Producing free nitrous acid - A green and renewable biocidal agent - From anaerobic digester liquor

Recent studies have shown that free nitrous acid (FNA) at parts per million is strongly biocidal to a broad range of microorganisms involved in wastewater management. Applications have been developed, where FNA is used to deactivate anaerobic sewer biofilms thus suppressing sulfide and methane production in sewers, or to lyse secondary sludge resulting in reduced sludge production and enhanced biogas production. This study examines the feasibility of producing FNA from a waste stream namely the anaerobic sludge digestion liquor, thus providing a source of FNA for the above applications within wastewater systems. Complete nitritation was achieved in a lab scale sequencing batch reactor (SBR) treating reject wastewater. Under stable operation, the system sustained more than 90% conversion of the 1.0 and 0.8g NH4 +-N/L contained in the synthetic and real digester liquor, respectively, to nitrite. Each liter of this nitrite rich effluent could be acidified to pH 2 with only 66 mmol of H+, due to the low level of alkalinity in the effluent. This converts almost all of the nitrite to FNA providing an ample source of FNA for sewer and sludge pretreatment applications. Despite the high nitrite concentration in the reactor, minimal N2O was produced with an emission factor of 0.08% of the ammonium nitrogen converted. Finally, an economical assessment of a theoretical full-scale installation for FNA production was conducted and compared with the costs of producing this FNA from a commercial nitrite supply

Polyphosphate-accumulating organisms in full-scale tropical wastewater treatment plants use diverse carbon sources

Enhanced biological phosphorus removal (EBPR) is considered challenging in the tropics, based on a great number of laboratory-based studies showing that the polyphosphate-accumulating organism (PAO) Candidatus Accumulibacter does not compete well with glycogen accumulating organisms (GAOs) at temperatures above 25 °C. Yet limited information is available on the PAO community and the metabolic capabilities in full-scale EBPR systems operating at high temperature. We studied the composition of the key functional PAO communities in three full-scale wastewater treatment plants (WWTPs) with high in-situ EBPR activity in Singapore, their EBPR-associated carbon usage characteristics, and the relationship between carbon usage and community composition. Each plant had a signature community composed of diverse putative PAOs with multiple operational taxonomic units (OTUs) affiliated to Ca. Accumulibacter, Tetrasphaera spp., Dechloromonas and Ca. Obscuribacter. Despite the differences in community composition, ex-situ anaerobic phosphorus (P)-release tests with 24 organic compounds from five categories (including four sugars, three alcohols, three volatile fatty acids (VFAs), eight amino acids and six other carboxylic acids) showed that a wide range of organic compounds could potentially contribute to EBPR. VFAs induced the highest P release (12.0-18.2 mg P/g MLSS for acetate with a P release-to-carbon uptake (P:C) ratio of 0.35-0.66 mol P/mol C, 9.4-18.5 mg P/g MLSS for propionate with a P:C ratio of 0.38-0.60, and 9.5-17.3 mg P/g MLSS for n-butyrate), followed by some carboxylic acids (10.1-18.1 mg P/g MLSS for pyruvate, 4.5-11.7 mg P/g MLSS for lactate and 3.7-12.4 mg P/g MLSS for fumarate) and amino acids (3.66-7.33 mg P/g MLSS for glutamate with a P:C ratio of 0.16-0.43 mol P/mol C, and 4.01-7.37 mg P/g MLSS for aspartate with a P:C ratio of 0.17-0.48 mol P/mol C). P-release profiles (induced by different carbon sources) correlated closely with PAO community composition. High micro-diversity was observed within the Ca. Accumulibacter lineage, which represented the most abundant PAOs. The total population of Ca. Accumulibacter taxa was highly correlated with P-release induced by VFAs, highlighting the latter's importance in tropical EBPR systems. There was a strong link between the relative abundance of individual Ca. Accumulibacter OTUs and the extent of P release induced by distinct carbon sources (e.g., OTU 81 and amino acids, and OTU 246 and ethanol), suggesting niche differentiation among Ca. Accumulibacter taxa. A diverse PAO community and the ability to use numerous organic compounds are considered key factors for stable EBPR in full-scale plants at elevated temperatures.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore

MiDAS 4: A global catalogue of full-length 16S rRNA gene sequences and taxonomy for studies of bacterial communities in wastewater treatment plants

Microbial communities are responsible for biological wastewater treatment, but our knowledge of their diversity and function is still poor. Here, we sequence more than 5 million high-quality, full-length 16S rRNA gene sequences from 740 wastewater treatment plants (WWTPs) across the world and use the sequences to construct the ‘MiDAS 4’ database. MiDAS 4 is an amplicon sequence variant resolved, full-length 16S rRNA gene reference database with a comprehensive taxonomy from domain to species level for all sequences. We use an independent dataset (269 WWTPs) to show that MiDAS 4, compared to commonly used universal reference databases, provides a better coverage for WWTP bacteria and an improved rate of genus and species level classification. Taking advantage of MiDAS 4, we carry out an amplicon-based, global-scale microbial community profiling of activated sludge plants using two common sets of primers targeting regions of the 16S rRNA gene, revealing how environmental conditions and biogeography shape the activated sludge microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 966 genera and 1530 species that represent approximately 80% and 50% of the accumulated read abundance, respectively. Finally, we show that for well-studied functional guilds, such as nitrifiers or polyphosphate-accumulating organisms, the same genera are prevalent worldwide, with only a few abundant species in each genus.Fil: Dueholm, Morten Kam Dahl. Aalborg University; DinamarcaFil: Nierychlo, Marta. Aalborg University; DinamarcaFil: Andersen, Kasper Skytte. Aalborg University; DinamarcaFil: Rudkjøbing, Vibeke. Aalborg University; DinamarcaFil: Knutsson, Simon. Aalborg University; DinamarcaFil: Arriaga, Sonia. Instituto Potosino de Investigación Científica y Tecnológica; MéxicoFil: Bakke, Rune. University College of Southeast Norway; NoruegaFil: Boon, Nico. University of Ghent; BélgicaFil: Bux, Faizal. Durban University of Technology; SudáfricaFil: Christensson, Magnus. Veolia Water Technologies Ab; SueciaFil: Chua, Adeline Seak May. University Malaya; MalasiaFil: Curtis, Thomas P.. University of Newcastle; Reino UnidoFil: Cytryn, Eddie. Agricultural Research Organization Of Israel; IsraelFil: Erijman, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres"; Argentina. Universidad de Buenos Aires; ArgentinaFil: Etchebehere, Claudia. Instituto de Investigaciones Biológicas "Clemente Estable"; UruguayFil: Fatta Kassinos, Despo. University of Cyprus; ChipreFil: Frigon, Dominic. McGill University; CanadáFil: Garcia Chaves, Maria Carolina. Universidad de Antioquia; ColombiaFil: Gu, April Z.. Cornell University; Estados UnidosFil: Horn, Harald. Karlsruher Institut Für Technologie; AlemaniaFil: Jenkins, David. David Jenkins & Associates Inc; Estados UnidosFil: Kreuzinger, Norbert. Tu Wien; AustriaFil: Kumari, Sheena. Durban University of Technology; SudáfricaFil: Lanham, Ana. University of Bath; Reino UnidoFil: Law, Yingyu. Singapore Centre For Environmental Life Sciences Engineering; SingapurFil: Leiknes, TorOve. King Abdullah University of Science and Technology; Arabia SauditaFil: Morgenroth, Eberhard. Eth Zürich; SuizaFil: Muszyński, Adam. Politechnika Warszawska; PoloniaFil: Petrovski, Steve. La Trobe University; AustraliaFil: Pijuan, Maite. Catalan Institute For Water Research; EspañaFil: Pillai, Suraj Babu. Va Tech Wabag Ltd; IndiaFil: Reis, Maria A. M.. Universidade Nova de Lisboa; PortugalFil: Rong, Qi. Chinese Academy of Sciences; ChinaFil: Rossetti, Simona. Istituto Di Ricerca Sulle Acque (irsa) ; Consiglio Nazionale Delle Ricerche;Fil: Seviour, Robert. La Trobe University; AustraliaFil: Tooker, Nick. University of Massachussets; Estados UnidosFil: Vainio, Pirjo. Espoo R&D Center; FinlandiaFil: van Loosdrecht, Mark. Delft University of Technology; Países BajosFil: Vikraman, R.. VA Tech Wabag, Philippines Inc; FilipinasFil: Wanner, Jiří. University of Chemistry And Technology; República ChecaFil: Weissbrodt, David. Delft University of Technology; Países BajosFil: Wen, Xianghua. Tsinghua University; ChinaFil: Zhang, Tong. The University of Hong Kong; Hong KongFil: Nielsen, Per H.. Aalborg University; DinamarcaFil: Albertsen, Mads. Aalborg University; DinamarcaFil: Nielsen, Per Halkjær. Aalborg University; Dinamarc

The effect of pH on N2O production under aerobic conditions in a partial nitritation system

Ammonia-oxidising bacteria (AOB) are a major contributor to nitrous oxide (N2O) emissions during nitrogen transformation. N2O production was observed under both anoxic and aerobic conditions in a lab-scale partial nitritation system operated as a sequencing batch reactor (SBR). The system achieved 55 +/- 5% conversion of the 1 g NH4+-N/L contained in a synthetic anaerobic digester liquor to nitrite. The N2O emission factor was 1.0 +/- 0.1% of the ammonium converted. pH was shown to have a major impact on the N2O production rate of the AOB enriched culture. In the investigated pH range of 6.0-8.5, the specific N2O production was the lowest between pH 6.0 and 7.0 at a rate of 0.15 +/- 0.01 mg N2O-N/h/g VSS, but increased with pH to a maximum of 0.53 +/- 0.04 mg N2O-N/h/g VSS at pH 8.0. The same trend was also observed for the specific ammonium oxidation rate (AOR) with the maximum AOR reached at pH 8.0. A linear relationship between the N2O production rate and AOR was observed suggesting that increased ammonium oxidation activity may have promoted N2O production. The N2O production rate was constant across free ammonia (FA) and free nitrous acid (FNA) concentrations of 5-78 mg NH3-N/L and 0.15-4.6 mg HNO2-N/L, respectively, indicating that the observed pH effect was not due to changes in FA or FNA concentrations. (C) 2011 Elsevier Ltd. All rights reserved

The confounding effect of Nitrite on N2O production by an enriched Ammonia-Oxidizing culture

The effect of nitrite (NO2-) on the nitrous oxide (N2O) production rate of an enriched ammonia-oxidizing bacteria (AOB) culture was characterized over a concentration range of 0-1000 mg NIL. The AOB culture was enriched in a nitritation system fed with synthetic anaerobic digester liquor. The N2O production rate was highest at NO2- concentrations of less than 50 mg N/L. At dissolved oxygen (DO) concentration of 0.55 mg O-2/L, further increases in NO2- concentration from 50 to 500 mg NIL resulted in a gradual decrease in N2O production rate, which maintained at its lowest level of 0.20 mg N2O-N/h/g VSS in the NO2- concentration range of 500-1000 mg NIL. The observed NO2--induced decrease in N2O production was even more apparent at increased DO concentration. At DO concentrations of 1.30 and 2.30 mg O-2/L, the lowest N2O production rate (0.25 mg N2O-N/h/g VSS) was attained at a lower NO2- concentration of 200-250 mg N/L. These observations suggest that N2O production by the culture is diminished by both high NO2- and high DO concentrations. Collectively, the findings show that exceedingly high NO2- concentrations in nitritation systems could lead to decreased N2O production. Further studies are required to determine the extent to which the same response to NO2- is observed across different AOB cultures

Ammonium as a sustainable proton shuttle in bioelectrochemical systems

This work examines a pH control method using ammonium (NH4+) as a sustainable proton shuttle in a CEM-equipped BES. Current generation was sustained by adding NH3 or ammonium hydroxide (NH4OH) to the anolyte, controlling its pH at 7. Ammonium ion migration maintained the catholyte pH at approximately 9.25. Such NH4+/NH3 migration accounted for 90±10% of the ionic flux in the BES. Reintroducing the volatilized NH3 from the cathode into the anolyte maintained a suitable anolyte pH for sustained microbial-driven current generation. Hence, NH4+/NH3 acted as a proton shuttle that is not consumed in the process

Modeling N2O production by ammonia oxidizing bacteria at varying inorganic carbon concentrations by coupling the catabolic and anabolic processes

Several mathematical models have been proposed to describe nitrous oxide (NO) production by ammonia oxidizing bacteria (AOB) under varying operational conditions. However, none of these NO models are able to capture NO dynamics caused by the variation of inorganic carbon (IC) concentration, which has recently been demonstrated to be a significant factor influencing NO production by AOB. In this work, a mathematical model that describes the effect of IC on NO production by AOB is developed and experimentally validated. The IC effect is considered by explicitly including the AOB anabolic process in the model, which is coupled to the catabolic process with the use of the Adenosine triphosphate (ATP) and Adenosine diphosphate (ADP) pools. The calibration and validation of the model were conducted using experimental data obtained with two independent cultures, including a full nitrification culture and a partial nitritation culture. The model satisfactorily describes the NO data from both systems at varying IC concentrations. This new model enhances our ability to predict NO production by AOB in wastewater treatment systems under varying IC conditions

N(2)O production rate of an enriched ammonia-oxidising bacteria culture exponentially correlates to its ammonia oxidation rate

The relationship between the ammonia oxidation rate (AOR) and nitrous oxide production rate (N2OR) of an enriched ammonia-oxidising bacteria (AOB) culture was investigated. The AOB culture was enriched in a nitritation system fed with synthetic anaerobic digester liquor. The AOR was controlled by adjusting the dissolved oxygen (DO) and pH levels and also by varying the initial ammonium (NH4+) concentration in batch experiments. Tests were also performed directly on the parent reactor where a stepwise decrease/increase in DO was implemented to alter AOR. The experimental data indicated a clear exponential relationship between the biomass specific N2OR and AOR. Four metabolic models were used to analyse the experimental data. The metabolic model formulated based on aerobic N2O production from the decomposition of nitrosyl radical (NOH) predicted the exponential correlation observed experimentally. The experimental data could not be reproduced by models developed on the basis of N2O production through nitrite (NO2-) and nitric oxide (NO) reduction by AOB