The coagulation of a kaolinite suspension with aluminium sulphate

A study has been made of the coagulation of a 50 mg l⁻¹ aqueous suspension of kaolinite for a range of aluminium sulphate and hydrogen ion concentrations. The rate of flocculation was determined from jar tests after stirring for 1 h. The data permitted a stability limit diagram to be drawn from which some indication of the coagulation mechanisms of the system could be ascertained.     

Lead contamination in tap water of households with children in Lower Saxony, Germany

Lead has numerous acute and chronic adverse effects on human beings. This is especially true for infants and children. The main path of lead ingestion in children can be different according to housing and living situation. The intake of lead through drinking water is commonly due to metal corrosion. The users plumbing can be an important factor. In recent years, many lead pipes in Germany have been replaced by pipes made of an alternative material. The aim of this study is to assess the present state of drinking water contamination and the resulting exposure of infants to lead. For this purpose mothers of new-born babies were offered a free examination of their drinking water. After a written declaration of consent had been obtained and after the infant in question had reached an age of 3 months, a stagnation sample of cold tap-water after overnight stagnation together with a random daytime sample was obtained from the family. The collected samples were analysed by atomic absorption spectrometry for their lead concentration. In total, 1485 samples from households were collected. Of the 1434 stagnation samples, 3.1% had lead concentrations greater than 0.01 mg/l (recommended limit of the WHO) and 0.6% had concentrations above the limit of the German drinking water regulation (0.04 mg/l). The values for the 1474 random daytime samples were 2.1% above 0.01 mg/l and 0.2% greater than 0.04 mg/l, respectively. By region, the areas Bovenden, Friedland, Duderstadt, Northeim and Rosdorf were particularly affected. The highest measured concentrations of lead in the stagnation samples were 0.11 mg/l and 0.15 mg/l in the random daytime samples, respectively.     

Object–Oriented Enterprise Modeling and Simulation of AEC Projects

In this paper we describe an object–oriented framework for developing enterprise models of Architecture, Engineering, Construction projects, and a methodology for formalizing these models such that they can be used for discrete event simulation of information processing and coordination in project execution. The simulation results can be used to predict the probable effects of carrying out proposed changes in planning and managing projects.
In our enterprise modeling framework we represent engineering design projects in terms of deliverables (requirements and solutions), plans (activities and process relations), and organization (participants and organizational relations). The resulting project model is the starting point for identifying coordination requirements between project team participants. Our methodology uses matrix techniques derived from qualtiy function deployment (QFD) to identify interactions between project requirements and solutions and calculate measures of product complexity . We then describe information flow between project activities in a similar matrix and calculate measures of process uncertainty . Finally, we identify the responsibilities of project team members and use a matrix to point out organizational interdependencies .
We apply our framework and methodology to model and simulate engineering design for a major extension of an electrical power substation. Our simulation results demonstrate how project performance is contingent on the fit between the project policies and the objectives and preferences of the project team.     

Interaction of bacteriophage R17 and reovirus type III with the clay mineral allophane

A study has been made of the adsorption of bacteriophage R17 and reovirus type 3 by the amorphous aluminosilicate clay mineral allophane. In agreement with previous studies of virus adsorption to other minerals such as montmorillonite and aluminium hydroxide, the principal factors influencing adsorption were found to be mixing time, pH and the concentrations and isoelectric points of both the virus and the absorbent. However, allophane was found to be a much better adsorbent for reovirus and R17 over the pH range 5–7, the natural pH range of many fresh waters.By using highly purified radioactive reovirus it was possible to follow both the distribution of radioactive virus in a clay suspension and the specific infectivity of the virus. This study revealed that when adsorbed virus was eluted by neutral phosphate solutions it retained its physical integrity but was of a lower specific infectivity.     

Method of Determining Strength and Deformation Characteristics of Soils from Results of Deep Impression of Rod Plates

The possibility of determining strength and deformation characteristics of soils under field conditions using rod plates is discussed. The mutual relationship between these characteristics is established from results of deep impression of these rods.     

A new fire management policy on Forest Service lands

A new Forest Service policy, effective February 1978, allows some wildfires to burn under prescribed conditions, urges a multidisciplinary approach to fire control, and has applications to rural and urban situations. Note: The author, formerly with the Pacific Southwest Forest and Range Experiment Station, Berkeley, Calif., is now with the Forest Fire and Atmospheric Sciences Research Staff, Washington, D.C.     

Concurrent denitrification and oxygen uptake in microbial films

Mixed microbial films were grown on the inner walls of a tubular reactor with recirculation of the reactor contents and continuous flow-through of nutrient solution. The loss of total oxidized nitrogen was correlated to the film population, the nitrite concentration and the dissolved oxygen concentration in the reactor. When film population was greater than 0.5 × 10⁹ cells cm⁻², reactor dissolved oxygen concentration greater than 1 mg l⁻¹ had little effect on the nitrate loss. Nitrate loss declined for film populations greater than 2 × 10⁹ cells cm⁻². Models based on Monod and zero-order microbial kinetics were calibrated using these data and a nonlinear least squares method. There was little difference in the residual errors with these methods.     

Tunnelling projects in Southern Africa

Until some thirty years ago tunnelling in southern Africa for civil engineering purposes had been on a relatively small scale and of a sporadic nature. The first major tunnel to be built in the region was the 82 km long Orange-Fish Tunnel. Since 1970 more than 175 tunnels with an aggregate length of just over 400 km have been built. Much of the first phase of the Lesotho Highlands Water Project, which will have more than 100 km of tunnels, is about to be completed. The last thirty years represent the busiest period of tunnelling by civil engineers that southern Africa has ever known. The paper starts by summarising the early history of tunnelling in the region, and goes onto describe recent and current tunnelling projects. It also gives an indication of the possible demand for tunnels in the future.     

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.     

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.