The introduction of new limits for surface water discharge proposed by the European Water Framework Directive (WFD) and the Dutch regulation (Vierde Nota Waterhuishouding, NWH4), stimulates the research for potential techniques to upgrade the effluent quality of existing Wastewater
Treatment Plant's (WWTP). In particular, in Holland, the national legislation introduced the so-called MTR-concentrations (Maximal Tolerable Risk), including new limits for nutrients (Ntot < 2.2 mg/l; Ptot < 0.15 mg/l). In this paper, research
about the upgrade of secondary effluent of the municipal wastewater treatment plant Horstermeer to MTR-quality, with respect to nutrients, is presented. Therefore, the starting point is an effluent in compliance with modern discharge criteria: NO3-N < 10 mg/l, NNtot
< 14 mg/l, PO4-P < 1,0 mg/l, PNtot < 1.5 mg/l and suspended solids concentration < 10 mg/l. The multiple-targets removal takes place in one single reactor, a discontinuous rapid dual-media filter. In this unit, conventional filtration is combined
with biological nitrogen removal and chemical phosphorus precipitation, resulting in reduced suspended solids and nutrients content down to MTR-quality. Nitrate conversion rates above 3 kgN/d/m3 were established. A removal of phosphorus around MTR-quality has been achieved
but breakthrough of small particulate phosphorus (0.45 μm–2 μm) can cause totalphosphorus concentrations above 0.15 mgPNtot/l. Fractionation of phosphorus has been executed in order to examine the filterability of phosphorus contents within the filtration process.
This fractionation showed slightly different distributions of phosphorus with two different poly aluminium chlorides. The variation of the initial mixing showed no influence on the distribution. At last, the phosphorus content in the different fractions corresponds to turbidity measurements
of those fractions.
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