Part Two – Water with Membranes
Having travelled in South East Asia for several months now, we have learned how people value the environment and go about with the resources they have been blessed with. Sadly, they are not doing a great job. Since water treatment is an area I have got the most experience with, this is the aspect I observe the most. Asia with its populous countries and growing life standard, becomes thirstier and produces more waste water. However, the infrastructure has not managed to cope with this rise in demand, and is lagging behind severely. Water gets pumped out too fast and it returns into the environment without proper treatment. The consequences are clear and the trend is not sustainable. In Europe, we have managed to build large networks of pipes that bring pristine water from a drinking water plant into our homes, and return the waste to well managed conventional treatment plants which in turn put water back into the cycle. This system is called “centralised”, where thousands of households are connected to large plants taking care of water. This has been a costly and slow process, but we had enough time and money. Now in Asia, I don’t think the same can be said. Copying the system built in Europe or America in the past is impractical. In order to tackle this burning issue, we would like to propose an alternative: decentralised water treatment with membranes.
Fresh water is right under your feet!
The most of fresh water on Earth is locked as ice in the polar ice caps. The second largest is ground water. It’s no secret, and many people have got a well to provide for farming and utility purposes. Even the tap water comes therefore quite frequently from the ground. It is usually clean since it’s been filtered by porous rock, however, sometimes it contains undesirable minerals such as Arsenic and Fluoride, and is sometimes contaminated by microorganisms.
Membranes for ground water upgrading
Before you drink this water, it needs to be upgraded. But wait! You don’t need to clean all the water. Two to three liters per day is enough to be upgraded to drinking water (see part one). The rest is fine just as it is. Such a small amount is done easily by a counter top system at home – for example based on membrane filtration – Ultrafiltration, Nanofiltration or Reverse Osmosis. Sometimes carbon or ion exchange might be necessary to complement.
Okay, now to the waste water. Water from your home contains dirt, sweat, poo, soap, dish-washing liquid, washing powder, hair etc. It is mostly still just water, but it can’t be dumped into the environment like that. Using a septic tank is the least that can be done, but it is not enough. Septics are smelly, inefficient and they let dirty water seep into the ground where it contaminates ground water by microorganisms.
Membrane bioreactors for waste water treatment at home
The best available technology for waste water treatment are membrane bioreactors (MBRs). They combine the cleaning power of bacteria and the separating power of membranes. They are not hugely used for waste water treatment as of now, because the current design makes them too costly. If MBRs are well designed and operated correctly, they deliver the cleanest water you can get and all that with a very small footprint (floor size of the unit). Even more interestingly, since water from them is free of “fecal bacteria” and dangerous pathogens it can be used in agriculture to cultivate food crops. If an MBR operated anaerobically(AnMBR), without oxygen, they can transform waste into biogas- a green energy resource. Furthermore, the effluent rich in nutrients can be used in irrigation. How come everyone does not have one already? The answer is: they are not available yet!
The poor man’s AnMBR
At the start of 2016 we started to contemplate the idea to develop a small scale AnMBR (Anaerobic Membrane Bioreactor) with my colleagues from R&D – Roy, Henry and Patrick. The concept was based on an external circulation tubular membranes design with the Helix technology. The plan was to use standardised off the shelf components and minimalist design to keep the cost low and reliability high. In simple terms, every MBR consists of a tank or several, and a filtration unit. The filtration unit is compact and small and can be assembled and shipped worldwide easily on a pallet. The bioreactors can be made from water tanks from polypropylene which are available worldwide already at a commodity price. A skid + tanks + a few hours of final assembly work and the AnMBR is born. We built a prototype of this AnMBR, but haven’t managed to start it up yet.
We proudly presented the prototype at the WECT in Glanerbrug, Netherlands at the occasion of inauguration of Prof. Harry Futselaar, a great AnMBR enthusiast and protagonist. I also presented a poster at the conference of African Membrane Society in Sfax, Tunisia and got some enthusiastic feedback. So the idea is out there, the prototype is existing, but there is nobody to start it up and operate it at the moment. Let us put the idea into the drawer for a moment and when Flo-Bro has got the resources, we will pick it the idea up from where it was left and bring it to life. There are others trying to apply membrane bioreactors to improve sanitation- During Daniel Yeh’s visit in Enschede we discussed his concept and how he applies their design to help India.
Why decentralise then?
Building long pipe networks is expensive and the logistics are challenging. Before water reaches your home, it needs to travel through kilometers of piping and is in fact of excessive quality for most of the purposes.
In case something breaks, many people suffer at the same time.
Sewerage is a massive underground network which often gets plugged by rubbish from the streets and needs substantial maintenance which is also expensive. Since Asian cities are so densely populated and busy, building such large centralised plants is hardly imaginable and breaking up the pavements and roads to build the piping is even more sci-fi-ish. Decentralised systems can be placed in each house, or a neighbourhood can share one. Due to lower distance travelled by water, they are less energy demanding. Being decentralised, they are less prone to calamities. Water produced by such systems can be reused and nutrients recovered. These are in summary the best reasons to go decentralised! Now the challenge remains, to get the systems up and running.
Your water between the membranes
Membranes are a powerful physical separation technology and can revolutionise the way ground water is upgraded into drinking water at home. The waste water that you produce can be treated by membrane bioreactors to a sufficient quality to be discharged onto your vegetables or lawn. AnMBR permeate is a nutritious mix of fatty acids and inorganic ions that will feed the soil bacteria and boost your garden productivity. Excess water will seep into the soil and keep the ground water level topped up. Am I being overly enthusiastic over membranes? Is this concept flawed or Utopian? Let us know in the comments or send us an email!