Operating Days Research Articles

Dynamic modeling of partial nitrification in a rotating disk biofilm reactor: Calibration, validation and simulation

Partial nitrification to nitrite saves oxygen and organic matter. A dynamic model of a rotating disk biofilm reactor was developed in order to determine optimal operation conditions for partial nitrification. The biofilm model considered the active biomass fraction as a state variable; it was calibrated at steady state using the adjustment of two parameters – μ max, AOB (1.32 d −1) and k L (0.44 m h −1) and validated with long-term experiments. The experimental data were attained running the reactor in continuously and in batch modes for more than 700 days at different pH values, oxygen concentrations and nitrogen load rates (NLRs). A good agreement between the measured and modeled results was obtained with a Theil inequality coefficient lower than 0.3 for both calibration and validation. The model predicts that the active biomass fraction does not reach steady-state before 40 operating days, and the active nitrite-oxidizing bacteria fraction is much more sensitive than the ammonia-oxidizing bacteria fraction to the pH. Results demonstrated that nitrite accumulation ( β) is strongly influenced by the NLR and the pH. The optimal operation zone for β > 70% is reached for NLRs between 8.5 and 11.5 g N m −2 d −1, pH > 8 and dissolved oxygen concentration <3 mg O 2 L −1.

Treatment of two industrial wastewaters in a submerged membrane bioreactor

A membrane biological reactor (MBR), Zenon ZW-10, with a 220 L volume, was used during 120 days for treating two different wastewaters with different characteristics. During the first 50 operating days the unit was fed with an influent similar to the streams generated in wineries. From day 50 on, the MBR treated a wastewater generated in a tannery factory. The major differences between both wastewaters were the absence of both suspended solids and particulate chemical oxygen demand (COD) in the winery stream and the presence of these compounds in the wastewater from the tannery. Efficiency of the MBR was high: COD removal efficiency above 97% was obtained with winery wastewater, and about 86% during the period in which the tannery wastewater was used. COD concentration in the permeate of the unit varied between 60–80 mg COD/L during the whole experimental period, despite the differences in both wastewater characteristics and the operating conditions applied. Biomass concentration, in terms of volatile suspended solids (VSS), ranged between 0.5 and 15 g VSS/L. Apparent biomass yield was estimated at 0.14 g VSS/g COD and 0.16 g VSS/g COD for winery and tannery wastewater, respectively. A drop in the oxygen transfer efficiency was observed when the system operated with biomass concentrations above 8 g VSS/L.

Scheduling of Elective Surgical Cases within Allocated Block-times: Can the Future be Drawn from the Experience of the Past ?

We determined a strategy to regulate the elective occupation of operating rooms; it was based on the determination of a median operating room occupation time, per procedure and per operator.Methods: Median occupation times were determined from a retrospective analysis of 12 consecutive months of operating activity (966 patients). These data were prospectively used in surgical planning, with a daily occupation limit set at 10 hours. After four months collecting data, daily recorded (ROT) and predicted (POT) occupation times were compared. The surgical activity during that test period (group A) was compared to the activity of the same period in the previous year (group B) and the evolution of the waiting lists for surgery were analysed for each of the operators. Results: At the end of the four-month observation period, 317 surgical cases spread over 105 operating days were recorded. The correlation between ROT and POT was strong (r = 0.911, p < 0.001). The relative error in this prediction was 13 ± 11 min. In comparison with group B, group A was characterized by a significant reduction in occurrence (p = 0.015) and duration (p = 0.007) of time limit overruns and in variability of daily occupation time (p < 0.001). The waiting list was reduced for all operators at the end of the test period.Conclusion: Determination of individualized median occupation times, associated with definition of a daily limit, resulted in reduction of time overruns and delays before surgery.

Membrane Separation of Wool Scour Effluent

Norway's largest yarn factory, Sandnes Uldvarefabrikk, produces knitting wool from 1,000 tons of raw wool a year. The raw wool is washed in 55°C water with high pH detergents. The resulting wastewater has a chemical oxygen demand, COD, of up to 100,000 mg/l and was previously piped directly to the public sewer. The Norwegian Environmental Protection Agency ordered the factory to reduce the COD loading by 75%, effective at the end of 1989. The winter and spring of 1989 was used to test membranes and gather design information for a fullscale separation plant for treating the wool washwater. The results from the pilot testing were encouraging and a fullscale membrane plant was designed, manufactured and installed during the fall of 1989. The wool factory gradually increased the wool scouring capacity, however, and two years later the capacity of the full scale membrane plant was doubled simply by doubling the membrane area of the original plant. The membrane separation plant is tubular ultrafiltration (UF) and the treatment is on a batch basis with a volume reduction of ten. The 31 m2 UF membrane area has an average permeate production capacity of 2 m3/h at 8 kg/cm2 inlet pressure and 3.8 m/s fluid velocity. The feed temperature is never allowed below 40°C due to the high concentration of fat which tends to solidify at lower temperatures and would plug the membranes. The retentate from UF separation is returned to the feed tank whereas the permeate is routed through a heat exchanger to the public sewer. The start volume of each batch is between 15 m3 and 25 m3 with the UF plant manually started. The shutoff is automatic by a level switch set at 2 m3 batch volume. The retentate or sludge is pumped to a second holding tank and the accumulated sludge is once a week transported and dewatered in a lagoon at the local sanitary landfill. The UF membrane plant has a 10 kW power consumption and has more than 700 operating days since 1989. The operator spends two hours a day managing the UF plant including cleaning the membranes after each daily batch, pumping the sludge, logging the data and reporting to the plant management. Membrane replacement is performed once a year at a cost of ₤3,800. The COD, fat and solids reductions have consistently been above 80%.

The Effects of Labor Unions on Employment, Wages, and Days of Operation: Coal Mining in West Virginia

We present a framework for measuring the joint impact of labor unions on wages, employment, and days of work. Our particular application uses county level observations to measure the impact of unionism in West Virginia coal mining from 1897 to 1938. The widespread belief is that union-nonunion wage differentials in coal mining during this period were of the order of 50 percent or more. Our estimates are substantially less. We measure negligible differences in union-nonunion employment, while, in the 1920s, operating days in unionized mines were about 25 percent below those in nonunion mines.

Design and Field Testing of Whole-stalk Sweet Sorghum Harvester

A pull-type, single-row whole-stalk harvester was designed, built, and tested. Power was delivered via a u-joint driveline to five pumps (five hydraulic circuits) on the harvester. Stalks were captured with gathering chains, cut at the base with a disk cutter, and conveyed rearward in a vertical position. As the top was released from the gathering chains, the butt was captured between two rotating disks and the stalk rotated 90° onto a cross conveyor, and thus conveyed to a bin (accumulator). The accumulator periodically dumped bundles to produce windrows of aligned-stalk bundles across the field. Bundles weighed approximately 180 kg (400 lb), and in a field yielding 36 Mg/ha (16 ton/acre), windrows were spaced 62.5 m (205 ft) apart. Stalk height ranged from 3 to 4 m (9 to 13 ft). The harvester operated best at 3.56 km/h (2.2 mph), the same speed used for a forage chopper in the same field. Estimated field capacity was 1.56 ha/day (3.9 acre/day), or 54 Mg/day (60 ton/day). Over a season with 30 operating days, 1620 Mg (1,780 ton) could be harvested. A bond graph model and simulation of the accumulator dump drive showed that bundles up to 300 kg (660 lb) could be dumped without the hydraulic motor over-running.

The Single Steel Drilling Caisson: A New Arctic Drilling Unit

Summary Dome Petroleum Ltd.'s experience with a new mobile offshore drilling unit - the single steel drilling caisson (SSDC) - is described. The SSDC's design enables offshore exploratory drilling operations in the Beaufort Sea to continue beyond the short open-water season. The SSDC proved to be well-suited to offshore arctic operations. The operator's requirements for storage facilities and rig equipment are discussed and the drilling and testing of the first well are described to illustrate the success of this innovative drilling unit. Problems associated with Beaufort Sea operations are discussed with specific reference to ice management and drilling problems. A brief update describes the relocation of the SSDC to a second wellsite and its successful operation through a second winter. Introduction Dome has been drilling offshore wells in the Canadian Beaufort Sea with drilling units owned by its subsidiary Canadian Marine Drilling Ltd. (Canmar) since 1976. Initially, drillships modified for arctic conditions were used for offshore operations in this area during the short open-water season. Ice breakup typically occurs between mid-June and early July. During the summer, drilling operations are interrupted occasionally by incursions of multiyear ice. New ice usually begins to form in October. As freeze-up progresses, ice breakers are used to prevent interference with drilling operations. Drilling operations may be suspended at any time from October to late November, depending on government regulations, drilling program, anticipated ice conditions, and well progress. Occasionally, operations have continued to the limit of operational capability in severe ice conditions. For the last 9 years, season length, from first to last operating day, has ranged from 85 to 150 days. The average number of operating days on location is 100. An average of 13 days per year waiting on ice or weather reduces the effective number of operating days to 87. Restriction of floating drilling operations to this brief period means that it is not possible to drill and to test a typical deep Beaufort well in one summer season when a drillship is used. Because of this limitation, we considered a variety of alternative drilling systems. Modifications to the most recently acquired drillship, Explorer 4, extended its operating ability beyond that of the other three drillships. It was evident, however, that the drilling season could not be extended throughout the winter with existing floating rigs. The limiting factor in the case of a floating rig was station-keeping ability. Existing mooring or dynamic-positioning systems could not resist the forces generated by moving first-year ice. A much heavier mooring system and higher-class icebreaker support would be required to operate a floating rig beyond the existing season. The alternative was a bottom-founded structure that was designed to operate in ice conditions. Artificial, dredged islands have been built for drilling in the Beaufort Sea. These islands are built with "sacrificial" beaches and sandbag protection. The berm slope is relatively low, and berm volume is high. These islands are restricted to relatively shallow water on economic grounds and are susceptible to summer storm damage. Generally, the accepted economical water-depth limit for these islands is about 20 m [66 ft]. To provide a platform for winter drilling operations in deeper water outside the landfast ice zone, we determined that a bottom-founded structure that rested on a subsea berm would be most appropriate and cost-effective. Canmar's first arctic winter drilling system was a sandfilled, concrete multiple-caisson structure placed on a subsea berm - Tarsiut artificial island. Tarsiut island was built in 1981. Gulf Canada Resources Inc. operated Tarsiut during the winter of 1981–82 and the spring and summer of 1982.1 This caisson-retained island provided a stable drilling platform throughout, and two wells were drilled. The system had disadvantages, however, including limited mobility and "deck" space. Also, relocation of the structure would require considerable time because of the need to rig down completely, to excavate the caissons, and then to reconstruct the structure and rig up completely at the new location. Canmar's second-generation system, the SSDC, overcame many of the disadvantages of the Tarsiut system and has proved to be an excellent solutions to the problems of arctic drilling operations.

Reducing Poultry Processing Electric Demand

ABSTRACT SEVERAL methods are available for the reduction of electric demand in poultry processing plants. This paper discusses opportunities for energy reduction in two operations: ice making and ventilation for live broilers. A program designed to reduce demand in one plant reduc-ed the peak demand by about 15 percent by installing more energy efficient fans in the live-holding area and changing the time of ice-making operations during the warm months. In addition, a method of using electric hot water heaters for heating scalder water without incurring added demand charges is presented. A large, two-shift processing plant can pay for the cost of an electric hot water heater in 50 operating days when compared to us-ing No. 2 fuel oil.

COMPARING THE RESULTS OF ANALYSIS FOR MILK FAT USING THE MILKO-TESTER AND BABCOCK METHODS UNDER NORMAL PLANT CONDITIONS

At Giant Food Dairy Plant, both the Babcock test and Milko-tester, MKII, are used to determine and monitor the milk fat content of raw and finished milk products. On 50 operating days, 8 random samples were taken each day from 8 separate incoming milk truck tanks. Milkfat content was determined by the Babcock method and also by the Milko-tester. Correlation coefficients, regression equation, confidence limits for the regression line, and standard deviations were computed by IBM System 360 Model 40. Results showed a correlation coefficient of 0.8951, a standard deviation of the differences of 0.0478, a regression equation y = 0.19 + 0.95x, and confidence limits for the regression line of ± 0.07.