Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation（IC） reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste（MSW）incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates（OLR） of 21.06–25.16 kg chemical oxygen demand（COD）/（m3？ day）. The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50 m3/kg COD.The formation of extracellular polymeric substances（EPS） was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7 mg/g Volatile Suspended Solid（VSS） during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from-26.2 m V and 30.35% to-10.6 m V and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy（3 D-EEM） and Fourier transform infrared spectroscopy（FT-IR）analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.

Inorganic nitrogen removal of toilet wastewater with an airlift external circulation membrane bioreactor

Removal of inorganic nitrogen （inorganic-N） from toilet wastewater, using a pilot-scale airlift external circulation membrane bioreactor （AEC-MBR） was studied. The results showed that the use of AEC-MBR with limited addition of alkaline reagents and volumetric loading rates of inorganic-N of 0.19-0.40 kg inorganic-N/（m^3·d） helped achieve the desired nitrification and denitrification. Furthermore, the effects of pH and dissolved oxygen （DO） on inorganic-N removal were examined. Under the condition of MLSS at 1.56-2.35 g/L, BODs/ammonia nitrogen （NH4＋-N） at 1.0, pH at 7.0-7.5, and DO at 1.0-2.0 mg/L, the removal efficiencies of NH4^＋-N and inorganic-N were 91.5% and 70.0%, respectively, in the AEC-MBR. The cost of addition of alkaline reagent was approximately 0.5-1.5 RMB yuan/m^3, and the energy consumption was approximately 0.72 kWh/m^3 at the flux of 8 L/（m^2-h）.

Influence of external circulation on sludge characteristics during start-up of internal circulation reactor

The start-up of external circulationadded internal circulation(IC) reactor was finished in 26 d, 32 d fewer than that of IC reactor. To evaluate the influence of the added external circulation on the development of granular sludge, the characteristics of the granular sludge taken from the two tested laboratory-scale reactors during start-up were studied. The results show that the added external circulation can enhance biomass granulation, accelerate granule development and improve sludge characteristics. At the end of start-up, the granular size of sludge in external circulation-added IC reactor greatly increases with a size distribution much better than that of sludge in IC reactor. The granular sludge originated from external circulationadded IC reactor contains more extracellular polymers and has a greater settling velocity than that from IC reactor. Methanogenic activity of the granular sludge from the external circulationadded IC reactor started 26 d ago reaches 358.23mL·g -1 ·d -1 , 1.66 and 1.20 times as great as that of the sludge from the IC reactor started 26 d and 58 d ago respectively.

Treatment of methanol wastewater in external circulation anaerobic reactor with different inoculums

In order to guide the inoculums selection for the anaerobic treatment of methanol wastewater in the engineering application,two 7 L bench-scale external circulation (EC) anaerobic reactors were operated to investigate the inoculums of anaerobic granular sludge and anaerobic digested sludge,focusing on the efficiency and process stability.The effect of impact concentration and temperature on the performance was studied.The results demonstrated that anaerobic granular sludge as the inoculums could complete the start-up more rapidly than the anaerobic digested sludge,and above 90% COD removal were achieved at the organic loading rate of 10 to 15 kgCOD/(m3·d).The effect of impact COD on the methanogenic activity of sludge was weak and the removal efficiencies recovered gradually in the two reactors.The COD removal efficiencies reduced swiftly to 50%-60% due to the impact temperature.The results indicated that the complex bacterial groups in anaerobic digested sludge benefited to enhance the reactor's capacity for withstanding the temperature shock at some extent.

CFD-PBE simulation of gas-phase hydrodynamics in a gas-liquid-solid combined loop reactor

The computational fluid dynamics （CFD）-population balance equations （PBE） coupled model is employed to investigate the hydrodynamics in a gas-slurry internal loop reactor with external slurry circulation. The predicted radial profiles of local gas holdup and bubble diameter are in good agreement with the corresponding experimental data. The spatio-temporal velocity profile of the gas phase reveals that the upward movement of gas is slowed down and the residence time of gas is prolonged by the downward momentum of the slurry, introduction of the external slurry can greatly improve the uniformity of gas holdup distribution in the reactor, especially in the downcomer-tube action region. Moreover, the interaction between the downward slurry and upward gas can lead to small bubble size and high interfacial area as well as good mass and heat transfer. The above results suggest the function of external slurry circulation for the internal loop reactor and would be helpful for optimizing the design and scale up of reactors.

Simulation of the flow and thermal breakthrough of a forced external circulation standing column well

The flow and thermal breakthrough phenomenon in a forced external circulation standing column well(FECSCW)directly affects heat transfer efficiency and load-carrying capacity.A numerical model for FECSCW is developed to analyze the migration of the temperature and velocity front under the flow and thermal breakthrough.The results indicated that thermal breakthrough began after simulation running 2.5 min and was completely formed after 12 min.The inlet water,which directly entered the production well without heat exchange with the aquifer,accounted for 12.8%.When the porosity of the backfill material decreased from 0.35 to 0,the coefficient of per-formance(COP)of the heat pump unit increased by 1.6%on average,and the thermal breakthrough strength decreased by an average of 45.3%within 25 min.Where seepage velocity near the well wall was greater than 1×10^(−3) m·s^(−1),faster velocity front migration was observed,while the migration advantage of the temperature front was more prominent outside of this region.Through quantitative analysis of flow and thermal breakthrough,temperature and velocity front migration,and COP change of heat pump unit,theoretical suggestions were pro-vided for the thermal transfer mechanism near the thermal well wall.The extended research in this study can be applied to the design and optimization of forced external circulation standing column well system.

Treatment of methanol wastewater with two-stage and two-phase anaerobic process

The two-stage and two-phase anaerobic process (TSTP) composed of hydrolytic acidification reactor,first-order and second-order external circulation anaerobic reactors (EC) was taken to treat methanol wastewater. Test results show that TSTP process is quick start-up in 51 d, and the maximum VFA of hydrolytic acidification reactor effluent reaches 876 mg/L. Under the condition of volume loading of 6.56 kgCOD/m3·d, COD removal rate of the first-order EC reactor is about 85%, and under the condition of volume loading of 1.02 kgCOD/m3·d, COD removal rate of the second-order EC reactor is about 50%. When the inflow COD of TSTP process is between 7000-11000 mg/L, its effluent COD is lower than 600 mg/L. In the biological conversion process of methanol into methane,the production of acetic acids as an intermediate product can be ignored and the direct production of methane from methanol is predominant.