A technological, economic and social exploration of phosphate recovery from centralised sewage treatment in a transitioning economy context
Phosphate is an important, non-substitutable nutrient for all life forms and is essential in ensuring universal food security. In the past, waste water treatment works (WWTW) typically installed effluent polishing technologies to eliminate phosphate and lower concentrations of both nitrogen and phosphate to below regulatory levels. More recently, there has been a global shift towards treating waste water as a "water-carried waste", presenting opportunities for both nutrient and energy recovery. South Africa is yet to embrace this shift, as it battles to provide universal access to basic sanitation needs and is faced with massive infrastructure maintenance and upgrading backlogs in the sanitation sector. Mature phosphate recovery technologies that produce high quality struvite for use in food production do exist. However, there is little evidence to indicate that similar phosphate recovery techniques would be economically viable or socially accepted in South Africa. Therefore, this dissertation sets out to investigate the viability of a simpler and cheaper phosphate recovery technology. The dissertation addresses the hypothesis that the South African market is better suited for low quality struvite for use in secondary (non-food) markets and that this would be cheaper than both traditional chemical precipiation (phosphate elimination) methods and high quality struvite production. This dissertation attempts to answer two key questions derived from this hypothesis by means of two separate methodologies. A qualitative methodology explores socio-technical issues to understand the potential of sewage-recovered struvite in the South African markets. This sets out to explore: What space there is for fertilizer production (such as struvite) from human waste in the South African markets? The second research component uses standard engineering economic methods, to investigate the potential for centralized recovery of nutrients through the conceptual design and a techno-economic pre-feasibility assessment of two phosphate recovery options at the largest WWIW in the Western Cape. These options are contrasted with a more traditional chemical precipitation process.
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