Clogging of pipes by struvite is a common problem happening at biogas plant, yet it still has no environmental friendly solution to solve this problem until now.
Generally, it can be solved by adjusting its pH or the ratio of the three elements: magnesium, ammonia and phosphate (1:1:1), however for biogas plant which operate at pH 7, it is hard to adjust the pH as it will affect the bacterial activity and manipulate the ratio of the three elements need additional chemical which is an added cost to the project. So, i would think of there must have a better and cost effective approach to solve this problem effectively.
Some people suggested to reduce the amount of elbow, tee etc., but this is very hard and sometimes it can't be avoided, moreover, struvite also generated at straight pipe if low flow occur at there. So, this method is not feasible to do so.
Another approach to solve this problem is by interfere the electromagnetic field of the flow in the pipeline, however there is no track record on using this approach to wastewater containing pipe other than clean water/tap water.
Besides, as biogas is a renewable energy which has environmental friendly system, therefore chemical is not suitable to use in our case and most importantly it will affect the bacterial activity to generate biogas.
Lastly, a simple mechanical approach by using water jet to wash out the struvite from clogged pipelines. This approach can only applied if the clogging of pipeline noticed at very early stage where thin layer of struvite is form. This approach is not feasible if the built up struvite is thick, where it is very hard to remove even though by shovel aided with hammer.
Therefore, i'm appreciate if anyone can share some ideas to solve this problem and make biogas sector get more smoothly.
Can you explain your process a little better for me. Is the clogging in a specific place in the plant flow?
I am assuming you are using a digester of some sort and collecting the gas? Is it in the gas piping or is there some sort of "waste" flow that is plugging?Could you explain that?
I was involved in making gas from woodchips and we had problems with tar plugging pipes but I am not familiar with Struvite.
Did you say it formed in low flow areas? Not in high flow? Is there a way to recycle some of the product flow back to increase the flow through the troubled areas ?
Does heat or cold effect the formation of the crystals?
Yes. It is clogged at specific place which i mentioned reduce flow area or stagnant flow area it will have high possibility to form struvite. Area where there is high kinetic energy (high turbulence), struvite formation also can occurs.
We are using palm oil mill effluent as the substrate for the biogas digester to generate the biogas. This substrate contains the 3 minerals (magnesium, ammonium and phosphate) for struvite formation. There are many kind of clogging depending on the mineral in the wastewater, for my case is struvite (NH4.MgPO4.6H2O).
There is another precipitate that could form a crystalline scale within the pipe is Vivianite precipitation (purple color). If your wastewater contains Iron(II) ion, then this precipitate is possible to form.
Therefore clogging of pipe by minerals will only happen at pipe that convey wastewater provided that the wastewater has the content of mineral for crystallization.
Regarding to your problem, you may send your crystal sample to the lab for testing of its components. First of all you need to determine your crystal is what kind of crystal and then the parameters that make it to form. You may find out its component and send your sample to lab for testing. The following link describes another kind of clogging. Link
Low temperatures foster the environment for struvite formation.
Examples of area that form struvite:
- Anaerobic digesters
- Places where there is high kinetic energy (high turbulence)
- Pipe connections – especially elbows
- Pumps are a prime location
- Internal pumping components
- Plant overflow box of the anaerobic digester
- Wastewater Sludge transfer line
- Plant Centrifuges
- Rollers of the Belt Press
For experts, please help him if you have similar case.
Charles, I have no experience with your process, but have a couple of suggestions.
Is it possible to add a process ahead of the clog prone areas to intentionally form the struvite? somewhere easily/cheaply cleaned, with the effect of robbing the fluid of the constituents before they form in "expensive" locations of the process? Basically create the BEST conditions for struvite, and isolate it from your process.
In my area, we deal with hard water, and plumbing fixtures suffer a buildup of lime which slows things down and clogs small orifices like shower heads. Our newest shower head, instead of having orifices drilled in metal, has the orifices molded in a rubber membrane which is supported by a metal plate with holes for these rubber orifice "nipples" to poke through. Now, if I notice a clog forming and the jet of water stopped or going sideways, I just rub my hand over the the nipples and flex them, cracking the lime scale which then gets rinsed out.
Is it possible to make some of the plumbing using flexible pipe instead of rigid PVC (what your photo looks like) allowing you to crack the struvite formations loose while they are still thin?
Maybe pulsing a higher pressure to stretch the pipes enough to crack the struvite?
Or possibly a double wall system, rigid on the outside, with rubber pipe inside, and pulsing a high pressure in the in-between space to collapse the inner tube to crack the struvite?
Flexible piping also eliminates some elbows, right?
Nails are sold by the pound, that makes sense.
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