Anammox cultivation in a closed sponge-bed trickling filter

Methods Influence in Surface Area Result from Polyurethane Used as Support Media

We evaluated if different measurement methods influence the surface area results from a polyurethane sponge used as support media in biofilm reactors. The surface area values are normally used to characterize and present advantages from supported medias. However, the methodology to determine it is barely discussed. We compared two specific surface area methodologies: Brunauer-Emmett-Teller (BET) and analysis of images obtained by a scanning electron microscope (SEM). Specific surface area by BET was 93769.1 m2 m-3 (average); for SEM methodology, 10586.6 m2 m-3. The BET value was higher than expected in reality, and the SEM method result was more suitable and used as data input in a mathematical modeling.

Performance of vertical up-flow-constructed wetlands integrating with microbial fuel cell (VFCW-MFC) treating ammonium in domestic wastewater

Vertical up-flow-constructed wetlands integrating with microbial fuel cell (VFCW-MFC) were evaluated for NH4+-N removal and bioelectricity recovery. The experiments were carried out in lab-scale VFCW-MFC microcosms treating synthetic domestic wastewater under different operational conditions of pH, hydraulic retention time, and mass loading rate. Effects of wild ornamental grass (Cenchrus setaceus) on treatment performance and voltage output were investigated simultaneously. Experiments demonstrated that the neutral pH of influents favoured NH4+-N removal and power generation. Extended retention time improved treatment capacity and power output but likely depended on the substrate availability. COD removal and power output increased, while NH4+-N removal decreased with increasing mass loading rates. At the loading rate of 88.31 mg COD/L.day, planted VFCW-MFCs exhibited better NH4+-N treatment performance (36.9%) and higher voltage output (132%-143%) than unplanted systems. Plants did not affect the COD removal efficiency of VFCW-MFCs (>95%). Power density was in the range of 1.26-1.59 mW/m² in planted microcosms with a maximum CE of 13.6%. The anode layer accounted for a major proportion of NH4+-N removal in VFCW-MFCs. This study implies that NH4+-N in domestic wastewaters with relatively high COD:N ratios can be treated effectively in up-flow CW-MFCs via anaerobic processes, including anammox and heterotrophic denitrifying processes. The mass loading rate could be a critical parameter to balance different microbial processes, thus, coincidently determining the potential of power recovery from wastewaters.

Beyond an Applicable Rate in Low-Strength Wastewater Treatment by Anammox: Motivated Labor at an Extremely Short Hydraulic Retention Time

The application of anammox technology in low-strength wastewater treatment is still challenging due to unstable nitrite (NO₂^--N) generation. Partial denitrification (PD) of nitrate (NO₃^--N) reduction ending with NO₂^--N provides a promising solution. However, little is known about the feasibility of accelerating nitrogen removal toward the practical application of anammox combined with heterotrophic denitrification. In this work, an ultrafast, highly stable, and impressive nitrogen removal performance was demonstrated in the PD coupling with an anammox (PD/A) system. With a low-strength influent [50 mg/L each of ammonia (NH₄⁺-N) and NO₃^--N] at a low chemical oxygen demand/NO₃^--N ratio of 2.2, the hydraulic retention time could be shortened from 16.0 to 1.0 h. Remarkable nitrogen removal rates of 1.28 kg N/(m³ d) and excellent total nitrogen removal efficiency of 94.1% were achieved, far exceeding the applicable capacity for mainstream treatment. Stimulated enzymatic reaction activity of anammox was obtained due to the fast NO₂^--N jump followed by a famine condition with limited organic carbon utilization. This high-rate PD/A system exhibited efficient renewal of bacteria with a short sludge retention time. The 16S rRNA sequencing unraveled the rapid growth of the genus Thauera, possibly responsible for the incomplete reduction of NO₃^--N to NO₂^--N and a decreasing abundance of anammox bacteria. This provides new insights into the practical application of the PD/A process in the energy-efficient treatment of low-strength wastewater with less land occupancy and desirable effluent quality.

Development of a single-stage mainstream anammox process using a sponge-bed trickling filter

Anaerobic ammonia oxidation to nitrogen gas using nitrite as the electron acceptor (anammox process) is considered a cost-effective solution for nitrogen removal after an anaerobic pre-treatment process. In this study, we conducted a laboratory-scale experiment to develop a single-stage partial nitritation-anammox process in a sponge-based trickling filter (STF) reactor, inoculated with anammox sludge, simulating the treatment of anaerobically pretreated concentrated domestic sewage without mechanical oxygen control. The influent ammonia concentration was 100 mg-N·L^-1. The K_La of the STF reactor was higher than those observed for conventional activated sludge processes. The STF reactor performed at 89.8 ± 8.2% and 42.7 ± 16.9% ammonia and TN removal efficiency, respectively, with a nitrogen loading rate of 0.55 ± 0.20 kg-N·m^-3·day^-1 calculated based on sponge volume. Microbial community analysis of the STF-retained sludge indicated that both autotrophic and heterotrophic nitrogen removal occurred in the reactor.

Pilot-scale enrichment of anammox biofilm using secondary effluent as source water

Enough biomass of anaerobic ammonium oxidation (anammox) bacteria is essential for maintaining a stable partial nitrification/anammox (PN/A) wastewater treatment system. Present enrichment procedures are mainly labor-intensive and inconvenient for up-scaling. A simplified procedure was developed for enrichment of anammox biofilm by using secondary effluent as source water with no supplement of mineral medium and unstrict control of influent dissolved oxygen (DO). Anammox biofilm was successfully enriched in two pilot-scale reactors (XQ-cul and BT-cul) within 250 and 120 days, respectively. The specific anammox activity increased rapidly during the last 2 months in both reactors and achieved 2.54 g N₂-N/(m²·d) in XQ-cul and 1.61 g N₂-N/(m²·d) in BT-cul. Similar microbial diversity and community structure were obtained in the two reactors despite different secondary effluent being applied from two wastewater treatment plants. Anaerobic ammonium oxidizing bacteria genera abundance reached up to 37.4% and 43.1% in XQ-cul and BT-cul biofilm, respectively. Candidatus Brocadia and Ca. Kuenenia dominated the enriched biofilm. A negligible adverse effect of residual organics and influent DO was observed by using secondary effluent as source water. This anammox biofilm enrichment procedure could facilitate the inoculation and/or bio-augmentation of large-scale mainstream PN/A reactors.

Enrichment of microbial communities for hexavalent chromium removal using a biofilm reactor

Given the toxicity and widespread occurrence of hexavalent chromium [Cr(VI)] in aquatic environments, we investigated the feasibility of a down-flow hanging sponge (DHS) biofilm reactor for the enrichment of microbial communities capable of Cr(VI) removal. In the present study, a laboratory-scale DHS reactor fed with a molasses-based medium containing Cr(VI) was operated for 112 days for the investigation. The enrichment of Cr(VI)-removing microbial communities was evaluated based on water quality and prokaryotic community analyses. Once the DHS reactor began to operate, high average volumetric Cr(VI) removal rates of 1.21-1.45 mg L-sponge^-1 h^-1 were confirmed under varying influent Cr(VI) concentrations (approximately 20-40 mg L^-1). 16S rRNA gene amplicon sequencing analysis suggested the presence of phylogenetically diverse prokaryotic lineages, including phyla that contain well-known Cr(VI)-reducing bacteria (e.g., Bacteroidetes, Firmicutes, and Proteobacteria) in the polyurethane sponge media of the DHS reactor. Therefore, our findings indicate that DHS reactors have great potential for the enrichment of Cr(VI)-removing microbial communities.

Technologies for biological removal and recovery of nitrogen from wastewater

Water contamination is a growing environmental issue. Several harmful effects on human health and the environment are attributed to nitrogen contamination of water sources. Consequently, many countries have strict regulations on nitrogen compound concentrations in wastewater effluents. Wastewater treatment is carried out using energy- and cost-intensive biological processes, which convert nitrogen compounds into innocuous dinitrogen gas. On the other hand, nitrogen is also an essential nutrient. Artificial fertilizers are produced by fixing dinitrogen gas from the atmosphere, in an energy-intensive chemical process. Ideally, we should be able to spend less energy and chemicals to remove nitrogen from wastewater and instead recover a fraction of it for use in fertilizers and similar applications. In this review, we present an overview of various technologies of biological nitrogen removal including nitrification, denitrification, anaerobic ammonium oxidation (anammox), as well as bioelectrochemical systems and microalgal growth for nitrogen recovery. We highlighted the nitrogen removal efficiency of these systems at different temperatures and operating conditions. The advantages, practical challenges, and potential for nitrogen recovery of different treatment methods are discussed.

Characterization of the start-up of single and two-stage Anammox processes with real low-strength wastewater treatment

In order to promote the application of anaerobic ammonium oxidation (Anammox) for municipal wastewater treatment, single and two-stage Anammox processes were started up for real low-strength wastewater treatment under similar conditions for the comparison. Results showed that the anaerobic baffled reactor (ABR)-Nitritation-Anammox and the ABR-Completely Autotrophic Nitrogen removal Over Nitrite (CANON) process took 75 days and 101 days to start up with a total nitrogen removal rate of 86-92% and 81-87% under steady state, respectively. The 16 S rRNA sequencing analysis revealed that the phylum of Proteobacteria dominated in CANON system and Anammox system with the relative abundance of 35.39% and 15.27%, respectively. Phylogenetic analysis showed that Anammox species, related to Ca. Brocadia Sinica JPN1 and Ca. Kuenenia stuttgartiensis, dominated in these two systems, respectively. The nitrogen removal performance of two-stage process was 5% higher than that of single stage process, while the start-up period and dominated Anammox species were different.

Anammox-based processes: How far have we come and what work remains? A review by bibliometric analysis

Nitrogen contamination remains a severe environmental problem and a major threat to sustainable development worldwide. A systematic analysis of the literature indicates that the partial nitritation-anammox (PN/AMX) process is still actively studied as a viable option for energy-efficient and feasible technology for the sustainable treatment of N- rich wastewaters, since its initial discovery in 1990. Notably, the mainstream PN/AMX process application remains the most challenging bottleneck in AMX technology and fascinates the world's attention in AMX studies. This paper discusses the recent trends and developments of PN/AMX research and analyzes the results of recent years of research on the PN/AMX from lab-to full-scale applications. The findings would deeply improve our understanding of the major challenges under mainstream conditions and next-stage research on the PN/AMX process. A great deal of efforts has been made in the process engineering, PN/AMX bacteria populations, predictive modeling, and the full-scale implementations during the past 22 years. A series of new and excellent experimental findings at lab, pilot and full-scale levels including good nitrogen removal performance even under low temperature (15-10 °C) around the world were achieved. To date, pilot- and full-scale PN/AMX have been successfully used to treat different types of industrial sewage, including black wastewater, sludge digester liquids, landfill leachate, monosodium glutamate wastewater, etc. Supplementing the qualitative analysis, this review also provides a quantitative bibliometrics study and evaluates global perspectives on PN/AMX research published during the past 22 years. Finally, general trends in the development of PN/AMX research are summarized with the aim of conveying potential future trajectories. The current review offers a valuable orientation and global overview for scientists, engineers, readers and decision makers presently focusing on PN/AMX processes.

Impacts of salt shocking and the selection of a suitable reversal agent on anammox

In this study, an anaerobic ammonium oxidation (anammox) reactor, which was inhibited by a salinity of 50 g NaCl L^-1 during a long-term experiment, was rapidly restarted by decreasing the salinity to 20 g NaCl L^-1 and adding biomass. The effects of exposure time and shock concentrations on the anammox reactor indicate that anammox granular sludge has a high tolerance to salinity and strong ability for self-recovery. The nitrogen removal efficiency was higher than 50% after exposure to 50 g NaCl L^-1 for 66 h. To shorten the time taken for effluent nitrogen concentrations to attain national standards (GB18918-2002) after the anammox reactor was shocked with NaCl, reactor performance (i.e., recovery) after the addition of K⁺, glycine betaine, Fe²⁺, and hydroxylamine were compared after the reactor was inhibited by 80 g NaCl L^-1. The results indicate that hydroxylamine was the best reversal agent. The recovery time of the anammox reactor could be shortened by 50% following the addition of hydroxylamine. The most favorable NH₂OH-N/NO₂^--N concentration ratio for improving nitrogen removal of anammox was 1:11. The abundances of Planctomycetes and its genera Candidatus Kuenenia and Brocadiaceae_g_unclassified increased after repeated salinity shock-recovery phases, indicating that Candidatus Kuenenia and Brocadiaceae_g_unclassified are able to adapt to NaCl shocking and recovery.

Mainstream partial nitritation-anammox in municipal wastewater treatment: status, bottlenecks, and further studies

Driven by energy neutral/positive of wastewater treatment plants, significant efforts have been made on the research and development of mainstream partial nitritation and anaerobic ammonium oxidation (anammox) (PN/A) (deammonification) process since the early 2010s. To date, feasibility of mainstream PN/A process has been demonstrated and proven by experimental results at various scales although with the low loading rates and elevated nitrogen concentration in the effluent at low temperatures (15-10 °C). This review paper provides an overview of the current state of research and development of mainstream PN/A process and critically analyzes the bottlenecks for its full-scale application. The paper discusses the following: (i) the current status of research and development of mainstream PN/A process; (ii) the interactions among aerobic ammonium-oxidizing bacteria, aerobic nitrite-oxidizing bacteria, anammox bacteria, and heterotrophic bacteria; (iii) the suppression of aerobic nitrite-oxidizing bacteria; (iv) process and bioreactors; and (v) suggested further studies including efficient and robust carbon concentrating pretreatment, deepening of understanding competition between autotrophic nitrogen-converting organisms, intensification of biofilm anammox activity, reactor design, and final polishing.

Long-term operation performance and variation of substrate tolerance ability in an anammox attached film expanded bed (AAFEB) reactor

An anammox attached film expanded bed (AAFEB) reactor was operated to study the long-term performance and the variation of substrate tolerance ability. The results indicated that the nitrogen loading potential (NLP) was significantly enhanced from 13.56gN·(L·d)(-)(1) to 20.95gN·(L·d)(-)(1) during the stable operation period. The inhibitory concentration of 10% (IC10) for free ammonia (FA), free nitrous acid (FNA) and SNinf (diluted substrate concentration) increased from 18mg/L, 12μgL(-1) and 370mgNL(-)(1) to 31mg/L, 19μgL(-1) and 670mgNL(-)(1), respectively. However, the substrate shock of 2500mgNL(-)(1) for 24h terribly weakened the treatment performance and substrate tolerance ability of the reactor. The results of batch tests indicated that the existence of lag phase made the AAFEB reactor more vulnerable to substrate variation. The SNinf was accurate to be used to monitor the reactor performance and should be maintained below 320mgNL(-)(1) to ensure the absolute stable operation.

The effect of magnetite on the start-up and N2O emission reduction of the anammox process

A reactor combined with magnetite could enhance the anammox performance and enrich morePlanctomycetesbacteria.

Autotrophic nitrogen removal over nitrite in a sponge-bed trickling filter

Partial nitritation in sponge-bed trickling filters (STF) under natural air circulation was studied in two reactors: STF-1 and STF-2 operated at 30°C with sponge thickness of 0.75 and 1.50cm, respectively. The coexistence of nitrifiers and Anammox bacteria was obtained and attributed to the favorable environment created by the reactors' design and operational regimes. After 114days of operation, the STF-1 had an average NH4(+)-N removal of 69.3% (1.17kgN/m(3)sponged) and a total nitrogen removal of 52.2% (0.88kgN/m(3)sponged) at a Nitrogen Loading Rate (NLR) of 1.68kgN/m(3)sponged and Hydraulic Retention Time (HRT) of 1.71h. The STF-2 showed an average NH4(+)-N removal of 81.6 % (0.77kgN/m(3)sponged) and a total nitrogen removal of 54% (0.51kgN/m(3)sponged), at an NLR of 0.95kgN/m(3)sponged and HRT of 2.96h. The findings suggest that autotrophic nitrogen removal over nitrite in STF systems is a feasible alternative.