Microeconomic theory of chemical production processes: application to aqueous VOC air stripping operations

A novel microeconomic formalism for chemical processes is applied to air stripping of harmful volatile organic compounds (VOCs) from aqueous streams in a conventional packed tower. A simplified conceptual process model is combined with techno-economic aggregation rules to obtain an engineering production function, which relates process inputs (capital, material, labor, and energy) to output (stripped water flow rate). Process relationships determine column length and diameter required to achieve a specified VOC percent recovery from an aqueous stream of given composition and flow rate. Total capital is determined using a defined capital unit (1 capital unit=10 foot of 6-inch schedule 40 carbon steel welded pipe=$122, Jan. 1990) to put all installed capital equipment on the same basis and multiplying by 3.37 to account for the necessary plant infrastructure. Process labor is obtained from an empirical correlation, which relates workerhours to mass throughput. Simulations were made for four systems comprised from each of two representative random packings (i.e. 25-mm plastic Pall rings and 25-mm ceramic Raschig rings) and two model VOCs (i.e. 1,2-dichloroethane and trichloroethylene). Several examples are given, and process, technical and economic analyses of the results are presented. Two-dimensional (capital-energy) optimization was effective in determining the least cost combination of inputs for a plant to produce a specified output of stripped water. Furthermore, conventional economic models (e.g. Cobb-Douglas model) and associated methods (e.g. linear programming) were shown to be ineffective for air stripping plant design and optimization. Moreover, increasing returns to scale with economies of scale (declining long-run average cost) are prevalent.     

Revised estimates and projections of down syndrome births in the United States,and the effects of prenatal diagnosis utilization, 1970–2002

The objectives of this study were to: (1) calculate revised estimates and projections of United States annual Down syndrome (DS) births for 1970–2002, and (2) estimate the effects of amniocentesis on these baseline DS birth projections. Three models of amniocentesis utilization among 30–34 and ≧ 35-year-old women were considered. The recently revised Census Bureau birth projections, and new single year maternal age DS risk rates estimated from a 1970–1983 Ohio data set, were used. Data from all three Census Bureau projection series were analysed; series II was considered in depth since it is consistent with recent fertility levels. Assuming no use of amniocentesis, total estimated DS births dropped from about 4770 in 1970 to 4120 in 1980 (a 14 per cent decline), but are projected to a plateau of about 5100 by the year 1990 (a 24 per cent increase). DS births to women ≧ 35 would increase dramatically from about 1050 in 1980 to 1900 in 2000 (an 81 per cent increase). Assuming 1983 Ohio prenatal diagnosis ratios for women aged 30–34 (1.7 per cent) and ≧ 35 (23.4 per cent) are used nationally, an annual reduction of about 7 per cent of DS births in 1986 and 9 per cent in 2002 would result. Fifty and 70 per cent utilization among women 30–34 and 235, respectively, would reduce DS births by about 33 per cent in 1986 and 38 per cent in 2002. Therefore, if the projected increase in DS births is to be averted, utilization of prenatal diagnosis by ≧ 30-year-old women must increase substantially.     

Sclerochronological records of temperature and growth from shells of Mercenaria mercenaria from Narragansett Bay,Rhode Island

Annual internal growth increments in shells of hard clams (Mercenaria mercenaria) provide an accurate record of both growth history and some types of environmental change. These increments were used to determine age and growth rate of hard clams collected in 1984–1985 from ten sites in Narragansett Bay, Rhode Island, USA, and to assess geographic variation in growth within the bay. The regional comparisons were facilitated by modeling the clam growth using the von Bertalanffy equation and the parameter of Gallucci and Quinn. The optimum region for hard clam growth was near the head of the bay, with areas further north (Providence River) and south (lower bay) not as productive. The relationship between size and age was similar to that reported for hard clams from northern New Jersey. Using dendrochronological techniques, variations in growth were analyzed on a temporal (year-to-year) basis. The comparative longevity of the hard clams (individuals with 40 annual bands were encountered) demonstrated that sclerochronologies of several decades were possible. A 26 yr growth record based upon 100 individuals was established, covering the years 1959–1984. Significant temporal variations occurred in bivalve growth, and a broad trend of increasing growth indices over the last two decades of the record was noted. The yearly standardized growth index values were highly and positively correlated with mean annual water temperatures in Narragansett Bay for the same time interval. The incremental shell records of these bivalves provide a quantitative indication of marine climatic (temperature) variability and growth which can be used in hindcasting the effects of natural or anthropogenic environmental perturbations.     

CALIBRATION OF SNYDER COEFFICIENTS FOR PENNSYLVANIA1

ABSTRACT Unit hydrograph theory is one of the most widely used techniques to predict surface runoff. The present study is concerned with the Snyder unit hydrograph and the calibration of the Snyder coefficients for Pennsylvania. Twenty-seven study basins were selected, located randomly across the state. With the rainfall and runoff recorded for several events for each basin (more than 500 events were analyzed) unit hydrographs were calculated and the Snyder coefficients determined. A map of the coefficients was drawn to illustrate the variability in the coefficients and two equations using multiple regression theory were developed. The unexplained variability of the coefficients suggests that upper and lower bounds on the peak flow might be placed on storm hydrographs developed for ungaged watersheds.     

Tourism and town planning in Catalonia

The coastal tourist areas of Spain have seen open conflict between planners and the public over the flood of tourist developments. The Costa Brava in the region of Catalonia is chosen for the purpose of this study which looks at the effects of the Land Use law of 1976 requiring all municipalities to prepare General Plans. The failure of plans which attempted to severely restrict tourist growth, and this paper's conclusions, that the expansion of tourist pressure into new areas may create new conditions, suggest a regional approach to policy.     

EVALUATION OF PHILODINA ACUTICORNIS (ROTIFERA) AS A BIOASSAY ORGANISM FOR HEAVY METALS1

ABSTRACT: A technique for using the rotifer Philodina acuticornis as a bioassay organism is described. The rotifer was exposed to a range of concentrations for each of 14 toxicants. The effects of the heavy metals cadmium, chromium, cobalt, copper, lead, mercury, nickel, silver and zinc were studied. Based upon 96 hours exposure in soft water the sensitivity of the rotifer to the metals from the most toxic to least toxic was: cadmium, mercury and copper, zinc, silver, nickel (chloride), chromium, nickel (sulfate), lead and colbalt. In hard water with 96 hours exposure the most to least toxic respectively were: cadmium, copper, mercury, chromium and lead. The 48 hour EC₅₀ value suggests that zinc will follow mercury in relative toxicity when Philodina is tested in hard water. In a comparison of the toxicity of the chloride and sulfate salts of cadmium, nickel and zinc in soft water cadmium sulfate and zinc sulfate were more toxic after 96 hours; nickelous chloride was more toxic than nickelous sulfate. Increased water hardness decreased the toxicity of the heavy metals studied. The results suggest that this rotifer may be more sensitive than the bluegill sunfish to the salts of cadmium, copper, nickel, zinc and chromium and less sensitive to lead. Data for cobalt, silver and mercury were not available. Philodina was extremely tolerant of ammonium chloride and phenol. The feasibility and economics of using an inexpensive, readily cultured and available organism such as Philodina acuticornis as a bioassay organism were discussed.