Membranes provide a physical system of solids recovery and the quality of the filtrate is normally almost independent of feed variations. Membrane systems use no flocculating coagulation agents or other additives. The output from a membrane system is split into two streams. A small stream of “concentrate” flow (containing almost all the suspended and dissolved solids in the original effluent) and a much larger “permeate” water stream which is essentially sterile and which can have a COD level similar to tap water. This water is clean and can be used for many secondary functions and indeed not be sent directly to sewer.
Membrane filtration for the treatment of dairy effluent offers the following benefits:
- Main operating savings accrued from the reduction in costs incurred by the Mogden formula.
- Reduced effluent loading
- Effluent processed immediately, no smells!
- Recovery of between 90%-95% of recycled, pure water for reuse in CIP, washdown or discharge to sewer (at the same temperature as the feed water)
- Unlike DAF processes, no flocculating or coagulation chemicals required for treatment of effluent
- Small footprint which is relatively light and compact
The following example shows the estimated costs for a 700 cubic metre per day automatic treatment plant using Ultrafiltration and followed by double Reverse Osmosis (the ultrafiltration permeate is passed twice through an RO membrane to provide very high quality water).
|Factor||Assumptions||£/day operating costs
|Labour||4 hours/day at £15/hr||60.00
|Membrane replacement||3 year life assumed||106.20
|Cleaning chemicals||Sodium hydroxide, nitric acid, sodium hypochlorite||28.00
|Mechanical maintenance||Pump seals, valve seals||31.30
|Cost of effluent treated, £/cubic metre = £0.66||