What's the ecologic endgame of septic sludge?

Anyone have a good handle on what the ecologic impacts of poo in a septic system really are?

Location is western Wisconsin. I'm considering a bucket composting poo system, but it will cost me more money, and more energy, to bucket compost my own poo, and I don't really think I'll miss the added compost, what with all the animals pooping everywhere already and organic matter in decay. The ONLY reason I would spend the additional money and energy on poo compost infrastructure, and the continual energy to make it function (carrying and washing buckets etc), would be to spare my environment my share of whatever the ecologic endgame of the septic sludge in theory hauled "away" happens to be, so, what is that? Bear in mind I'm pretty confident I legally have to hire a pumper to come to my home and pump the tank every so often, regardless of if I put any poo in there.

On an entirely different note, is a septic system unhappy when it doesn't get it's intended poo/pee for any reason? How about water lines, does absence of water flow at plumbed toilet stations (but with no toilet hooked up) cause any problems I should be concerned about, if switching to a toilet box with a bucket in it? I've shot myself in the foot before, with things that are designed to be used or otherwise start a downward slide (an automobile for example). Thank for any insight.

I can take a shot at your second question. I'm not a plumber so someone with more knowledge can certainly trump my comments and I won't be offended.

I believe that as long as you are sending something into your septic it will be happy. For the bacteria to work in there they need something to eat. So if you still shower or send dishwater in there they would likely have their food. One other concern that you may have is keeping it from freezing in winter. Here (WI) they are usually about 8' deep at the bottom. So they harvest some heat from the soil beneath but they also get some from shower/laundry/sink/dishwasher water that is room temp or higher. If you are going to dramatically reduce your water into the septic you might want to put hay bales or other insulation over the tank for the winter.

I also think that the plumbing will be fine if you don't use your toilets. You might have to pour water into your toilet bowls once in a great while to offset evaporation so you maintain the p-trap effect that keeps sewer gas from getting into the house. Unless you're removing the toilet all together to install your box. Then you'd need to cap off the toilet flange at the floor to make sure sewer gasses don't come up into the house.

In my part of the state you only need to get the septic tank "inspected" every 3 years. You might want to call a septic pumper in your area to see the cost difference for an inspection vs a pump job. Heck, just ask them all these questions and they may have some good input for you as well.

I'll have a go at this.

Most areas require the septic tank waste to be disposed of in a certified sewer plant, usually the city system. My grandpa worked at one for years. I'm pretty sure the basic system is the same, although I'm sure the control system is much fancier now. Basically they provide lots of oxygen, agitation and the bacteria break it all down into CO2, water and more bacteria. Then they kill the bacteria in the outflow and put it back into the drainage system.

The only big problems with the system are Birth Control pills (and maybe other meds) and industrial waste that goes ends up down the drain.

The Birth Control pills aren't broken down enough and in Sweden are leading to hermaphrodite fish. No telling what else is going on that hasn't yet been identified as a problem.

The industrial waste is a huge problem, bacteria aren't as eager to break down some of these. Govts are trying to separate the two waste flows, but people often do what's cheapest even if it screws everyone else up.

Septic system waste breakdown is a function of temp and available moisture. In a normal septic system, moisture isn't a problem. When I lived in South central Alaska I had to get my septic pumped every year, but the soil temp is probably much lower there and I had 12 - 13 well fed people dumping into my septic system. With high load and low temps my system couldn't handle it. When I moved to Indiana, still lots of people crapping, but when I had it pumped after a couple years, the guys said it was basically empty. Temp matters. It was also a different designed system, injecting air into the water.

Either way, the crap and pee eventually turn into water and CO2 and re enter the eco system.

I've had systems work for years without cost or incident. That can change if you move someone really stupid into the home. It's not a garbage can or a toxic waste dump. Some people will never be able to figure it out. Others never seem to have trouble.

Easy question first. No your septic should not freeze if it sits dormant, don't let it sit empty. This one is personal experience with a winter in 2014 that was in the top ten for cold in the last 100 years plus statements by others in the same type of climate. Secondly the end game of sludge is different depending on the area you are in. Some areas allow tank sludge to go on monitored fields, others use what are called septage trenches and others dump into treatment plants. All of these have a trucking carbon footprint and treatment plants regularly have massive failures. Local composting is by far the safest and greenest method of dealing with human and pet feces and urine. I don't like to use the term human waste because it isn't.