Liquid purification or separation – With gas-liquid surface contact means – With separator
Reexamination Certificate
2001-03-31
2003-03-04
Upton, Christopher (Department: 1724)
Liquid purification or separation
With gas-liquid surface contact means
With separator
C210S194000, C210S197000, C210S220000
Reexamination Certificate
active
06527948
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
An embodiment of the present invention relates to a biological process for continues purification of wastewater by converting its constituents to a solid form that can be easily separated using retainable biological catalysts. An embodiment of the present invention also relates to a novel reactor hereafter referred to as “Reverse Fluidized Loop Reactor” (RFLR) for performing the above said process.
2. Related Art Description
Microorganisms have been used for a long time for treatment of water as well as waste water. Some of the newer applications of micro-organisms include oxidation of sulphide and dissolved iron salts to elemental sulphur and iron slats of oxidized forms that can be are removed by precipitation respectively [see for example: Buisman, C. J. N., et al., Biotechnol. and Bioengng. 35, 50-56, (1990)]. Such applications are feasible in the case of dissolved manganese also. The biological removal of sulphide as mainly elemental sulphur, which is essentially insoluble in water, finds application in treatment of sulphide containing wastewater from a variety of industries, in particular, pulp and paper mill effluent and refinery and petrochemical effluents. Sulphide is also generated during the anaerobic treatment of wastewater containing sulfates such as distillery effluents and pharmaceutical effluents. Removal of hydrogen sulphide from gases by scrubbing with water or alkaline or carbonate absorbents also result in a sulphide containing liquor that can be treated and recovered by biological sulphide oxidation processes.
Dissolved iron is present in coal mining and other mining area drainages. These waters are highly acidic and require treatment. Biological oxidation converts dissolved ferrous iron to hydroxide or carbonate ferric ion precipitates which can be easily removed from water. Such a process has been applied for the treatment of acid mine discharges [see for example: Nakamura, K. et al., Water Research 20,1, 73-77 (1986)]. Another application for biological iron removal is for the treatment of drinking water particularly groundwater, which in certain regions contains unacceptable levels of dissolved iron. Manganese is also present in groundwater from certain regions, industrial effluents from steel and manganese plants and in drainage water from coal and iron ore mines. Removal of Manganese is also feasible by biologically oxidizing manganese to form insoluble manganese dioxide and hydroxide precipitates. Although, such processes are currently used only in the form of natural oxidation in systems such as constructed wet lands, it is conceivable that reactor systems operating at higher rate for the controlled removal of manganese by biological oxidation can be developed. Note that all these systems result in the formation of insoluble precipitates.
Another application which results in solid precipitate is biological sulfate reduction when applied for the removal of metals from wastewater. The reduction of sulfate to sulphide is carried out by organisms known as “sulfate reducing bacteria.” These bacteria require an energy source or electron donor, which can be simple organic compounds such as methanol or gases containing hydrogen such as producer gas. The use of gas as the energy source is considered a more economic option for larger scale applications. Here again, we have a situation where the desired bacteria—sulfate reducing bacteria—is to be retained within the reactor, provided with a sparingly soluble gaseous reactant, and the final solid product is to be efficiently removed from the reactor.
Conventionally, the aerated reactors have utilized two techniques for maintaining a high concentration of micro-organisms in the reactor. In the widely used activated sludge reactors (see for example Metcalf and Eddy Inc. “Wastewater Engineering: Treatment, Disposal and Reuse”, Tata McGraw-Hill Publishing Co., New Delhi), sludge is recycled after separation by sedimentation from the effluent liquor. The high concentration of micro-organisms in the reactor takes the form of solid flocs kept in suspension by agitation or aeration in the reactor. The mixed and turbulent nature of suspension ensures effective contact of the biocatalyst—i.e., the micro-organisms with the reactants i.e., oxygen and pollutant materials. When these systems are applied to processes which produce solid waste products, these products cannot be separated from the active biocatalysts in an ordinary sedimentation separation. Thus, there would be an accumulation of the products in the reactor, leading to lower efficiency and possible failure. It is conceivable that expensive post treatment measures to selectively remove the solid waste products from active biocatalysts would enable the functioning of the system.
It is also common to retain micro-organisms as a film on stationary inert packing materials inside the reactor. Such a device is called “biofilm reactor”. These systems are better suited to anaerobic process which have no requirement of oxygen or aeration and have an intrinsic slow reaction rate as compared with aerobic systems. When applied to aerated process, the slow mass transfer of reactants to the stationary biofilm does not help in improving the performance.
In aerated process, the biofilm system takes the form of trickling filters where the liquid is sprinkled on top of reactor filled with packing materials which may be either natural random packing of stones or synthetic manufactured media in the form of random packing or structured packing. In these system, it is noteworthy that the liquid is present as discontinuous phase and air as continuous phase. It is also evident that such reactors are unsuited when solid products are generated during the reaction as these products will accumulate on the media. In fact, these systems are not recommended even when sedimentable inert solid are present in the raw wastewater for the same reasons.
There are some systems—“aerated filters”—in which a synthetic packing, submerged in the liquid pool, is aerated from below using diffused aeration apparatus. Such systems again have all the oxygen mass transfer deficiencies of biofilm systems but have the advantage of retained biofilm thus avoiding post sedimentation, and being less affected by variability in the wastewater characteristics such as shock loads or transient toxic loads. It is evident that effective removal of solid products is not possible in the submerged aerated filter.
Another biofilm system is the fluidized bed bioreactor. Here the biofilm is present on carrier material which is retained in suspension within the bioreactor using the liquid velocity applied in upward direction. The constant state of agitation of the carrier particles ensures that mass transfer limitations of stationary biofilm reactors are minimized. The velocity applied is in the “fluidization” regime, i.e.., the upward drag force applied on the biocarrier particle is equal and opposite to the buoyant weight of the particle. In solid-liquid fluidized bed reactors, there is a narrow range of velocity where this is effective. The situation is complicated by the application of aeration. At the top of the fluidized bed reactor, there is a disengagement section where gas, liquid and solids carried over are separated. The liquid velocity that has to applied is quite large and hence, energy consumption of fluidized bed reactors is usually higher than for other types of reactors. The fluidized bed reactor has been used for anaerobic wastewater treatment applications but for aerated systems such application is rare due to the hydrodynamic complication of maintaining stability in a 3 phase fluidized bed. The removal of solid products is also problematic as it requires application of velocities that would carry out the solid product while ensuring the retention of bi
Haridas Ajit
Majumdar Swachchha
Agarwal, P.C. Dinesh
Council of Scientific and Industrial Research
Upton Christopher
LandOfFree
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