Study On Integrated Process In Polluted Water Treatment

At present, the traditional water treatment techniques could not remove organic substance, ammonia nitrogen and other matters from the polluted raw water sometimes. Thus it is not enough for the strict drinking water quality standard. Based on the situation of china, an integrated technique was developed and removal mechanism and operation parameters were studied in this paper. The study gained financial support from State Small Towns Technology Development Project (grant 2003BA808A17).In the study, dissolved air flotation process and microbe reactor were integrated, and zeolite was applied as the filling material for aerated filter to form "O3-zeolite-GAC" process. The operation conditions effect on the removal efficiency was studied in a pilot experiment. Then the reactor mechanism was discussed on the base of experiment.During biofilm cultivation, it took twenty days in the summer to grow up, judging by the criteria that NH3-N and COD_Mn removal rate stabilized and nitrite concentration in the effluent approaches low after fluctuation. With the increase of dissolved air pressure or pressurized water rate, DO in DAF effluent would grow 50～350% more than raw water. Dissolved oxygen of zeolite filter effluent raised 0.8 ～ 1.5 mg/L under the help of special contact filling.In the process, turbidity would be removed 90% by dissolved air flotation technique. Under high inlet flow or turbidity concentration, the turbidity could be removed more, which would be lower than 2.0 NTU in final effluent. Even under high algae concentration or flow, the chlorophyll removal efficiency was up to 90%, which was removed by DAF and filter. Algae growth potential was influenced by the temperature and coagulant and it would be enhanced in summer. The removal rate of COD_Mn would be 80% or so under high temperature, which about 50% in winter.Organic molecular weight experiment results showed that big molecular organics were removed by DAF and small those by microbe life action. UV₂₅₄ and UV₄₁₀ would be reduced by DAF and filter. DOC removal rate in any part of integrated process could be 26～38% The effluent absorbency was in the ultraviolet zone, which rose great in 190～235 nm and fell in 235～400 nm.In the dissertation, new method was introduced to revise grey weighted related degree calculation. The results displayed that factors ranging from great effect to low on turbidity removal were influent turbidity, pressurized water rate, coagulant, temperature and flow. Filter performance was evaluated by the index derived from theory and fuzzy mathematics. Furthermore, the performance index value was relatively small under 1.0 HRT, which resulted from short hydraulic retention time and favorable effluent quality.NH₃-N would decrease above 50% after treated by contact filling microbe film. However, NO₂-N and NO₃-N could increase 10 times. In the filter effluent, NH₃-N dropt about half with low NO₂-N concentration. Under 1.5m³/h, NH₃-N removal rate of contact part and filter could be more than 50% and the former was influenced by influent COD_Mn. In summer, the ammonia volatilization velocity could be 4.8 mgN/m²/d under wind speed 4.5m/s and kinetic constants were higher than in winter. Analyzing the equation on the contact velocity of ammonia and air bubble, the diameter would grow under high temperature and short space from water surface. According to small molecular weight,the velocity could be bigger.The tests results of nitrification showed that both nitrification rates of upper layer rotating fillings and zeolite were higher than 1.0 mg/L/h in an hour, and then obviously fell. Upper layer rotating fillings and low layer zeolite had better nitrification capacity. But the oxygen uptake rate(OUR) of under layer fillings was 0.7743 mgO₂/L/h, higher than that of upper ones. OUR of zeolites was only half of the fillings'.In the aspect of floatation removal theory, fraetal dimension decreased at first and then increased when coagulant dosage increased. When the dosage was 15 mg/L, fractal dimension was smaller and removal effect of turbidity was better. For hydrophobic flocs, air bubbles preferred occurring on their surfaces since surface free energy of system decreased largely and the whole flocculation system became stable. The air bubbles had minimum diameter and became larger to balance pressure in ascending. The equation of adhesion rate showed that augmenting the volume density of air bubbles, increasing the adhesion probability of flocs and air bubbles and lengthening floatation time could improve the removal effect by floatation. Analyzing the forces on air bubbles and flocs, the relation between ascending velocity and maximum adhesion quantity of flocs by air bubbles was deduced that when the floc number is smaller than critical value, air bubbles would ascend and the ascending rate could change with the number of flocs and increase with floc diameter.Air dissolution velocity increased more slowly with time. Lengthening length of mixing tank, increasing wetted perimeter and improving frictional coefficient were efficient measures to enhance air dissolution. By deduced air dissolution equation, it was found that when air dissolved and then released the proportion of oxygen would decrease and the air space in the dissolved air vessel would probably accumulate oxygen. The adhesion model of filter material indicated that the reaction constant was influenced by activation energy, temperature, thickness of adhesion layer, zeolite and particle diameter. Adherence rate was largely influenced by adsorbate concentration. Biodegradation model of the filter showed that reaction rate was obviously affected by hydraulic loading and membrane age by backwash rate and filter runtime. Stable biofilm quantity was the difference value between maximum saturation and coefficient of quotient of attenuation to propagation.Some problems such as silt deposit, back wash and enhanced treatment in low temperature and their measures were discussed. The snail removal experiment revealed that the removal was not effective by prechlorination, sodium hypochlorite or hydraulic wash, but it would be better by back wash after emptying. However by putting floatation before biological contact process, there were never any snails. When this integrated process was applied to treat heavily polluted water in a plant as a model project, the removal effects of turbidity, alga and ammonia nitrogen were satisfactory that efficiently guaranteed the security of drinking water. This dissertation discussed four design methods on theory or experience that are substrate loading method, multiple factor fitting method, experience drawing method and substrate dynamics.