Leading Edge Nutrient Removal-design and Operating Development under Stringent Australian Conditions
Abstract:Australia does not have major inland waterways and has sensitive coastal waterways, resulting in stringent effluent quality requirement. Concerns related to salinity have often precluded the use of chemical phosphorus removal, resulting in the widespread adoption of enhanced biological phosphorus reduction. In meeting stringent effluent quality requirements, conservative effluent goals have been essential to provide safety in operation. This has resulted in a number of plants over the past 15 years nearing, or actually achieving, 3 mg/L Total Nitrogen and less than 0.3 mg/L Total Phosphorus without chemical addition. This level of performance has been achieved under the high nitrogen loads experienced in Australia (typically in excess of 55 mg/L) due to the preservation of red meats with nitrate based preservatives. This success has relied on the development of refinements to the existing models and increased understanding of the operation of these types of plants not addressed by existing models nor addressed generally in the literature. Using case examples from successfully operating plants, this paper presents the design and operating features demonstrated to reliably and consistently achieve 3 mg/L total nitrogen and 0.3 mg/L Total Phosphorus without the need for chemical addition.
The three case histories to be presented in this paper represent the progressive development and refinement of Biological Nutrient Removal technology within Australia. The full paper will present complete data, from start-up through current operation. All of these plants are near substrate limited due to the high influent nitrogen concentrations, and performance reported is without tertiary filtration. The design and optimisation of these plants has therefore identified a number of key design features and operating features that appear critical to the achievement of high nutrient removal performance and the achievement of low effluent nutrient concentrations. Specific aspects include: (1) Bioreactor configuration, (2) Aerobic, anoxic and anaerobic mass fractions, (3) Extent of compartmentalisation of zones, (4) Dissolved oxygen set points and profiles, (5) Monitoring equipment, (6) Aeration control, (7) Configuration to minimise power consumption, (8) Greenhouse gas generation including nitrous oxide, (9) Solids settling characteristics and secondary clarifier operation. These issues, and other lessons learned, are presented in the paper.
Document Type: Research Article
Publication date: January 1, 2009
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