Benefits of primary filtration systems in the downstream biological treatment of overloaded wastewater treatment plants (WWTPs)

Energy and nutrient recovery for municipal wastewater treatment: How to design a feasible plant layout?

Study on kinetics and bio-oil production from rice husk, rice straw, bamboo, sugarcane bagasse and neem bark in a fixed-bed pyrolysis process

A new systematic methodology for screening retrofit options to improve the economics of a continuous chemical process is organized in three stages: 1. base case analysis; 2. generation of retrofit options; and 3. rough economic evaluation of the retrofit options. In stage 1, the flowsheet of a process, based on the steady‐state mass and energy balances of a representative process operating state (base case), is decomposed into open and cycle component path flows with their corresponding flow rates. In the path flow assessment, variable process costs are then allocated to these component flows through two economic indicators representing raw material consumption, and energy and waste cost. Additional physico‐chemical path flow indicators characterizing the degree of nonideality of the process are also calculated. In stage 2, the results of the path flow assessment are used to identify possible retrofit options with the help of recommended retrofit actions. In stage 3, the impact of retrofit options on variable costs of the base case is estimated and discussed in terms of its technical feasibility. This method has been applied to the hydro‐dealkylation process for the toluene production. Several promising retrofit options were identified through this method. The results demonstrate how the new method supports the systematic identification of economically beneficial retrofit options for chemical processes.

Investigating a new model-based calibration procedure for optimizing the emissions and performance of a turbocharged diesel engine

Zeolites have potential to increase efficiency of medium-temperature drying in the food industry. This work concerns the comparison between conventional dryers and dryers using air dehumidified by zeolite. Steady-state mass and energy balances have been used and the work concerns drying temperatures ranging from 52 to 70°C. Process integration based on pinch analysis has been applied and nine different heat exchanger networks for energy recovery are compared. Results indicated that dryers using air dehumidifier by zeolites are 10–18% more efficient than conventional dryers.

The purpose of this work is to implement an integrated ventilation and heat transport model of a clothed human subject to external wind. Each segment of the human body is modeled as a vertical cylinder with an air annulus separating the ventilated clothing from the skin with open or closed end to the environment. The developed ventilation model takes into consideration natural convection induced by the temperature difference between the skin and the annulus air. The steady-state mass and energy balance equations of the annulus microclimate air and clothing were solved numerically. The model is integrated with a segmental bioheat model to determine the local skin temperature, which is used as boundary condition. The clothing ventilation model was validated by conducting experiments on an isothermally heated vertical clothed cylinder with an open lower end aperture and subject to a uniform cross wind. Good agreement was found between the model predictions and experimental measurements of temperature at different angular and vertical locations in the air layer. The combined clothed cylinder and segmental bioheat model was validated with published experimental data on ensemble total ventilation for different permeabilities and wind speeds. It was found that clothed segments opened from the bottom increased ventilation by 40% when compared to clothed segments opened from the top. An increase of wind speed by 1.0 m/s leads to an increase in ventilation rate of about 36%. Natural convection was also found to enhance the ventilation of highly permeable clothing at low wind speeds compared to less permeable clothing.

Design for dynamic operation - A review and new perspectives for an increasingly dynamic plant operating environment

The riser reactor in a resid fluidised-bed catalytic cracking (resid-FCC) unit is simulated using a multigrain model of the catalyst in which the amorphous matrix as well as the embedded Y-zeolite crystals are porous and reactive. A seven-lump kinetic model is proposed to describe the reactions involved in resid-FCC. The steady-state mass and energy balance equations are formulated for the resid-FCC riser assuming it to be an adiabatic flow reactor. The multigrain catalyst model developed by our group earlier is incorporated in the riser model to account for the cracking inside the catalyst macro-particle. Some data from a pilot plant unit are used to tune the kinetic parameters. The model is used to study the effect of important process variables and catalyst properties such as catalyst to oil ratio, feedstock properties, matrix activity and surface area on the yield of the different lumps. As expected intuitively, the activity of the matrix can significantly affect the conversion and the product distribution.

A previously developed model for mono-component droplet evaporation is revisited using new mathematical tools for its analysis. The analysis is based on steady-state mass, momentum, and energy balance equations for the vapor and air mixture surrounding a droplet. The previously obtained solution to these equations was based on the assumption that the parameter ε (proportional to the squared ratio of the diffusion coefficient and droplet radius) is equal to zero. The analysis presented in the paper is based on the method of integral manifolds, and it allowed us to present the droplet evaporation rate as the sum of the evaporation rate predicted by the model based on the assumption that ε=0 and the correction proportional to ε. The correction is shown to be particularly important in the case of small water and methanol droplets (diameters less than 5 μm) evaporating in air at low pressure (0.1 atm.). In this case, this correction could reach 35% of the original evaporation rate. In the case of evaporation of relatively large droplets (with radii more than 10 μm) in air at atmospheric and higher pressures, these corrections are shown to be small (less than 10−3 of the evaporation rate predicted by the model based on the assumption that ε=0).

Two decision support software to support the natural ventilation and forced ventilation systems design were developed using MATLAB. The first program, entitled 'NV', short for Natural Ventilation, is based on steady-state energy balance. The second program, entitled 'VETH', is based on simultaneous steady-state energy balance and mass balance analysis. VETH deals with the coupled relationships of Ventilation, Evapotranspiration, Temperature and Humidity. Forced ventilation alone, pad and fan evaporative cooling system and fogging system designs are all within the scope of analysis utilizing the VETH software. Subprograms to calculate amount of water evaporated of a fogging system was included in VETH program. An example for designing and/or operating a fogging system is demonstrated using the VETH program. Both programs are user friendly and can be used as teaching/research tools in the field of controlled environment agriculture (CEA).

Antibiotic contamination attracts growing concerns because of their deleterious effects on the ecosystem and human health. In this study, 43 antibiotics in wastewater from a variety of sources and water of the Yangtze River in Chongqing City in western China were measured. Thirty compounds were detected, and their concentrations were highest in leachates from the municipal solid waste treatment facilities (landfills and incineration plants) with total concentrations of 3584-57,106ng/L. The total concentrations in influents of municipal and industrial wastewater treatment plants (WWTPs) were comparable (401-7994ng/L versus 640-8945ng/L). The concentrations in raw sewage from swine farms (with a total of 10,219-39,195ng/L) and poultry farms (1419-36,027ng/L) were noticeably higher than those from other farms (54.0-5516ng/L). Fluoroquinolones were the dominant antibiotics contributing over 50% in all the sources, and sulfonamides and imidazole fungicides contributed 3.2-34%, whereas tetracyclines and macrolides had minor contributions. The overall antibiotic removal rates were highest in solid waste treatment facilities (88% on average), comparable between municipal and industrial WWTPs (61%), and lowest in animal farms (39%). The mass loads to the investigated municipal WWTPs via influent wastewater ranged from 7.80 to 1531kg/year (53.2-2482μg/day per capital). The influent mass loads to the industrial WWTPs and farms were 3.7-50kg/year and 0.9-5437g/year, respectively. We estimated that the mass inventories of antibiotics from these sources to the environment via effluent discharges were approximately 2044kg for municipal WWTPs, 61kg for industrial WWTPs, and 34kg for animal farms in the whole city. Antibiotic concentrations in the Yangtze River water were substantially low (< 492ng/L, with a mean of 57.8ng/L) suggesting dissipation during the movement.

For several decades, it had been believed that ammonia-oxidizing bacteria (AOB) is the only microorganisms that are responsible for the oxidation of ammonia to nitrite in the global nitrogen cycle. Recently, a few evidences have shown that autotrophic ammonia oxidation is not only restricted to the domain Bacteria, but also the domain Archaea. The presence of an ammonia monooxygenase (amoA) genes of ammonia-oxidizing archaea (AOA) has been revealed in a few marine and soil environments; in addition, the first AOA, Nitrosopumilus maritimus, has been isolated from sea water. Abundances of amoA genes of AOA over those of AOB have been found in few studies using quantitative real-time PCR technique. As results, AOA is questionable of the major environmental microorganisms that oxidize ammonia to nitrite. In this study, communities of AOB and AOA in ten full-scale wastewater treatment plants (WWTPs) (four industrial WWTPs and six municipal WWTPs) that are different in influent characteristics, system configuration and system operation were observed. In addition, effect of ammonium loads on AOB and AOA communities was investigated by enriching sludge taken from a municipal WWTP with inorganic medium containing different ammonium concentrations of 2, 10, and 30 mM NH⁺₄-N (NAS2, NAS10, and NAS30, respectively). The communities of AOB and AOA were analyzed using specific PCR amplification followed by DGGE and sequencing of AOB 16S rRNA genes and specific PCR simplification followed by clone libraries and sequencing of AOA amoA genes, respectively. Results from full-scale WWTPs showed that AOB communities in four industrial WWTPs were more diverse than those in the six municipal WWTPs. AOB found in industrial WWTPs fell into 4 clusters that are unknown Nitrosomonas cluster, N. europaea-Nc. mobilis cluster, N. communis cluster, and N. oligotropha cluster, while AOB found in municipal WWTPs were restricted to only N. communis cluster and N. oligotropha cluster. The difference of influent wastewater characteristic (ammonium concentration) might be the key factor causing distinct distribution patterns of AOB communities in both types of WWTPs. Almost all municipal WWTPs in this study were activated sludge processes with exception for one plant that was aerated lagoon system. The communities of AOB in all municipal WWTPs were similar. As results, system configuration and system operation were less significant than influent wastewater characteristics. A total 72 AOA amoA sequences, recovered from eight out of ten WWTPs, could be categorized into 38 OTUs, and distributed in 12 clusters. Unlike AOB, communities of AOA in the industrial WWTPs were less diverse than those in the municipal WWTPs. Only 2 industrial WWTPs with moderate ammonium loads (40 -70 mg-N/l), contained AOA (clusters G and K). Negative PCR amplification occurred with another two industrial WWTPs with low (13 mg-N/l) and high (422 mg-N/l) ammonium loads. In contrast, all six municipal WWTPs, that received low ammonium loads of 5 – 13 mg-N/l, possessed AOA (cluster A, B, C, E, F, G, I, J, K, L, M, and N). Five out of the six municipal WWTPs were activated sludge processes, whereas another was an aerated lagoon system. For each sample of activated sludge processes, only 1 – 3 clusters of AOA were observed, while in the sample from an aerated lagoon system much more AOA clusters of 6 were found. Therefore, system configuration and system operation might be significant for the distribution of AOA in WWTPs. Results from enriched NASs suggested that AOB communities obviously shifted from seed sludge to enriched NASs and in each enriched NAS, communities of AOB varied particularly. Sludge taken from a municipal WWTP used as a seed for all reactors contained members of N. communis cluster and N. oligotropha cluster. After it was enriched under various ammonium loads, members of N. communis cluster disappeared from all enriched NASs. AOB with high affinity to ammonia presented in NAS 2 (N. oligotropha cluster), AOB with low affinity to ammonia presented in NAS 30 (N. europaea cluster), and both types of AOB survived in NAS 10 (unknown Nitrosomonas cluster and N. europaea cluster). In contrast to AOB, almost all AOA clones from NAS2 (19 out of 21), NAS10 (23 out of 26), and NAS30 (30 out of 30) fell in the same cluster (cluster K). AOA communities in NAS2 and NAS10 were more diverse than those of NAS30. These demonstrated that ammonium load significantly influenced AOB communities, but not AOA communities in enriched NASs.

Analyzing a micro-solid oxide fuel cell system by global energy balances

Design for dynamic operation – A review and new perspectives for a dynamic manufacturing environment

Combined leachate treatment at municipal wastewater treatment plants (WWTPs) is applicable to a certain extent depending on the leachate composition, treatment plant configuration and its capacity. Co-treatment of leachate at WWTPs has several advantages, but due to increasingly stringent discharge standards applied in WWTPs, it has become more problematic. This study was undertaken to investigate the impact of leachate feeding strategies on effluent quality and the aeration energy costs of WWTPs. A modified version of Benchmark Simulation Model No.1 was used to develop, test and compare several leachate feeding and WWTP control strategies in the context of dynamic pollutant loads and energy prices. The results highlighted that combined leachate treatment led to a deterioration in the quality of discharged wastewater, as indicated by a 12–20% increase in effluent quality index. Additionally, it adversely affected aeration energy demand and cost of the plant by increasing them 1.7–2.3% and 0.8–2.5%, respectively. The impacts could be mitigated by adjusting leachate flow based on effluent ammonium concentrations and by using advanced process control, i.e. feedback ammonium control for dissolved oxygen regulation in aerobic reactors. The study demonstrates that modeling can be used as a valuable tool to assess the potential impacts of leachate co-treatment and develop better management strategies.