Diversity and enrichment of nitrite-dependent anaerobic methane oxidizing bacteria from wastewater sludge

Recently discovered microorganisms affiliated to the bacterial phylum NC10, named “Candidatus Methylomirabilis oxyfera”, perform nitrite-dependent anaerobic methane oxidation. These microorganisms could be important players in a novel way of anaerobic wastewater treatment where ammonium and residual dissolved methane might be removed at the expense of nitrate or nitrite. To find suitable inocula for reactor startup, ten selected wastewater treatment plants (WWTPs) located in The Netherlands were screened for the endogenous presence of M. oxyfera using molecular diagnostic methods. We could identify NC10 bacteria with 98% similarity to M. oxyfera in nine out of ten WWTPs tested. Sludge from one selected WWTP was used to start a new enrichment culture of NC10 bacteria. This enrichment was monitored using specific pmoA primers and M. oxyfera cells were visualized with fluorescence oligonucleotide probes. After 112 days, the enrichment consumed up to 0.4 mM NO2− per day. The results of this study show that appropriate sources of biomass, enrichment strategies, and diagnostic tools existed to start and monitor pilot scale tests for the implementation of nitrite-dependent methane oxidation in wastewater treatment at ambient temperature

Thermophilic anaerobic digestion of cattle manure and improving the hydrolysis yield

Due to global warming and the depletion of fossil fuels, there is a trend towards renewable energy sources, such as solar power, bio-ethanol and biogas. Anaerobic digestion is an established technology for the recovery of chemical energy from e.g. wastewater and manure as biogas [1,2]. Although a proven technology, research is required to increase biogas yields and productivity. In the present research, the thermophilic anaerobic digestion of cattle manure, codigested with food waste, is studied. Inoculum and substrate are sampled at a thermophilic anerobic digester of G\uf6teborg Energi AB (S\ue4vsj\uf6, Sweden). At this site, cattle manure and food waste are pretreated at 70 \ub0C (1 h for hygienisation). Hereafter, the substrate is digested at 55 \ub0C in a continuously fed stirred tank reactor. It is expected that hydrolysis of the lignocellulosic material contained in the substrate is a limiting step [3]. This will be verified in laboratory studies, mimicking the conditions at the plant. The substrate will be characterized, focusing on the lignocellulosic material and the changes this material undergoes during anaerobic digestion. Moreover, the responsible organisms and the enzymes they excrete will be characterized, which will indicate how to improve hydrolysis. It is expected this may be done through adjusting micro and macro nutrient availability [4] and selection of process conditions. The effect of the selected parameters on the microbial community and the hydrolysis yield will be established. Moreover, the effect of particle size will be studied.The expected outcome of the study is that by an improved understanding of the microbial community, esp. the organisms responsible for hydrolysis of lignocellulosic material, the biogas yield, biogas productivity and system stability can be increased

Thermophilic anaerobic digestion of cattle manure and improving the hydrolysis yield

Due to global warming and the depletion of fossil fuels, there is a trend towards renewable energy sources, such as solar power, bio-ethanol and biogas. Anaerobic digestion is an established technology for the recovery of chemical energy from e.g. wastewater and manure as biogas [1,2]. Although a proven technology, research is required to increase biogas yields and productivity. In the present research, the thermophilic anaerobic digestion of cattle manure, codigested with food waste, is studied. Inoculum and substrate are sampled at a thermophilic anerobic digester of G\uf6teborg Energi AB (S\ue4vsj\uf6, Sweden). At this site, cattle manure and food waste are pretreated at 70 \ub0C (1 h for hygienisation). Hereafter, the substrate is digested at 55 \ub0C in a continuously fed stirred tank reactor. It is expected that hydrolysis of the lignocellulosic material contained in the substrate is a limiting step [3]. This will be verified in laboratory studies, mimicking the conditions at the plant. The substrate will be characterized, focusing on the lignocellulosic material and the changes this material undergoes during anaerobic digestion. Moreover, the responsible organisms and the enzymes they excrete will be characterized, which will indicate how to improve hydrolysis. It is expected this may be done through adjusting micro and macro nutrient availability [4] and selection of process conditions. The effect of the selected parameters on the microbial community and the hydrolysis yield will be established. Moreover, the effect of particle size will be studied.The expected outcome of the study is that by an improved understanding of the microbial community, esp. the organisms responsible for hydrolysis of lignocellulosic material, the biogas yield, biogas productivity and system stability can be increased

Co-digestion to support low temperature anaerobic pretreatment of municipal sewage in a UASB–digester

The aim of this work was to demonstrate that co-digestion improves soluble sewage COD removal efficiency in treatment of low temperature municipal sewage by a UASB-digester system. A pilot scale UASB-digester system was applied to treat real municipal sewage, and glucose was chosen as a model co-substrate. Co-substrate was added in the sludge digester to produce additional methanogenic biomass, which was continuously recycled to inoculate the UASB reactor. Soluble sewage COD removal efficiency increased from 6 to 23%, which was similar to its biological methane potential (BMP). Specific methanogenic activity of the UASB and of the digester sludge at 15°C tripled to a value respectively of 43 and 39mg CH4-COD/(gVSSd). Methane production in the UASB reactor increased by more than 90% due to its doubled methanogenic capacity. Therefore, co-digestion is a suitable approach to support a UASB-digester for pretreatment of low temperature municipal sewage.</p

Effect of temperature on denitrifying methanotrophic activity of \u27Candidatus Methylomirabilis oxyfera\u27

The activity of denitrifying methanotrophic bacteria at 11-30 \ub0C was assessed in short-term experiments. The aim was to determine the feasibility of applying denitrifying methanotrophic bacteria in low-temperature anaerobic wastewater treatment. This study showed that biomass enriched at 21 \ub0C had an optimum temperature of 20-25 \ub0C and that activity dropped as temperature was increased to 30 \ub0C. Biomass enriched at 30 \ub0C had an optimum temperature of 25-30 \ub0C. These results indicated that biomass from low-temperature inocula adjusted to the enrichment temperature and that low-temperature enrichment is suitable for applications in low-temperature wastewater treatment. Biomass growth at ≤20 \ub0C still needs to be studied

Effect of temperature on denitrifying methanotrophic activity of 'Candidatus Methylomirabilis oxyfera'

The activity of denitrifying methanotrophic bacteria at 11-30 °C was assessed in short-term experiments. The aim was to determine the feasibility of applying denitrifying methanotrophic bacteria in low-temperature anaerobic wastewater treatment. This study showed that biomass enriched at 21 °C had an optimum temperature of 20-25 °C and that activity dropped as temperature was increased to 30 °C. Biomass enriched at 30 °C had an optimum temperature of 25-30 °C. These results indicated that biomass from low-temperature inocula adjusted to the enrichment temperature and that low-temperature enrichment is suitable for applications in low-temperature wastewater treatment. Biomass growth at ≤20 °C still needs to be studied

Effect of low concentrations of dissolved oxygen on the activity of denitrifying methanotrophic bacteria

Chemical energy can be recovered from municipal wastewater as biogas through anaerobic treatment. However, effluent from direct anaerobic wastewater treatment at low temperatures still contains ammonium and substantial amounts of dissolved CH4. After nitritation, CH4 can be used as electron donor for denitrification by the anaerobic bacterium Candidatus Methylomirabilis oxyfera. The effect of 0.7% (0.35 mg dissolved O2/L), 1.1% (0.49 mg dissolved O2/L), and 2.0% (1.0 mg dissolved O2/L), on denitrifying activity was tested. Results demonstrated that at 0.7% O2, denitrifying methanotrophic activity slightly increased and returned to its original level after O2 had been removed. At 1.1% O2, CH4 consumption rate increased 118%, nitrite consumption rate increased 58%. After removal of O2, CH4 consumption rate fully recovered, and nitrite consumption rate returned to 88%. These indicate that traces of O2 that bacteria are likely to be exposed to in wastewater treatment are not expected to negatively affect the denitrifying methanotrophic process. The presence of 2.0% O2 inhibited denitrifying activity. Nitrite consumption rate decreased 60% and did not recover after removal of O2. No clear effect on CH4 consumption was observed.</p

The effect of sludge recirculation rate on a UASB-digester treating domestic sewage at 15 °C

The anaerobic treatment of low strength domestic sewage at low temperature is an attractive and important topic at present. The upflow anaerobic sludge bed (UASB)-digester system is one of the anaerobic systems to challenge low temperature and concentrations. The effect of sludge recirculation rate on a UASB-digester system treating domestic sewage at 15 WC was studied in this research. A sludge recirculation rate of 0.9, 2.6 and 12.5% of the influent flow rate was investigated. The results showed that the total chemical oxygen demand (COD) removal efficiency rose with increasing sludge recirculation rate. A sludge recirculation rate of 0.9% of the influent flow rate led to organic solids accumulation in the UASB reactor. After the sludge recirculation rate increased from 0.9 to 2.6%, the stability of the UASB sludge was substantially improved from 0.37 to 0.15 g CH4-COD/g COD, and the biogas production in the digester went up from 2.9 to 7.4 L/d. The stability of the UASB sludge and biogas production in the digester were not significantly further improved by increasing sludge recirculation rate to 12.5% of the influent flow rate, but the biogas production in the UASB increased from 0.37 to 1.2 L/d. It is recommended to apply a maximum sludge recirculation rate of 2-2.5% of the influent flow rate in a UASB-digester system, as this still allows energy self-sufficiency of the system.</p