Full-scale application of partial nitritation and anammox in a single suspended-growth sequencing batch (SBR) reactor presented here confirm the process suitable for removing nitrogen from ammonium-rich wastewater with low concentrations of BOD and suspended solids: details of simple and robust process control based on online ammonium or conductivity signals are discussed by describing the full-scale startup at three municipal plants (five reactors in total). Ammonium oxidation rates of up to 500 gN m(-3) d(-1) with conversion to N2 of over 90% are achieved in a full-scale plant, but pilot results indicate that significantly higher rates are feasible. With continuous aeration at dissolved oxygen concentrations <1 mgO2 x L(-1), the nitrite oxidation and the anammox reaction occur simultaneously, allowing increased overall performance and simplified process control compared to separate aerobic end anaerobic phases (segregated either temporally or in different reactors). Sedimentation of the sludge requires special attention only during startup. Although the observed N2O emissions were slightly higher than in conventional nitrogen removal, the overall greenhouse gas emissions were lower, mainly due to energy-saving.

A pilot-scale hospital wastewater treatment plant consisting of a primary clarifier, membrane bioreactor, and five post-treatment technologies including ozone (O3), O3/H2O2, powdered activated carbon (PAC), and low pressure UV light with and without TiO2 was operated to test the elimination efficiencies for 56 micropollutants. The extent of the elimination of the selected micropollutants (pharmaceuticals, metabolites and industrial chemicals) was successfully correlated to physical-chemical properties or molecular structure. By mass loading, 95% of all measured micropollutants in the biologically treated hospital wastewater feeding the post-treatments consisted of iodinated contrast media (ICM). The elimination of ICM by the tested post-treatment technologies was 50-65% when using 1.08 g O3/gDOC, 23 mg/L PAC, or a UV dose of 2400 J/m(2) (254 nm). For the total load of analyzed pharmaceuticals and metabolites excluding ICM the elimination by ozonation, PAC, and UV at the same conditions was 90%, 86%, and 33%, respectively. Thus, the majority of analyzed substances can be efficiently eliminated by ozonation (which also provides disinfection) or PAC (which provides micropollutants removal, not only transformation). Some micropollutants recalcitrant to those two post-treatments, such as the ICM diatrizoate, can be substantially removed only by high doses of UV (96% at 7200 J/m(2)). The tested combined treatments (O3/H2O2 and UV/TiO2) did not improve the elimination compared to the single treatments (O3 and UV).

Fifty years ago when only BOD was removed at municipal WWTPs primary clarifiers were designed with 2-3 hours hydraulic retention time (HRT). This changed with the introduction of nitrogen removal in activated sludge treatment that needed more BOD for denitrification. The HRT of primary clarification was reduced to less than one hour for dry weather flow with the consequence that secondary sludge had to be separately thickened and biogas production was reduced. Only recently the ammonia rich digester liquid (15-20% of the inlet ammonia load) could be treated with the very economic autotrophic nitritation/anammox process requiring half of the aeration energy and no organic carbon source compared to nitrification and heterotrophic denitrification. With the introduction of this new innovative digester liquid treatment the situation reverts, allowing us to increase HRT of the primary clarifier to improve biogas production and reduce aeration energy for BOD removal and nitrification at similar overall N-removal.

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