title: Review: Denitrifying bioreactors—An approach for reducing nitrate loads to receiving waters

authors: Schipper, Louis A.

subjects: denitrification

abstract: Low-cost and simple technologies are needed to reduce watershed export of excess nitrogen to sensitive aquatic ecosystems. Denitrifying bioreactors are an approach where solid carbon substrates are added into the flow path of contaminated water. These carbon (C) substrates (often fragmented wood-products) act as a C and energy source to support denitrification; the conversion of nitrate (NO³⁻) to nitrogen gases. Here, we summarize the different designs of denitrifying bioreactors that use a solid C substrate, their hydrological connections, effectiveness, and factors that limit their performance. The main denitrifying bioreactors are: denitrification walls (intercepting shallow groundwater), denitrifying beds (intercepting concentrated discharges) and denitrifying layers (intercepting soil leachate). Both denitrifcation walls and beds have proven successful in appropriate field settings with NO³⁻ removal rates generally ranging from 0.01 to 3.6 g N m⁻³ day⁻¹ for walls and 2–22 g N m⁻³ day⁻¹  for beds, with the lower rates often associated with nitrate-limitations. Nitrate removal is also limited by the rate of C supply from degrading substrate and removal is operationally zero-order with respect to NO³⁻ concentration primarily because the inputs of NO³⁻ into studied bioreactors have been generally high. In bioreactors where NO³⁻ is not fully depleted, removal rates generally increase with increasing temperature. Nitrate removal has been supported for up to 15 years without further maintenance or C supplementation because wood chips degrade sufficiently slowly under anoxic conditions. There have been few field-based comparisons of alternative C substrates to increase NO³⁻ removal rates but laboratory trials suggest that some alternatives could support greater rates of NO³⁻ removal (e.g., corn cobs and wheat straw). Denitrifying bioreactors may have a number of adverse effects, such as production of nitrous oxide and leaching of dissolved organic matter (usually only for the first few months after construction and start-up). The relatively small amount of field data suggests that these problems can be adequately managed or minimized. An initial cost/benefit analysis demonstrates that denitrifying bioreactors are cost effective and complementary to other agricultural management practices aimed at decreasing nitrogen loads to surface waters. We conclude with recommendations for further research to enhance performance of denitrifying bioreactors.

text: Review: Denitrifying bioreactors—An approach for reducing nitrate loads to receiving waters Low-cost and simple technologies are needed to reduce watershed export of excess nitrogen to sensitive aquatic ecosystems. Denitrifying bioreactors are an approach where solid carbon substrates are added into the flow path of contaminated water. These carbon (C) substrates (often fragmented wood-products) act as a C and energy source to support denitrification; the conversion of nitrate (NO³⁻) to nitrogen gases. Here, we summarize the different designs of denitrifying bioreactors that use a solid C substrate, their hydrological connections, effectiveness, and factors that limit their performance. The main denitrifying bioreactors are: denitrification walls (intercepting shallow groundwater), denitrifying beds (intercepting concentrated discharges) and denitrifying layers (intercepting soil leachate). Both denitrifcation walls and beds have proven successful in appropriate field settings with NO³⁻ removal rates generally ranging from 0.01 to 3.6 g N m⁻³ day⁻¹ for walls and 2–22 g N m⁻³ day⁻¹  for beds, with the lower rates often associated with nitrate-limitations. Nitrate removal is also limited by the rate of C supply from degrading substrate and removal is operationally zero-order with respect to NO³⁻ concentration primarily because the inputs of NO³⁻ into studied bioreactors have been generally high. In bioreactors where NO³⁻ is not fully depleted, removal rates generally increase with increasing temperature. Nitrate removal has been supported for up to 15 years without further maintenance or C supplementation because wood chips degrade sufficiently slowly under anoxic conditions. There have been few field-based comparisons of alternative C substrates to increase NO³⁻ removal rates but laboratory trials suggest that some alternatives could support greater rates of NO³⁻ removal (e.g., corn cobs and wheat straw). Denitrifying bioreactors may have a number of adverse effects, such as production of nitrous oxide and leaching of dissolved organic matter (usually only for the first few months after construction and start-up). The relatively small amount of field data suggests that these problems can be adequately managed or minimized. An initial cost/benefit analysis demonstrates that denitrifying bioreactors are cost effective and complementary to other agricultural management practices aimed at decreasing nitrogen loads to surface waters. We conclude with recommendations for further research to enhance performance of denitrifying bioreactors.

year: 2010

title: Approximative filtering of XML documents in a publish/subscribe system

authors: Hinze, Annika

subjects: computer science

abstract: Publish/subscribe systems filter published documents and inform their subscribers about documents matching their interests. Recent systems have focussed on documents or messages sent in XML format. Subscribers have to be familiar with the underlying XML format to create meaningful subscriptions. A service might support several providers with slightly differing formats, e.g., several publishers of books. This makes the definition of a successful subscription almost impossible. This paper proposes the use of an approximative language for subscriptions. We introduce the design of our ApproXFilter algorithm for approximative filtering in a publish/subscribe system. We present the results of our performance analysis of a prototypical implementation.

text: Approximative filtering of XML documents in a publish/subscribe system Publish/subscribe systems filter published documents and inform their subscribers about documents matching their interests. Recent systems have focussed on documents or messages sent in XML format. Subscribers have to be familiar with the underlying XML format to create meaningful subscriptions. A service might support several providers with slightly differing formats, e.g., several publishers of books. This makes the definition of a successful subscription almost impossible. This paper proposes the use of an approximative language for subscriptions. We introduce the design of our ApproXFilter algorithm for approximative filtering in a publish/subscribe system. We present the results of our performance analysis of a prototypical implementation.

year: 2006-01-16

title: The challenges of culture to psychology and post-modern thinking

authors: Waldegrave, Charles

subjects: Maori

abstract: Someone at a workshop in the Waikato once said to us, “You know a Maori, if they want to, can always learn to be a psychologist, but a psychologist can’t learn to be a Maori”. Cultural knowledge may or may not be accompanied by social science knowledge. Cultural knowledge can stand on its own. Those who possess it, and choose to work in the institutions we are associated with, have gifts this country desperately needs. All our organisations require such people, and they need to be properly resourced, have employment security and control over their work. Their own work away from our organisations also requires adequate resourcing. They can heal their own in ways that we will never be able to. They will almost certainly offer the field rich alternative metaphors and meanings that can free us from the tired old medical, biological and social science ones. This also has implications for those in other branches of psychology, including research, experimental and industrial psychology. There is perhaps a unique opportunity for psychologists in this country of Aotearoa/New Zealand to recognise other ways of describing events, which will lead to creative practices and enable the health and welfare resources to get to those who most need them, on their own terms. It would also enable other people, other workers from other cultures to develop new paradigms, and new shifts in our field. This will not lead to the abandonment of social science, but it will enable that body of knowledge, to sit appropriately along side other realms of knowledge such as gender knowledge, and cultural knowledge, without dominating. A new experience for the social scientists, but I suspect a liberating one!

text: The challenges of culture to psychology and post-modern thinking Someone at a workshop in the Waikato once said to us, “You know a Maori, if they want to, can always learn to be a psychologist, but a psychologist can’t learn to be a Maori”. Cultural knowledge may or may not be accompanied by social science knowledge. Cultural knowledge can stand on its own. Those who possess it, and choose to work in the institutions we are associated with, have gifts this country desperately needs. All our organisations require such people, and they need to be properly resourced, have employment security and control over their work. Their own work away from our organisations also requires adequate resourcing. They can heal their own in ways that we will never be able to. They will almost certainly offer the field rich alternative metaphors and meanings that can free us from the tired old medical, biological and social science ones. This also has implications for those in other branches of psychology, including research, experimental and industrial psychology. There is perhaps a unique opportunity for psychologists in this country of Aotearoa/New Zealand to recognise other ways of describing events, which will lead to creative practices and enable the health and welfare resources to get to those who most need them, on their own terms. It would also enable other people, other workers from other cultures to develop new paradigms, and new shifts in our field. This will not lead to the abandonment of social science, but it will enable that body of knowledge, to sit appropriately along side other realms of knowledge such as gender knowledge, and cultural knowledge, without dominating. A new experience for the social scientists, but I suspect a liberating one!

year: 1993