Brackish water was treated with reverse osmosis process. The fouling mechanism of RO and its control method was studied. In the treatment of brackish water, the salt removal efficiency was above 95% and the effluent quality was up to the standard for drinking water quality (GB5749-2006). The SDI of the influent of RO was less than 5 after the raw water was pretreated by the combination of coagulation and sedimentation process and filtration process, which met the demand of the water quality of the RO influent. If ultrafiltration was added, the water quality of the pre-treatment was better. Coagulation and precipitation was not very effective for the removal of dissolved organic compounds, especially for the removal of organic compounds with molecular amount ranging from 1000 to 10000. The formation of RO membrane fouling can be divided into five stages, which is membrane surface coarseness stage by inorganic substrate, organic compounds adsorption stage, organism adhesion stage, microbial film development stage, and irreversible membrane block stage. The membrane fouling was effectively alleviated by the strategy of first alkali solution cleaning and then acid solution cleaning.

The optimal condition of polysilicon ferric chloride (PFSC) flocculant was established by thinking of the factors , such as Si/Fe molar ratios,the reaction temperature and the pH value of the solution. When the molar ratio of Si and Fe = 1, pH value = 0.6, curing temperature at 30 ~40 °C, poly ferric chloride dosage of 0.75mg/L, the rate of turbidity removal of seawater is up to 96.5%. Experimental results show that poly ferric chloride seawater turbidity removal effect is obvious.

carboxymethyl chitosan modified to determine the optimum conditions for desalination pretreatment carboxymethyl chitosan (CMC): the optimal dosage of 8mg / L, turbidity removal efficiency of up to 92.8 %, COD removal rate was 53.25%; on this basis, polysilicon ferric chloride (PFSC) and carboxymethyl chitosan (CMC) for seawater flocculation experiments, the best dosage of carboxymethyl chitosan 2mg / L, polysilicon ferric chloride 0.2mg / L, turbidity of seawater reached 96.6%, COD removal efficiency reached 81.4%; and with a single flocculant for seawater flocculation effect is carried out.