Method and system for synergic production of fresh water from sewage plant secondary effluent and strong brine

The invention provides a method and system for synergic production of fresh water from sewage plant secondary effluent and strong brine. The method comprises the following phases: (1) suction and cross flow filtration are carried out for secondary effluent of the sewage plant to pass through a micro-filtration membrane, and suspensions are removed; (2) pretreated secondary effluent flows to one side of a forward osmosis membrane and is used as a feed solution, strong brine generated from seawater desalination flows to the other side of the forward osmosis membrane and is used as a draw solution, and the secondary effluent is condensed and strong brine is diluted; (3) diluted strong brine passes through a reverse osmosis membrane to form fresh water, and diluted strong brine is condensed till the concentration is equal to the salt content of seawater and discharged to sea; (4) a ferric salt agent for removing phosphate is added into the condensed secondary effluent, after phosphate removal, denitrification treatment is carried out for nitrogen removal; the system comprises a pretreatment pool, a forward osmosis separation pool, a desalted water recycling tank and a concentrated water treatment pool. A fresh water resource can be extracted from the secondary effluent, in order to realize zero discharge of the waste water; strong brine discharged from seawater desalination can be utilized, in order to avoid influence of discharge on marine site.