The role of COD/N ratio on the start-up performance and microbial mechanism of an upflow microaerobic reactor treating piggery wastewater

Effects of carbon to nitrogen ratio on nitrogen removal in a single-stage microaerobic system: A model-based evaluation

Single-stage microaerobic systems have been proven to be effective for concurrent removal of ammonium and organic carbon from sewage. While mechanistic models derived from activated sludge models (ASMs) have simulated nutrients removal under microaerobic conditions, classic ASMs exhibit limitations in capturing the intricate effects of carbon to nitrogen (C/N) ratio on nitrogen removal performance. To address this issue, a mechanistic model modified from the classic ASMs was proposed to capture the combined inhibitory effects of carbon and ammonium on microaerobic systems. This modified model was established based on experimental data from a single-stage microaerobic reactor encompassing simultaneous nitrification-denitrification and anammox processes. The inhibition coefficient of C/N ratio was integrated into the process rate equations, and its effectiveness was validated through model performance evaluation. Compared to the classic models, the modified one achieved superior predictions for nitrite and nitrate nitrogen concentrations. Simulations revealed that under optimized conditions with a C/N of 4.57 and a dissolved oxygen (DO) of 0.41 mg/L, the system could achieve up to 95.5% of total nitrogen (TN) removal efficiency. Based on the simulation of substrate uptake/production rate, increasing the nitrogen loading rate (NLR) rather than organic loading rate (OLR) was crucial for efficient nitrogen removal. The proposed modified model served as a valuable tool for designing and optimizing similar biological wastewater treatment systems.

Integrated effects of operational temperature, HRT, and influent ammonium concentration on a CANON coupling with denitrification process treating for digested piggery wastewater: performance and microbial community

In this study, an improved system called the completely autotrophic nitrogen removal over nitrite (CANON) process was presented and coupled with denitrification for the treatment of digested piggery wastewater (DPW). The effects of operating parameters, including hydraulic retention time (HRT) (1.6 d → 1.0 d), influent NH₄⁺-N concentration (350 mg L^-1 → 600 mg L^-1), and temperature (41 ℃ → 17 ℃), on the nitrogen removal performance and response characteristics of microbial population were investigated. Results showed that all considered parameters caused a remarkable effect on NH₄⁺-N and total nitrogen removal efficiencies, and the chemical oxygen demand was more markedly affected by temperature. Candidatus_Kuenenia, Candidatus_Brocadia, Denitratisoma, norank_o_Xanthmonadales, norank_p_WWE3, and SM1A02 were the dominant genera influencing nitrogen removal in the improved CANON system for treating DPW. Redundancy discriminant analysis showed that the biological structure was positively correlated with the influent ammonium concentration, temperature, and HRT. The relative abundance of Candidatus_Kuenenia was perfectly correlated with HRT and temperature. However, environmental factors did not affect Candidatus_Brocadia and norank_p_WWE3. norank_c_Ardenticatenia, SM1A02, and norank_f_SJA-28 were all positively correlated with influent ammonium nitrogen concentration, but not correlated with HRT and temperature. The improved CANON process realized the nitrogen removal under high ammonium (NH₄⁺-N) concentration and low C/N wastewater.

COD/TN ratios shift the microbial community assembly of a pilot-scale shortcut nitrification-denitrification process for biogas slurry treatment

In this study, effects of carbon to nitrogen (COD/TN) ratios of biogas slurry on shortcut nitrification-denitrification in a pilot-scale integrated fixed film activated sludge (IFAS) system were investigated. Lowering the COD/TN ratio from 11.7 to 6.2 exerted a negative impact on shortcut nitrification-denitrification performance. Accordingly, the NH₃-N and TN removal rates decreased from 94.4 to 91.2% and 92.3 to 85.9%, respectively. The dynamics of microbial assembly was analyzed by MiSeq sequencing, and the denitrifying functional genes were quantified by qPCR. The results showed that ammonia oxidizing bacteria and amoA gene were more abundant on the biofilm of oxic tank, indicating they play a key role in NH₃-N removal. Autotrophic, endogenous, and fast heterotrophic kinetics denitrifiers were coexisted and enriched in the IFAS system with a decreasing of COD/TN ratio. TN removal was mainly affected by denitrifiers (including Arenimonas, Acidovorax, and Thaurea) harboring narG and nirS genes. Canonical correspondence analysis proved that COD/TN ratio was the most critical factor driving the succession of microbial community. Dissolved oxygen (DO) and pH were found positively correlated with denitrifiers at low COD/TN ratio conditions. As a result, NH₃-N and TN removal were effectively enhanced when the DO level in the oxic tank of IFAS system was increased to 1.0-3.0 mg/L.

A continuous-flow non-aerated microalgal-bacterial granular sludge process for aquaculture wastewater treatment under natural day-night conditions

This study developed a continuous-flow non-aerated microalgal-bacterial granular tubular reactor for aquaculture wastewater treatment under natural day-night conditions. Results showed that daytime was favorable for ammonia removal while nighttime for nitrate removal. Over 99% of nitrite-N could be removed over the day-night cycles at a hydraulic retention time of 6 h. However, the phosphorus removal was found to be sensitive to the weather condition, ranging from 35.0% to 96.6%. It was also observed that dissolved oxygen produced by microalgae in daytime was sufficient for creating a 6-h aerobic condition in nighttime for sustaining heterotrophic activity. Chlorella and Leptolyngbya were identified as the most abundant algae related to weather changes. Metagenomics analysis revealed that the high nitrite removal relied mainly on nitrite reduction. These experimental findings offer new insights into the non-aerated microalgal-bacterial granular sludge for environmentally sustainable aquaculture wastewater treatment.

Performance and nitrogen removal mechanism in a novel aerobic-microaerobic combined process treating manure-free piggery wastewater

A novel combined sequencing batch reactor (SBR) - up-flow microaerobic sludge reactor (UMSR) process was developed to treat manure-free piggery wastewater characterized by low COD/TN ratio and high NH₄⁺-N. The front-end SBR was designed to get an effluent with COD/TN ≤ 1 by removing COD, allowing the back-end UMSR to practice anammox for the simultaneous removal of TN and NH₄⁺-N. Fed with the raw piggery wastewater, the combined SBR-UMSR process was started up at 27℃ with a reflux ratio of 15:1 in the UMSR. After 230-days running, the removal of COD, TN, and NH₄⁺-N in the combined SBR-UMSR process reached 78.41%,85.05%, and 92.21%, respectively. 50.22% of COD in the wastewater was removed in the SBR, while 87.11% of NH₄⁺-N and 79.69% of TN were removed in the UMSR. Stoichiometry and bacterial function analysis revealed that the partial nitrification - anammox process was the dominant nitrogen removal approach in the UMSR.

Synergistic denitrification, partial nitrification - Anammox in a novel A2/O2 reactor for efficient nitrogen removal from low C/N wastewater

A biofilm-based anaerobic-aerobic (A²O²) reactor was constructed to treat manure-free piggery wastewater. The reactor contained four compartments, among which the first two were anaerobic (A phase) and the last two were aerobic (O phase). Throughout around one-year operation, high-level nutrient removal was demonstrated. At an optimal reflux ratio of 100%, the average NH₄⁺-N, TN, and COD removal efficiencies were high as 99.4%, 91.7%, and 79.4%, respectively, with the influent concentration of 220.6, 231.6 and 332 mg/L, respectively. The NH₄⁺-N, TN, and COD concentrations in the final effluent were only 1.4, 18.5 and 65 mg/L, respectively. COD and nitrogen removal were mainly removed in the A phase and O phase, respectively. This result revolutionizes the previous perception that nitrogen is only removed in the A phase of conventional A-O configuration. Achievement of PN/A in the O phase was critical to the efficient nitrogen removal. Heterotrophic denitrification in the anaerobic compartments removed the nitrate produced by anammox, ensuring the high-level nitrogen removal. Anaerobic organic degradation was a major pathway for COD removal, as abundant methanogens detected in the A phase. This study provides a feasible technical scheme for the efficient nutrient removal from ammonium-rich wastewater.

Insights into complete nitrate removal in one-stage nitritation-anammox by coupling heterotrophic denitrification

Nitritation-anammox has been considered to be the most promising process for nitrogen (N) removal from wastewater. However, the anammox reaction still produces an amount of nitrate, which cannot be removed further. This study hypothesizes that heterotrophic denitrification can be an appealing option to remove the residual nitrate in the one-stage nitritation-anammox process. Through monitoring N-removal performance and microbial community succession of a laboratory microaerobic reactor, the effect of four different levels of oxygen supply on nitrate removal was investigated. The reactor was continuously fed with real manure-free piggery wastewater containing ~240 mg NH₄⁺-N/L and chemical oxygen demand (COD)/total nitrogen (TN) ratio of less than 1 for 180 days. With a high influent loading rate of 0.7 kg N/(m³·d), efficient total nitrogen removal (>80 %) was achieved during stable operation of dissolved oxygen (DO) concentrations between 0.3 and 0.6 mg O₂/L, indicating N-removal via the nitritation-anammox pathway in the low-carbon wastewater treatment. At the same time, the effluent nitrate reduced with decreased oxygen supply and completely depleted at DO of 0.3 ± 0.1 mg O₂/L. In addition to oxygen, preventing ammonia nitrogen from falling to very low levels (<10 mg/L) could be also useful for the complete nitrate removal and stable nitritation-anammox. 16S rRNA gene-based analyses confirmed a complex microbial community including nitrifiers, denitrifiers and anammox bacteria in the biomass of the reactor. Collectively, this study provides new insights into high-level N-removal of a nitritation-anammox process by complete nitrate depletion.

Challenges in Treatment of Digestate Liquid Fraction from Biogas Plant. Performance of Nitrogen Removal and Microbial Activity in Activated Sludge Process

Even thoughdigestate, which is continually generated in anaerobic digestion process, can only be used as fertilizer during the growing season, digestate treatment is still a critical, environmental problem. That is why the present work aims to develop a method to manage digestate in agricultural biogas plant in periods when its use as fertilizer is not possible. A lab-scale system for the biological treatment of the digestate liquid fraction using the activated sludge method with a separate denitrification chamber was constructed and tested. The nitrogen load that was added tothe digestate liquid fraction accounted for 78.53% of the total nitrogen load fed into the reactor. External carbon sources, such as acetic acid, as well as flume water and molasses, i.e., wastewater and by-products from a sugar factory, were used to support the denitrification process. The best results were obtained using an acetic acid and COD (Chemical Oxygen Demand)/NO3–N (Nitrate Nitrogen) ratio of 7.5. The removal efficiency of TN (Total Nitrogen), NH4–N (Ammonia Nitrogen) and COD was 83.73%, 99.94%, 86.26%, respectively. It was interesting to see results obtained that were similar to those obtained when using flume water and COD/NO3–N at a ratio of 8.7. This indicates that flume water can be used as an alternative carbon source to intensify biological nitrogen removal from digestate.

Understanding of signaling molecule controlled anammox through regulating C/N ratio

Anammox as a novel biological process in natural nitrogen cycle has been introduced into wastewater treatment process. However, the regulation mechanism of anammox metabolism remained to be investigated. In this study, the specific quorum sensing (QS) signaling molecules for mediating anammox were identified in anammox activity tests. Anammox was valve-regulated by the collaboration of QS signaling molecules N-butyryl-homoserine lactone (C14-HSL) and N-(3-oxotetradecanoyl)-homoserine lactone (3-oxo-C14-HSL), and prompted with the C14-HSL/3-oxo-C14-HSL mole ratio above 1.0. Moreover, the ratio of chemical oxygen demand to total nitrogen (C/N) was identified as an effective regulator for the distribution of C14-HSL and 3-oxo-C14-HSL. An engineering method for control anammox through regulating C/N ratio was proposed and demonstrated based on the performance of two microaerobic reactors treating piggery wastewater and anammox activity tests. The discovery should be of great significance to understanding the social behaviors of anammox bacteria in organic wastewater treatment processes.

Response Characteristics of Nitrifying Bacteria and Archaea Community Involved in Nitrogen Removal and Bioelectricity Generation in Integrated Tidal Flow Constructed Wetland-Microbial Fuel Cell

This study explores nitrogen removal performance, bioelectricity generation, and the response of microbial community in two novel tidal flow constructed wetland-microbial fuel cells (TFCW-MFCs) when treating synthetic wastewater under two different chemical oxygen demand/total nitrogen (COD/TN, or simplified as C/N) ratios (10:1 and 5:1). The results showed that they achieved high and stable COD, NH₄ ⁺-N, and TN removal efficiencies. Besides, TN removal rate of TFCW-MFC was increased by 5-10% compared with that of traditional CW-MFC. Molecular biological analysis revealed that during the stabilization period, a low C/N ratio remarkably promoted diversities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in the cathode layer, whereas a high one enhanced the richness of nitrite-oxidizing bacteria (NOB) in each medium; the dominant genera in AOA, AOB, and NOB were Candidatus Nitrosotenuis, Nitrosomonas, and Nitrobacter. Moreover, a high C/N ratio facilitated the growth of Nitrosomonas, while it inhibited the growth of Candidatus Nitrosotenuis. The distribution of microbial community structures in NOB was separated by space rather than time or C/N ratio, except for Nitrobacter. This is caused by the differences of pH, dissolved oxygen (DO), and nitrogen concentration. The response of microbial community characteristics to nitrogen transformations and bioelectricity generation demonstrated that TN concentration is significantly negatively correlated with AOA-shannon, AOA-chao, 16S rRNA V4-V5-shannon, and 16S rRNA V4-V5-chao, particularly due to the crucial functions of Nitrosopumilus, Planctomyces, and Aquicella. Additionally, voltage output was primarily influenced by microorganisms in the genera of Nitrosopumilus, Nitrosospira, Altererythrobacter, Gemmata, and Aquicella. This study not only presents an applicable tool to treat high nitrogen-containing wastewater, but also provides a theoretical basis for the use of TFCW-MFC and the regulation of microbial community in nitrogen removal and electricity production.

The effects of influent and operational conditions on nitrogen removal in an upflow microaerobic sludge blanket system: A model-based evaluation

Recently, upflow microaerobic sludge blanket (UMSB) system has been developed to remove ammonium and organic matter simultaneously. This study aims to establish influent and operational conditions promoting anammox-based nitrogen removal process in the UMSB reactor by using a modified Activated Sludge Model. Experiments were performed on a laboratory-scale UMSB reactor treated piggery wastewater for over two years. With the experimentally determined model parameters, the established model well simulated the UMSB reactor performance. The maximum anammox growth rate was calibrated to be 0.41 d^-1 at 35 °C. Further simulations showed that UMSB reactor operated with high influent organics or nitrogen loading rates at temperature above 15 °C can achieve efficient nitrogen removal (>70%). The nitrogen loading over 0.6 kg N/(m³·d)) significantly favors anammox activity. UMSB could also be a promising system for nitrogen removal from low-strength ammonium wastewater with fluctuated COD influence. These results provide support to UMSB design and operational optimization.

Performance, microbial community evolution and neural network modeling of single-stage nitrogen removal by partial-nitritation/anammox process

Single-stage nitrogen removal by anammox/partial-nitritation (SNAP) process was proposed and explored in a packed-bed-EGSB reactor to treat nitrogen-rich wastewater. With dissolved oxygen (DO) maintained within 0.2-0.5 mg/L, reactor performance and microbial community dynamics were evaluated and reported. To ascertain whether control/prediction of the SNAP process was feasible with mathematical modeling, a novel 3-layered backpropagation-artificial-neural-network-(BANN) was also developed to model nitrogen removal efficiencies. When NLR of 300 gN/m³·d and DO of <0.3 mg/L was employed, the SNAP-process demonstrated autotrophic nitrogen removal pathways with NH₄⁺-N and TN removal of 91.1% and 81.9%, respectively. Microbial community succession revealed by 16S rRNA high-throughput gene-sequencing indicated that Candidatus-Kuenenia-(33.83%), Nitrosomonas-(3.4%) Armatimonadetes_gp5-(1.39%), Ignavibacterium-(1.80%), Thiobacillus-(1.33%), and Nitrospira-(1.17%) were the most pronounced genera at steady-state. The proposed BANN-model demonstrated high-performance as computational results revealed smaller deviations (±3%) and satisfactory coefficient of determination-(R² = 0.989), fractional variance-(FV = 0.0107), and index of agreement-(IA = 0.997). Thus, forecasting the efficiency of a SNAP-process with neural-network modeling was highly feasible.

Effective removal of nitrate by denitrification re-enforced with a two-stage anoxic/oxic (A/O) process from a digested piggery wastewater with a low C/N ratio

The combined process of a long-term biogas digester and double anoxic/oxic tanks is very commonly used in piggery wastewater treatment in South China, but the effluent does not meet the discharge standard of total nitrogen (TN) and chemical oxygen demand (COD_Cr) due to a low C/N ratio and insufficient organic carbon in digested piggery wastewater. Thus, a typical two-stage anoxic/oxic (A1/O1/A2/O2) process, which is widely used to treat digested piggery wastewater in the engineering application, was selected for study on a laboratory scale. Finally, the average removal efficiency of ammonia nitrogen in the two-stage AO process was 98.7%; at the same time, the content of nitrate increased to 180-190 mg/L. To further eliminate nitrogen, an anaerobic tank (S1), which was equipped the sludge that was acclimated in our laboratory by a high nitrogen loading slurry, was employed to treat the effluent from the two-stage AO process and contributed more than 70% removal efficiency. Further analysis showed that ammonia-oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in the O1 and O2 tanks together contributed to the conversion of ammonia nitrogen to nitrate, but the process of heterotrophic denitrification was inhibited in the A1 and A2 tanks because of insufficient carbon sources. In addition, most of the nitrate concentration was reduced under conditions with insufficient carbon sources, while Thauera-dominated the bacterial population in the sludge sample of the S1 tank.

Nutrient removal from high ammonium swine wastewater in upflow microaerobic biofilm reactor suffered high hydraulic load

To understand the ability of an upflow microaerobic biofilm reactor (UMBR) to remove nutrient from manure-free swine wastewater rich in NH₄⁺ with a COD/TN ratio less than 1.00, effect of hydraulic loading rate (HLR) on the microaerobic process was evaluated with a constant reflux ratio of 25 at 25 °C. The results showed that changes in HLR had a remarkable effect on the performance of the UMBR in nutrient removal from the wastewater. With the favorable HLR 3.0 m³/(m³·d) (Hydraulic Retention Time (HRT) 8 h), average removal of COD, NH₄⁺ and TN in the microaerobic process reached 59.3%, 87.7% and 84.7%, respectively, though the COD/TN ratio was as low as 0.84. With an over HLR of 4.0 m³/(m³·d) (HRT decreased to 6 h), bad performance of the UMBR was observed with an average removal of COD, NH₄⁺ and TN as low as 45.0%, 59.0% and 57.5%, respectively. Since the HLR was decreased to 2.4 m³/(m³·d) (HRT 10 h), the microaerobic process regained the efficiency in nutrient removal with a removal of COD, NH₄⁺ and TN averaged 59.0%, 95.3% and 87.8%, respectively. The microaerobic condition allowed anammox bacteria, ammonia-oxidizing bacteria and archaea, nitrite-oxidizing bacteria and denitrifiers to all thrive in the UMBR, resulting in the efficient synchronous removal of organic carbon and nitrogen. As the dominant approach to nitrogen removal, anaerobic ammonium oxidation (anammox) pathway contributing to the TN removal in the microaerobic process exceeded 59.5% at HLR 3.0 m³/(m³·d). The results demonstrated that the UMBR can remove nitrogen and carbon from swine wastewater, with a suitable HLR.

Efficiency, granulation, and bacterial populations related to pollutant removal in an upflow microaerobic sludge reactor treating wastewater with low COD/TN ratio

In this study, a novel upflow microaerobic sludge reactor (UMSR) was constructed to conduct anaerobic digestion of municipal wastewater with low carbon and nitrogen ratio (C/N). Oxygen in the UMSR was supplied by falling water and external recirculation. Excellent nitrogen removal performance was obtained in the UMSR for treating wastewater with low C/N ratio at a temperature of 25 °C and a hydraulic retention time of 24 h. Ammonium and total nitrogen removal efficiencies averaged 92.35% and 90.41%, respectively, and sludge granulation occurred during acclimation. The inferred metabolism of nitrogen removal and ecological positions of functional microbe were integrated into a granule model by scanning electron microscopy. Additionally, the analysis of microbial community indicated that aerobic nitrifying bacteria and heterotrophic bacteria survived on the surface of sludge floc and granules while the anaerobic autotrophic, heterotrophic denitrifying, and anaerobic ammonia oxidation bacteria were present in the inner layer.