.

Changes in functional properties of biological denitrification in the long-term use of methanol were explored in both pre- and post-denitrification processes. The two systems employed were sequencing batch reactor (SBR) using post-denitrification in temporal sequence, and Carrousel oxidation ditch, which was equipped with a separate pre-denitrification zone. In the SBR, stable nitrate reduction rates reached after 37 days elapsed with addition of methanol (TOC/N = 1.4-1.8) at the start of anoxic phase, and specific denitrification rate increased from 0.378 mgNOx-N·(gVSS·h)-1 to 2.406 mgNOx-N·(gVSS·h)-1. Besides, by means of nitrogen uptake rate (NUR) batch tests based on methanol-adapted sludge, the appropriate range of TOC/N ratios for complete denitrification was estimated to be 1.10-2.68. By comparison, the Carrousel oxidation ditch that was fed with methanol in the anaerobic zone took fewer days (29 days) to obtain a constant effluent nitrate. Moreover, the denitrification yield in ditch was elevated from an initial value of 0.082 mgTN/mgCOD to 0.123 mgTN/mgCOD, and the nitrogen removal efficiency reached up to a level of 68%. The focus on denitrification potential with external methanol is valuable to provide information for developing carbon dosage control, as well as predict the nitrate effluent quality of the plant.

MODEL ESTIMASI BIOKINETIKA UNTUK PROSES POST-DENITRIFIKASI AIR LIMBAH DOMESTIK PADA UNIT ANAEROBIC BAFFLED REACTOR

This study developed a combination of Continuous Stirred Tank Reactor (CSTR) for the acid fermentation and the Anaerobic Baffled Reactor (ABR) post-denitrification through high nitrite injection. Volatile Fatty Acids (VFAs) as a substrate for the post-denitrification process were optimally produced in the acid fermentation process. The aim of this study was to obtain the estimation of biokinetic values to predict the effluent wastewater quality in ABR post-denitrification process under unsteady state. The reactor was operated for HRT 7 days at temperature 25-28 ˚C and pH 6-7,2. The influent and effluent substrate concentration were monitored continuously for 160 days. Post-denitrification biokinetic from the Contois equation resulted in the value of hydrolysis rate (Kh) of 0.077 day-1, the substrate transport rate (k) of 4.364×10-6 Lmg-1day-1, maximum specific growth rate (μmax) of 0.559 day-1, half saturation constant (KS) of 0.209 mgL-1, microbial decay coefficient (b) of 0.0145 days-1; yield coefficient (Y) of 0.084 g-VSSg-COD-1. The validation of biokinetic parameters based on statistical analysis showed fairly precise results following the trend of experimental data to determine the substrate concentration in the effluent unit. Therefore, the biokinetic values can be applied in the design of ABR post-denitrification using primary sludge incorporation with high strength nitrate.Keywords: Anaerobic baffled reactor, biokinetics, Contois, hydrolysis, post-denitrification.

Testing of a novel IFAS-MBR process with co-precipitation

Abstract IFAS-MBR with co-precipitation, not yet commonly used in practice, will result in a very compact process for nutrient removal. The process, based on a combined pre- and post-denitrification IFAS process with membrane separation (IFAS-MBR), was tested in two parallel small-scale plants. Train A was operated with co-precipitation in order to achieve high removal of total P (TP). Train B, without co-precipitation, served as a control. Due to the coagulant (Al) addition, the concern was precipitation on the biofilm carriers in the aerobic reactor in Train A. A small internal air-lift pump proved to be very efficient in controlling biofilm thickness and removing excess biofilm mass as needed. A coagulant dose equivalent to an Al/TP molar ratio of 1.9 was necessary to achieve 99% TP removal and 0.10 mg TP/l in the effluent of Train A. Very good removal of total N was achieved in both trains. Train A had a biofilm nitrification rate of 0.65 g NH4-N/m2d at 12–13 °C and 5.2–5.6 mg O2/l. The tests demonstrated that an IFAS-MBR process with co-precipitation and an aerobic suspended biomass SRT of 5–10 days is feasible, and that all the performance goals set up for the full-scale plant were achieved.

Oxygen mass transfer and post-denitrification in a modified rotating drum biological contactor

A lab-scale rotating drum biological contactor (RDBC) was implemented and accessed concerning abiotic oxygen transfer rate and treatment capacity for domestic sewage. The dissolved oxygen (DO) transfer test showed that the rotational speed and the submergence level of drum greatly affected the DO in bulk liquid with the volumetric oxygen transfer coefficient KLa of 2.3-25.9 h−1, effectively achieving anaerobic/anoxic/aerobic conditions in the reactor. The post-denitrification process was proposed using the RDBC to degrade the synthetic nitrogen-containing sewage wastewater. When the hydraulic retention time was 16 h, the flow distribution ratio was 3:1 and the anoxic rotational speed was 6 rpm, the effluent NH4+-N and TN were 2.3 mg L−1 and 7.3 mg L−1 with the NH4+-N and TN removal efficiency of 94.1% and 80.9%, respectively. The Nitrosomonas europaea and Candidatus Kuenenia dominated in the anoxic carried-biofilm, indicating that the coexisting of aerobic and anaerobic ammonium oxidation bacteria enhanced the TN loss in the post-anoxic tank. This study provides an innovative non-aeration technology for biological wastewater treatment and has implications to simplify operation and save energy.

Coupled Sulfur and Iron(II) Carbonate-Driven Autotrophic Denitrification for Significantly Enhanced Nitrate Removal.

Sulfur-based denitrification process has attracted increasing attentions because it does not rely on the external addition of organics and avoids the risk of COD exceeding the limit. Traditionally, limestone is commonly employed to maintain a neutral condition (SLAD process), but it may reduce the efficiency as the occupied zone by limestone cannot directly contribute to the denitrification. In this study, we propose a novel sulfur-based denitrification process by coupling with iron(II) carbonate ore (SICAD system). The ore was demonstrated to play roles as the buffer agent and additional electron donor. Moreover, the acid produced through sulfur driven denitrification was found to promote the Fe(II) leaching from the ore and likely extend the reaction zone from the surface to the liquid. As a result, more biomass was accumulated in the SICAD system compared with the controls (sulfur, iron(II) carbonate ore and SLAD systems). Owing to these synergistic effects of sulfur and iron(II) carbonate on denitrification, SICAD system showed much higher denitrification rate (up to 720.35 g·N/m3·d) and less accumulation of intermediates (NO2- and N2O) than the controls. Additionally, sulfate production in SICAD system was reduced. These findings offer great potential of SICAD system for practical use as a highly efficient postdenitrification process.

A novel storage driven granular post denitrification process: Long-term effects of volume reduction on phosphate recovery

Anoxic granular biomass with enhanced biological phosphorus (P) removal was used in a post-denitrification configuration to concentrate P in wastewater. The study examined the use of anoxic granules to facilitate application of volume reduction to create a P-enriched stream (>100 mg-P/L). The results indicated the importance of maintaining a food to microorganism (F/M) ratio of ∼0.124 g-COD/g-MLSS.d to achieve P and nitrogen (N) removal close to 100%. While granulation required a short settling time and a high-volume exchange ratio, biomass wasting was essential to control the F/M ratio to maintain a suitable microbial diversity and abundance. Diversity and abundance were also impacted by volume reduction, but the effect of this was marginal compared with the effect of decreasing F/M ratio. Furthermore, a decrease in the F/M ratio enhanced sedimentation (SVI5 decreased from 55.5 to 32.0 mL/g-MLSS) but decreased dewaterability (capillary suction time increased from 15.5 s to 19.4 s). Recovery of P as a concentrated liquor had minimal impact on the bacterial diversity.

The ability of PAOs to conserve their storage-driven phosphorus uptake activities during prolonged aerobic starvation conditions

A post-denitrification process, known as enhanced biological phosphorus removal and recovery (EBPR-r), was recently developed to facilitate phosphorus (P) recovery from municipal wastewater. This process utilises a biofilm containing phosphate-accumulating organisms (PAOs) to capture P from wastewater and then release the captured P into a separate smaller stream for recovery. The addition of external carbon in the EBPR-r process is expected to be a main operating cost. Hence, it is important to ensure that the added carbon, which is stored internally as poly-β-hydroxy-alkanoates (PHA) within PAOs, is predominately used for P uptake. This study explored the ability of PAOs to conserve their storage-driven P uptake activities following exposure of the biofilm to oxidising and P-deficient conditions for extended periods (up to 7 days). Even after 2 days of exposure the biofilm retained a similar ability to up take P (1.20 ± 0.09 mg-P/g total solids). Beyond 2 days of exposure, a decline in P uptake activity was noted, with only 15% activity remaining by day 7. This study provides the first evidence of the ability of PAOs to conserve their storage-driven P uptake activities. This unique behaviour of PAOs may enable flexible operational strategies, such as infrequent carbon replenishment, to be implemented (i.e. facilitate multiple P uptake phases before an anaerobic carbon replenishment). Such flexibility may reduce the capital and operational costs of the EBPR-r process, increasing the economic incentive for P recovery from wastewater.

Acid Fermentation Process Combined with Post Denitrification for the Treatment of Primary Sludge and Wastewater with High Strength Nitrate

In this study, an anaerobic baffled reactor (ABR), combined with a post denitrification process, was applied to treat primary sludge from a municipal wastewater treatment plant and wastewater with a high concentration of nitrate. The production of volatile fatty acids (VFAs) was maximized with a short hydraulic retention time in the acid fermentation of the ABR process, and then the produced VFAs were supplied as an external carbon source for the post denitrification process. The laboratory scale experiment was operated for 160 days to evaluate the VFAs’ production rate, sludge reduction in the ABR type-acid fermentation process, and the specific denitrification rate of the post denitrification process. As results, the overall removal rate of total chemical oxygen demand (TCOD), total suspended solids (TSS), and total nitrogen (TN) were found to be 97%, 92%, 73%, respectively, when considering the influent into ABR type-acid fermentation and effluent from post denitrification. We observed the specific VFAs production rate of 0.074 gVFAs/gVSS/day for the ABR type-acid fermentation, and an average specific denitrification rate of 0.166 gNO3−-N/gVSS/day for the post denitrification. Consequently, we observed that a high production of VFAs from a primary sludge, using application of the ABR type acid fermentation process and the produced VFAs were then successfully utilized as an external carbon source for the post denitrification process, with a high removal rate of nitrogen.

Removal of pharmaceutical residues using ozonation as intermediate process step at Linköping WWTP, Sweden

Pilot tests as basis for the design, implementation and operation of a future full-scale oxidation plant completing the existing sewage treatment in Linköping, Sweden, were performed. Using an ozonation step between bio-sedimentation and post-denitrification processes, the primary goal was the removal of the highest priority substances to effluent water levels that will not cause adverse effects in the recipient considering the natural dilution. The study included initial emission screenings, dose control trials, treatment performance studies and eco-toxicity studies. At an ozone dose of 5 mg O3/L, most substances could be removed. Ecotoxicological tests showed no negative effect for the tested ozone doses. High levels of oxygen into the denitrification could be rapidly reduced in the biology. The number of bacteria in the treated water could be significantly reduced even at relatively low ozone doses. Based on these results, the planning for the full-scale implementation of the treatment system was initiated in 2015.

Characteristics of Nitrogen and Phosphorus Removal in Multiple Post-Denitrification Process with Different Aeration Rates

The nutrient (nitrogen and phosphorus) removal from municipal wastewater was investigated by sequencing batch reactor (SBR) with different aeration rates. The results indicated that the removal performances of nitrogen and phosphorus both increased first and then decreased with increasing aeration rates, and that the aeration rate should be controlled at 25 L.h–1 (dissolved oxygen = 2.7 mg.L–1) in order to achieve ideal removal efficiencies of total nitrogen (TN) and total phosphorus (TP). Aeration rate had a prominent effect on the occurrence of nitrification and denitrification (SND), and excessive aeration would weaken nitrogen removal during SND process. In contrast, excessive aeration had no effect on the release rate of the anaerobic phosphorus, and the decrease of these polyhydroxyalkanoates (PHAs) could significantly influence phosphorus uptake, which was very essential for controlling the biological phosphate removal.

S107 Characteristics of Nitrogen and Phosphorus Removal in Multiple Post-Denitrification Process with Different Aeration Rates

S107 Characteristics of Nitrogen and Phosphorus Removal in Multiple Post-Denitrification Process with Different Aeration Rates

Dissolved organic nitrogen (DON) during batch denitrification of low concentrations of nitrate using suspended and attached biomass.

The occurrence and removal of dissolved organic nitrogen (DON) is an issue of increasing importance for the reclamation of treated wastewater. Effluent DON may act as a precursor of disinfection by-products during wastewater disinfection and may contribute to eutrophication of receiving surface waters. The aim of this study was to understand the effect of the post-denitrification process on final effluent DON (organic nitrogen filtered by 0.45 μm pore size) concentration to further gain knowledge on how to optimize denitrifying filtration, in order to reach the required discharge standards. To evaluate DON variation, denitrification batch experiments were carried out with suspended and attached biomass under different shear conditions. For both conditions, with suspended and attached biomass, DON concentration did not increase or decrease during the denitrification process with addition of an external carbon source. Moreover, the increase of shear rate did not affect the DON concentration. Apparently, there is no direct link between DON evolution and the denitrification process itself.

Simultaneous phosphorus uptake and denitrification by EBPR-r biofilm under aerobic conditions: effect of dissolved oxygen

A biofilm process, termed enhanced biological phosphorus removal and recovery (EBPR-r), was recently developed as a post-denitrification approach to facilitate phosphorus (P) recovery from wastewater. Although simultaneous P uptake and denitrification was achieved despite substantial intrusion of dissolved oxygen (DO >6 mg/L), to what extent DO affects the process was unclear. Hence, in this study a series of batch experiments was conducted to assess the activity of the biofilm under various DO concentrations. The biofilm was first allowed to store acetate (as internal storage) under anaerobic conditions, and was then subjected to various conditions for P uptake (DO: 0-8 mg/L; nitrate: 10 mg-N/L; phosphate: 8 mg-P/L). The results suggest that even at a saturating DO concentration (8 mg/L), the biofilm could take up P and denitrify efficiently (0.70 mmol e(-)/g total solids*h). However, such aerobic denitrification activity was reduced when the biofilm structure was physically disturbed, suggesting that this phenomenon was a consequence of the presence of oxygen gradient across the biofilm. We conclude that when a biofilm system is used, EBPR-r can be effectively operated as a post-denitrification process, even when oxygen intrusion occurs.

An innovative membrane bioreactor (MBR) system for simultaneous nitrogen and phosphorus removal

Membrane filtration was integrated with a post-denitrification process to form an innovative membrane bioreactor (MBR) system for effective organic degradation and nutrient (N and P) removal. The system comprised of an aerobic tank, an anoxic tank, an intermediate sedimentation tank, and a membrane filtration tank. The sedimentation tank functioned not only as a rough settler for sludge–water separation before membrane filtration but also as an anaerobic chamber for P release. While half of the influent flowed into the aerobic tank, the other half was fed into the anoxic tank to favor the proliferation of phosphorus accumulating organisms (PAOs). The experiment was conducted continuously for about 430 days. With a short overall treatment time of less than 10h for municipal wastewater, the MBR-based process could achieve the total organic carbon, total nitrogen, and total phosphorus removals of around 94%, 85%, and 87%, respectively. The growth and activity of PAOs in the MBR system were evidenced by the significant P release in the anaerobic chamber followed by the luxury P uptake in the membrane tank. With the DAPI and PAOmix probe staining, the increases of PAOs and polyhydroxybutyrate (PHB) in sludge during the experiment were well observed under the fluorescent microscope.

MBR/NF/RO를 이용한 가축폐수처리와 후탈질/응집가압부상을 이용한 잉여슬러지 및 농축수 처리 기술

MBR/NF/RO를 이용한 가축폐수처리와 후탈질/응집가압부상을 이용한 잉여슬러지 및 농축수 처리 기술