Question 1: Design for a water treatment plant taking 15MLD of water from a lake at 750mAOD, passing it via settlement tanks on to pressure sand filters, and from there into a chlorine contact tank to TR60 of 30 minutes HRT and 1m water depth at 575mAOD. Distance from Lake to CCT is 1500m. Fall on ground is constant all along this 1500m.
Question 2: Numbers and diameters for circular settlement tanks and sand filters, external and internal dimensions of CCT, theoretical and actual pipe diameters sizes will be required to be computed as a minimum.
Rules of thumb for design:
A) Surface loading settlement tanks 1m/h
B) HRT settlement tanks 2h.
C) Max diameter settlement tanks 30m.
D) Surface loading sand filters 15m/h.
E) Sand filter depth 2m.
F) Max diameter sand filters 3m.
G) Static head needed for sand filter operation 10m.
H) Superficial velocity pipe-work 1.5m/s.
TLAs:
AOD: above ordnance datum
HRT: hydraulic residence time
CCT: chlorine contact tank
MLD: megalitres per day