Application of anammox-based processes in urban WWTPs: are we on the right track?

The application of partial nitritation and anammox processes (PN/A) to remove nitrogen can improve the energy efficiency of wastewater treatment plants (WWTPs) as well as diminish their operational costs. However, there are still several limitations that are preventing the widespread application of PN/A processes in urban WWTPs such as: (a) the loss of performance stability of the PN/A units operated at the sludge line, when the sludge is thermally pretreated to increase biogas production; (b) the proliferation of nitrite-oxidizing bacteria (NOB) in the mainstream; and (c) the maintenance of a suitable effluent quality in the mainstream. In this work, different operational strategies to overcome these limitations were modelled and analyzed. In WWTPs whose sludge is thermically hydrolyzed, the implementation of an anerobic treatment before the PN/A unit is the best alternative, from an economic point of view, to maintain the stable performance of this unit. In order to apply the PN/A process in the mainstream, the growth of ammonia-oxidizing bacteria (AOB) should be promoted in the sludge line by supplying extra sludge to the anaerobic digesters. The AOB generated would be applied to the water line to partially oxidize ammonia, and the anammox process would then be carried out. Excess nitrate generated by anammox bacteria and/or NOB can be removed by recycling a fraction of the WWTP effluent to the biological reactor to promote its denitrificationThis research was funded by the Chilean Government through the Projects ANID/FONDECYT/1200850 and CRHIAM Centre grant number ANID/FONDAP/15130015. FCC Aqualia, S.A. as coordinator of the LIFE ZERO WASTE WATER consortium would like to thank the European Commission for its support through LIFE financial instrument LIFE19ENV/ES/000631S

Nitrite oxidizing bacteria suppression based on in-situ free nitrous acid production at mainstream conditions

"This is the accepted manuscript of the following article: Pedrouso A., Val del Río Á., Morales N., Vázquez-Padín J. R., Campos J. L., Méndez R. and Mosquera-Corral A. (2017). Nitrite oxidizing bacteria suppression based on in-situ free nitrous acid production at mainstream conditions. Separation and Purification Technology 186, 55-62, which has been published in final form at: https://doi.org/10.1016/j.seppur.2017.05.043. This article may be used for non-commercial purposes in accordance with Elsevier."The application of autotrophic nitrogen removal processes in the main line of wastewater treatment plants will contribute to achieve its self-energy-sufficiency. However, the effective suppression of nitrite oxidizing bacteria (NOB) activity at the conditions of low temperature and low ammonium concentration (mainstream conditions) was identified as one of the main bottlenecks. In this study, stable partial nitritation at 16 °C and 50 mg NH4+-N/L was achieved maintaining inside the reactor free nitrous acid (FNA) concentrations inhibitory for NOB (>0.02 mg HNO2-N/L), without dissolved oxygen concentration control. The FNA inhibitory concentration was generated by the partial nitritation process, and its stimulation was studied with two different inhibitors: sodium azide and nitrite. The microbiological analysis revealed that, throughout the operational period with inhibitory FNA levels, the NOB populations (dominated by Nitrospira) were effectively washed out from the reactor. This is an advantage that allowed maintaining a good stability of the process, even when the FNA concentration was not enough to inhibit the NOB, taking about 40 days to develop significant activity. The observed delay on the NOB development is expected to enable the establishment of corrective actions to avoid the partial nitritation destabilization. The use of the FNA to achieve a stable partial nitritation process is recommended to profit from the natural pH decrease associated to the nitritation process and from its favoured accumulation at low temperatures as those from the mainstream. In this research study an analysis about the influence of ammonium and alkalinity concentrations was also performed to know in which scenarios the FNA inhibitory concentration can be achievedAuthors want to thank the Pioneer_STP (ID 199) project funded by the WaterWorks2014 Cofunded Call (Water JPI/Horizon 2020). This work was also funded by the Spanish Government through FISHPOL (CTQ2014-55021-R) and GRANDSEA (CTM2014-55397-JIN). The authors from the USC belong to CRETUS (AGRUP2015/02) and the Galician Competitive Research Group (GRC 2013-032). All these programs are co-funded by FEDER funds. This work was as well funded by the Chilean Government through the Project FONDECYT 1150285 and CONICYT/FONDAP/15130015S

Treatment of the Supernatant of Anaerobically Digested Organic Fraction of Municipal Solid Waste in a Demo-Scale Mesophilic External Anaerobic Membrane Bioreactor

Conventional aerobic biological treatments of digested organic fraction of municipal solid waste (OFMSW) slurries–usually conventional activated sludge or aerobic membrane bioreactor (AeMBR)–are inefficient in terms of energy and economically costly because of the high aeration requirements and the high amount of produced sludge. In this study, the supernatant obtained after the anaerobic digestion of OFMSW was treated in a mesophilic demo-scale anaerobic membrane bioreactor (AnMBR) at cross flow velocities (CFVs) between 1 and 3.5 m⋅s–1. The aim was to determine the process performance of the system with an external ultrafiltration unit, in terms of organic matter removal and sludge filterability. In previous anaerobic continuous stirred tank reactor (CSTR) tests, without ultrafiltration, specific gas production between 40 and 83 NL CH4⋅kg–1 chemical oxygen demand (COD) fed and removals in the range of 10–20% total COD (tCOD) or 59–77% soluble COD (sCOD) were obtained, for organic loading rates (OLR) between 1.7 and 4.4 kg COD⋅m–3reactor d–1. Data helped to identify a simplified model with the aim of understanding and expressing the process performance. Methane content in biogas was in the range of 74–77% v:v. In the AnMBR configuration, the COD removal has been in the ranges of 15.6–38.5 and 61.3–70.4% for total and sCOD, respectively, with a positive correlation between solids retention time (SRT, ranging from 7.3 to 24.3 days) and tCOD removal. The constant used in the model expressing inhibition, attributable to the high nitrogen content (3.6 ± 1.0 g N-NH4+⋅L–1), indicated that this inhibition decreased when SRT increased, explaining values measured for volatile fatty acids concentration, which decreased when SRT increased and OLR, measured per unit of volatile suspended solids in the reactor, decreased. The alkalinity was high enough to allow a stable process throughout the experiments. Constant CFV operation resulted in excessive fouling and sudden trans-membrane pressure (TMP) increases. Nevertheless, an ultrafiltration regime based on alternation of CFV (20 min with a certain CFVi and then 5 min at CFVi + 1 m⋅s–1) allowed the membranes to filter at a flux (standardized at 20°C temperature) ranging from 2.8 to 7.3 L⋅m–2⋅h–1, over 331 days of operation, even at very high suspended solids concentrations (>30 g total suspended solids⋅L–1) in the reactor sludge. This flux range confirms that fouling is the main issue that can limit the spread of AnMBR potential for the studied stream. No clear correlation was found between CFV or SRT vs. fouling rate, in terms of either TMP⋅time–1 or permeability⋅time–1. As part of the demo-scale study, other operational limitations were observed: irreversible fouling, scaling (in the form of struvite deposition), ragging, and sludging. Because ragging and sludging were also observed in the existing AeMBR, it can be stated that both are attributable to the stream and to the difficulty of removing existing fibers. All the mentioned phenomena could have contributed to the high data dispersion of experimental results.info:eu-repo/semantics/publishedVersio

An optimised control system to steer the transition from anaerobic mono- to co-digestion in full-scale plants

Despite the rapid increase of anaerobic co-digestion works over the last years, the very small number of pilot- and full-scale studies available in the literature is a major barrier to its full-scale implementation. In this paper, a control strategy methodology was applied in a full-scale sludge digester to safely steer the transition from anaerobic mono- to co-digestion and to maximize methane production.Traditional wastewater treatment plants (WWTPs) are electrical consumers, with a usual high demand in the range of 0.3 to 0.6 kWh/m3 of wastewater treated. Their digesters are commonly oversized, and consequently operated at low organic loading rates (OLRs). This opens a great opportunity for anaerobic co-digestion (AcoD) as an interesting technology to increase methane productivity and the electrical self-production in WWTPs. However, there is a quite limited implementation of AcoD at full-scale plants, since the transition from mono- to co-digestion and the further AcoD optimisation is a crucial and delicate step that could lead to the inhibition of the process if not thoroughly controlled. In this study, a methodology based on an optimum control strategy is explained in detail and it was applied to safely and optimally steer the transition from mono- to co-digestion and to maximize methane production during AcoD. A lab-scale anaerobic digester of 14 L mimicking the full-scale one (3,500 m3) was operated 30 days in advance to anticipate and if needed correct any operational destabilization that might occurr. As a result, the treatment of sewage sludge with two co-substrates (coming from a pig slaughterhouse and from a frying industry), which accounted for just 11% of the feeding flowrate, at a hydraulic retention time of 20 days allowed to raise the OLR and the methane production by 2-fold and 3-fold, respectively, increasing the self-produced electricity from 25% to 75% of the total demand of the WWTP. The diagnosis indicators proved to be accurate to take decisions concerning wastes blending and the strategy of increasing OLR. Besides, the proposed control system provides the steps to ensure a safe transition from anaerobic mono- to co-digestion and further optimisation at full-scale plantsThis work was supported by SmartGreenGas project (Spanish Government, AEI, 2014-CE224). The authors from Universidade de Santiago de Compostela belong to the Galician Competitive Research Group ED431C 2017/029 and to the CRETUS Strategic Partnership (AGRUP2017/01). All these programs are co-funded by FEDER (EU)S

Rapid start-up and stable maintenance of the mainstream nitritation process based on the accumulation of free nitrous acid in a pilot-scale two-stage nitritation-anammox system

Two-stage partial nitritation (PN) and anammox (AMX) systems showed promising results for applying autotrophic nitrogen removal under mainstream conditions. In this study, a pilot-scale (600 L per reactor) two-stage PN/AMX system was installed in a municipal wastewater treatment plant (WWTP) provided with a high-rate activated sludge (HRAS) system for organic carbon removal. The PN/AMX system was operated without temperature control (ranging from 11 to 28 °C) and was subjected to the same variations in wastewater characteristics as the WWTP (22 to 63 mg NH4+- N/L). The developed strategy is simple, does not require the addition of chemicals and is characterised by short start-up periods. The PN process was established by applying a high hydraulic load and maintained by in situ accumulated free nitrous acid (FNA) of 0.015–0.2 mg HNO2-N/L. Based on pH value, a controlled aeration strategy was applied to achieve the target nitrite to ammonium ratio in the effluent (1.1 g NO2–-N/g NH4+-N) to feed the AMX reactor. Although NOB were not fully washed out from the system, nitrite accumulation remained (>99 %) stable with no evidence of NOB activity. In the AMX reactor, an overall nitrogen removal efficiency of 80 % was achieved. Regarding effluent quality, 12 ± 3 mg TN/L was obtained, but 5 mg NO3–-N/L was already in the HRAS effluent. The relative abundance of NOB showed a strong negative correlation with the FNA concentration, providing a good strategy for establishing PN under mainstream conditionsThis work has been financed by the European Commission (EU) through the LIFE project ZERO WASTE WATER (LIFE19 ENV/ES/000631), the Waterworks 2014 Cofounded Call (Water JPI/Horizon) through the Pioneer_STP (PCIN-2015-022 MINECO(AEI)/ID 199 (UE)) and by the Spanish Government (AEI) through GRANDSEA (CTM2014-55397-JIN), TREASURE (CTQ2017-83225-C2-1-R) and ECOPOLYVER (PID2020-112550RB-C21 and PID2020-112550RB-C22) projects. Alba Pedrouso also acknowledges the Xunta de Galicia (Spain) for her postdoctoral fellowship (ED481B-2021-041). Authors from the USC belong to the Galician Competitive Research Group (GRC D431C-2021/37)S

Pilot-scale ELAN® process applied to treat primary settled urban wastewater at low temperature via partial nitritation-anammox processes

A single stage partial nitritation and anammox granular pilot scale reactor (600 L) was operated to treat primary settled sewage in an urban wastewater treatment plant. The fed wastewater contained low total nitrogen concentrations of 6–25 mg TN/L and the system operated without temperature control ranging from 18 to 12 °C. A control strategy, based on the pH value, was applied to stop the aeration supply. The pH set-point was fixed at 6.0 and allowed obtaining a total nitrogen removal efficiency approximately of 50% treating a load of 67 mg TN/(L·d) without the addition of any chemicals. Although nitrite oxidizing bacteria were present in the inoculated sludge, when the pH-based control was implemented (day 30) the ammonium oxidation was favored compared to the nitrite oxidation activity. Then, the system operated stable the rest of the operational period (days 30–94) despite the presence of organic matter in the wastewater and the high variability of nitrogen load and temperature during the operation. Nitrogen was autotrophically removed accomplishing the stringent discharge limits (10 mg TN/L) and nitrate concentrations in the effluent lower than 3 mg NO3−-N/L. Both biomass concentration and granules size increased during the operational period indicating the growth of the biomass inside the reactor and therefore the potential treatment capacity.Authors want to thank the Pioneer_STP (ID 199) project funded by the WaterWorks2014 Cofunded Call (Water JPI/Horizon 2020). This work was also funded by the Spanish Government through FISHPOL (CTQ2014-55021-R) and GRANDSEA (CTM2014-55397-JIN) projects and by Galician Government by the MEDRAR (IN852A 2016) project. The authors from the USC belong to CRETUS (AGRUP2015/02) and the Galician Competitive Research Group (GRC ED431C 2017/29). All these programs are co-funded by FEDER. This work was as well funded by the Chilean Government through the Project FONDECYT 1150285 and CONICYT/FONDAP/15130015S

Mainstream anammox reactor performance treating municipal wastewater and batch study of temperature, pH and organic matter concentration cross-effects

The anammox process is an energy efficient promising alternative to biologically remove the nitrogen. Thus, a 5-L anammox granular reactor was inoculated with sludge coming from a sidestream partial nitritation and anammox reactor (>200 mg TN/L and 30 °C) and it was directly subjected to 15 ± 1 °C treating mimicked municipal wastewater (50 mg TN/L). Results indicated that an acclimation period (commonly used) to progressive reach the mainstream conditions is not needed, shortening the start-up periods. The long-term anammox process stability was proved to treat synthetic wastewater with decreasing alkalinities and nitritified primary settled municipal wastewater. The low pH values (6.2 ± 0.1) of the municipal wastewater fed did not affect the process stability. Residual organic matter concentrations augmented the nitrogen removal efficiency from 80 % (with the synthetic medium) to 92 % achieving effluent concentrations below 10 mg TN/L. Finally, the effect of pH (6–8), temperature (15–30 °C) and organic matter concentration (0–75 mg TOC/L) over the specific anammox activity (SAAMX) was evaluated at short-term. pH and temperature and their interactions exerted significant influence on the SAAMX value while the TOC concentrations itself did not significantly change the SAAMXThis work was done within the Pioneer_STP (ID 199(UE)/PCIN-2015-022(AEI)) project funded by the WaterWorks2014 Cofunded Call (Water JPI/Horizon 2020). The Spanish Government (AEI) also financed this research by the TREASURE (CTQ2017-83225-C2-1-R). The authors from the USC belong to CRETUS Strategic Partnership (ED431E 2018/01) and to the Galician Competitive Research Group (GRC-ED431C 2017/29). Both programs co-funded by FEDER (EU) funds2022-08-04S

Performance of a two-stage partial nitritation-anammox system treating the supernatant of a sludge anaerobic digester pretreated by a thermal hydrolysis process

A two-stage system (partial nitritation (PN) and anammox processes) was used to remove nitrogen from the dewatering liquor originating from the thermal hydrolysis/anaerobic digestion (THP/AD) of municipal WWTP sludge. Two strategies were tested to start up the PN reactor: 1) maintaining a fixed hydraulic retention time (HRT) and increasing the ammonium loading rate (ALR) by decreasing the feeding dilution ratio and 2) feeding undiluted dewatering liquor and gradually decreasing the HRT. With diluted feeding, the reactor performance had destabilization episodes that were statistically correlated with the application of high specific ammonium (> 0.6 g NH4+-N/(g TSS·d)) and organic (> 0.7 g COD/(g TSS·d)) loading rates. The second strategy allowed stable PN reactor operation while treating ALR up to 4.8 g NH4+-N/(L·d) and demonstrating that dilution of THP/AD effluents is not required. The operating conditions promoted the presence of free nitrous acid levels (> 0.14 mg HNO2-N/L) inside the PN reactor that inhibited the proliferation of nitrite oxidizing bacteria. Batch activity tests showed that the inhibitory effects of organic compounds present in the THP/AD dewatering liquor on the ammonia oxidizing bacteria activity can be removed in the PN reactor. Thus, aerobic pretreatment would not be necessary when two-stage systems are used. The PN reactor effluent was successfully treated by an anammox reactor. An economic analysis showed that using two-stage systems is advantageous for treating THP/AD dewatering liquor. The implementation of an aerobic pre-treatment unit is recommended for WWTPs capacities higher than 5·105 inhabitants equivalent when one-stage systems are usedThis research was funded by the Chilean Government through the Projects ANID/FONDECYT/1200850 and CRHIAM Centre grant number ANID/FONDAP/15130015, by the Spanish Government through TREASURE [CTQ2017-83225-C2-1-R] and by the European Commission LIFE ZERO WASTE WATER [LIFE19ENV/ES/000631] projects. The authors from Universidade de Santiago de Compostela belong to CRETUS Strategic Partnership [ED431E 2018/01] and the Galician Competitive Research Group [GRC ED431C 2017/29]. All the Spanish programs are co-funded by FEDER (EU)2023-07-15S