• Energy Research
• Closed Access close
• Restricted close
• Open Source close
• 6. Clean water close
• Tsinghua University close

Abstract To study the concentration characteristics of mechanical vapor compression (MVC) technology on the wastewater concentration process, a single-effect MVC system for concentrating dimethylacetamide wastewater was investigated. The performance of the MVC experimental system was evaluated under different levels of distillation pressure and concentrations of the raw solution. We demonstrated that under conditions of atmospheric distillation (evaporating temperature was 100 °C), the COP and distilled water production rate of the experimental system reached 20.17 and 70.80 kg/h, respectively. In the distillation operating cycle, the DMAC solution was concentrated from 6% to 83.5%. In addition, when the system was under vacuum conditions (evaporating temperature was 55.8 °C), the COP and distilled water production rate were 5.44 and 18.2 kg/h, respectively, and the concentration of the DMAC dilute solution was only 0.2%.

A novel configuration of microbial desalination cell (MDC) packed with ion-exchange resin (R-MDC) was proposed to enhance water desalination rate. Compared with classic MDC (C-MDC), an obvious increase in desalination rate (DR) was obtained by R-MDC. With relatively low concentration (10-2 g/L NaCl) influents, the DR values of R-MDC were about 1.5-8 times those of C-MDC. Ion-exchange resins packed in the desalination chamber worked as conductor and thus counteracted the increase in ohmic resistance during treatment of low concentration salt water. Ohmic resistances of R-MDC stabilized at 3.0-4.7 Ω. By contrast, the ohmic resistances of C-MDC ranged from 5.5 to 12.7 Ω, which were 55-272% higher than those of R-MDC. Remarkable improvement in desalination rate helped improve charge efficiency for desalination in R-MDC. The results first showed the potential of R-MDC in the desalination of water with low salinity.

This paper presents a new scheme of an inverter air cooling heat pump system with domestic hot water. A water reheater is placed between the compressor outlet and the four way valve inlet to utilize the sensible heat of the superheated gas exhausted from the compressor, and a water preheater is placed between the condenser and the throttling device to use the sensible heat of the subcooled liquid flowing out of the condenser. With these two parts of heat, the domestic hot water can be heated to a temperature high enough for domestic use. In order to maintain the system efficiency in the period of part load, an inverter compressor is adopted as the substitute for the constant speed one used in the conventional heat pump system. A hot water storage tank with a circulation pump is placed in the system to reduce the peak load of the system. Compared with the traditional system, this new design is able to reduce energy consumption by 31.1% and decrease thermal pollution to the environment.

Biohythane is alternative fuel to replace fossil fuel for car combustion, and biohythane generation could be potential pathway for energy recovery from wastewater treatment. Microbial electrolysis cell (MEC) is electrochemical technique to convert waste to methane and hydrogen gas for biohythane generation, but the feasibility and stability of MEC needs further investigation to assure sustainable energy recovery. System configuration is paramount factor for electrochemical reaction and mass transfer, and this study was to investigate the configuration impact (single vs dual chamber) of MEC for biohythane generation rate and stability. This study showed that dual-chamber MEC could separate methane and hydrogen gas production in the anode and cathode, and combined both together to produce biohythane. To reduce ohmic resistance for higher current, cation exchange membrane (CEM) was removed from dual-chamber to single-chamber MEC. However, free hydrogen diffusion was allowed in the single chamber since CEM was removed. The diffused hydrogen and substrate towards the cathode would favor the methanogen growth, and thus the hydrogen was consumed to reduce the biohythane generation and energy recovery efficiency (i.e., 7.5 × 10-3 reduced to 5.7 × 10-3 kWh kg-1 degraded COD day-1 after converting dual-chamber to single-chamber MEC). Absolute abundance of methanogen in single-chamber MEC was greatly boosted, as Methanosarcina and Methanobacteriale on the anode surface, increased by 132% and 243%, respectively, while the original dual-chamber MEC could maintain Geobacter growth for high current generation. This is the keystone study to demonstrate the importance of dual-chamber MEC for the feasibility and stability for the biohythane generation, building up the foundation to use electrochemical device to convert the organic waste to the alternative biohythane.

Summary Urban metabolism is a critical component of urban sustainability. On the basis of the driving force−pressure−state−response (DPSR) model and using material flow analysis, this article proposes a framework for sustainable urban management and policy assessment. A case study city in China, Suzhou, illustrates this framework. The results show that resource consumption (excluding water), water consumption, and waste generation (excluding carbon dioxide) in Suzhou after implementation of proposed policies will be 14% lower than 2005 levels, 4.5% higher, and 28.9% higher, respectively, in 2015. Carbon dioxide (CO2) emissions in Suzhou will increase by 71.0% in 2015 over 2005 levels, whereas carbon intensity (CO2 emissions per unit of gross domestic product) will decrease by 44.9%. Future pollution control in Suzhou should pay more attention to pollution from vehicles. In addition, goals for relative dematerialization of energy and decarbonization in Suzhou will be achieved before absolute ones are. In the short term, the urban metabolism of Suzhou in 2015 may meet corresponding urban objectives. In the longer term, however, reducing the city's resource demand and waste generation will pose challenges for the sustainability of Suzhou.

Assimilable organic carbon (AOC) is recognized as an important parameter to evaluate the biostability of water. Studies have been carried out to investigate the easier and faster AOC detection methods in recent years. In our study, the relationship between AOC and excitation-emission matrix (EEM) was investigated through analysis of wastewater from a coal chemical industrial corporation, including biochemical effluent, ultrafiltration effluent, and reverse osmosis concentrate. Considering the influence of water sample properties on AOC distribution, these water samples were fractionated according to their hydrophilicity and acid/base properties. Neutrals and hydrophobic acids were major components of total organic carbon and AOC concentration of these fractions was measured. EEM spectra of water samples were divided into five regions according to fluorescence peaks. Distribution of fluorescence region integration (FRI) of water samples was also calculated, as well as other fluorescence parameters. Statistical analysis showed that the concentration of AOC presented high positive correlation with the FRI in region H2, with R2 = 0.696. Monte Carlo simulation also proved that the proportion of significant R2 (p < 0.05) was high at 89.1%, suggesting that the model was reliable at least at the qualitative level. In that case, FRI in Region H2 could be an indication for AOC concentration in water samples. Our findings focus on fundamental insights into establishing relationship between spectroscopy method and AOC in wastewater and provide an easier way of accessing AOC in coal chemical industrial wastewater. Further investigation could be oriented to the dynamic analysis of AOC transformation and tracing.

This paper presents an experimental study with the aim to understand the relation between the flow conditions - the riser pressure drop and fluidization velocity - in a CFB riser and the net (external) solids flux (Gs [kg/m(2) s]), applying a riser geometry and overall flow conditions similar to CFB boilers. The experiments are carried out in a CFB unit operated under ambient conditions. The riser has a cross section of 0.7 m x 0.12 m and a height of 8.5 m, yielding a riser height-to-width aspect ratio of 10.6 (in the wide dimension), similar to that of CFB boilers. The unit is equipped with densely spaced pressure taps providing a fine resolution of the measured vertical pressure profile along the riser and an automatic system to accurately measure G5. The experiments cover fluidization velocities of 03-7 m/s, riser pressure drops of 1.7-10.5 kPa and loop-seal fluidization velocities of 0.12-0.54 m/s (secondary air flow is not included). These ranges correspond to conditions both with and without a dense bottom region. The results show that G(s) is determined by the solids concentration at the riser top, which in turn depends on riser pressure drop and fluidization velocity, and the backflow effect, which depends on the configuration and flow conditions of the loop seal and the exit region. For operating conditions with a dense bottom bed present, G(s) is independent of riser pressure drop at any fluidization velocity, whereas when operating without a dense bed an increase in riser pressure drop increases G(s).

In eutrophic shallow lakes, cyanobacterial blooms will occur frequently and then accumulate on sediments, leading to the variation in the surface sediment properties. In this study, the influence of accumulated cyanobacterial blooms biomass (CBB) content on surface sediment properties was determined in microcosm experiments through monitoring surface sediment physicochemical and rheological properties. During one-month incubation, it was found that surface sediment volume increased, and the density decreased from 1.36 g cm-3 to 1.13 g cm-3 with increase in accumulated CBB contents. The results of particle size distribution indicated that CBB accumulation in sediments led to sediment flocculation and agglomeration. In the meantime, there were high ratios polysaccharide/protein in extracellular polymeric substances (EPS) with a decrease in bound EPS/colloid EPS under high CBB contents, which enhanced the sediment particle agglomeration and reduced fluid sediment stability. Further, the critical shear stress in rheological test for sediments on day 30 presented an exponential decay (R2 = 0.97) with increase in accumulated CBB contents. And a threshold value at 0.15% accumulated CBB content indicated sediments could be resuspended easier when accumulated CBB content was higher than 0.15%. Altogether, this study showed that the accumulated CBB content had a strong influence on surface fluid sediment properties. The results were important in sediment management since CBB affects sediment suspension for eutrophication shallow lakes.

Abstract Microencapsulated n-octadecane with titanium dioxide (TiO2) shell was prepared by a sol–gel method in a nonaqueous oil-in-water (o/w) emulsion using a green solvent as the dispersion medium. The morphology, chemical structure, and crystalloid phase of the resultant microcapsules were determined by scanning electronic microscope (SEM), Fourier transformation infrared spectroscope (FT-IR), and X-ray diffractometer (XRD), respectively. The differential scanning calorimeter (DSC) and the thermogravimetric analyzer (TGA) were used to investigate the thermal properties and thermal stabilities of the samples. The resulting microcapsules presented spherical shape with average size of 2–5 μm. The results of FT-IR and XRD showed that n-octadecane was well microencapsulated in TiO2 shell. DSC and TGA results indicated that the samples exhibited good performance of storing and releasing the latent heat during phase-change cycles and high thermal reliability. The microencapsulation process in this study is simple, high-efficiency, and environmentally friendly. The microencapsulated n-octadecane with TiO2 shell will be a potential candidate material for thermal energy storage applied in the fields of solar energy storage, building energy conservation, air-conditioning systems, and waste heat recovery.