Optimising the Treatment Performance of the Otorohanga Oxidation Pond System
Annual Conference
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A normal procedure when improving performance of a wastewater treatment plant would see an engineer lead the design and over-view the construction, later handing the plant back to the operators and not having any further involvement. In the case of the oxidation pond-based treatment plant that serves Otorohanga the author has been privileged to have continued the over-view for at least 9 years and to implement further improvements based on sound monitoring and analysis of performance. All of the improvements have been based on a “simple is best” philosophy.
When the author was engaged late in 2010 the treatment plant was in a sorry state and had a high level of non-compliance with the (then current) Resource Consent. In addition there was less than a year before an application for new Resource Consent(s) had to be submitted. By the time the hearing for a new resource consent was held the plant had been desludged, upgraded and was operating at an acceptable level at a modest upgrading cost. A very practical consent with a 25-year life was secured. The upgrade included installing curtains, increasing the water depth and modifying the wetlands.
Through his involvement in the ensuing years the author has been able to gain a high level of understanding of the key drivers of success with oxidation pond treatment systems and has been instrumental in introducing some further improvements to fine-tune the operation. In particular the installation of a bottom-deployed diffused aeration system and further desludging of the oxidation pond have improved the consistency of compliance with the resource consent conditions. A trial has been introduced to deal with the daily mass-load of phosphorous in the discharge.
Through this paper the author gives his personal viewpoint on the importance of managing solids in the oxidation pond in ensuring reliable treatment with minimal operating costs and shares the knowledge that he has gained. The paper also gives information on the initial results from the trial to reduce phosphorous levels in the discharge. The intention is to improve the overall understanding of the key drivers of successful improvements to old oxidation ponds which can still provide effective treatment of domestic wastes well into the future.