Process performance and anammox community diversity in a deammonification reactor under progressive nitrogen loading rates for swine wastewater treatment

Recent advances in swine wastewater treatment technologies for resource recovery: A comprehensive review

Swine wastewater (SW), characterized by highly complex organic and nutrient substances, poses serious impacts on aquatic environment and public health. Furthermore, SW harbors valuable resources that possess substantial economic potential. As such, SW treatment technologies place increased emphasis on resource recycling, while progressively advancing towards energy saving, sustainability, and circular economy principles. This review comprehensively encapsulates the state-of-the-art knowledge for treating SW, including conventional (i.e., constructed wetlands, air stripping and aerobic system) and resource-utilization-based (i.e., anaerobic digestion, membrane separation, anaerobic ammonium oxidation, microbial fuel cells, and microalgal-based system) technologies. Furthermore, this research also elaborates the key factors influencing the SW treatment performance, such as pH, temperature, dissolved oxygen, hydraulic retention time and organic loading rate. The potentials for reutilizing energy, biomass and digestate produced during the SW treatment processes are also summarized. Moreover, the obstacles associated with full-scale implementation, long-term treatment, energy-efficient design, and nutrient recovery of various resource-utilization-based SW treatment technologies are emphasized. In addition, future research prospective, such as prioritization of process optimization, in-depth exploration of microbial mechanisms, enhancement of energy conversion efficiency, and integration of diverse technologies, are highlighted to expand engineering applications and establish a sustainable SW treatment system.

Response of nutrients removal efficiency, enzyme activities and microbial community to current and voltage in a bio-electrical anammox system

The effects of different current intensities and voltage levels on nutrient removal performance and microbial community evolution in a Bio-Electrical Anammox (BEA) membrane bioreactor (MBR) were evaluated. The nitrogen removal efficiency increased with the current intensity within the range of 64-83 mA, but this improvement was limited at the current further increased. The phosphorus removal in the BEA MBR was attributed to the release of Fe2+, which was closely associated with the applied current to the electrodes. Heme c concentration, enzyme activities, and specific anammox activity exhibited a decreasing trend, while the functional denitrification genes showed a positive correlation with rising voltage. The nitrogen removal efficiency of the BEA system initially increased and then decreased with the voltage rose from 1.5V to 3.5V, peaking at 2.0V of 94.02% ± 1.19%. Transmission electron microscopy and flow cytometry results indicated that accelerated cell apoptosis/lysis led to an irreversible collapse of the biological nitrogen removal system at 3.5V. Candidatus Brocadia was the predominant anammox bacteria in the BEA system. In contrast, closely related Candidatus Kuenenia and Chloroflexi bacteria were gradually eliminated in electrolytic environment. The abundances of Proteobacteria-affiliated denitrifiers were increased with the voltage rising since the organic matter released by the cell apoptosis/lysis was accelerated at a high voltage level.

A pilot-scale SNAD-MBBR process for treating anaerobic digester liquor of swine wastewater: performance and microbial community

In this pilot-scale study, simultaneous partial nitrification, anammox, and denitrification (SNAD) process was achieved successfully in a moving bed biofilm reactor (MBBR) for treating anaerobic digester liquor of swine wastewater. After 95 days of operation, when the total nitrogen loading rate of SNAD-MBBR process was 1.09 kg TN/m3/day, the total nitrogen removal rate could reach 0.87 kg TN/m3/day, and the removal efficiencies of ammonium and total nitrogen were 92.0% and 79.7%, respectively. The optimum pH and temperature for SNAD-MBBR process were 8.5 and 35 °C, respectively, and the optimum dissolved oxygen for SNAD1 and SNAD2 were 0.30 and 0.07 mg/L, respectively. The 16S rRNA sequencing suggested that Candidatus Kuenenia, Candidatus Brocadia, Nitrosomonas, and Denitratisoma were the dominant nitrogen removal bacteria. Some of the co-existing bacteria (Truepera, Limnobacter, and Anaerolineaceae uncultured) promoted ammonium oxidation and guaranteed the growth of the anammox bacteria under adverse environmental conditions. Overall, this study demonstrated that the SNAD-MBBR process would be an energy-saving and cost-effective method for the removal of nitrogen from swine wastewater and provided important process parameters for stable operation of the full-scale SNAD process.

Treatment and utilization of swine wastewater - A review on technologies in full-scale application

The management of swine wastewater has become the focus of attention in the farming industry. The disposal mode of swine wastewater can be classified as field application of treated waste and treatment to meet discharge standards. The status of investigation and application of unit technology in treatment and utilization such as solid-liquid separation, aerobic treatment, anaerobic treatment, digestate utilization, natural treatment, anaerobic-aerobic combined treatment, advanced treatment, are reviewed from the full-scale application perspective. The technologies of anaerobic digestion-land application is most appropriate for small and medium-sized pig farms or large pig farms with enough land around for digestate application. The process of "solid-liquid separation-anaerobic-aerobic-advanced treatment" to meet the discharge standard is most suitable for large and extra-large pig farms without enough land. Poor operation of anaerobic digestion unit in winter, hard to completely utilize liquid digestate and high treatment cost of digested effluent for meeting discharge standard are established as the main difficulties.

The potential and sustainable strategy for swine wastewater treatment: Resource recovery

Swine wastewater is highly polluted with complex and harmful substances that require effective treatment to minimize environmental damage. There are three commonly used biological technologies for treating swine wastewater: conventional biological technology (CBT), microbial electrochemical technology (MET), and microalgae technology (MT). However, there is a lack of comparison among these technologies and a lack of understanding of their unique advantages and efficient operation strategies. This review aims to compare and contrast the characteristics, influencing factors, improvement methods, and microbial mechanisms of each technology. CBT is cost-effective but has low resource recovery efficiency, while MET and MT have the highest potential for resource recovery. However, all three technologies are affected by various factors and toxic substances such as heavy metals and antibiotics. Improved methods include exogenous/endogenous enhancement, series reactor operation, algal-bacterial symbiosis system construction, etc. Though MET is limited by construction costs, CBT and MT have practical applications. While swine wastewater treatment processes have developed automatic control systems, the application need further promotion. Furthermore, key functional microorganisms involved in CBT's pollutant removal or transformation have been detected, as have related genes. The unique electroactive microbial cooperation mode and symbiotic mode of MET and MT were also revealed, respectively. Importantly, the future research should focus on broadening the scope and scale of engineering applications, preventing and controlling emerging pollutants, improving automated management level, focusing on microbial synergistic metabolism, enhancing resource recovery performance, and building a circular economy based on low-cost and resource utilization.

Response of nitrite accumulation to elevated C/NO- 3-N ratio during partial denitrification process: Insights of extracellular polymeric substance, microbial community and metabolic function

This study investigated the response of nitrite accumulation to elevated COD/NO₃^--N ratio (C/N) during partial denitrification (PD). Results indicated nitrite was gradually accumulated and remained stable (C/N = 1.5 ∼ 3.0), while that rapidly declined after reaching the peak (C/N = 4.0 ∼ 5.0). The polysaccharide (PS) and protein (PN) content of tightly-bound extracellular polymeric substances (TB-EPS) reached the maximum at C/N of 2.5 ∼ 3.0, which might be stimulated by high level of nitrite. Illumina MiSeq sequencing showed Thauera and OLB8 were dominated denitrifying genera at C/N of 1.5 ∼ 3.0, while Thauera was further enriched with fading OLB8 at C/N of 4.0 ∼ 5.0. Meanwhile, the highly-enriched Thauera might enhance the activity of nitrite reductase (nirK) promoting further nitrite reduction. Redundancy analysis (RDA) showed positive correlations between nitrite production and PN content of TB-EPS, denitrifying bacteria (Thauera and OLB8) and nitrate reductases (narG/H/I) in low C/N. Finally, their synergistic effects for driving nitrite accumulation were comprehensively elucidated.

Improved Properties and Enhancement Strategies of Hydroxyapatite-Based Functional Granular Sludge for a High-Rate Partial Nitritation/Anammox System

Retaining sufficient anammox bacteria (AnAOB) while keeping the anammox-based process stable is the focus of the study of anammox technology, especially in a one-stage partial nitritation/anammox (PNA) process. The use of hydroxyapatite (HAP) granules in an anammox-based process is innovative for its potential to improve the nitrogen removal rate and achieve simultaneous removal of phosphorus. In this study, the HAP-based granular sludge was employed using enhancement strategies for an excellent nitrogen removal performance in a one-stage PNA process. Compared to those of other granular sludge PNA systems, a remarkable sludge volume index of 7.8 mL/g and an extremely high mixed liquor volatile suspended solids of 15 g/L were achieved under a low hydraulic retention time of 2 h. Consequently, an unprecedented nitrogen removal rate as high as 4.8 kg N/m3/d at 25 °C was obtained under a nitrogen loading rate of 6 kg N/m3/d. After a long-term operation of 870 days, the enhancement strategies underlying the superior performance of the granular sludge were identified. These findings clearly demonstrate that the enhancement strategies are crucial for the superior operating performance of the PNA process, and they can promote the application of the anammox-based process.

A review of anammox-based nitrogen removal technology: From microbial diversity to engineering applications

The anaerobic ammonium oxidation (anammox) process has the advantages of high efficiency and low energy consumption, so it has broad application prospects in biological denitrification of wastewater. However, the application of anammox technology to existing wastewater treatment is still challenging. The main problems are the insufficient supply of nitrite and the susceptibility of anammox bacteria to environmental factors. In this paper, from the perspective of the diversity of anammox bacteria, the habitats and characteristics of anammox bacteria of different genera were compared. At the same time, laboratory research and engineering applications of anammox technology in treating wastewater from different sources were reviewed, and the progress of and obstacles to the practical application of anammox technology were clarified. Finally, a focus for future research was proposed to intensively study the water quality barrier factors of anammox and its regulation strategies. Meanwhile, a combined process was developed and optimized on this basis.

Key enzymes involved in anammox-based processes for wastewater treatment: An applied overview

The anaerobic ammonium oxidation (anammox) process has attracted significant attention as an economic, robustness, and sustainable method for the treatment of nitrogen (N)-rich wastewater. Anammox bacteria (AnAOB) coexist with other microorganisms, and particularly with ammonia-oxidizing bacteria (AOB) and/or heterotrophic bacteria (HB), in symbiosis in favor of the substrate requirement (ammonium and nitrite) of the AnAOB being supplied by these other organisms. The dynamics of these microbial communities have a significant effect on the N-removal performance, but the corresponding metabolic pathways are still not fully understood. These processes involve many common metabolites that may act as key factors to control the symbiotic interactions between these organisms, to maximize N-removal efficiency from wastewater. Therefore, this work overviews the current state of knowledge about the metabolism of these microorganisms including key enzymes and intermediate metabolites and summarizes already reported experiences based on the employment of certain metabolites for the improvement of N-removal using anammox-based processes. PRACTITIONER POINTS: Approaches knowledge about the biochemistry and metabolic pathways involved in anammox-based processes. Some molecular tools can be used to determine enzymatic activity, serving as an optimization in nitrogen removal processes. Enzymatic evaluation allied to the physical-chemical and biomolecular analysis of the nitrogen removal processes expands the application in different effluents.

Diversity and Ecophysiology of the Genus OLB8 and Other Abundant Uncultured Saprospiraceae Genera in Global Wastewater Treatment Systems

The Saprospiraceae family within the phylum Bacteroidota is commonly present and highly abundant in wastewater treatment plants (WWTPs) worldwide, but little is known about its role. In this study, we used MiDAS 4 global survey with samples from 30 countries to analyze the abundance and distribution of members of Saprospiraceae. Phylogenomics were used to delineate five new genera from a set of 31 high-quality metagenome-assembled genomes from Danish WWTPs. Newly designed probes for fluorescence in situ hybridization (FISH) revealed rod-shaped morphologies for all genera analyzed, including OLB8, present mostly inside the activated sludge flocs. The genomes revealed potential metabolic capabilities for the degradation of polysaccharides, proteins, and other complex molecules; partial denitrification; and storage of intracellular polymers (glycogen, polyphosphate, and polyhydroxyalkanoates). FISH in combination with Raman microspectroscopy confirmed the presence of intracellular glycogen in Candidatus Brachybacter, Candidatus Parvibacillus calidus (both from the former genus OLB8), and Candidatus Opimibacter, and the presence of polyhydroxyalkanoates in Candidatus Defluviibacterium haderslevense and Candidatus Vicinibacter. These results provide the first overview of the most abundant novel Saprospiraceae genera present in WWTPs across the world and their potential involvement in nutrient removal and the degradation of macromolecules.

Effect of organic matter on the anammox performance of constructed rapid infiltration systems

Anaerobic ammonia oxidation (anammox) process was achieved in a constructed rapid infiltration (CRI) system and the effect of organic matter on the anammox performance and microbial community structure was investigated. The results showed that the removal efficiencies of NH4+-N, NO2-N and TN were 99.7 ± 0.3%, 99.8 ± 0.2% and 91.3 ± 0.2% respectively after 83 days of acclimation without the presence of organic matter in the influent. The average TN removal efficiency increased by 3.2%-7.7% due to the synergistic effect of anammox and denitrification at a low level of organic matter concentration (10-30 mg COD/L). At medium or high organic matter concentration (50-100 mg COD/L), denitrification gradually replaced anammox as the predominant nitrogen removal route due to its stronger ability to compete with substrate, resulting in a significant decline in anammox activity. The contribution rate of anammox to nitrogen removal dropped by 70.3% with the influent COD increased from 0 to 100 mg/L, and the TN removal efficiency decreased to 68.4 ± 3.6% since the anammox was seriously suppressed. 16S rRNA high-throughput sequencing analysis illustrated that the genus Candidatus Kuenenia was the predominant anammox bacteria (AAOB) with a relative abundance of 12.63% when no organic matter was applied. While the heterotrophic denitrifying bacteria (DNB) Thauera gradually dominated the community with the elevated organic matter introduction. The findings of this study provide useful information for the stable operation and optimal regulation of anammox in the CRI system when the influent contains organic matter.

Mesophilic condition favors simultaneous partial nitrification and denitrification (SPND) and anammox for carbon and nitrogen removal from anaerobic digestate food waste effluent

Three simultaneous partial nitrification and denitrification (SPND) bioreactors were established on ambient (30 °C), mesophilic (40 °C) and thermophilic condition (50 °C) at high dissolved oxygen levels (2-7 mg L^-1) to remove nitrogen and carbon from anaerobic digestate food waste effluent (ADFE). The bioreactor performed best under mesophilic condition, with TN and COD removal efficiency of 96.3 ± 0.1% and 91.7 ± 0.1%, respectively. Free ammonia (FA) and free nitrous acid (FNA) alternately ensured selective inhibition of nitrite-oxidizing bacteria (NOB) in long-term operation of SPND systems. Candidatus Brocadia, known as anammox bacteria, was observed unexpectedly in the bioreactors. The analysis of microbial community and metabolic pathways revealed that mesophilic strategy stimulated SPND and anammox process. Mesophilic condition helped autotropic microbes resist the competitive pressure from heterotrophic bacteria, improving the balance between nitrifiers, anammox bacteria and other co-existing heterotrophs. Overall, this study offers new insights into the linkage among temperature, pollutant removals (carbon and nitrogen) and metabolic potential in the SPND bioreactors.

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.

Microbial commensalism-assisted fast acclimation of HAP-anammox granules to dewatered liquid of dry methane fermentation

The treatment of a dewatered liquid of dry fermentation via the anammox process was investigated in the present study. Fast acclimation was established: within 2-months of operation, nitrogen removal rate reached 5 times (5.5 g-N/L/d) higher than it was at startup, which was achieved by inoculation with cold-stored HAP-anammox granules and inhibition control. The specific anammox activity of the dewatered liquid was highly improved and quite comparable to that of synthetic wastewater. Ca. Kuenenia with the relative abundance of 31.1% was revealed to be the only anammox genre and maintained its dominance throughout the operation. Simultaneously, Ca. D. denitrificans was proliferated, with its relative abundance increasing from 1.5% to 14.9%. The microbial co-occurrence network of HAP-anammox granules developed during the treatment of the dewatered liquid of dry fermentation. The experience of this work provides valuable strategies facilitating fast acclimation of the anammox process for the treatment of high-strength wastewater.

Responses of simultaneous anammox and denitrification (SAD) process to nitrogen loading variation: Start-up, performance, sludge morphology and microbial community dynamics

The effects of loading variation on the efficiency, EPS, sludge morphology and microbial population of simultaneous anammox and denitrification (SAD) were thoroughly investigated with the low-abundance SAD sludge. Results indicated that the first stage lasted the longest (33d), and the average removal rate of TN can be maintained above 95%. The specific anammox activity (SAA), specific denitrification activity and PN/PS continued to increase, but the excessive loading caused the effluent to deteriorate rapidly, and SAA and PN/PS also decreased slightly, but it could be recovered quickly. The contribution rate of anammox and denitrification to N removal reached 87.6% and 12.4% eventually, respectively. The abundance of AnAOB was 10.68%-18.01%, 9.01%-15.54%, 5.74%-12.88% in the upper, middle and lower layers, respectively. Candidatus Kuenenia was always the dominant AnAOB, especially after high loading inhibition. The abundance of denitrifying bacteria (mainly Bacillus, Comamonas and Denitratisoma) gradually became the highest.

Layered inoculation of anaerobic digestion and anammox granular sludges for fast start-up of an anammox reactor

Layered inoculation of anaerobic digestion (AD) and anammox granular sludges was performed for fast start-up of anammox using an expanded granular sludge bed (EGSB) reactor (R1) with the cell lysis phase and the lag phase being shortened. The maximum nitrogen loading rate (NLR) and nitrogen removal rate (NRR) of R1 were 11 kg N/m³ d and 9.9 kg N/m³ d on day 42, respectively. The domesticated AD granular sludge on the upper layer was collected to another EGSB reactor (R2) to investigate its anammox activity. The results showed that AD granular sludge in R1 had anammox activity and could be cultured into anammox granular sludge. Adsorption, interception and domestication enhanced the biomass of anammox bacteria in R1, accelerating the start-up of the reactor. The findings of this work were expected to solve the problem of fast start-up of an anammox reactor with insufficient anammox seeding sludge in industrial application.

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.

Reactors and active biomass potential as inoculum for nitrogen removal

The potential of three different kind of reactors and active biomass to be used as inoculum for nitrogen removal was verified. Sludge samples were collected from a Membrane Bioreactor (MBR), a previous tank of a Moving Bed Biofilm Reactor (MBBR) and a Trickling Filter (TF). Samples were compared according to bacterial activity in batch tests and their microbiology (16 s rRNA sequences). The microorganisms examined were: AOB, NOB, anammox bacteria and OHO. Results showed that the richest sample was from MBR (Chao value equals 581). However, the bacterial activity was greater in MBBR sample (q_AOO,NH4 equals 0.002 mgN·mgVSS^-1·h^-1; q_{NOO,NO2_NO3} equals 0.001 mgN·mgVSS^-1·h^-1 and q_{NOX_N2,SB} equals 10.0 mgN·mgVSS^-1·h^-1). Therefore, MBBR WWTP was shown to have the best inoculum and operating conditions for nitrogen conversion and removal. Besides, if aeration is provided as low as necessary for AOB to start the activity in denitrification tank, simultaneous partial nitrification, and denitrification (SPND) can occur.

Anammox bacteria in treating ammonium rich wastewater: Recent perspective and appraisal

The discovery of anammox process has provided eco-friendly and low-cost means of treating ammonia rich wastewater with remarkable efficiency. Furthermore, recent studies have shown that the possibility of operating the anammox process under low temperatures and high organic matter contents broadening the application of the anammox process. However, short doubling time and extensive levels of sensitivity towards nutrients and environmental alterations such as salinity and temperature are the limitations in practical applications of the anammox process. This review article provides the recent yet comprehensive viewpoint on anammox bacteria and the key perspectives in applying them as an efficient strategy for wastewater treatment.

A new kinetic model to predict substrate inhibition and better efficiency in an airlift reactor on deammonification process

A collection of kinetic models to explore the bacteria pathway inhibition by high-ammonia during deammonification process was fitted. The main goal was to determine the substrate concentration to operate the deammonification with efficiency, performance and low impact to ANAMMOX and ammonia-oxidizing bacteria (AOB) by substrate. A new mathematical model was created to describe the deammonification behavior, since the empirical theoretical models showed inconsistent parameters to describe the process. The proposed model showed significant prediction to the estimable parameters and according to it, until 550 mg NH₃-N L^-1 no inhibitions by ammonia and nitrite were observed. However, concentrations higher than this promote the decrease on specific bacterial activity and nitrite accumulation, since it was not quickly consumed by the bacteria. The proposed model can be applied to predict microorganism affinity and inhibition by substrate over a wide range of ammonia concentrations (<900 mgNH₃-N L^-1) in reactors treating high-ammonia concentration swine wastewater.