along the same lines, making it possible to recover large volumes of phosphate, as well as significant volumes of biogas. It is recommended that biofuel production from land-based crops be replaced as far as possible by biofuel production in algal farms along coastlines, not only because on land it competes with food production and scarce irrigation water, but also because algae make more efficient use of the available phosphate. 55 4. Recovery of phosphate from bio-energy waste streams An increasing amount of energy is being derived from biomass, either by biomass fermentation or by biofuel production. Bio-energy production does result in waste (i.e. ash, chars or residues after fermentation). Phosphate is accumulated in this waste which is a potential source for phosphate recovery. Several routes for phosphate recovery are currently being investigated (Schoumans, 2010). Traditional waste burning methods will be replaced in the near future by other more energy yielding methods (gasification, pyrolysis, torrefaction). Although the focus is on improving the performance of the energy production, new lines on phosphate recovery are being entered. One of these lines is the char (biochar) that remains after manure pyrolysis. This char can be reused as a soil phosphatecontaining amendment. As a soil amendment, biochar improves the soil condition, and returns the phosphate extracted for biomass production thereby closing the agricultural P-cycle. Biochar acts as a sink for atmospheric carbon dioxide as the carbon is fixed strongly into the biochar and thereby delays oxidation and subsequent CO2 production. Last, but certainly not least, ash from burning waste does contain a considerable amount of phosphate and it is a potential source of phosphate. Selected ash is used as a phosphate source. One of these sources is ash from burning sewage sludge. Currently about 30-50% is recycled but there are prospects to increase this to 90% re-use (W. Schipper in Smit et al., 2009). 6.5 Recommendations Increased consumption and the resultant future scarcity of phosphate resources are good reasons to move on to a more sustainable use of phosphate: Geological/Geo-political: the Netherlands is fully dependent on the import of phosphate from abroad, and the worldwide resources of phosphate are limited. Economic: future phosphate prices are likely to remain high at 50 – 100 US$/ton, which increases the cost of fertiliser and subsequently of animal feed prices. Economic/Environmental: elevated phosphate prices have increased the economic feasibility of different forms of phosphate recycling. Environmental: the need to balance input and output (soil balance) to reduce nutrient losses to surface water and groundwater in order to meet EU water quality targets. Pagina 64

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