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Authors
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Sikosana, M. ; Randall, D. G. ; Blottnitz, H. von
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Title
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A technological and economic exploration of phosphate recovery from centralised sewage treatment in a transitioning economy context
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Date
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26.04.2017
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Number
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53006
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Abstract
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Phosphate is one of the substances which wastewater treatment works (WWTW) have to lower in order to meet the <br />South African regulatory discharge standard of 1 mg/L. Wastewater is increasingly viewed as a ‘water-carried waste’, <br />presenting opportunities for resource recovery. South Africa has commenced its transition to a low-carbon and resource-<br />efficient economy, all whilst it struggles to provide universal access to basic needs and is faced with massive infrastructure <br />maintenance as well as upgrading backlogs in the sanitation sector in particular. Although phosphate recovery methods <br />exist, there is little evidence to indicate that these techniques would be economically viable or socially accepted in South <br />Africa. This paper explores the potential for centralized recovery of nutrients, through the conceptual design and techno-<br />economic pre-feasibility assessment of two phosphate recovery options, at the largest WWTW in the Western Cape, South <br />Africa. This assessment revealed that the digestate stream at the 200 ML/d Cape Flats WWTW (CFWWTW) has the <br />potential to produce ~470 kg/d of struvite fertilizer, whilst recovering 4–8% of the plant’s costs in 20 years. When contrasted <br />with the more familiar, yet less sustainable, chemical precipitation process, low-grade and high-grade struvite production <br />establishment costs are 10 and 25 times higher, respectively. Still, to reduce effluent phosphate loading to within regulated <br />standards, the low-grade struvite production option at an estimated net present cost of R25.4 million over a 20-year lifetime <br />is more affordable than chemical precipitation at a net present cost of R51.2 million. Low-grade struvite production is <br />thus concluded to be technically feasible and the economically most affordable option from a lifecycle-costs perspective. <br />Although it is a simple process, it is not cheap. Municipalities will need to consider the lower operating costs, as well as the <br />environmental benefit of producing a useful phosphate fertilizer, over the immediate capital investment, if they decide to <br />install such an operation
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Publisher
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Water SA
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Wikidata
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Citation
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Water SA 43 (2017) 343-353
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