Recent wrca_wp items

Membrane Bioreactors: Past, Present and Future?

Fri, 13 May 2011 00:00:00 +0000

A brief description of membrane bioreactor (MBR) historical evolution has been presented with emphasis on continual decline of treatment costs and energy requirements. Although MBR can operate at biomass (MLSS) concentrations 5 to 10 times higher than activated sludge these concentrations are limited in practice by increasing biomass suspension viscosity that in turn increases “reversible” membrane fouling and decreases oxygen transfer rates. “Irreversible” fouling is a major operational challenge since it depends on subtle interactions of membranes with various fractions of soluble microbial products resulting from microbial metabolism.

Sustainable Development: Physical and Moral Issues

Tue, 5 Dec 2006 00:00:00 +0000

Sustainable development gradually becomes an important concept embedded in many societal activities including economy, politics and perhaps even regulations. Sustainability is now a growing concern of businesses, governments, civic groups and individuals. These concerns are often linked to energy efficiency, reduction of environmentally harmful emissions, ecosystem preservation and other "save the Earth" efforts. They are becoming a part of a "triple bottom line" for business accounting: financial, social and environmental. Despite its increasing importance, current definitions of "sustainability" are somewhat vacuous. This paper presents a possiblity to characterize sustainability in terms of system theory and chaotic dynamics with strong links to to moral and ethical issues.

Is Scarcity a Real Driver for Water Reuse ?

Tue, 25 Jul 2006 00:00:00 +0000

Conventional knowledge suggests that water reclamation and reuse is implemented as a response to scarcity of natural water resources. As water demand increases natural water resources (surface waters or groundwater) become insufficient and individual communities or larger regions turn to water reuse to meet an increasing fraction of their needs. However, the analysis of data on water consumption and water reuse collected by the US Geological Survey indicate that water scarcity is perhaps only one factor behind water reuse. This work suggests that relative variability, measured as the coefficient of variantion combined with the Hurst exponent may explain to a large extent differences in water reuse in different parts of the U.S.

Sustainability in Water Resources Management: Changes in Meaning and Perception

Tue, 10 Jan 2006 00:00:00 +0000

The meaning of sustainability in the context of water resources management has changed through the time. Initially meeting water demand was the dominant concern. While later quality issues became more important followed by wider water reuse, today sustainability must include a whole range of aspects (e.g., energy, pollution, persistent chemicals), spatial and time scales. New approaches to define sustainability metrics are needed. A possible approach is to use fundamentallybased entropy and energy flows.

Entropy and Energy: Toward a Definition of Physical Sustainability

Tue, 10 Jan 2006 00:00:00 +0000

Sustainable development is a growing concern expressed by many businesses, organizations and individuals. Yet, no workable quantifiable definition of sustainability is available for evaluation of specific projects or operations. This paper attempts to set a framework for such a definition in terms of the first and second law of thermodynamics. Specifically, the proposed description of sustainability relates the fundamental processes of chemical, physical or biological transformation, and mass transport to energy and entropy changes. Unlike previous applications of these concepts, the proposed definition is focused on the smallest unit operations and processes while allowing for aggregation into larger systems. The proposed description also explicitly considers the time horizon for sustainability. An example of sustainability analysis for a water treatment process is included.