P. Aarne Vesilind

Dilatometric measurement of bound water in wastewater sludge

The dilatometric technique is used to measure bound water in aerobically digested sludge. It is found that air liberated from the sludge sample during the freezing of the sludge water affects the quantity of unfrozen water (interpreted as bound water) determined by dilatometry. Both the freezing temperature and the solids concentration affect the measured bound water content. It is also found that the precision of dilatometry decreases with decreasing solids concentration and that the accuracy of dilatometry cannot be determined since there is no independent measure of unfrozen water.

Pathogen reduction capabilities of freeze/thaw sludge conditioning

Abstract Freezing and thawing sludge has become an economically feasible technique of sludge conditioning in regions where natural freezing is available. Even though the dramatic effects of freeze/thaw on dewatering have been studied extensively, its effects on the survival of pathogenic microorganisms have not been investigated. If freeze/thaw conditioning can be shown to reduce pathogenic microorganisms, then sludges treated in this fashion can be disposed of on land with less risk of health effects. In this paper, the effects of freezing rate, temperature and time in the frozen state on the removal of pathogens are tested. The response of seven indicators of microbial contamination; fecal coliforms, Salmonella , plaque forming units, fecal streptococci, poliovirus, helminths and protozoa to the freeze/thawing of both aerobically and anaerobically digested sludges is examined. Fecal coliforms, fecal streptococci, and plaque forming units are chosen as the commonly used indicators of bacteria and viruses, respectively in wastewater sludges. Pathogenic bacteria ( Salmonella ), virus (Poliovirus) and parasites ( Ascaris suum and Cryptosporidium parvum ) tested in the second phase are chosen as sample microorganisms in their respective classes. Freeze/thaw sludge conditioning is proven to be an effective means of removing most pathogenic microorganisms. Fecal streptococci are found to be the best indicator of the effectiveness of freeze/thawing on enteric bacteria. Results of this study indicate that freeze/thaw conditioning coupled with sludge digestion can significantly enhance the overall pathogenic microorganism reduction achieved in a wastewater treatment plant. Added effectiveness by freeze/thaw treatment may become critical for a plant in meeting the pathogen reduction requirements by U.S. regulations prior to any practice of land application or land disposal of sludge.

Assessing the true cost of landfills

The most common means for disposing of municipal solid waste is burial in a sanitary landfill. However, many landfill owners significantly underestimate the total cost of landfill disposal by considering only land and operating costs, ignoring external physical and social costs associated with landfills. This paper proposes an approach to estimating (in monetary terms) the external costs arising from the development and operation of a landfill. All cost information is based on typical U.S. landfill cost structures. The approach is illustrated by applying it to a case study of a proposed landfill in Durham, North Carolina (U.S.A.). This case study demonstrates that the method can be applied easily and yields reasonable results.

Testing and evaluation of air classifier performance

Abstract This paper introduces a new parameter for describing air classifier performance, “Total Efficiency”, found by first calculating the fractions recovered of both light and heavy fractions at specific air speeds and then multiplying the two fractions. Total Efficiency can be plotted against air speed, and such plots yield information about peak efficiencies and sensitivity to air flow rate variations. This method allows the comparison of different air classifiers and also leads to a technique in which the data can graphically express contamination of the light or heavy fraction at different air speeds. These curves can then be used to determine the optimum air speed in terms of market value of the product produced. Data on three different throat designs — the zigzag throat and two variations of the zigzag, are used to illustrate the method.

Zinc adsorption by lime‐treated montmorillonite clay

Abstract In this research, lime‐treated montmorillonite clay is used to adsorb Zn(II) in a wide range of Zn(II) concentrations. Batch test results show that the adsorption of Zn(II) by montmorillonite appears to be dominated by different adsorption mechanisms. At low Zn(II) concentrations, chemisorption affects the amount of Zn(II) adsorbed by montmorillonite. When lime is added, physisorption becomes increasingly important. At high Zn(II) concentrations, physisorption is the dominant mechanism for Zn(II) adsorption. Lime also enhances the ability of montmorillonite to adsorb Zn(II) at low initial Zn(II) concentrations, and does not significantly affect the ability of montmorillonite to adsorb Zn(II) at high initial Zn(II) concentrations. In chemisorption, montmorillonite provides cation exchange sites for the adsorption of Zn(II). In physisorption, montmorillonite acts as not only nucleation center to adsorb zinc hydroxide‐oxides but also helps to coagulate the zinc hydroxide‐oxides. Lime‐treated clay ca...

Planning Hazardous Waste Reduction and Treatment Strategies: an Optimization Approach

An industry faced with escalating off-site waste disposal costs will often consider increasing on-site waste treatment capacity or the implementation of a waste reduction program. Waste reduction program options include input and process changes that decrease waste quantity and waste toxicity. Tradeoffs between capital investment and economy-of-scale in development are required, and will depend on the industry and the current level of waste reduction. A dynamic programming model is developed that allows the investigation of waste reduction and treatment strategies for industries in a changing regulatory and economic environment. The applicability of the optimization approach to industrial waste generators is illustrated through a hypothetical but representative industrial waste management example.

Predicting particle behavior in air classifiers

Abstract A test to predict the behavior of irregularly shaped particles in a vertical air flow is developed and evaluated. The fundamental aspects of particle behavior are discussed, while irregularly shaped particles are highlighted. Dropping such particles in calm air at a height to establish a defined terminal settling velocity is the basis for the test. Meaningful comparisons are made as the same particles are injected in a vertical air flow. Conclusions point to the usefulness of the drop test for predicting particle behavior in a vertical air flow in general and organic/inorganic solid waste particles in air classifiers in particular.

Thermal conductivity of sludges

Abstract The time needed to naturally thaw sludge in a freezing bed depends on the thermal conductivity of the settled sludge layer deposited on the thawing sludge. The objective of this research is to measure the thermal conductivity of this layer. Six different sludges are tested, and it is found that thermal conductivity decreases with increasing solids concentration. At normal solids concentrations, the thermal conductivity is found to be about 0.85 × 10−3 cal cm−1 s °C.

Effect of feed rate on air classifier performance

Abstract The objective in this study is the development of an understanding of how feed rate affects air classifier performance. Although bridging and choking are known to occur at very high feed rates, separation can also be adversely affected with lower than choking feed rates. The effect of loading can be examined by varying the feed rate into the experimental air classifier while maintaining a constant superficial air velocity.

Engineering Ethics: Looking Back, Looking Forward

The eight pieces constituting this Meeting Report are summaries of presentations made during a panel session at the 2011 Association for Practical and Professional Ethics (APPE) annual meeting held between March 3rd and 6th in Cincinnati. Lisa Newton organized the session and served as chair. The panel of eight consisted both of pioneers in the field and more recent arrivals. It covered a range of topics from how the field has developed to where it should be going, from identification of issues needing further study to problems of training the next generation of engineers and engineering-ethics scholars.