Nitrification of urine for H₂S control in pressure sewers

Urine separation has great interest from different water boards in the Netherlands. Separate treatment of urine will lead to lower nitrogen emissions from wwtp's with substantial energy savings. Furthermore, it is possible to recover phosphates and remove medicine residues and hormones from urine. In this project, urine collected with urinals and urine-separation toilets, was nitrified in a CSTR. An average ammonium conversion to nitrate of 97% was achieved. The nitrate rich urine was pumped into a small pressure sewer to prevent sulphate reduction. H₂S in the gas phase of the sewer system was reduced significantly. From the required amount of nitrate (for >95% H₂S reduction) the feasibility of urine nitrification for H₂S control was determined. The costs of the concept mainly depend on transport and addition of sodium hydroxide. If urine can be collected undiluted (minimal 3 g N/l) and can be stored in big storage tanks (minimal 10 m³), nitrification of urine can be an alternative for Nutriox addition to pressure sewers.