[VoxAure]

I've built and am currently maintaining a liquid-phase digester at home. The system is simple: waste food is blended into a slurry before it goes into a 55 gallon barrel, bacteria digest the food, aerator nozzles provide O² to the bacteria, and the system produces raw nutrients. Liquid is drawn off the top and added to water sprayers, while undigested sludge is drawn off the bottom and tilled into the soil.

I'll be photographing and logging the various properties of the digester and putting them online as a demonstration of chemical analysis. I'll also be putting it in my resume under Oh God Someone Please Hire Me.

My bacteria colony was started with 1L of bacteria from a local wastewater treatment plant and I'm already 2 weeks in, with what appears to be a healthy digester. Of course, without any testing methods, all I can tell is that it hasn't been taken over by mold yet. That's like saying my car is in good repair because it's not on fire.

Help me design some tests to run!

I've already got plans for some tests, but I want to check their realistic viability.

• Total Suspended Solids
• Total Volatile Suspended Solids
• pH
• Temperature
• Viscosity
• Plant Test
• Nutrient Concentration

TSS and TVSS will be simple. Pour a volume of the liquid into a coffee filter, dry and weigh it, then stick it in a kiln until it's reduced to ash and weigh it again. This will give me a g/L number and won't take too much time or equipment.

pH, Temperature, Viscosity should all be fairly easy as well. Both pH and temperature meters are cheap, and viscosity can be done with a 5mm hole in a bucket.

Plant Testing will be done with a matrix of potted plants, and it'll be the long-term test for the digester. Unfortunately, it's going to take months to get results from this test and I'm hoping for something a little more relevant than plant measurements.

Nutrient Concentration is tricky - normally a test for Phosphorus concentration would be expensive and very accurate, but I don't need either of those. My current plan is to take a sample and use NaOH or HCl to titrate it to a certain pH. From there, I can calculate the buffering ability of the liquid and use that as a rough judge of concentration.

Does anyone have ideas, suggestions or tips? I'm all ears.

[billnotgatez]

I am curious about the odor mitigation?

[Arkcon]

Since you intend to release microbial digested products to the environment, I'm most interested in how you will mitigate bacterial load, and quantitate that.  Just because you're sure that you're not releasing pathogens, doesn't mean you get to dump bio-burden that could leach or runoff to outside of your property.

[VoxAure]

I am curious about the odor mitigation?

Hasn't been an issue so far. It's got an odor, but it's most noticeable when aerated and even then it's quite tolerable. Less "rotting garbage" and more a "freshly turned dirt" sort of smell.

Since you intend to release microbial digested products to the environment, I'm most interested in how you will mitigate bacterial load, and quantitate that.  Just because you're sure that you're not releasing pathogens, doesn't mean you get to dump bio-burden that could leach or runoff to outside of your property.

I'm not 100% sure how to deal with what you've mentioned, but here's my first impressions:

Bacterial load should be quite variable, since the organisms I seeded the tank with are able to survive temporarily in anoxic conditions (that's why they survive being aerated only 2x/day) I expect them to remain the dominant bacteria there unless there's something I'm missing. Periodically starving for oxygen helps them out-compete most other aerobic bugs, and refreshing the oxygen content helps keep them alive enough to out-compete molds and anaerobic bugs.

I haven't got a clue how to measure bacterial load, either. I have to choose my tests based on their cost in dollars as well as in time - which means that all the tests I know of are out. I have a microscope, but regularly testing with that is impossible. Oxygen probes are too expensive, so BOD tests are out. Could I extrapolate bacterial activity from some other variable, like pH? I've got access to plenty of standard compounds, so I was thinking an acid digestion... it'd be a hatchet-job of a test, but better than nothing.

As far as bio-burdens and runoff possibilities go, I understand your concern but please believe me: it's a non-issue. First of all, we're the lowest point for quite some distance geographically. We are the runoff point. Second of all, this will be a very small reactor (55 gallon barrel, possibly upgrading to a second barrel for anaerobic digestion if I get ambitious) and any time I release material it will be immediately absorbed by a bio-active area (big friggin' garden) that can easily handle the inflow.

From a biohazard safety point of view, I don't see any difference between this reactor and a compost heap.

EDIT - - - - - - - - - - - -

So far, here's my plan for testing:

TSS - Aerate the tank to mix, then draw off 500mL. Run it through a coffee filter, weigh the sample once it's dry. Run twice weekly, results in grams per liter.
TVSS - Take the dry TSS filter and put it in a kiln until all that's left is ash. Weigh the ash. Run every time TSS is tested, results in grams per liter.
pH - Cheap analog pH meter from a garden supply store. Still need to buy/make calibration solutions. Run 1x/day if not more frequently, results in pH.
Temperature - Log nightly low temperatures and daily highs for environmental data, use infrared thermometer to get liquid temperature. Check every time the tank is accessed, results in degrees Centigrade.
Viscosity - 2L bottle with a 5mm hole in the bottom. Fill it, then record time until the jug is empty. This should help indicate when I need to add more water to the tank, or when particulate matter isn't being blended finely enough. Comparative to previous data only, results in seconds per liter.
Plant Test - Long term test with a matrix of plants, watered (daily?) with supernatant at various dilutions in water. Record plant health, look for fertilizer burns daily and measure plant growth 1 or 2 times per week. Results after processing might give me plant inches per ppm supernatant.
Nutrient Concentration - Draw off supernatant, add pH indicator, and titrate with HCl and/or NaOH until a set of arbitrary pH values are reached. Using titration data, calculate the buffering ability of the supernatant. This won't be a true test of nutrients, but it's a good way to judge concentration of salts. Phosphoric acid is triprotic and I expect it to be a good buffer.
Bio-available Nutrients - Aerate and draw off mixed fluid into a mason jar. Seal and leave out in the sun. Measure the time (hours? days?) before it transitions to anaerobic, septic, fungal or mold growth. Should tell me a combination of available nutrients and oxygen in solution. Results in hours/days until bio-death.

Do any of these tests seem flawed? I know they're far from perfect, but they seem like good balances between accuracy, cost, and time invested. I'm entertaining the idea of using some nitrate/nitrite test strips, but that's a continuous operational cost I'm not 100% ready to commit to.