Development And Application Of New Flotation System Based On High Dissolved Air Content

In2012, the State Council’s energy-saving and emission-reduction "12thFive-Year Plan" wasintroduced formally. According to the Plan, the State Council put forward clearly that: we should increasethe strength and depth of the industrial wastewater treatment, such as paper-making wastewater，printingand dyeing wastewater; and we should strengthen the comprehensive management of water sources forurban drinking; and we should strengthen the protection of the ecological environment of lakes. China isone of the ten Countries in the world which are extreme shortage of freshwater resource now. Meanwhile,the water pollution situation of our country is very serious, and freshwater resources utilization rate is low.In this context, treatment and purification of water will catch people’s attention more and more, which willgreatly promote the development of technology and equipment for water treatment in China.As an important technology for water treatment, the air flotation is rapidly developing in China. It hasachieved good results in slightly polluted water purification. Meanwhile, it has been widely applied inwastewater treatment, such as printing and dyeing wastewater, paper-making wastewater, oil refiningwastewater and catering wastewater. In addition, anaerobic biodegradation is one of the most commonlyused water treatment technology, which is recognized as an environmental friendly treatment method forwastewater. Anaerobic biodegradation has good effect in the treatment of dye wastewater and domesticsewage, which can remove pollutant in water and produce methane at the same time. So that anaerobicbiodegradation can achieve the purpose of turning waste into treasure finally. With this background, thereactive yellow KE-4RN was regarded as the processing object. Two kinds of methods for its treatmenteffect: flotation-coagulation treatment by new floatation system and traditional anaerobic biodegradation ofreactive yellow KE-4RN was studied. This paper is divided into the following two parts:The first part: on the basis of traditional pressurized dissolved air flotation, a new kind of flotationsystem based on high dissolved air content was developed, and its performance was tested. The newdissolved gas technique by liquid membrane method and the technique of micro-nano bubble formationwere introduced in the new system. The new flotation system had many advantages such as goodoxygenation capacity, low operating pressure, high dissolved air contemt, small footprint, small bubble size, without packing, low energy consumption and so on. The volume of dissolving tank is about one-fifth ofthe traditional one. It worked under0.30Mpa, and the content of saturated dissolved oxygen in clean waterwas over11.00mg·L^-1. The mass transfer coefficient of O2K_La（20） was0.4151min^-1. The energyconsumption can save15%than traditional flotation. The produced micro-bubbles had a mean diameter of38μm, and the residence time of bubbles was more than30minutes. A removal rate of99.0%could beachieved for reactive yellow KE-4RN simulating wastewater by coagulation and air flotation under theexperimental conditions of dye concentration100mg·L^-1, dosage of polymerization aluminum chloride（PAC）800mg·L^-1and dosage of polyacrylamide （PAM）20mg·L^-1.The second part: refer to the experimental method of ECETOC （1988） and ISO13641（2003）, theanaerobic biodegradability of reactive yellow KE-4RN was studied in batch experiments under35℃, onthe basis of lots of literatures about biodegradation of azo dyes. The factors such as decolorization rate,VFAs （volatile fatty acids）, CODCr（chemical oxygen demand） removal rate, sludge adsorption, gasproduction and composition, were detected to evaluate its decolorization form and degree. Meanwhile, themechanism of anaerobic decolorization and the type of anaerobic sludge adsorption of dyes were discussedpreliminary. The results of experiments were as follows: Reactive yellow KE-4RN was difficult to beanaerobic biodegraded into CO2and CH4completely, and only a little was mineralized. The decolorizationrate increased with the decrease of the dye concentration. Under the condition of dye concentration≤80mg·L^-1（calculated by C）, the decolorization rate could attain94%and the removal rate of CODCrcould beover90%during the tests of14days. The sludge adsorption process of reactive yellow KE-4RN wasdescribed by the Langmuir isotherm model correctly, and the maximum adsorption capacity was12.20mg·g^-1. The decolorization was mainly due to synergy effects of sludge adsorption and anaerobic primarybiodegradation. The wavelength of absorbance maximum underwent a significant hypsochromic shift withthe change of solution color, which indicated the formation of new coloured intermediate products inbiodegradation process. The combination of anaerobic and aerobic biodegradation methods may have agood effect in the treatment of dye wastewater.