Solutions

How does this happen ?

How do large, up to one metre long, ropes of agglomerated hair and fibre appear in the process tanks when the inlet screen openings are so small at 3 mm ? The answer is that the hair and fibre material that pass the inlet screens end up in the aeration and MBR tanks and remain trapped there. Some, of course will get ejected in the sludge wasting process but the large majority stays in place. And then this hair and fibre start to ‘weave’ themselves together in the turbulent, aerated water.

The frames that hold the membranes employ vigorous air diffusion at their base, the is sets up an upward water flow ( the scouring action) through the membranes, bringing with it all of the biomass. The hair and fibre rags are also pulled up in the water flow and when they are big enough, the get trapped in the underside of the float sheet membranes as shown in Photo 2 or get wrapped around the hollow fibre membranes as shown in Photo 1.

The trapped hair and fibre agglomerations prevent the correct scouring action and leading the sludge bridging between membrane, loss of permeate, increased trans membrane pressure and eventually a failure to deliver any flow. The scouring action delivered by the sir diffusers continues regardless and all of the scouring will find it’s way through fewer openings, leading to a “excess” of scouring on some membranes. These will fail by tearing. See photo 5

What is the Solution to the Hair and Fibre Fouling in MBR Plants ?

The industry answer is two fold.

• Membrane manufacturers and designers request finer and finer inlet screens with 0.5 mm being specified.This leads to complex screen designs with pre-screens and very high pressure back wash systems. Screening raw sewage to 0.5 mm is pretty unacceptable.
• Operators put in place a regular programme of membrane lifting and physical cleaning, often as frequently as every 8 - 12 weeks. The task of lifting the heavy frames, disassembling them, physically cleaning the individual membranes, re assembly before putting the membranes back into use is also unacceptable. Photos 5 & 6 show membrane cleaning by hand.

If the membranes foul, the consequences are dire. The inflow of sewage does not stop and the plant has no by pass or any facility to discharge at the design rate even if the effluent quality is below par. Flooding of the plant due to loss of permeate means a constant demand for sewage tankers to remove the excess. If the plant floods, then the valuable biomass is lost first as it spills over. Even when the plant is re-instated with clean membranes, it takes some time to get back to full performance due to the lost biomass.

There is a Better Solution…….

Eflo have a great deal of experience in designing and operating MBR plants. They have designed, built and operated some of the largest MBR plants in the Middle East. Recently two plants for Abu Dhabi were completed with capacities of 30,000 and 15,000 m3 per day. For Sharjah a plant of 7,500 m3 per day was built and Eflo have built and delivered numerous small packaged MBR plants. Everyone of these plants uses a standard 3 mm inlet screen and none suffer from any of the air and fibre fouling problems described above. Our operations teams don’t lift the membranes for physical cleaning and Eflo now have experience of operating plants for two years without lifting a membrane. Permeates remain to the design specifications and the trans membranes pressures remain extremely low.

How ?

Eflo have developed a special Full Flow Biomass Screen which is currently under patent pending. It is of a greater opening then the inlet screens, yet it sits downstream of the inlets screens. It’s job is to capture and remove the small and growing agglomerations of hair and fibre before they start to foul the membranes.
The Eflo Biomass Screen is fitted to all of our EfloMBR plants and also retro fitted to plants we are awarded the operation and maintenance (O & M) contracts. A good example of this is the MBR plant on the Palm Jameirah, Dubai. This is a regular MBR plant using flat sheet membranes. It was suffering all of the above hair and fibre fouling problems. The excessive manual cleaning was damaging the membranes and shortening their lives.
Eflo were awarded the O & M contract and immediately Eflo Biomass Screens were fitted. All of the fouling problems ended and in 18 months since commencing the maintenance, not a single membrane has been lifted.
If your MBR plant is suffering for fouling by hair and fibre, talk to Eflo for a permanent solution.

Other Types of Fouling

Scaling by dissolved solids occurs and this is treated using Clean-in-Place chemical cleaning, generally on a 6 monthly basis. The operation of the plant is not interrupted.