Sunday, April 3, 2011

Learning to Deal with Wastewater:

Sewerage engineering practice operates within a paradigm in the sense that the engineering community reached a consensus earlier last century that a narrow range of treatment options would form the basis of its subsequent practice. This consensus prevents serious consideration of alternative technologies and constrains innovative research at a time when the paradigm is no longer adequate in a changing environment where sustainability is crucial. A technological revolution is required but is unlikely to emerge from within the sewerage engineering community unless that community recognises that their existing paradigm is inadequate to the needs of the community and the broader environment.
For the past decade Western Bay District Council engineers have been accused of choosing a sewage treatment solution from a small range of technologies that are consistent with the water-carriage of the sewage (in pipes) to a waterway for disposal. Conventional treatment methods are classified into stages. The preliminary stages involve grit removal and the screening of gross solids from the sewage. Primary treatment removes some suspended solids from the sewage by sedimentation in tanks. Secondary treatment utilises micro-organisms to break down organic matter, mainly with biological filters or activated sludge treatment. All of these processes had been invented and were in use as early as 1920.
Yet today alternative sewage treatment technologies that have proved to be effective in the past have largely been dropped from the engineer's code of practice despite their public appeal. Sewage irrigation and other forms of sewage farming were successfully used in the nineteenth century and remnants of those early farms still operate today in the 21st Century such as the Werribee sewage farm in Melbourne. For the most part though, these technologies have been abandoned as victims of a wastewater paradigm.
Engineers and health inspectors alike within this paradigm are also becoming increasingly dissatisfied with conventional primary and secondary treatment methods. Secondary treatment plants are expensive to build, operate and maintain. They are land intensive which is a problem and communities like Maketu are forced to install secondary treatment on prime real estate near estuaries and ocean outfalls. They also create a large amount of bi-product called sludge which is difficult and costly to deal with. The problem is exacerbated by the tendency for viruses and heavy metals to concentrate in the sludge making alternative disposal forms like incineration and reuse as fertiliser potentially hazardous.
It can be argued that the debate of this wastewater paradigm from last century is outdated and a new paradigm is emerging as the debate is polarised. In a recently published article in Te Puke Times March 23, 2011 community leaders of Maketu have once again demonstrated a united position objecting to council’s application for resource consent for a reticulation sewage scheme yet agree doing nothing is not an option. What did they do? they provided council and engineering staff an alternative a ‘bio-filtro’ as a win/win option.
It is not my intention to take sides but Mayor Ross Paterson is quoted as saying “council investigated an alternative wastewater treatment method recently suggested by some Maketu residents but it was not convinced it would satisfy resource consent conditions”. So after a 12 year journey Western Bay District Council made a decision to construct a $16.3 million sewage system for Maketu and Little Waihi based on an outdated paradigm.   

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