Pretreatment Technologies For Removal Of Oil And Phenol From Coal Chemical Industry Wastewater

Coal chemical industry wastewater is a kind of typical recalcitrant industrial wastewater,mainly produced in the process of coal gasification,coal hot working and chemical products refining.There are many organic pollutants in the wastewater,such as tar,phenol,ammonia nitrogen,PAHs and so on.The wastewater from coal chemical industry has very complex composition with high toxicity and poor biodegradability.Thus,it is of great practical significance to develop the pretreatment technologies for removal of contaminants from industrial coal-gasification wastewater.Among them,the coalescence of dissolve or suspended oils from the wastewater,followed by flotation,is one of the well-received technologies.Considering the low removal efficiency of oil and phenol by existing flocculants,in this work,a range of hydrophobically associating cationic copolymers,namely,poly(AM-DMD-MMA),were synthesized via a micellar free radical copolymerization of acrylamide(AM),dimethyldially-ammonium chloride(DMDAAC)and methyl methacrylate(MMA)in aqueous solution.The resulting polymer,was then applied to the coagulation-air flotation process in an attempt to improve the removal efficiency of oil and phenol from coal chemical wastewater.The effects of synthesis conditions,such as initiator concentration,monomers mass fraction,cationic monomer mass fraction,hydrophobic monomer mass fraction and surfactant mass fraction,on the properties of copolymers were studied.For the coagulation-air floatation process,the various influencing factors or operating parameters on removal efficiency were systematically investigated,including inorganic coagulant dosage,organic flocculants dosage,cationic degree and intrinsic viscosity of organic flocculants,pH value,air flotation time,dissolved air pressure,initial oil concentration in raw water and wastewater quality.The results showed that the synthesis conditions had profound influence on the properties of the polymer,which in turn determined their efficiency in oil and phenol removal.When the cationic degree was 16.1%,intrinsic viscosity was 443 ml/g,the polymeric flocculant performed best.Its overall performance was better than traditional organic polymer flocculants.In conjunction with PAC as coagulant at150 mg/L,the copolymer P(AM-DMD-MMA)added at 10 mg/L without pH adjustment of the pH enabled the maximal removal rate of oil,phenol and COD in raw wastewater to reach 57.3%,61.2% and 56.2% respectively.In the coagulation-air flotation processes,the optimal conditions were found as follows: PAC dosage at100 mg/L,P(AM-DMD-MMA)dosage at 8 mg/L,air flotation time for 8 min,and dissolved air pressure at 0.4 MPa.Under such conditions,the oil removal rate of coal-gasification wastewater and simulated oily wastewater with the same oil concentration could reach as high as 70.1% and 75.4%,respectively.