sludge buildup

[foodchain]

Organic matter in tanks, grow beds, ponds, etc build up over time. Especially if there's not enough DO or water turn over in a system. Ponds are an excellent example of this.

In order for the bacteria to break it down quickly, it requires DO, low levels of DO are one of the more typical limiting factors in how fast sludge can be broken down into completely water solouble solutions.

So, the million dollar question is....how long does it take? IF the rate bacteria breaks it down is relative to the amount of DO....what is the ratio? And, what ratio at what amount of time?

Since I can't count bacteria, nor have a way to measure it's concentration in a given sample, I can't wrap my mind around a plausable experiment that would answer this.

We all know how to seed a system with new bacteria....and we have all read about the additives you can add to jump start your culture. BUT how do you know when you have enough? Obviously the system as a whole will balance out. But as I read, it seems that the amount of food available AND the amount of DO control the growth and reproduction rate of bacteria.
This is important to know, especially from the approach of sludge control as the bacteria that doesn't require DO breaks it down much slower. So we want the right bacteria, in the right amounts, without spending the extra money/time in over populating them just to have them die back to match the food/DO levels.

Ideas, opinions, and the like welcome. I have always trusted a system to balance..but now wonder if there may have been a more practical way.

[David - WI]

I don't think it's quite that simple, from what little I remember, "sludge digestion" doesn't require very much DO in order to remain "aerobic"... like 1mg/l or something?

But don't the temperature, pH, and composition of the nutrients in the water also affect how the various types of bacteria grow?

On the other hand, it probably is simple in that it's most likely been studied to death; so you may not have to "experiment" as much as "google" to find the answers?


In order to achieve proper digestion without offensive odors, the organisms that are involved must be kept at their highest level of metabolism. This is known as "endogenous respiration" and it keeps the bugs at their peak operating efficiency. http://www.ragsdaleandassociates.com/WastewaterSystemOperatorsManual/Chapter%205%20-%20Digesters.pdf


Generally, higher temperatures produced higher fractions of nitrifiers and denitrifiers in the biomass.
Total sludge production increased from 0.16 to 0.48 g/d as temperature was decreased from 30 to 10°C. This was partly due to the corresponding decrease in endogenous respiration rate from 0.14 to 0.02 1/d.
http://dspace.hil.unb.ca:8080/handle/1882/35660

Lower temperature = less "endogenous respiration" and more sludge?

[urbanfarmer]

Yes, but how does it taste?

[Eleven11]

Good digester article. A little hard to absorb though. Know of any documentary videos on the topic?

I added an auxiliary sump that is connected to the main sump by a siphon line so the water in the aux sump rises and falls with the sump tank level and gradually, the particle solids collect in the aux sump which is now a sort of digester. It doesn't look like sludge in the water... more link silt... very light weight brown particles ... settled like sand dunes. Some worms have settled in there now and live in the brown dunes. The DO level should be pretty high since the worms appear to be ok. The water in the aux sump is constantly cycled in and out, mixing with the oxygenated water from the fish tank overflow. I'm not sure if the dunes are actually disappearing (being digested) though.

[urbanfarmer]

Nice documents. I will have to read through them when I get the chance.

[foodchain]

Temp always plays a major role in bacteria. But we are getting off track from the original question.

TIME....of course this is relative to DO, temp, particle size, etc. But there must be an algorithym or at least a general consensus of how long it takes to digest...say a leaf?

Your right, it's not so much an experiment as it is a google exercise. BUT it has already been proven in many of my other posts, that just becuase it's on the net or in a book, doesn't mean it's accurate. Possibly accurate to the best of anyone's knowledge when it was written, but has since been proven an error.

Ideally, no one wants sludge build up or excessive nutrients in a system....I get that. But as I push the limits of size and production volume I find that the systems get less the optimal readings and buildup.
Which then in turn lead me to asking off the wall questions like this. Obviously anyone can clean it out and keep on going that's the easiest way. But when we take this topic and we apply it to a farm pond or small lake...those bodies of water slowly fill themselves in over the years. The excess nutrients never truly become water soluable, and eventually dish in the bottom of the pond making slightly shallower each year.

[keith_r]

i was trying to wrap my head around your question yesterday...
if you're "pushing the limits" of your growbeds carrying capacity from a lightly stocked, growbed only (for filtration) backyard system..say towards a more "commercial" type system, i think some method of solids removal should be employed.. these solids could be used in the dirt, or even to make a "tea" for foliar sprays.. some people believe that any aquaponics system must have some type of solids removal..
there's a spreadsheet that dr. james rakocy made that breaks down how many square feet of growbeds are required to handle a set amount of fish food - which would determine your fish load, but even with that, he recommends periodic cleaning of the gb's..i think he's trying to get a commercial system going - i don't think there are really any commercial ap systems running.. at least any "self-supporting" for profit places relying solely on the production of veggies and fish...

but to measure the miniralization of the solids? thats one of those "how long is a string" questions.. it will certainly depend on tons of variables.. what kind of feed is being used, what kind of fish, what else is in the system like worms, gammarus, and other creatures living in the system, not just the beneficial bacteria, the highest concentration of which is "growing" on surfaces..

[belikeh2o]

Good question.. I'm looking to use the sludge in my system for further nutrients.. Eventually I want to have a "cell" which processes sludge in a bio-gas digester and powers the system with methane. John Todd uses anaerobic digestion to complement the aerobic action going on and further close the loops in which waste is created. If you have a sludge excess or creation problem the problem is more biotic deficiency in dealing with excess nutrients. I just go back to the river model in nature and think where in a river this process will take place and what processes are involved in creating and sequestering nutrients and mineral.

The digestion is done in two stages I believe.. The sludge is run through a tank with introduces lots of dissolved oxygen in the first stage if I'm right, and this takes care of most of the solids separation and nutrient cycling before it goes into an anaerobic digester for further processing and power extraction

[dead_sled]

The digestion is done in two stages I believe.. The sludge is run through a tank with introduces lots of dissolved oxygen in the first stage if I'm right, and this takes care of most of the solids separation and nutrient cycling before it goes into an anaerobic digester for further processing and power extraction

That is how I understand it. That is how the process works at a waste water treatment plants, more or less. I have seen sludge digesters that work on a timed cycle. DO might also be a good way of controlling the process. Waste water plant operation information should be full of good guidelines. I worked on the controls at a ww plant that used the digester gas to heat the sludge during the winter. I can't remember what they considered the optimal temp was for digesting.