How long does raw sewage contamination from floods remain in soil & is absorbed by food crops?

Rain cannot remove all harmful microbes from the sewage contaminated fields. You can apply lime (calcium carbonate) to these fields to minimise the population of these harmful microbes. You can cultivate crops, where the edibile portions are not in contact with soil. Avoid cultivating tuber crops, ground nut, leafy vegetables etc. The sewage sludge from domestic areas are very rich in nitrogen, phosphorus, potassium, sulphur and other micronutrients for supporting agricultural crops. But, the main problem is the harmful microbes.