"Because human waste contains shigella bacteria..." we wouldn't put human waste directly on the land. We currently do spread treated human waste that has been digested on land, commonly called biosolids.
Water treatment plants let quite a lot of biological contamination through... If you use that to water crops that people eat, you get quite a nice disease spreading loop...
Specifically, no water treatment process today tests for viruses in treated water, and there are plenty of viruses that can survive sitting in a bubble tank for a few hours..
Boiling the water for 10 minutes first would satisfy me that very little biological contamination can make it out, but it is a huge amount of energy required to boil all the wastewater.
Probably not, but can be a source. Which is why it is regulated and steps are taken to a) reduce E. coli in the sludge and b) apply it at certain times, etc. per the EPA link.
Treatment methods eliminate more than 95% of the pathogens in sewage sludge; the risk of disease from those that remain in biosolids is short-term because most of them do not survive beyond 30 days in the soil environment. In addition to requiring pathogen reduction treatment, Pennsylvania's biosolids regulations contain several risk reduction and management requirements that reduce the likelihood of disease to very low levels. These requirements include:
treatment and management practices to reduce the attraction of disease vectors and thus the probability that pathogens would be transferred from biosolids to humans or animals
application setback requirements from occupied dwellings and from water sources
minimum time requirements from biosolids application to harvest, ranging from 30 days for forage and feed crops to 38 months for some food crops
no grazing allowed within 30 days of biosolids application to pastures
If carefully followed, these requirements make the risk of disease from land-applied biosolids similar to or lower than that of land-applied manures. In fact, there are no documented cases of human or animal diseases being contracted from land-applied biosolids.
Changes in microorganisms have undoubtedly contributed to this increase, as have changes in growing, harvesting, distribution, processing and consumption practices. Listeria monocytogenes, Clostridium botulinum and Bacillus cereus are naturally present in some soils. Their presence on fresh produce is not uncommon. Salmonella, E. coli O157:H7, Campylobacter jejuni, Vibrio cholerae, parasites and viruses can contaminate produce through raw or improperly composted manure, irrigation water containing untreated sewage or manure, and contaminated wash water. Contact with mammals, reptiles, fowl, insects and unpasteurized animal products are other sources of contamination.
Add in the cost of the human waste disposal that you make unnecessary (ah, I guess that's the "nitrogen pollution" bit). But I understand that phosphates are at least as serious a problem; and I believe nitrates are much less persistent than phosphates.
If I remember a fragment of chemistry from 50 years ago, it's something like "all inorganic nitrate salts are soluble in water at STC". Ammonia's also water-soluble (and volatile); rivers and groundwater can recover from nitrogen pollution more quickly than from phosphate pollution.
One other thing: phosphate fertilisers basically have to be dug out of the ground, and as reserves begin to run low, prices are increasing. But human poo is very high in phosphates.
I mean, even if there's a yick factor, let's face it: every glass of water we drink, whether from the tap or the mineral spring, has probably passed through the kidneys of dozens of animals, including fish, mammals and insects, and certainly hundreds of dinosaurs and millions of bateria. Why should we be concerned if the phosphate salt we use was once a part of human poo, which probably contained nasties at some point? And nobody's proposing that humans should chow-down on phosphate salts extracted from human poo; stick to bananas, and put the fertiliser on the banana tree.
See the section on meat, dairy, fruits, vegetables, etc... It would be a decent diet.
And obviously within a year or so, land use could be adjusted to make it an even better diet.