Study On Technology Of Waste Emulsions Treatment

Emulsion serves the functions of lubrication, cooling, surface cleaning and corrosion prevention in metal working process, which may be composed of oil (mineral, vegetable or synthetic), fatty acid, surfactants, corrosion inhibitors, bactericide and other additives. Because of thermal and biological degradation and contamination by substances in suspension after use, and therefore they will become ineffective and need periodical replacement. Because of their high toxicity to aquatic ecosystem and human, much care should be taken to this kind of wastewater.Oils have been chemically emulsified, so normal separation processes such as gravity, flotation and skimming are not very efficient to separate oil from emulsions. Many physical and chemical technologies have been developed and used to treat stable emulsions. Among them, membrane separation such as microfiltration, reverse osmosis, especially ultrafiltration, are the most promising methods, because of no needing chemical additives, high oil rejection, low cost and compact structure. However, the main disadvantage of traditional membrane separation technologies is the permeate flux decline with time which is mainly caused by membrane flouling and concentration polarization and frequent backwashing is unavoidable.Vibrating membrane (VSEP) was used to treat waste emulsions in this study. The effect of VSEP on treatment of different waste emulsions was invesgated. According to the changes of membrane flux, performance of VSEP has been evaluated and principle of VSEP has been also analyzed. Futhermore, effect of using combination of A/O process to treat filtrates after ultrafiltration and process stability is invesgated in this study. In order to reduce organic loading and improve stability of waste water treatment system, Fenton reagent was used to oxidize organics of mixed filtrates. Both optimal dose and ratio of hydrogen peroxide and ferrous iron are fixed. Influence of Fenton oxidation pretreatment on biodegradability of mixed filtrates is tested by aerobic batch bioassay and BOD5.The removal rate of VSEP on different emulsions was between 36 and 97%. but above 87% oil and complete SS could be rejected. The obsearvation could be attributed to different composition of various emulsions. Membrane flux of sample remained rather stable. The reason was that high-speed shear forces of vibrating membrane, which resulted in rise of temperature and decrease of kinetic viscosity of emulsions. Decrease of viscosity of water samples in turn was causing enhancement of both shear rate and permeability of water molecules. The experimental results indicated that VSEP performed very well in waste emulsions treatment.After treatment by VSEP, organic concentration of filtrates was still very high due to containing a large amout of surfactants and other addictives. The results of biaassays (BOD5 and COD30) showed that most filtrates can be biodegraded, but microbial activity may be inhibited under high initial concentration. The experiment of A/O process(3 months) included sludge domestication, test and operation. When volume loading rate of A and O tank were 0.88-2.73 and 0.09～0.3kgCOD·m-3d-1 removal rate of COD could reach 87%, and anaerobic tank was more stable in comparison to aerobic treatment, and foaming became a problem for aerobic tank. Anaerobic process was resistant to influent variation and increase of organic loading, while these two factors could lead to defloculation of sludge and loss of fuction of aerobic unit. Flocculation of A/O effluent was also invisgated (PFS as coaugulant, PAM as coagulant aids). Under optimal circumstance, the removal rate of COD was above 20%.Under the condition of mixed filtrate concentration 20000mg/L, dosage of 30% H2O2 was 5%, optimal [Fe2+]/[H2O2] mole ratio was 0.1, the COD of effluent could beep below 8300mg/L. Under this circumstance, above 0.67g COD could be removed by using 1g H2O2. The extent and rate of biodegradation of industrial wastewater containing surfactants could be enhanced by Fenton's oxidation. and this effect was more significant with increase of hydrogen peroxide dosages. So, taking Fenton oxidation as pretreatment technology was available.Finally, based on the aforementioned experiment, full-scale application advice and comprehensive waste emulsions treatment process were proposed in this study.