We often say we operate in Leonardo da Vinci Renaissance Mode – given our odd ‘portfolio of diverse services’. But as much as the Chief Engineer does not like to work with mortar, cement, or any other slimy substances I tried to avoid pondering about the intricacies of living beings and chemicals so far.
But slimy, smelly species were to strike back.
For two years we could confirm with confidence that the water in our underground water tank / heat sink does never smell. Until two weeks ago when the water appeared a bit turbid and there was the signature ‘rotten eggs’ smell of hydrogen sulfide.
Water in ponds can ‘die’ – due to eutrophication: Algae bloom due to too much nutrients, die, and their decomposition by bacteria consumes all the oxygen in the water. This can kill fish and other species who need the oxygen.
Since the tank is dark there are no algae but there might be other biomass, subject to decomposition. The most recent rebuilding of the solar collector and brine piping has probably invited some curious or suicidal life-forms.
Researching cisterns in a German forum (‘The water in our cistern stinks’) I learned the following:
“Clean your gutters and check your filters.”
“Install an air pump to supply the bacteria in the water with oxygen. Otherwise there will be anaerobic decomposition, such as turning sulfate into sulfide. The pump resolved this issue within two days.”
“Use chlorine, as for swimming pools.”
“Absolutely don’t use chlorine – cisterns are designed to work without intervention. We use a cistern for twenty years and never had to use chemicals.”
“If the black layer of mud at the bottom of the cistern gets too thick there will be anaerobic decomposition.”
“The black layer of mud at the bottom of the cistern is like a natural sewage plant.”
“Our cistern smelled, too, and we found six dead birds at its bottom.”
Insights are somewhat contradictory but there were more accounts of people advocating the additional supply of oxygen and otherwise letting the bacteria do their work. Proper filters and sealings should prevent the invasion of animals of course.
We still wondered about the coincidence of the H2S accident and recent repairs – was it only due to a sudden invasion of (more) worms, snails, and frogs because of some pipes that were open for a short period of time?
But several users reported that a small amount of brine from their solar collectors had trickled into their cisterns and gave rise to the rotten eggs smell. With cisterns brine could be collected by the gutters, from leaky collectors mounted at the rooftop.
And yes – we had a leak in the new part of the brine piping. The Chief Engineer had heroically cleaned the emptied tank and used the ‘synergy effects’ of being able to do some other maintenance.
A few days after having refilled the tank the water showed turbid streaks again – and we finally spotted the leak in the new part of the brine piping. Now it is leakproof again!
The good thing finally is:
- It all boils down to simply following ‘cistern best practices’.
- The smell provides for a sensitive early warning systems that signals a leak in brine piping.
And we have a new gadget now:
Why is brine so detrimental? Brine used for solar collectors contains about 40% ethylene glycol – frost protection. This provides a feast for bacteria – like sugar. On airports the fluid used for de-icing airplanes is collected and then decomposed by bacteria in a biological sewage plant. It seems that in a tank bacteria reproduce like hell, die, and are finally decomposed anaerobically when there is no more oxygen left.
Tiny amounts of brine alone seem to be suffcient to trigger that chain reaction within days – whereas the occasional earth worm did not do any harm in the past years. But blowing oxygen into the tank with this tiny air pump obviously made the chemical reaction (and the smell) stop.
We hope we will be able to keep the right variety of bacteria happy in the future rather than fight them!
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Edit: As I have asked about the treatment systems on airports: Treating glycol runoff from airport deicing operations
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