Sewage is simply the raw material, and it is very dangerous as such. Composting is a natural way to treat it. Once the human waste has been thoroughly composted, you won't find and viable seeds (i.e., tomatoes) because the heat of the process will have killed them and objects that passed through are destroyed in the composting. In spite of this, the U.S. banned various forms of produce from Japan for a long time because they used the composted human waste. Personally, I think this comes more from humans putting themselves in a "above Nature" position (human waste must be more potent than anything else!) than good science. There is no argument that untreated waste is dangerous; it's deadly. But these days there is also much better understanding of how the natural process works and it is widely accepted as safe.
If you have a compost pile of mixed vegetable and animal waste and you tend it carefully (keeping it pretty hot) you can break down the material over the space of several weeks. I haven't gone to any links for exact quotes, if someone has the time to find some good science, that would be welcome. But to make a compost heap (or bin or whatever you use) work, you need to mix your ingredients with plenty of water and air. Turn it frequently. You can add animal waste to yard compost with no special treatment most easily when yard heaps have a high percentage of vegetable waste. If you're doing a strictly human waste process then you're dependent on more specific containers, chemicals, and bacteria to break it down. I think that to play it safe those systems take longer. The Texas State Parks folks boosted the process with heat (solar panels) so they probably composted faster being somewhat less passive.