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Filter-based microbiological wastewater treatment systems (such as subsurface flow constructed wetlands, trickling filters and recirculating sand filters) require a thorough understanding of system hydraulics for their correct design and efficient operation. As part of the treatment process, the filter media will gradually become clogged through a combination of solids filtration and retention, biomass production and chemical precipitation. Eventually the media may become so clogged that hydraulic malfunctions ensue, such as untreated wastewater bypassing the system. To achieve good asset lifetime a balance must be struck between these essential treatment mechanisms and the hydraulic deterioration that they cause. For many wastewater filtration systems the exact mechanism of clogging is not obvious, and few specialised techniques have been developed which allow the cause and extent of clogging to be measured in typical systems. The resultant lack of understanding regarding clogging hinders the ability of operators to maintain good hydraulic performance. In this chapter, for the first time, we compare three different families of standard hydraulic measurement techniques and discuss the information that they can provide: hydraulic conductivity measurements; clog matter characterisation and hydrodynamic visualisation. Each method is assessed on its applicability to typical wastewater filtration systems using horizontal subsurface flow constructed wetlands as a case study. Furthermore, several new techniques will be considered which have been specifically developed to allow in situ determination of hydraulic health for subsurface flow constructed wetland wastewater filtration systems. These include in situ constant and falling head permeameter techniques and embeddable magnetic resonance probes. Discussion is given to the ways in which different methods can be combined to gather detailed information about the hydraulics of wastewater filtration systems before exploring methods for condensing heterogeneous hydraulic conductivity survey results (that vary by several orders of magnitude) into a single representative value to describe the overall hydraulic health of the system.

Clogging is a major operational and maintenance issue associated with the use of subsurface flow wetlands for wastewater treatment, and can ultimately limit the lifetime of the system. This review considers over two decades of accumulated knowledge regarding clogging in both vertical and horizontal subsurface flow treatment wetlands. The various physical, chemical and biological factors responsible for clogging are identified and discussed. The occurrence of clogging is placed into the context of various design and operational parameters such as wastewater characteristics, upstream treatment processes, intermittent or continuous operation, influent distribution, and media type. This information is then used to describe how clogging develops within, and subsequently impacts, common variants of subsurface flow treatment wetland typically used in the U.S., U.K., France and Germany. Comparison of these systems emphasized that both hydraulic loading rate and solids loading rate need to be considered when designing systems to operate robustly, i.e. hydraulic overloading makes horizontal-flow tertiary treatment systems in the U.K. more susceptible to clogging problems than vertical-flow primary treatment systems in France. Future research should focus on elucidating the underlying mechanisms of clogging as they relate to the design, operation, and maintenance of subsurface flow treatment wetlands.

In this work we demonstrate the potential of permanent magnet based magnetic resonance sensors to monitor and assess the extent of pore clogging in water filtration systems. The performance of the sensor was tested on artificially clogged gravel substrates and on gravel bed samples from constructed wetlands used to treat wastewater. Data indicate that the spin lattice relaxation time is linearly related to the hydraulic conductivity in such systems. In addition, within biologically active filters we demonstrate the ability to determine the relative ratio of biomass to abiotic solids, a measurement which is not possible using alternative techniques.

Michael Sidnell has drawn attention to the potential for dramatic monologue to be dialogic in ways that dialogue in the theatre rarely is, and he has pointed to a recent proliferation of dialogic monologue in Canadian theatre. This essay will examine the potentially dialogic function of monologue in some contemporary Canadian plays. Questions central to this examination will be: when is monologue dialogic, and what are the effects of dialogic monologue? Considering that the actor often stands indexicallyfor an autonomous subject which is easily conflated with the character the actor is playing, we are interested in looking at how the dialogism of the character's monologue might destabilize subjectivity. Looking at monologues from a range of contemporary Canadian scripts and performances, we will consider how the dialogic configuration of subjectivity affects gender, race, and sexuality. And considering that dialogism may be (as Helene Keyssar has argued it was for Bakhtin) "key to the deprivileging of absolute, authoritarian discourses," we are interested in what specific "authoritarian discourses" contemporary Canadian dialogic monologue deprivileges., Michael Sidnell a attiré notre attention sur le fait que le monologue dramatique au théâtre peut être dialogique d'une manière très différente du dialogue, et il a noté que le monologue dialogique est désormais très fréquent dans le théâtre canadien. Notre essai analyse la fonction potentiellement dialogique du monologue dans quelques pièces canadiennes contemporaines et il s'articule autour des questions suivantes: quand le monologue est-il dialogique, et quels en sont les effets. Considérant le fait que l'acteur est lui-même souvent le signe d'un sujet autonome pouvant être assimilé-identifié facilement au personnage qu'il joue, nous nous attacherons à observer comment le dialogisme du monologue du personnage peut déstabiliser la subjectivité. En analysant des monologues extraits de plusieurs pièces et spectacles canadiens contemporains, nous essayerons de comprendre comment la configuration dialogique de la subjectivité influence la représentation des genres, des races et de la sexualité. Enfin, et considérant que le dialogisme (selon Helen Keyssar, Bakhtin serait d'accord avec cette théorie) dépouille de leurs privilèges les discours absolus et autoritaires, nous nous intéresserons particulièrement aux discours autoritaires que déprivilégie le monologue dialogique canadien contemporain.