Study On The Pretreatment Of Oily Wastewater From Restaurant With Far Ultraviolet Oxidation Technology

Oily wastewater discharged from restaurant contains highly pollutants and characterized by high levels of animal and vegetable oils. Meanwhile,because of its fluctuation of quality and quantity, it is a kind of wastewater difficult to be treated and there is still not an efficient method for its treatment.In this paper, the far ultraviolet oxidation technology was applied for the treatment of wastewater from restaurant. Advanced oxidation processes of UV (185nm) oxidation was investigated for its pretreatment in wastewater, has the characters of UV direct break on oil molecule chain and generation of ozone to form UV/O₃ operational mechanism to degrade organic compounds. The main factors affecting the UV oxidation have been studied and optimal reaction conditions have also been confirmed; XRD and TEM were used for crystal phase identification and estimation of the anatase to rutile ratio and the crystallite size of each phase present and consequently choosed one most ideal titanium dioxide catalyst from other three ones applies to photocatalytic reaction and seeking optimal technics parameters; the intermediates of simulant oi(lmethyl oleate)degraded by UV oxidation were concluded by the results of GC/MS and traditional analysis method and the possible oxidation pathway was still poorly defined.; furthermore,an photocatalytic apparatus dealing with 10 tons wastewater per day was designed by employing a Tymoschuk mathematical model and economic analysis was completed simultaneously.The main results are as follows:(1)Optimal reaction conditions of UV oxidation are: 10min of UV radiation time,range of pH is 6.0 to 8.0. Under optimal experimental conditions,the removal efficiency of oils was between 80 and 88%, COD was between 48 and 62%, BOD5 was between 35 and 53% and the ammoniac nitrogen was about 18%. The removal efficiencies of COD and BOD5 increased with their concentration decrease and dissolved oxygen descend, oil has the highest removal efficiency when the range of its initial concentration from 2000 mg/L to 3500 mg/L and has a slight effect from dissolved oxygen. The removal efficiency of COD versus its concentration is first oder at an initial concentration of 3727.4mg/L, equation is V_COD = -d C_COD/dt=0.0451 C_COD(mg/L·min). The concentration of ozone and hydroxyl radical in equipment and sample increased with prolonging irradiation time, steadying in 50 and 15min respectively. (2) The photocatalyst used for reaction is pure anatase crystal titanium dioxide and has the particle sizes of 18.5nm. when it exists in suspension, the optimal reaction conditions are: dosage of titanium dioxide is 150mg/L, pH has been dispensed with adjusting , flow rate of air is 40～60 litre per hour. Under these conditions average removal efficiency of COD and BOD₅ increased notably just achieved 64.02 and 42.79 %, but the removal efficiency of oil droped to 68～69 % for catalyst limited the penetration depth of UV-radiation.(3)The unsaturation of oil gradually declined with prolonging irradiation time,the average molecular weight of oil and fatty acid are also fallen,at the same time have a mass of peroxide and acid come into being;the initial intermediates of methyl oleate degradation are HOC(CH₂)₇COH and CH₃(CH₂)₇COOH.(4) The unit cost of wastewater attaind permission to discharge is 2.37 yuan per m3.The research indicated that far ultraviolet oxidation applied to high concentration wastewater from restaurant treatment characterized by notable effect, no secondary pollution, low cost and easy operation compared with conventional methods.