Pretreatment
Due to the high content of phenol, ammonia and fluorine in coal gasification wastewater, and the recovery can not only avoid the waste of resources, but also substantially reduce the difficulty of treating wastewater after pretreatment. Usually, the physical and chemical pretreatment processes of coal gasification wastewater are: phenol removal, ammonia removal, fluorine removal, etc.
Biochemical treatment
After pretreatment, the COD of coal gasification wastewater is still high, the ammonia nitrogen is 50-200mg/l, and the BOD5/COD range is 0.25-0.35, so the biological combination technology with nitrogen removal function is mostly used. The widely used biological denitrification process mainly includes: anoxic - aerobic method (A/O process), anaerobic - anoxic - aerobic method (A-A/O process), SBR method, oxidation ditch, aeration biofilter method (BAF), etc.
In-depth treatment
After multi-stage biochemical process, the effluent COD is still in the range of 100-200mg/l, and further deep treatment need to achieve the discharge or reuse of effluent. At present, the main methods of deep treatment at home and abroad are coagulation and sedimentation, advanced oxidation, adsorption or membrane treatment technology.
Concentrated brine treatment
For gasification wastewater with high salt content, the TDS concentration is generally around 10000mg/L. In addition to pretreatment and biochemical treatment, ultrafiltration and reverse osmosis membranes are usually used to remove salt, and the membrane produced water is reused, and the concentrated water enters the evaporation crystallization facility, which is also the key and difficult point to achieve zero discharge of wastewater.