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Germantown, Maryland
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Sat Dec 15 2018
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Waste & Wastewater: DAFF Treatment

By The Environmental Group Limited

EGL and it’s team of people have been involved in a number of filtration projects treating water for both potable water consumption and for the re-use of treated sewage effluent. The technology is based upon well proven and reliable designs. This technology combines both the flotation and filtration steps into one compact and efficient process.

How it Works

The untreated raw water is initially dosed with conventional water treatment chemicals and rapidly mixed to improve the solids separation in the flotation stage. The chemically treated water flows into a multi-stage flocculation tank to provide optimum flocculation. Prior to the flocculated water entering the filtration stage it is injected with an air saturated water solution. Suddenly reducing the pressure of the air saturated water causes ‘micro bubbles’ to form. These bubbles attach to the flocculated material and carry it to the surface as a floating sludge. This sludge layer is periodically removed by either a sludge scraper or by raising the water level of the filter.

The flotation stage removes a large proportion of the suspended solids prior to filtration in either mono-media sand, multimedia sand and coal or granular activated carbon. This allows for extended filtration times between backwash periods. The filter operates at a constant water level with the flow controlled by a modulating valve on the outlet.

Backwashing of the filter is initiated by either a reduction in the filtered water quality, the period of time since the last backwash or the filter bed becoming blocked. The backwashing is achieved by using stored filtered water with or without assisted air scouring. The reject backwash water can be stored and returned to the process inlet for recovery. The backwash storage tank can also be used a contact tank for disinfection purposes.

Advantages

  • Compact, integrated process
  • Rapid response to process changes
  • Suitable for high algal laden effluent
  • Can be operated without polymers
  • Can be built using either concrete or re-locatable steel structures
  • The system can controlled by PLC and monitored via SCADA
  • Can produce re-use effluent in accordance with recommended guidelines

Performance

The filtration system is capable of:

  • Treating surface water that will meet the WHO drinking water guidelines
  • Producing treated effluent that will meet the Australian Re-use Guidelines
  • Achievable filtration rates up to 12 m3/m2/hr
  • The surface sludge is approximately 2 – 4% w/w.
  • A power consumption rate of 45 kWhr/ML, excluding peripheral supporting equipment.
  • Based on one backwash per day the washwater requirement is approximately 3% of the raw water feed flowrate.