Project Profile

CASS™ - Cyclic Activated Sludge System

Location: Forfar, Scotland, United Kingdom

Client: North of Scotland Water Authority.

Type:

Value: U.S. $9 million

Date: Commissioned September 1998

Project Description :
This project was designed to replace and upgrade the existing works utilizing the small footprint CASS™ sequential batch reactor to meet stringent discharge requirements and produce a nitrified effluent with nutrient (Phosphorus and Nitrogen) removal for discharge into the sensitive Forfar loch.

The aerial photograph shows both the old works which treated a peak flow of 246 l/s (without nitrification) and consisted of primary settlement, aeration tanks, biological trickling filters and final clarifiers, and the new CASS™ plant which treats a peak flow of 346 l/s plus 804 l/s storm flow settlement.

This four-basin CASS™ facility was the first of its kind in Scotland, but several more have been built since its successful completion. The CASS™ design features a sophisticated control panel and S.C.A.D.A. system, which control the 12m VARI-SKIM™ decanters amongst the other specialized pieces of equipment. This system will enable process performance data collection between the plant in Scotland and remote terminals throughout the world. This affords the client the advantage of 24 hour per day monitoring.

Average Design Flow: 7,940 m3/d.
Influent Conditions:   COD 455 mg/L, BOD 227 mg/L, TSS 220 mg/L, NH3-N 21 mg/L, P 8 mg/L
Effluent Limits (99%iles): COD 75 mg/l, BOD 10 mg/l, TSS 15 mg/l, NH3-N 3 mg/l, P 2 mg/l, TN 15 mg/l
Actual (avg): COD 32 mg/L, BOD 3 mg/L, TSS 5 mg/L, NH3-N 1.2 mg/L, P 0.85 mg/L, TN 4.2 mg/L

Key Features:
  • Inlet Pumping Station
  • Inlet Works with fine screening & grit removal
  • Four basin CASS™ plant
  • Supplementary Ferric Sulphate dosing system for additional phosphorus removal (if required)
  • Storm tank conversion from existing primary tanks
  • Odour Control Facilities
  • Sludge Thickening and storage
  • Population Equivalent 30,000

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