Contaminant washout in a hydraulically integrated serial turbidostat algal reactor (HISTAR)

A hydraulically integrated serial turbidostat algal reactor (HISTAR) was mathematically modeled and designed for large-scale production of microalgae. HISTAR, which combines turbidostats with a series of continuous-flow stirred-tank reactors (CFSTRs), was designed with contaminant mitigation as a primary design parameter. The concept of contaminant mitigation in the series of CFSTRs is discussed and three mathematical models presented to predict contaminant washout within the CFSTRs. Model simulations indicated that the hydraulic regime within each CFSTR is crucial to the contaminant mitigation process in the series of CFSTRs. Experiments on the HISTAR system with a liquid volume of about 8500 l, culturing Chaetoceros muelleri (CHAET 10), demonstrated that 0.8 million live rotifers, intentionally added to the first CFSTR, were washed out of the six CFSTRs at a local dilution rate of 4 day⁻¹. In another experiment, Thalassiosira sp. cultured at a dilution rate of 0.667 day⁻¹ fell victim to a few rotifers that inadvertently entered the CFSTRs. The validity of the washout concepts was demonstrated further when the ≈300 million live rotifers in the CFSTRs were completely washed out by simply increasing the dilution rate to 4 day⁻¹.     

Development of a Model for Describing Accumulation of Color and Subsequent Destruction by Ozone in a Freshwater Recirculating Aquaculture System

The purpose of this study was to develop a mathematical model to assist in the determination of design numbers for color destruction by ozone as a function of feed rate. A mass balance model was developed that takes into account methods of introduction and removal of color, including removal by ozone. Because direct measurement of color mass or concentration is difficult, a representative unit was developed during this study called the color mass equivalent (CME). The CME represents a direct measurement of absorbance at 436 nm, which is a unitless measurement, multiplied by the system volume. The CME is directly proportional to the true concentration of color causing compounds at that wavelength. Once the model was developed, two studies were run to test the model. A 1,500-L recirculating fish system was set up with a 57-L bead filter and six 1-L fluidized sand beds. Approximately 45 kg of channel catfish Ictalurus puncfatus were placed in the system and fed 0.25 kg of 32% protein feed per day (0.55% body wt.). Once the system reached stable conditions, the system was flushed with clean water and samples were taken to estimate the accumulation rate of color in the system. After 5 wk, an ozone unit was activated and samples were taken to determine the destruction rate for color. Once an accumulation rate had been determined, a second study was performed to corroborate this value. The same ozone unit was installed on a 5,000-L recirculating fish system being fed 0.49 kg per day with a 171-L bead filter. Samples were taken to determine the destruction rate for color. The accumulation rate for color was 12.6 CME/kg feed and the destruction rates were 1.7 CME/g O₃ in the first study and 0.82 CMWg O₃ in the second study. This calculates to a range of 7 to 15 g O₃/kg feed to remove the color produced by the feed.     

Microalgal production using a hydraulically integrated serial turbidostat algal reactor (HISTAR): a conceptual model

A hydraulically integrated, serial turbidostat algal reactor (HISTAR) was mathematically modeled and developed for the mass production of microalgae. HISTAR, which hydraulically links precisely controlled turbidostats with continuous-flow stirred-tank reactors (CFSTRs) into a single production technology, was conceptualized emphasizing contaminant mitigation at the design stage to maintain system stability. This paper discusses the conceptual basis for the development of HISTAR and presents a theoretical overview of the CFSTRs. Mathematical modeling, using first-order algal growth kinetics combined with CFSTR reactor kinetics, was used to investigate the effects of system dilution rate, D_s; net algal specific growth rate, U_a; number of reactors, N; input algal biomass, X_i; and contaminant concentration, C_n, on algal productivity, as well as local dilution rate, D_n, on suspended contaminant washout. The simulation results allowed the determination of preliminary design ranges for prototype development.     

Design of Nonionic Surfactants for Supercritical Carbon Dioxide

Interfacially active block copolymer amphiphiles have been synthesized and their self-assembly into micelles in supercritical carbon dioxide (CO2) has been demonstrated with small-angle neutron scattering (SANS). These materials establish the design criteria for molecularly engineered surfactants that can stabilize and disperse otherwise insoluble matter into a CO2 continuous phase. Polystyrene-b-poly(1,1-dihydroperfluorooctyl acrylate) copolymers self-assembled into polydisperse core-shell-type micelles as a result of the disparate solubility characteristics of the different block segments in CO2. These nonionic surfactants for CO2 were shown by SANS to be capable of emulsifying up to 20 percent by weight of a CO2-insoluble hydrocarbon into CO2. This result demonstrates the efficacy of surfactant-modified CO2 in reducing the large volumes of organic and halogenated solvent waste streams released into our environment by solvent-intensive manufacturing and process industries.     

Seismic precursors to the mount st. Helens eruptions in 1981 and 1982

Six categories of seismic events are recognized on the seismograms from stations in the vicinity of Mount St. Helens. Two types of high-frequency earthquakes occur near the volcano and under the volcano at depths of more than 4 kilometers. Medium- and low-frequency earthquakes occur at shallow depths (less than 3 kilometers) within the volcano and increase in number and size before eruptions. Temporal changes in the energy release of the low-frequency earthquakes have been used in predicting all the eruptions since October 1980. During and after eruptions, two types of low-frequency emergent surface events occur, including rockfalls and steam or gas bursts from the lava dome.     

Deep earthquakes beneath mount st. Helens: evidence for magmatic gas transport?

Small-magnitude earthquakes began beneath Mount St. Helens 40 days before the eruption of 20 March 1982. Unlike earlier preeruption seismicity for this volcano, which had been limited to shallow events (less than 3 kilometers), many of these earthquakes were deep (between 5 and 11 kilometers). The location of these preeruptive events at such depth indicates that a larger volume of the volcanic system was affected prior to the 20 March eruption than prior to any of the earlier dome-building eruptions. The depth-time relation between the deep earthquakes and the explosive onset of the eruption is compatible with the upward migration of magmatic gas released from a separate deep reservoir.     

Mitochondrial heredity: a determinant in the toxic response of maize to the insecticide methomyl

Mitochondria isolated from etiolated Texas male-sterile (TMS) cytoplasm maize (Zea mays L.) seedlings were adversely affected by methomyl (Lannate, 90 wettable powder), while those isolated from normal-fertile seedlings were not. In a manner analogous to that reported for Bipolaris (Helminthosporium) maydis (race T) toxin, experiments with TMS mitochondria showed that 1 to 3 millimolar methomyl inhibited the state 4 oxidation rate of combined malate and pyruvate while stimulating that of succinate or exogenous reduced nicotinamide adenine dinucleotide. Similar concentrations of methomyl effected an inhibition of phosphorylation, an increase in the percentage of transmittance of light through mitochondrial suspensions, and a decrease in the density of the mitochondrial matrix. Methomyl (15 millimolar) had little effect on the physiological activity or ultrastructure of isolated normal-fertile mitochondria. These observations provide the opportunity to specifically assess the homogeneity, or lack of it, of a cytoplasmic heritable characteristic in a widely divergent group of higher plants.     

Sludge Production and Management for Recirculating Aquacultural Systems

Waste discharge from recirculating aquacultural systems is typically in the form of sludge composed of partially stabilized excreta, uneaten food particles, and bacterial growth. The amount of solids produced can be estimated using an equation presented in this paper. In a typical recirculating system, total suspended solids (TSS) is the major pollutant of the sludge produced. The production of TSS ranges from 10 to 30% of the feeding rate on a dry weight basis. The ratio of 5-d biochemical oxygen demand to total suspended solids (BOD_S/TSS) of the sludge ranges from 0.10 to 0.2, the total Kjeldahl nitrogen (TKN) content of the TSS ranges from 4 to 6%, and total phosphorus ranges from 0.2 to 2%.
The nature of the waste and the economics of the treatment processes dictate the disposal of aquacultural sludge. Effective clarification of aquacultural waste is critical in reducing sludge volume. Using lagoons for stabilization and storage is the most practical option. While direct disposal by land application seems feasible for rural areas with dry climates, additional stabilization/storage in a lagoon with eventual disposal through land application seems most feasible for a variety of conditions. The effluent produced from the sludge treatment processes can be used for irrigation or for direct discharge after further polishing (treatment).     

Constructing a nitrogen fertilizer recommendation system using a dynamic model: what do farmers want?

Abstract. An effective fertilizer recommendation system requires information on seasonal, soil-related and cultural variations in soil mineral nitrogen (N) and nutrient requirements of the crop. This can be provided by dynamic N turnover models, such as listed by Plentinger & Penning De Vries (1996). In this paper, we describe a survey of farmer opinion designed to ascertain what farmers want from such a decision support system. Over 100 farmers were surveyed. Surveyed farmers requested that default values be available for all model inputs. Inputs should be entered both by windows-based menu (for clarity) and tabular format (for speed), have user-selected units, and be fully supported by context-sensitive help. The system should have a hierarchical structure allowing access to fixed parameters, and be compatible with commonly used farm recording packages. Recommendations should be provided both for the field (single and optional application rates), and in tabular format across the whole farm. Simulations should be easily rerun using more recent crop and weather data. Turnover processes underlying recommendations should be illustrated by flow diagrams of flux between pools, pie charts of fertilizer fate, bar charts of movement down the soil profile and graphical plots of changes in N status against time.