Dynamic head loss in pilot- and full-scale wastewater sand filtration with phosphorus removal, denitrification, and associated bumping

Abstract

Limitations of the operation of down-flow sand filters were investigated without and with dosages of methanol, ethanol, or acetate for denitrification and dosages of ferrous sulphate to remove phosphorous. The dynamic head loss was developed due to clogging by suspended solids (SS) that originated from the secondary sedimentation tanks including sludge overflow and from SS in primary settled wastewater that bypassed the biological step. The dynamic head loss was also developed from clogging by gas bubbles formed during denitrification, not by the SS produced from cell growth. The dynamic head loss in sand filters after 24 h operation without and with denitrification increased by 0.9–1.3 and 2.3–2.4 mH2O, respectively. The total time of operation was prolonged by 50% after one water bumping, by 75% after two bumpings, and by 85% after six or seven bumpings. Operational time for filter cycles was prolonged by 4–5 h by one bumping in the full-scale and pilot-scale filters. The time of operation depended on hydraulic loading. With a carbon source dosage, one filter cycle lasted 20–40 h at 10 m/h and 60 h at 5 m/h in pilot-scale filters, and 15–27 h at 3.3 m/h in full-scale filters. HIGHLIGHTS Head loss in the main filter bed in denitrification was similar to the total head loss in non-denitrifying filters after 24 h.; Pilot-scale study results were confirmed by full-scale studies.; The dynamic head loss was developed from SS or gas clogging.; Bumping could prolong the time of operation but was rejected due to increased filtrate SS concentration.; Operational time defined the functionality of abruptly gas-clogged filters.;

Keywords

• bumping
• denitrification
• dynamic clogging
• filtration
• head loss
• sand filter