Practically Speaking

If we'd carefully save our droppings rather than ship em down to Oak Creek in that over priced sewer, we could do the same thing right here in river city. Hey the sewer savings would probably cover operating cost, and we could power all city vehicles on our own methane.

Actually Mr. Elf, the city sells that stuff to a farmer to spread on his field. It's being recycled!

I always thought the hot air coming out of city hall was wasted myself...

Hi Kyle,

Actually the biomethane process is being done at a few dairy farms in WIsconsin, and methane is collected at some wastewater facilities in the area, mostly to produce heating for the facilities in the winter. It is definitely a good source of some energy, but probably would never account for more than a few percent of the energy needs. Since methane is also a strong greenhouse gas (I think around 15-20 times stronger than CO2), burning it off is good in that manner also, and that is one of the reasons why some landfill sites burn a flame, to burn off the methane and help disintegrate other compounds.

The problem with household production is that you would need a more steady flow of material to feed, and need some scrubbers and pumps to clean and pump the gas and it actually does take some energy input. If the feed flow was not good enough for the digestion process, you would end up with a dirty process that would not work very well. It is certainly possible in some some industrial settings (diary farms, breweries), but for households it would be extremely difficult to make it work consistently.

"Actually Mr. Elf, the city sells that stuff to a farmer to spread on his field. It's being recycled!"

Wait a second. Isn't there a federal law prohibiting the use of human *** as fertilizer? I know that there are some health issues involved. By the way, what does this farmer grow? I'll want to avoid buying any!

Kyle's reply: Interesting observation, Elf. I thought the same. I don't know about a law, but I thought human waste contained cadmium, a toxin--one of the negatives with Milorganite?

I was taught that human or other carnivore waste, such as cat or dog waste, should never be used for food crops. They do do this in foreign countries however. (One of the many reasons I try to only buy American produced produce.) 

The farmer in question could be a tree farmer I suppose? 

Maybe you, Santa's Elf, could look into this more and report back? After all, this isn't your busy season at the pole, is it? 

Hi Kyle and Elf,

You are both right, it would be illegal to use human waste as fertilizer. Even for home composting, we are not supposed to use human or animal waste. Kyle, you are also right that Cadmium is present in human waste and milorganite and can be a problem. The main problems with using human waste directly on crop is that disease causing microorganisms and viruses would be present, as would some concentration of metals.

As waste is treated in the wastewater facilities, it is degraded to a point where the initial human and animal borne infectious agents are destroyed. Most municipal treatment facilities (including some in the area) sell or give their sludge to farmers to spread on fields. Try not to think of the sludge as human waste Elf, it would drive someone crazy because they spread it in many places and it would be difficult to track whether any of your food was coming from sources that spread sludge. It is of course tested regularly for various microorganisms, metals, and nutrient content, but probably not often enough. There are different classes of waste, and if there is a problem, or a high number for some metal, ie Cadmium, then is has to be incinerated or spread more thin. Of course, a farmer doesn't want something they have to spread so thin that the fertilizer value is mostly lost.  In the treatment process, microbes grow on the waste nutrients and grow, forming biomass (millions of microbe bodies), which has be wasted occasionally or it would fill up the digestor and flush into the effluent stream, This waste is called sludge. While the biomass is growing, it also binds and holds much of the toxic metals including Cadmium, Mercury, Molybdenum, Arsenic, Selenium, Lead to name a few. This is good because the flowing water effluent that leaves the treatment facility is very clean of toxins and the biomass also holds much of the nutrients (Phosphorus and Nitrogen) which help keep the rivers clean.  The Fox river would be pretty disgusting in the Brookfield and Waukesha areas if this process did not work very efficiently since both facilities flow a river out the back end and right into the river. The sludge is essentially concentrated version of the nutrients that entered the facility. They have all been broken down and dissolved, and eventually resuspended into the biomass in the process. The microbially based infectious agents are also destroyed throughout the process. In order to land apply, keeping the metals low is the important factor at the facilities, indicating whether the sludge needs to be incinerated at high cost to us, or sold to farmers. As we know, even those toxic metals are necessary at very low levels to the whole process does make sense. Even a sample of our turfgrass would result in measurable amounts of most of the mentioned metals. Facilities are usually on a schedule set by the DNR to test the sludge content. It is not a daily sample, so there is always a chance some person or company dumped a toxin illegally and it concentrated in the biomass and has been applied before the sample is tested.

My guess would be that the limits set by the EPA for metals will decrease again in the upcoming years. For the past 4-5 years, some of the metals limits have actually increased, allowing more concentrated spread. Of course, with fertilizer prices more than doubling in the past couple of years, the stuff will be more and more valuable.

One other tidbit about Milorganite, I have heard that they are actually having trouble reaching the Phosphorus amounts they want in the fertilizer because some of the companies like the yeast place and others have left downtown and the amount of phosphorus entering the plant is decreasing. They are running higher and higher metals content in the product because they need to concentrate it more to attain the concentration of phosphorus and nitrogen that they desire. The more they concentrate that sludge, the higher the concentration of good nutrients, but the same goes for the metals. To make matters even more tenuous, add pharmaceuticals to the mix, which have received press recently due to being found in waterways and wastewaters at trace amounts.

Be thankful for the regulations that are in place, and Even spending some tax money to keep an eye on some of these things, without them we would be eating and drinking alot more of this stuff and wouldn't even have a clue!

Kyle's reply: Wow, Mikeyd, that is quite the report. Thank you.

Interesting about the Milorganite having trouble reaching the Phosphorus %. Wasn't that the problem with that bad Milorganite spread in Milw. parks last year? I seem to remember the Milorganie was not up to standards to be sold, so they gave it to the parks. It later turned out to be too highly concentrated in those heavier metals--just like you explained--and had to be removed!

Hi Kyle,

Yes, they PO4 was falling too low for their fertilizer standards, I think 4% is the number they use, not sure on that though. Extra strange since most lawn fertilizers are going PO4 free now since it tends to wash away easily with rain and most lawns hold and retain more than enough Phosphorus anyway. I don't actually remember the whole story with the Milorganite, but I think it turned out after they gave it away, it was PCBs that were found in high concentrations. Later I think they found that possibly cleaning the sewer pipes washed some PCBs that had accumulated in them into the waste stream. Unfortunately, as I mentioned earlier, the same thing could happen with metals or PCBs, or other toxins on any sludge that is land applied. They like to hold up the lot until some tests are complete, but that isn't the case in many situations. On the land application issue, I used to be for it since it seemed like a great way to put our waste to use (much like making Methane while digesting), but they really should tighten the regulations and lower the concentrations of some of the metals to make me slightly more in favor of it.

Kyle's reply: Thanks again. I think we are on the same page here.