The effect and biological mechanism of COD/TN ratio on nitrogen removal in a novel upflow microaerobic sludge reactor treating manure-free piggery wastewater

Aerobic granular sludge for swine wastewater treatment: Implications for antibiotic and antibiotic resistance gene elimination

Swine wastewater (SW) contains high levels of traditional pollutants, antibiotics, and antibiotic resistance genes (ARGs), necessitating effective elimination. Two parallel aerobic granular sludge (AGS) reactors, R1 and R2, were constructed and optimized for treating SW from two pig farms, identified as SW1 and SW2. R2 showed higher antibiotic removal efficiency, particularly in the removal of sulfonamides, while fluoroquinolones tended to adsorb onto the sludge. Process optimization by introducing an additional anoxic phase enhanced denitrification and reduced effluent ARG levels, also aiding in the improved removal of fluoroquinolones. The nitrite-oxidizing bacteria (NOB) Nitrospira accumulated after the treatment process, reaching 12.8 % in R1 and 14.1 % in R2, respectively. Mantel's test revealed that pH, NH4+-N, and Mg significantly affected ARGs and microbial community. Sulfadiazine and sulfamethazine were found to significantly impact ARGs and the microbial communities. This study provides innovative insights into the application of AGS for the treatment of real SW.

Trickling filter systems for sustainable water supply: An evaluation of eco-environmental burdens and greenhouse gas emissions

Despite the global water crisis, the significant potential of trickling filter systems as a crucial auxiliary option for sustainable water supply has received insufficient attention. Therefore, this study presents the first-ever evaluation of the environmental impacts of trickling filter application in wastewater treatment, focusing on eco-environmental burdens. Additionally, the study explores greenhouse gas emissions, energy, and exergy footprints, providing novel insights into the environmental implications of using trickling filters for wastewater treatment. The study's findings indicate that the consumption of heat and electricity in trickling filters has significant environmental impacts, particularly on land use (93.24%), freshwater/marine eutrophication (∼81.98%), and human health (45.36%). The majority of the energy required for trickling filter operation is supplied by fossil fuels (96.02%), resulting in increased greenhouse gas emissions (65.58%). The exergy of trickling filters is highly efficient, accounting for over 95% of the system's energy. Mathematical modeling reveals that anaerobic digestion and secondary clarifier have the highest energy consumption, with contributions of 94.65% and 2.63%, respectively. Construction expenses account for almost 88% of the total cost, with anaerobic digestion (42.15%) and trickling filters (35.39%) being the most costly components. The cost of treating 1 m3 of wastewater is estimated at 0.52 $/m3. Sensitivity analysis demonstrates that electricity (14.66%) and heat (18.65%) significantly impact terrestrial ecotoxicity and land use, respectively. This study presents a framework for future investigations in this field.

A comparison of nitrogen removal systems through cost-coupled life cycle assessment and energy efficiency analysis

The global water crisis reflects the necessity of exploring the best approaches for the water supply. Therefore, for the first time, the current study compares nitrogen removal systems (NRSs) from life cycle assessment (LCA), economic, kinetic, thermodynamic, and synergistic perspectives. The assessed systems were sequential batch reactor (SBR), oxic/anoxic (OA), and oxic/anaerobic/oxic (OAO) bioreactors. Among all, the SBR configuration showed the best efficiency (98.74 %) for nitrogen removal. The environmental impacts notably presented by marine + freshwater ecotoxicity (53.76 %), and climate change categories (16.39 %), significantly because of metal emissions. Non-renewable sources supplied 95 % of total energy demand. The operation of NRSs showed the most impact on human health (63.67 %) through CH₄ and CO₂ emissions. The total costs significantly belonged to the construction (<86.37 %) > amortization> operation. The influent COD illustrated the most role in environmental burdens (16.44 %) based on the sensitivity analysis. The removal reaction was endothermic, physical, non-spontaneous, and followed a pseudo-second-order kinetic model (R² > 0.98). The chemical exergy provided the major portion of the total calculated exergy (83 %). The exergetic efficiency of the system was 69 %, which was predominantly supplied by biogas (∼50.75 %). Accordingly, this study can present a stepwise guideline for further related investigations.

Development of a post-treatment system using a downflow hanging sponge reactor - an upflow anaerobic reactor for natural rubber processing wastewater treatment

This study aimed to evaluate the nitrogen removal of a post-treatment system for natural rubber processing wastewater (NRPW) under low chemical oxygen demand to total nitrogen (COD/TN) ratios without any supplemental external carbon source. The system including a downflow hanging sponge (DHS) reactor and an upflow anaerobic reactor (UAR) was operated in two phases. In phase 1 (day 0-102), under a nitrogen loading rate (NLR) of 0.23 ± 0.06 kgN m^-3 d^-1 and COD/TN ratio of 0.63 ± 0.47, the DHS-UAR system removed 82.5 ± 11.8% and 83.9 ± 7.6% of TN and ammonium concentrations, respectively. In phase 2 (day 103-229), higher COD/TN ratio of 1.96 ± 0.28 was applied to remove increasing NLRs. At the highest NLR of 0.51 kgN m^-3 d^-1, the system achieved TN and ammonium removal efficiencies of 93.2% and 93.7%, respectively. Nitrogen profiles and the 16S rRNA high-throughput sequencing data suggested that ammonium, a major nitrogen compound in NRPW, was utilized by nitrifying and ammonium assimilation bacteria in DHS, then removed by heterotrophic denitrifying and anammox bacteria in the UAR. The predominance of Acinetobacter detected in both reactors suggested its essential role for the nitrogen conversion.

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.

Organic carbon bioavailability: Is it a good driver to choose the best biological nitrogen removal process?

Organic carbon can affect the biological nitrogen removal process since the Anammox, heterotrophic and denitrifying bacteria have different affinities and feedback in relation to carbon/nitrogen ratio. Therefore, we reviewed the wastewater carbon concentration, its biodegradability and bioavailability to choose the appropriate nitrogen removal process between conventional (nitrification-denitrification) and Anammox-based process (i.e. integrated with the partial nitritation, nitritation, simultaneous partial nitrification and denitrification or partial-denitrification). This review will cover: (i) strategies to choose the best nitrogen removal route according to the wastewater characteristics in relation to the organic matter bioavailability and biodegradability; (ii) strategies to efficiently remove nitrogen and the remaining carbon from effluent in anammox-based process and its operating cost; (iii) an economic analysis to determine the operational costs of two-units Anammox-based process when compared with the commonly applied one-unit Anammox system (partial-nitritation-Anammox). On this review, a list of alternatives are summarized and explained for different nitrogen and biodegradable organic carbon concentrations, which are the main factors to determine the best treatment process, based on operational and economic terms. In summary, it depends on the wastewater carbon biodegradability, which implies in the wastewater treatment cost. Thus, to apply the conventional nitrification/denitrification process a COD_b/N ratio higher than 3.5 is required to achieve full nitrogen removal efficiency. For an economic point of view, according to the analysis the minimum COD_b/gN for successful nitrogen removal by nitrification/denitrification is 5.8 g. If ratios lower than 3.5 are applied, for successfully higher nitrogen removal rates and the economic feasibility of the treatment, Anammox-based routes can be applied to the wastewater treatment plant.

Efficiency and mechanism of nitrogen removal from piggery wastewater in an improved microaerobic process

Characterized by high ammonium (NH₄⁺ - N) and low ratio of chemical oxygen demand (COD) to total nitrogen (COD/TN), discharge of piggery wastewater has been identified as a primary pollution source resulting in water eutrophication. An improved microaerobic reactor, internal aerating microaerobic reactor (IAMR), was constructed to treat manure-free piggery wastewater without effluent recycle at dissolved oxygen of 0.3 mg/L and 32 °C. A removal rate of COD, NH₄⁺ - N and TN averaged 77.9%, 94.6% and 82.6% was obtained in the reactor, with the concentration of 258.5, 235.5 and 335.2 mg/L in influent, respectively. 16S rDNA amplicon sequencing, carbon and nitrogen mass balance and stoichiometry indicated that heterotrophic nitrification-anammox was the dominant approach to nitrogen removal. Microbiome phenotypes showed that aerobic bacteria were the dominant microorganisms, and the microbiome oxidative stress tolerance was intensified along with the continuous operation of the IAMR, resulting in the survival of various facultative and anaerobic bacteria for nutrients removal. With the good nutrients removal, less energy consumption, and high tolerance to influent fluctuation, the improved IAMR was confirmed as a promising process for treating wastewater with high NH₄⁺ - N and low COD/TN.

Evaluation of a continuous flow microbial fuel cell for treating synthetic swine wastewater containing antibiotics

Microbial fuel cell (MFC) systems are promising technologies for wastewater treatment and renewable energy generation simultaneously. Performance of a double-chamber microbial fuel cell (MFC) to treat synthetic swine wastewater containing sulfonamide antibiotics (SMs) was evaluated in this study. The MFC was operated in continuous modes at different conditions. Results indicated that the current was successfully generated during the operation. The performance of MFC under the sequential anode-cathode operating mode is better than that under the single continuous running mode. Specifically, higher removal efficiency of chemical oxygen demand (>90%) was achieved under the sequential anode-cathode operating mode in comparison with that in the single continuous mode (>80%). Nutrients were also be removed in the MFC's cathode chamber with the maximum removal efficiency of 66.6 ± 1.4% for NH₄⁺-N and 32.1 ± 2.8% for PO₄^3--P. Meanwhile, SMs were partly removed in the sequential anode-cathode operating with the value in a range of 49.4%-59.4% for sulfamethoxazole, 16.8%-19.5% for sulfamethazine and 14.0%-16.3% for sulfadiazine, respectively. SMs' inhibition to remove other pollutants in both electrodes of MFC was observed after SMs exposure, suggesting that SMs exert toxic effects on the microorganisms. A positive correlation was found between the higher NH₄⁺-N concentration used in this study and the removal efficiency of SMs in the cathode chamber. In short, although the continuous flow MFC is feasible for treating swine wastewater containing antibiotics, its removal efficiency of antibiotics requires to be further improved.

Comparative analysis of upward and downward vertical flow constructed wetlands on the nitrogen removal and functional microbes treating wastewater containing Ag nanoparticles

This study investigated impacts of silver nanoparticles (AgNPs) on nitrogen removal within constructed wetlands (CWs) with different flow directions. The obtained results showed that addition of AgNPs at 0.5 and 2 mg/L significantly inhibited NH₄⁺-N removal, resulting from lower abundances of functional genes (amoA and nxrA) within CWs. And higher abundances of amoA and nxrA genes at 0.5 mg/L were observed in downward flow CW, leading to better NH₄⁺-N removal, compared to upward flow CW. Besides, nitrifying genes amoA and nxrA in upward flow CW at 2.0 mg/L exhibited higher than downward flow CW, explaining better NH₄⁺-N removal in upward flow CW. 0.5 mg/L AgNPs significantly declined NO₃^--N and TN removal, resulted from decreasing abundances of nirK, nirS and nosZ. In contrast, abundances of nirK, nirS and nosZ genes had slightly lower or higher than before adding AgNPs in upward flow CW, leading to lower NO₃^--N and TN effluent concentrations. High throughput sequencing also indicated the changes of functional bacterial community after exposing to AgNPs.

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.

Responses of microbial structures, functions, metabolic pathways and community interactions to different C/N ratios in aerobic nitrification

The responses of microbial structures, functional profiles and metabolic pathways during nitrification to four C/N ratios (0, 5, 10 and 15) were investigated in four parallel SBRs denoted as S₀, S₅, S₁₀, S₁₅. Results indicated that microbial diversities were affected by C/N ratios, while the same dominant taxa were observed, mainly including Proteobacteria, Betaproteobacteria, Rhodocyclales, Rhodocyclaceae, Zoogloea. The unique biomarkers were identified in each sludge sample through LEfSe analysis. Functional genera/enzymes responsible for removing organics and nitrogen coexisted in four SBRs at different abundances, except for that ammonia oxidizing bacteria (AOB) Nitrosomonas (0.33%-0.66%) and ammonia monooxygenase (amo) (9.4 × 10^-7-2.8 × 10^-6) were only detected in S₀. Moreover, PICRUSt analysis indicated similar overall patterns of metabolic pathways in four sludge samples. The network analysis revealed that total nitrogen removal positively correlated with hcp (Spearman's ρ of 0.853), and ammonia oxidizing rate was associated with amo (Spearman's ρ of 0.096).

Biological nutrient removal and recovery from solid and liquid livestock manure: Recent advance and perspective

Rapid development of livestock industry produces large amount of livestock manure rich in nutrients, organic matters, antibiotics, and heavy metals, thus imposes great harms to human and environment, if the manure is not suitably treated. Biological removal and recovery of nutrients from manure as agriculture fertilizer is attractive due to low cost and simple operation. This review offers an overview of recent development in biological nutrient removal and recovery from livestock manure. Livestock manure is divided into solid manure and liquid manure. Composting and anaerobic digestion of solid manure are fully discussed and important parameters are investigated. Then various processes of nutrient removal and recovery from liquid manure are summarized. Brief economic sustainability and eco-environmental effects are carried out. Finally, current challenges and future prospects in this field are analyzed.

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 and recovery of a completely separated partial nitritation and anammox process treating phenol-containing wastewater

Anammox process is considered as a promising technology for removing total nitrogen from low-strength ammonium and phenol-containing wastewater. However, it is still a challenge for the anammox process to treat high-strength ammonium and phenol-containing wastewater. A completely separated partial nitritation and anammox (CSPN/A) process was developed to remove total nitrogen from high-strength phenol-containing wastewater. About 92% of COD, 100% of phenol, and 82.4% of total nitrogen were successfully removed at a NH₄⁺-N concentration of 200 mg L^-1 with a phenol/NH₄⁺-N mass ratio of 0.5 in the CSPN/A process. Furthermore, a shock loading of 300 mg phenol L^-1 with a phenol/NH₄⁺-N mass ratio of 1.5 led to a complete failure of partial nitritation, but the performance was rapidly recovered by the increase of NH₄⁺-N concentration. Although the activities of ammonium-oxidizing bacteria and anammox bacteria were severely inhibited at a phenol/NH₄⁺-N mass ratio of 1.5, the enrichment of efficient phenol degraders in the CSPN stage could strengthen the performance robustness of partial nitritation and anammox process. Therefore, this study presented a new insight on the feasibility of the anammox process for treating high-strength ammonium and phenol-containing wastewater.

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.

Dynamic changes of nitrogen and dissolved organic matter during the transport of mine water in a coal mine underground reservoir: Column experiments

Although the technology of coal mine underground reservoirs has been widely applied in the Western China, little is known about the variation of water quality induced by the removal transformation of nitrogen and dissolved organic matter (DOM) rich in mine water during its storage and transport in a coal mine underground reservoir. Column experiments were carried out at 30 °C and at Darcy fluxes ranging from 0.32 cm/h to 0.64 cm/h to investigate the transport parameters and dynamic changes of nitrogen and DOM in a simulated underground reservoir filled with coal gangue, which was composed of sandstone and mudstone. Results showed that chloride transport could be described by the convection-dispersion equation (CDE) well at a Darcy flux of 0.32 cm/h, wherein the dispersion role was obvious. Despite the high level of nitrite in the influent, the effluent concentrations of nitrite and nitrate fluctuated around the background values through complete denitrification. And the removal of total nitrogen (TN) with efficiencies between 55.1% and 76% were highly correlated with nitrite denitrification. Ammonification of organic nitrogen got weakened over time and the content of ammonium ion tended to be stable at the level of that in the input mine water. The delayed breakthrough curves of chemical oxygen demand (COD) and dissolved organic carbon (DOC) at a Darcy flux of 0.32 cm/h could be attributed to their adsorption onto the coal gangue during their transport through the simulated underground reservoir. Due to the variations of microbial and compositions of the input mine water, the removal efficiencies of COD and DOC increased slightly from 62% to 68%, 56% to 63%, respectively, when the Darcy flux increased from 0.32 cm/h to 0.62 cm/h. The findings would be helpful in evaluating the effectiveness of post-treatment of mine water during its storage in an underground reservoir in coal mine areas of Western China.

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.

The intensified constructed wetlands are promising for treatment of ammonia stripped effluent: Nitrogen transformations and removal pathways

This study investigated the treatment performance and nitrogen removal mechanism of highly alkaline ammonia-stripped digestate effluent in horizontal subsurface flow constructed wetlands (CWs). A promising nitrogen removal performance (up to 91%) was observed in CWs coupled with intensified configurations, i.e., aeration and effluent recirculation. The results clearly supported that the higher aeration ratio and presence of effluent recirculation are important to improve the alkalinity and pollutant removal in CWs. The influent pH (>10) was significantly decreased to 8.2-8.8 under the volumetric hydraulic loading rates of 0.105 and 0.21 d^-1 in the CWs. Simultaneously, up to 91% of NH₄⁺-N removal was achieved under the operation of a higher aeration ratio and effluent recirculation. Biological nitrogen transformations accounted for 94% of the consumption of alkalinity in the CWs. The significant enrichment of δ¹⁵N-NH₄⁺ in the effluent (47-58‰) strongly supports the occurrence of microbial transformations for NH₄⁺-N removal. However, relatively lower enrichment factors of δ¹⁵N-NH₄⁺ (-1.8‰ to -11.6‰) compared to the values reported in previous studies reflected the inhibition effect of the high pH alkaline environment on nitrifiers in these CWs.

Rapid start-up of a nitritation granular reactor using activated sludge as inoculum at the influent organics/ammonium mass ratio of 2/1

Partial oxidation of ammonium to nitrite is a pre- and crucial step to achieve shortcut biological nitrogen removal from ammonium-rich wastewater. In the present study, a nitritation granular reactor using activated sludge as inoculum was started up in a sequencing batch reactor (SBR) at a fixed influent C/N ratio of 2:1. Variations in the reactor performance, functional bacteria activities, sludge morphology and bacterial community structure were investigated. Results showed the formation of compact granules was achieved in 55 days, and a stable nitrite accumulation rate of 0.68 kg N·m^-3·d^-1 was maintained in the following period. With a rapid growth of granular size, the total nitrogen removal by simultaneous nitritation/denitritation was progressively increased to 50%. In sludge granulation, the significant enrichment of r-strategist ammonium oxidizing bacteria (Nitrosomonas) was identified. Additionally, both high free ammonia concentration and extra nitrite competition by heterotrophic denitrifiers were critical to suppress nitrite oxidizing bacteria effectively.

Bioprocessing for elimination antibiotics and hormones from swine wastewater

Antibiotics and hormones in swine wastewater have become a critical concern worldwide due to the severe threats to human health and the eco-environment. Removal of most detectable antibiotics and hormones, such as sulfonamides (SAs), SMs, tetracyclines (TCs), macrolides, and estrogenic hormones from swine wastewater utilizing various biological processes were summarized and compared. In biological processes, biosorption and biodegradation are the two major removal mechanisms for antibiotics and hormones. The residuals in treated effluents and sludge of conventional activated sludge and anaerobic digestion processes can still pose risks to the surrounding environment, and the anaerobic processes' removal efficiencies were inferior to those of aerobic processes. In contrast, membrane bioreactors (MBRs), constructed wetlands (CWs) and modified processes performed better because of their higher biodegradation of toxicants. Process modification on activated sludge, anaerobic digestion and conventional MBRs could also enhance the performance (e.g. removing up to 98% SMs, 88.9% TCs, and 99.6% hormones from wastewater). The hybrid process combining MBRs with biological or physical technology also led to better removal efficiency. As such, modified conventional biological processes, advanced biological technologies and MBR hybrid systems are considered as a promising technology for removing toxicants from swine wastewater.

Enhanced nitrogen removal from piggery wastewater with high NH4+ and low COD/TN ratio in a novel upflow microaerobic biofilm reactor

To enhance nutrient removal more cost-efficiently in microaerobic process treating piggery wastewater characterized by high ammonium (NH₄⁺-N) and low chemical oxygen demand (COD) to total nitrogen (TN) ratio, a novel upflow microaerobic biofilm reactor (UMBR) was constructed and the efficiency in nutrient removal was evaluated with various influent COD/TN ratios and reflux ratios. The results showed that the biofilm on the carriers had increased the biomass in the UMBR and enhanced the enrichment of slow-growth-rate bacteria such as nitrifiers, denitrifiers and anammox bacteria. The packed bed allowed the microaerobic biofilm process perform well at a low reflux ratio of 35 with a NH₄⁺-N and TN removal as high as 93.1% and 89.9%, respectively. Compared with the previously developed upflow microaerobic sludge reactor, the UMBR had not changed the dominant anammox approach to nitrogen removal, but was more cost-efficiently in treating organic wastewater with high NH₄⁺-N and low COD/TN ratio.

Single-stage autotrophic nitrogen removal process at high loading rate: granular reactor performance, kinetics, and microbial characterization

For the possible highest performance of single-stage combined partial nitritation/anammox (PNA) process, a continuous complete-mix granular reactor was operated at progressively higher nitrogen loading rate. The variations in bacterial community structure of granules were also characterized using high-throughput pyrosequencing, to give a detail insight to the relationship between reactor performance and functional organism abundance within completely autotrophic nitrogen removal system. In 172 days of operation, a superior total nitrogen (TN) removal rate over 3.9 kg N/(m³/day) was stable implemented at a fixed dissolved oxygen concentration of 1.9 mg/L, corresponding to the maximum specific substrate utilization rate of 0.36/day for TN based on the related kinetics modeling. Pyrosequencing results revealed that the genus Nitrosomonas responsible for aerobic ammonium oxidation was dominated on the granule surface, which was essential to offer the required niche for the selective enrichment of anammox bacteria (genus Candidatus Kuenenia) in the inner layer. And the present of various heterotrophic organisms with general functions, known as fermentation and denitrification, could not be overlooked. In addition, it was believed that an adequate excess of ammonium in the bulk liquid played a key role in maintaining process stability, by suppressing the growth of nitrite-oxidizing bacteria through dual-substrate competitions.

Simultaneous carbon and nitrogen removal from anaerobic effluent of the cassava ethanol industry

This study investigated the simultaneous carbon and nitrogen removal from anaerobic effluent of cassava stillage using a lab-scale integrated system consisting of an upflow anaerobic sludge blanket (UASB) reactor and an activated sludge (AS) process. Simultaneous denitrification and methanogenesis (SDM) was observed in the UASB with nitrate recirculation. Compared with the blank reactor without recirculation, the overall chemical oxygen demand (COD) removal efficiencies in the combined system with nitrate recirculation were similar (80-90%), while the TN removal efficiencies were significantly improved from 4.7% to 71.0%. Additionally, the anaerobic COD removal efficiencies increased from 21% to 40% as the recirculation ratio decreased from 3 to 1. Although the influent nitrate concentrations fluctuated (60-140 mg N/L), the nitrate removal efficiencies could be maintained at about 97% under different recirculation conditions. With the decreasing recirculation ratio from 3 to 1, the CH₄ content in biogas improved from 2% to 40% while the N₂ content reduced from 95.8% to 50.6%. The 16S rDNA sequencing results indicated that bacteria diversity in anaerobic SDM granular sludge was much higher than archaea. The effect of recirculation ratios on the bacterial and archaeal communities in SDM granular sludge could be further confirmed by the relative abundance of denitrifying bacteria.

Effect of reflux ratio on nitrogen removal in a novel upflow microaerobic sludge reactor treating piggery wastewater with high ammonium and low COD/TN ratio: Efficiency and quantitative molecular mechanism

A novel upflow microaerobic sludge reactor (UMSR) was constructed to treat manure-free piggery wastewater with high NH₄⁺-N and low COD/TN ratio. In the light of the potential effect of effluent reflux ratio (RR) on nitrogen removal, performance of the UMSR was evaluated at 35°C and hydraulic retention time 8h with RR decreased from 45 to 25 by stages. A COD, NH₄⁺-N and TN removal of above 77.1%, 80.0% and 86.6%, respectively, was kept with a RR over 35. To get an effluent of TN not more than 80mg/L with a TN load removal above 0.88kg/(m³·d), the RR should be at least 34. Real-time quantitative polymerase chain reaction of functional bacteria revealed that the RR of less than 34 stimulated ammonium oxidation but badly inhibited anammox, the dominant nitrogen removal pathway, resulting in the remarkable decrease of nitrogen removal in the reactor.

Partially aerated submerged fixed-film bioreactor for simultaneous removal of carbon and nutrients from high-strength nitrogen wastewaters: effect of aeration rate and C:N:P ratio

Influence of aeration rate and COD:N:P (C:N:P) ratio on the performance of an upflow partially aerated submerged fixed film (UP/ASFF) bioreactor for simultaneous carbon and nutrient removal from high-strength nitrogen wastewater was investigated during 6 months. Airflow rates at three levels of 1.5, 3, and 4.5 L/min and C:N:P ratios at four levels of 450:300:10, 450:150:10, 450:100:10, and 450:75:10 were selected as the two main input factors. All experiments were performed at constant chemical oxygen demand (COD), phosphorus (P) and hydraulic residence time of 450 mg COD/L, 10 mg PO₄^3- -P/L and 7.3 h, respectively. The results showed when the airflow rate increased from 1.5 to 4.5 L/min, complete COD removal was achieved. At an airflow rate of 4.5 L/min, total nitrogen removal reached a maximum value of 75% for the C:N:P ratio of 450:75:10. A maximum value of 54% for total phosphorus removal, however, was obtained at an airflow rate of 3 L/min for the C:N:P ratio of 450:75:10. Analysis of variance for the obtained data revealed that aeration rate and nitrogen concentration had more impact on phosphorus removal than COD and nitrogen removal. The study demonstrated that the UP/ASFF system has considerable potential for use in simultaneous removal of carbon and nutrients for high-strength nitrogen wastewater.

Effect of seed sludge on nitrogen removal in a novel upflow microaerobic sludge reactor for treating piggery wastewater

Anaerobic activated sludge (AnaS) and aerobic activated sludge (AerS) were used to start up a novel upflow microaerobic sludge reactor (UMSR), respectively, and the nitrogen removal in the two reactors were evaluated when treating low C/N ratio manure-free piggery wastewater with a COD/TN ration of about 0.85. With the same hydraulic retention time 8h and TN loading rate (NLR) 0.42kg/(m(3)d), the UMSR (R2) inoculated with AerS could reach its steady state earlier and obtained a better TN removal than that in the UMSR (R1) inoculated with AnaS. However, the accumulated AnaS made R1 show a better capability in bearing shock load and demonstrated an excellent NH4(+)-N and TN removal with a NLR as high as 1.07kg/(m(3)d). Microbial community structure of the accumulated AerS and AnaS were observable different. The decreased proportion of nitrifiers restricted the ammonium oxidation in R2, and resulting in a decrease in TN removal.