Simulation of a time dependent activated sludge wastewater treatment plant

A dynamic mathematical model has been developed for a general activated sludge wastewater treatment plant. The model includes a primary settler, aeration tank, and clarifier-thickener, each of which is represented by various configurations of a general tanks-in-series model. With the aid of the model, it was possible to simulate simultaneously the diurnal response of a number of significant variables including dissolved BOD, suspended solids, dissolved volatile solids, active mass, inert mass, soluble nonbiodegradable mass, Nitrosomonas mass, Nitrobacter mass, ammonium, nitrite, nitrate and dissolved oxygen. The equations for the model as well as the results of plant simulations using the model and a sensitivity analysis are presented.     

The extent of the Aznalcóllar pyritic sludge spill and its effects on soils

This paper presents some initial results from the Instituto Tecnológico Geominero de Espa?a's (ITGE) study of the Aznalcóllar mine spill. The spatial distribution of the pyritic sludge released was surveyed by using remote sensing data, aerial photography, and more than 700 field measurements on the sludge thickness. Initial estimation of the extent of the sludge was provided by radar data. Maps at 1:10,000 scale, drawn on the basis of field data and interpretation of aerial photos, show the distribution of the sludge, divided into 168 subsections on the basis of average thickness. GIS analysis provided estimates of the area and volume of the sludge. Three approaches were followed in order to survey the effects of the spill on the Guadiamar river alluvial soils: (1) Mineralogical and chemical characterization of the sludge and its evolution until its removal. Alteration products of the pyritic sludge were also analyzed. (2) Determination of geochemical background of soils in the Guadiamar river basin, in order to establish the content of heavy metals and other elements in the soil before the spill. (3) Assessment of the sludge effect on soils caused by the acid water and the deposited sludge, by comparison of the heavy metal content of soil under the sludge layer with that of background soil. Finally, an airborne multispectral survey was carried out over the Aznalcóllar-Do?ana area to evaluate its efficiency for monitoring soil condition during and after sludge removal.     

Effect of chlorination practice on soluble organics

As the practice of chlorination for the disinfection of waste effluents is apparently to be extended, this study was initiated to examine the possibility that chlorinated organics could be formed in the disinfection process. A group of pure compounds that had been demonstrated to be susceptible to chlorination were examined under conditions likely to apply under normal disinfection practice.From the results obtained, it appears only organics with ring structures and electron activating substituents, or amino groupings are capable of chlorination. The frequent presence of ammonia or amino groups means that chloramine formation with its asociated toxicity is likely. However, the presence of ammonia or amino groups will retard the reaction with other compounds making chlorination of these unlikely.     

Particulate and dissolved trace metals in Lake Ontario

Particulate metal concentrations in the nearshore waters of Lake Ontario have been determined to be 690 ng l⁻¹ for Cu; 40 ng l⁻¹ for Cd; 180 ng l⁻¹ for Ni; 1690 ng l⁻¹ for Zn; 2100 ng l⁻¹ for Mn; and 700 μg l⁻¹ for Fe. These values are considerably higher than the particulate metal concentrations in the offshore waters: 130, 8, 34, 230, 110, 260 and 9000 ng l⁻¹ for Cu, Cd, Ni, Zn, Pb, Mn and Fe respectively. In general, 50–80% of the Cu, 10–40% of the Ni, 20–60% of the Cd and >60% of the Pb in the lake water were bound to the suspended particulates. From the standing crop of the particulate metals and the estimated rates of their deposition on the lake bottom, the residence times of the particulate metals in the lake water column have been estimated to be about 0.5 yr. on the average. The suggestion is made that particulate organic matter may be an important vehicle for metal transport to the Lake Ontario sediments.     

Conceptual aspects of water re-use

A simplified model of a municipal water recycle system is presented and gives a clear picture of the relationship between process variables such as the intensity of the treatment, the accumulation of pollutants and the number of times the water is re-used. The model can be used to determine the necessary requirements for the treatment process in order to reach a certain desired drinking water quality. This model is extended to cover a variety of practical conditions. It is also shown that accumulation under practical conditions is limited, even if there is no treatment. The model predicts that the recycle system can utilise a low quality supplementary supply, e.g. brackish water. Although the model is derived for a recycle system for domestic water supply it can be used for any closed loop water system.     

Effect of adding phosphate to drinking water on bacterial growth in slightly and highly corroded pipes

The effect of phosphate addition in drinking water was tested under static conditions as batch tests and under dynamic conditions using continuously fed reactors. Phosphate supplements in batch tests from 0.1 to 2 mg P-PO4 L(-1) did not show any relationship between bacterial growth and phosphate concentration. Dynamic tests in slightly corroded reactor (stainless steel) treated at 1 mg P-PO4 L(-1) showed only a moderate improvement in the growth of microorganisms. On the contrary, phosphate treatment applied to the highly corroded reactor (unlined cast iron) led to an immediate, drastic drop in iron oxide release and bacterial production. Phosphate uptake by the reactor wall was less than 14% with the stainless-steel reactor and 70-90% with the corroded cast iron reactor. Moreover, about 5% of the phosphate associated to corroded iron pipe walls was released for 20 days after the end of treatment.     

Full-scale fire tests and the development of design criteria for sprinkler protection of mobile shelving units

In early 1991, a new sprinkler system was planned for the existing National Archives/National Library of Canada building in Ottawa. A major challenge in the design and installation of the sprinkler systems was to protect mobile compact shelving units located in the three levels below grade. Storage of documents in these shelving units is typically within 178 mm of the concrete slab ceiling. The minimum clearance permitted by the sprinkler system installation standard is 457 mm from the sprinkler deflector to the top of the storage. To conform with the sprinkler design standard, the top level or levels of storage would have had to be removed and additional storage space acquired. Because of the annual cost of this additional storage, an investigation was begun to determine feasible alternatives that would permit a reduction in clearances between sprinklers and storage, while maintaining an acceptable level of fire safety. This paper describes the series of five full-scale fire tests that were conducted to assess various fire protection options. Based on these tests, design criteria were developed for a sprinkler system using quick response horizontal sidewall sprinklers to protect the mobile shelving units. An overview of this technically based fire protection system for use in protecting shelving units with reduced clearance is also presented.     

Some chemical properties of hazelnut husk and its suitability for particleboard production

Hazelnut husk is a renewable natural resource that has not industrial utilization yet. The objective of this study was to examine some chemical properties (holocellulose, cellulose, lignin and ash contents, alcohol–benzene, hot and cold water solubility and solubility in dilute alkali (1% NaOH)) of hazelnut husk and to evaluate its suitability to produce composite panels. For this study, particleboards were produced using hazelnut husk as an alternative raw material for the forest products industry. Two panel density levels (0.6 and 0.7 g/cm³) and three types of resins (urea-formaldehyde (UF), phenol formaldehyde (PF), melamine-formaldehyde (MUF)) were selected as treatments. The findings indicated that hazelnut husk waste is a valuable renewable natural resource for particleboard production and could be utilized as a substitute for wood in board production. Its shortcomings, such as higher water absorption and thickness swelling could easily be controlled by adding water repellent chemicals in production. The bending and the internal bond strength properties of the hazelnut husk boards produced met the requirement for the general purpose product standards (TS-EN 312-2) at 0.70 g/cm³ density.     

Increased sediment oxygen uptake caused by oxygenation-induced hypolimnetic mixing

Hypolimnetic oxygenation systems (HOx) are increasingly used in lakes and reservoirs to elevate dissolved oxygen (O₂) while preserving stratification, thereby decreasing concentrations of reduced chemical species in the hypolimnion. By maintaining an oxic zone in the upper sediment, HOx suppress fluxes of reduced soluble species from the sediment into the overlying water. However, diminished HOx performance has been observed due to HOx-induced increases in sediment O₂ uptake. Based on a series of in situ O₂ microprofile and current velocity measurements, this study evaluates the vertical O₂ distribution at the sediment-water interface as a function of HOx operation. These data were used to determine how sediment O₂ uptake rate (JO₂) and sediment oxic-zone depth (z_max) were affected by applied oxygen-gas flow rate, changes in near-sediment mixing and O₂ concentration, and proximity to the HOx. The vertical sediment-water O₂ distribution was found to be strongly influenced by oxygenation on a reservoir-wide basis. Elevated JO₂ and an oxic sediment zone were maintained during continuous HOx operation, with z_max increasing linearly with HOx flow rate. In contrast, JO₂ decreased to zero and the sediment became anoxic as the vertical O₂ distribution at the sediment-water interface collapsed during periods when the HOx was turned off and near-sediment mixing and O₂ concentrations decreased. JO₂ and z_max throughout the reservoir were found to be largely governed by HOx-induced mixing rather than O₂ levels in the water column. By quantifying how JO₂ and z_max vary in response to HOx operations, this work (1) characterizes how hypolimnetic oxygenation affects sediment O₂ dynamics, (2) contributes to the optimization of water quality and management of HOx-equipped lakes and reservoirs, and (3) enhances understanding of the effect of mixing and O₂ concentrations in other systems.