A E Straume


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The first fully automated commercial facility in the UK to incorporate a membrane bio-reactor (MBR) enables up to 85% of water resources to be recovered for use in the wool scouring process by using high pressure reverse osmosis (RO) membrane technology. The site utilises approximately 13 m3h-1 of clean water on a continuous basis. A zero effluent discharge consent has driven the investment in the on-site treatment system with all wastes being concentrated and tankered away to the local water company. The chemical oxygen demand (COD) entering the process following wool scouring and dissolved air flotation (DAF) reaches 5000 mg/l with a total dissolved solids (TDS) of up to 8000 mg/l.

Supernatant from the DAF process is pumped to the aeration tank of the activated sludge system via an anoxic tank for denitrification. Return activated sludge is mixed with the DAF feed in this anoxic tank and chemical nutrient is added to promote biological growth in the activated sludge system. Following oxidation of the biomass the mixed liquor gravitates to the MBR. This micro-filtration membrane system is rated to remove particles above 0.1 mm and the filtered product is drawn up under vacuum through 24 membrane elements packed with polypropylene based hollow fibres. The separated biomass is pumped back to the anoxic tank as return activated sludge and periodically waste activated sludge is removed from the system to maintain the correct sludge age.

Filtered water from the MBR enters the first stage of the RO plant. The feed is pressurised to 40 bar g by an inverter controlled multi-stage centrifugal pump to maintain a fixed feed flowrate before entering a 2:1 array of pressure tubes each containing four high rejection thin film composite membranes.

The first stage recovers 70% of the MBR filtrate as permeate for re-use and utilisation in the wool scouring process. The concentrate stream from the first stage RO is further processed by the second stage RO plant. A fixed feed flowrate is again maintained onto a single pressure tube comprising five similar membranes but rated at 80 bar g pressure. 50% of the concentrate from the first stage RO plant permeates from the second stage to add to the first stage permeate recovered. The overall recovery of both RO systems in this two stage concentrator is thus 85%. RO permeate recycled to the wool scouring process is recovered at a continuous rate of 11.05 m3h-1 with a TDS of less than 300 mg/l and a COD of less than 10 mg/l.

In addition to a detailed process description, the paper will include a graphical representation of plant performance since commissioning along with details of the methods employed for optimising membrane cleaning frequency and the control of biofouling in the MBR and RO systems. An evaluation of system operating costs including power, chemicals and consumables will also be presented.

Project Details

Client: A E Straume

Industry: Membrane Technology

Application: Recovery of wool scouring effluent utilising membrane bioreactor (MBR) technology as part of the activated sludge system followed by two stage reverse osmosis (RO) membrane Concentration.

Technologies

Membranes
Reverse Osmosis / Desalination

Wastewater Treatment
Effluent Re-Use