is there any fixed time when the waste water can be treated?
Yes, we cannot store sewage water for a very long time. Water, if remains untreated, it will cause widespread water pollution. Increasingly agriculture will start use untreated waste water for irrigation. Under the prevailing climate, even we cannot store treated wastewater even after disinfected with chlorine. Bacteria will build in it. To keep environment clean and pollute free, water must be treated as early as possible. Farmers should not use polluted water directly to their crops which will lead to many diseases to the consumers.
Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and sometimes nutrients from wastewater. Treated sewage water cannot be used for every purpose. Typically it is used for irrigation.