Perhaps, like me, you hoped to never have to worry yourself about the details of the trip that the contents of your toilet make. However, if I have had to learn about it, then so dear reader should you! Thus I implore you to read on, and maybe you will find you are not wasting your time after all.
In this blogpost I will share with you three problems faced by the scrumptious world of sewage, and the possible solutions which I learnt about at the Stockholm International Water Institute conference.


The World Water Week conference center

The NEST water hub Switzerland

Let us begin our journey of curiosity at the City Conference Center, Stockholm. Oddly enough the next stage of our trip begins with the flush of a toilet. Urine for a treat.
The water from toilets sinks in the drain pipes and is mixed together, beginning its journey towards the sewer system. Yet, here lies the problem: by mixing the wastes together it is difficult to efficiently recycle valuable substances.
Instead, the water can be separated at the source and then treated accordingly to its type. This is what it has being discussed in the room above.
Research into how to best split and treat the different wastewater is being done at the NEST water hub Switzerland. The hub consists of a house in which all the waste water types (black, grey, urine) are separated and sometimes combined, for example what used to be shower water could be reused to flush toilets. By separating the wastewater and either reusing it or treating it separately the whole system can be more efficient, sustainable and save energy.


Wastewater pipes at the NEST hub, switzerland [Photocredit: Empa/Eawag]

Separated sewer system

If you listen carefully you can hear the drizzle of rain outside (if it is not raining, please imagine it is). This rainwater is collected by the drains and joins the sewage.
Historically sewer systems have collected both domestic sewage and rainwater, meaning that the latter is often treated even when it doesn't need to be. This is inefficient and leads to higher costs and lesser environmental benefits. If instead the sewer system was separated between rainwater and wastewater, several advantages could emerge.
With a separate system, unpolluted rainwater could be used as a resource and any drainage overflow would not pose as hazard, because there would be no sewage rising from the drains.
Although, some disadvantages do arise: implementing the new system will be costly and disruptive. Ultimate decisions to use a separate system depend on cost, long term planning and trade-offs.


Residential stormwater drainage

A peculiar fertiliser

And finally we arrived to the end of the system, where all excess (after treatment) is either deposited into water systems or incinerated. However, neither of these solutions are ideal as one pollutes the water system and the other requires lots of energy.
At the information stand of UNEP (I admit I only first went there for the free memory stick), the environmental branch of the UN has outlined several solutions to this problem. One such solution is reusing the fecal matter as a fertilising sludge. This is done by treating the sewage with an anaerobic process (anaerobic means no oxygen involved), dewatering it, then disinfect it (through prolonged alkaline stabilisation). During this time it is injected into the sludge to form 30-50 percent of the substance. This helps raise the alkaline levels and remove any pathogens. Finally after 30 days of curing the sludge is ready to be used as a fertiliser... Delicious!

Let's get real

So now that we have have examined some of the main problems faced in the sewage sector what conclusions can we draw from them? Well, perhaps one might be that the reason I was assigned to so many fecal related seminars was because someone was trying to send me a message. Nonetheless some more important conclusions may be what these innovations hold for developing nations, where they will have the largest impact:

  • In some regions which lack any real sewage system, setting up one which separates waste at its sources could allow communities to begin a more sustainable future.
  • In flood prone regions of the world, separating rainwater will prevent the spread of diseases when the sewer system is overloaded.
  • The recycling of fecal matter into a fertiliser can help famished regions grow more crops. Thus changing our approach towards waste could provide a brighter future for many.

Perhaps sewage is not that bad after all... unless you decided to read this blog while eating dinner.

Laatst aangepast op: 10-07-2024