Proceedings

Tertiary treatment of waste water is becoming the standard in order to meet ever stricter discharge levels for organic matter, solids, nitrogen, phosphorus and metals. Sand filtration has proved to be an effective method to meet most of the discharge levels. In-line coagulation extends the application with the removal of soluble phosphorus and colloidal solids.

Applying tertiary sand filtration paves the way to use quaternary treatment processes to either meet bathing water directives or to reuse effluent. UV technology is such a process which proves an effective bacteriological barrier while highly energy efficient in combination with sand filtration. Long term results of different waste water treatment plants, operated in the Netherlands and Sweden, equipped with sand filtration and UV technology, are presented. Optimized continuous filter plants, equipped with dedicated monitoring and control features to improve the transmittance of the filtrate, have been in operation for over 8 months. The results indicate the impact of transmittance on the
energy efficiency of the UV plant. While secondary waste water is typically characterized by transmittance levels in the range of 40 – 45% T10, sand filtration can raise this level of transmittance to 60 – 65% T10. With a major impact on the required specific energy input in Wh/m3
for UV treatment.

Simultaneously both investments, maintenance and lamp replacement costs are decreased. Collected field data are presented to support these findings.

The combination of sand filtration and UV technology showed excellent final effluent quality for nutrients, solids and bacteriology at a competitive costs level. The extra CO2 footprint is low, while the effluent quality meets the requirements for discharge in bathing waters and/or to reuse the water.

Keywords
Tertiary filtration, phosphorus removal, Sand-Cycle, continuous filtration, UV technology, water reuse