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 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

Can aquatic worms enhance methane production from waste activated sludge?

Although literature suggests that aquatic worms can help to enhance the methane production from excess activated sludge, clear evidence for this is missing. Therefore, anaerobic digestion tests were performed at 20 and at 30 °C with sludge from a high-loaded membrane bioreactor, the aquatic worm Lumbriculus variegatus, feces from these worms and with mixtures of these substrates. A significant synergistic effect of the worms or their feces on methane production from the high-loaded sludge or on its digestion rate was not observed. However, a positive effect on low-loaded activated sludge, which generally has a lower anaerobic biodegradability, cannot be excluded. The results furthermore showed that the high-loaded sludge provides an excellent feed for L. variegatus, which is promising for concepts where worm biomass is considered a resource for technical grade products such as coatings and glues

Can aquatic worms enhance methane production from waste activated sludge?

4 Figuras.-- 2 TablasAlthough literature suggests that aquatic worms can help to enhance the methane production from excess activated sludge, clear evidence for this is missing. Therefore, anaerobic digestion tests were performed at 20 and at 30 °C with sludge from a high-loaded membrane bioreactor, the aquatic worm Lumbriculus variegatus, feces from these worms and with mixtures of these substrates. A significant synergistic effect of the worms or their feces on methane production from the high-loaded sludge or on its digestion rate was not observed. However, a positive effect on low-loaded activated sludge, which generally has a lower anaerobic biodegradability, cannot be excluded. The results furthermore showed that the high-loaded sludge provides an excellent feed for L. variegatus, which is promising for concepts where worm biomass is considered a resource for technical grade products such as coatings and glues.This work was performed in the cooperation framework of Wetsus, European centre of excellence for sustainable water technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân, and the Northern Netherlands Provinces. The authors would like to thank the participants of the research theme “Aquatic worms” for the fruitful discussions and their financial support

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

Anaerobic treatment of raw domestic wastewater in a UASB-digester at 10 °C and microbial community dynamics

Direct anaerobic treatment of domestic wastewater is becoming attractive as it can change a wastewater treatment plant from energy consuming to energy producing. A pilot scale UASB-digester was studied to treat domestic wastewater at temperatures of 10–20 °C and an HRT of 6 h. The results show a stable chemical oxygen demand (COD) removal efficiency of 60 ± 4.6% during the operation at 12.5–20 °C. COD removal efficiency decreased to 51.5 ± 5.5% at 10 °C as a result of insufficient methanogenic capacity caused by low temperature and increased influent COD load (from 2.0 g/(L·d) to 3.0 g/(L·d)). Suspended COD removal was 76.0 ± 9.1% at 10–20 °C. Soluble COD removal fluctuated due to variation of the influent COD concentration, but the effluent COD concentration remained 90 ± 23 mg/L at temperatures between 12.5 and 20 °C. The methane production was 39.7 ± 4.4% of the influent COD, which was 80% of influent biological methane potential. The specific methanogenic activity of the UASB sludge and the digester sludge was 0.26 ± 0.03 and 0.29 ± 0.03 g CH4 COD/(g VSS d), respectively. The methanogenic community analysis revealed an overall dominance of the acetoclastic Methanosaetaceae and the hydrogenotrophic Methanomicrobiales during the operation between 10–20 °C. The results of the UASB-digester treating domestic wastewater at 10–20 °C as reported in this paper provide support for application of anaerobic domestic wastewater treatment in moderate climate zones.</p

Towards mainstream anammox: lessons learned from pilot-scale research at WWTP Dokhaven

The aim of this research was to study the biological feasibility of the Partial Nitritation/Anammox (PN/A) technology to remove nitrogen from municipal mainstream wastewaters. During stable process operations at summer temperatures (23.2 ± 1.3°C), the total nitrogen removal rate was 0.223 ± 0.029 kg N (m3 d)−1 while at winter temperatures (13.4 ± 1.1°C) the total nitrogen removal rate was 0.097 ± 0.016 kg N (m3 d)−1. Nitrite-oxidizing bacteria (NOB) suppression was successfully achieved at the complete temperature range of municipal mainstream wastewater. Despite the presence of NOB as observed in activity tests, their activity could be successfully suppressed due to a relative low dissolved oxygen concentration. An overcapacity of ammonia-oxidizing bacteria and anammox activity was always present. Long-term stability is a focus point for future research, especially in relation to the stability of the biological oxygen demand removing step, preceding the PN/A reactor.BT/Environmental Biotechnolog