Biological two-stage contaminated water treatment system

The systems may be used for treatment of water that contains contaminants. Water containing at least one of a nitrate, percholate, chromate, selenate and a volatile organic chemical is combined with nutrients and then is processed in an anoxic-anaerobic bioreactor. The combined effluent may also be oxygenated by dosing with hydrogen peroxide or liquid oxygen. The combined effluent of the bioreactor is dosed with a particle conditioning agent. The combined effluent treated water of the bioreactor is then filtered in a biofilter to produce a treated effluent stream. The influent water and combined effluent of the anoxic-anaerobic bioreactor may also be dosed with hydrogen peroxide to control biomass content in the system.

BACKGROUND OF THE INVENTION

This invention relates to processes and systems for treatment of groundwater or surface water that contains at least one of the following contaminants: nitrate, perchlorate, chromate, selenate, and volatile organic chemicals such as perchloroethylene, trichloroethylene, dichloroethylene, vinyl chloride, trichloropropanol, dibromochloropropane, and carbon tetrachloride. The new method implements a second treatment stage aerobic biofilter in combination with a first stage anoxic/anaerobic bioreactor with interstage oxygenation and particle conditioning addition.

Raw drinking water sources may contain nitrate, perchlorate, chromate, selenate, and one or more of various volatile organic chemicals, for example, perchloroethylene, trichloroethylene, dichloroethlyene, vinyl chloride, trichloropropane, dibromochloropropane and carbon tetrachloride. There are numerous processes and technologies available for removing one or more of these contaminants from drinking water, including ion exchange, reverse osmosis, electrodialysis reversal, granular activated carbon adsorption, air stripping, and advanced oxidation. Each of these processes and technologies has one or more of the following disadvantages: exerts a high energy demand, exerts a high operational cost, generates of a high-strength concentrated waste stream that must be further treated or disposed, adds considerable salt to a given watershed, does not address all of the cited contaminants, is sensitive to raw water quality, and sensitive to operating conditions.

Various biological processes have also been tested and used to treat one or more of the cited contaminants. These processes are typically single stage biological reactors with upstream nutrient addition. These processes have one of more of the following disadvantages in that they: cannot treat all of the cited contaminants, produce excess biomass that can slough into the effluent of the bioreactor, can experience clogging due to the production of excessive extracellular polymeric substances, and can leak nutrients into the effluent, thereby causing biological regrowth potential and disinfection by-product formation potential.

Some processes may include an additional element with a particulate filter unit that may be sand, granular activated carbon, anthracite or similar media and may have a backwash system to reduce clogging and to fluidize the bioreactor bed. However, the filtration in these systems is for high rate particle filtration rather than for degrading and removing dissolved contaminants.

SUMMARY OF THE INVENTION

The present invention is directed to processes and systems for treatment of water that contains contaminants. Water containing at least one of a nitrate, percholate, chromate, selenate and a volatile organic chemical is combined with nutrients and then is processed in an anoxic-anaerobic bioreactor. The combined effluent of the bioreactor is dosed with a particle conditioning agent. The combined effluent may also be oxygenated by dosing with hydrogen peroxide or liquid oxygen. The combined effluent treated water of the bioreactor is then filtered in a biofilter to produce a treated effluent stream. The influent water and combined effluent of the anoxic-anaerobic bioreactor may also be dosed with hydrogen peroxide to control biomass content in the system.

DETAILED DESCRIPTION

The following detailed description represents the best currently contemplated modes for carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention.

Referring toFIG. 1, a biological treatment system10for removing one or more contaminants from groundwater or surface water has a first stage bioreactor12and a second stage biofilter14. The bioreactor12may be an anoxic-anaerobic bioreactor that receives influent raw drinking water20with nutrients22added. The nutrients22that may include acetic acid, ethanol, and glycerin as carbon source/electron donors, phosphorus in the form of phosphoric acid, and nitrogen in the form of ammonia (e.g., liquid ammonium sulfate) may serve to achieve microbial degradation of water contaminants that may include nitrate, perchlorate, chromate, selenate, perchloroethylene, trichloroethlyene, trichloropropane, carbon tetrachloride, dibromochloropropane and other volatile organic chemicals. The dosing of the influent water with hydrogen peroxide24may limit biological clogging of the system10.

After the dosed water influent stream26is treated across the bioreactor12the effluent treated water30may be dosed with oxygen32and dosed with a particle conditioning agent34in the interstage flow between the bioreactor12and the aerobic biofilter14. The oxygenation32may be accomplished by dosing with hydrogen peroxide24, liquid oxygen, by an aeration process such as fine-bubble diffusion or cascade aeration, or by an eduction process. The particle conditioning agent34dosing may be by use of a coagulant such as alum or ferric, or by use of a polymeric compound such as cationic polymer. The dosage of hydrogen peroxide24may be approximately 1 to 2 mg/L for biomass control and approximately 10 to 12 mg/L for oxygenation.

The effluent treated water30with added dosing in the interstage flow that may increase the oxidation-reduction potential of the water, release trapped nitrogen gas bubbles as necessary, and condition sloughed biomass is then processed in the aerobic biofilter14. The aerobic biofilter14may be a granular media-based biofilter or a biologically active membrane filter. The aerobic biofilter14may degrade/remove remaining volatile organic chemicals, hydrogen sulfide, residual carbon nutrient, and sloughed biomass.

The system10control of biomass conditions in the anoxic-anaerobic bioreactor12and the aerobic biofilter14are important to the efficiency of removing the contaminants in the influent water20and in the effluent treated water30. The contaminants in the influent water20, the nutrients22from nutrient dosing, and the constituents in the resulting effluent treated water30are further treated in the aerobic biofilter14. The biomass conditions at each stage12,14may be monitored for turbidity and pressure loss to measure slime, sloughing, clogging and the like conditions. The dosing of influent water20and effluent treated water30with hydrogen peroxide24serves to chemically scour biomass and unclog the bioreactor12and biofilter14, and the conduit or piping for conducting fluids in the system10. The hydrogen peroxide24may be dosed intermittently or continuously as controlled by a program logic control system50. There may also be a backwash pump40and backwash tank42to control or minimize biomass in the system10to reduce biological clogging of the bioreactor12and biofilter14.

The two-stage system10with a wide range in oxidation-reduction potential allows enhanced processing of the range of contaminants that can be degraded and removed. The destruction of multiple contaminants may be accomplished with reduced energy input and without producing high-volume, high-strength waste streams. The contaminant removal performance has been demonstrated in analysis to be typically independent of raw water quality. The treated effluent stream38of the system10also has minimal biomass.

Sensors and control devices may be used to monitor and control dosing at the various stages of the system10. The dosed nutrients22concentration is a function of the dissolved oxygen and nitrate concentration in the raw drinking water20. Oxygen analyzers52,53and nitrate analyzers54,55measure the dissolved oxygen and nitrate in the raw drinking water20and effluent treated water30and transmit the data to the program logic controller50that correlates the data to then transmit control signals to a nutrient22dosing unit70or feed pump to dose at a calculated concentration. Generally the program logic controller50will be programmed with a range of dissolved oxygen and nitrate that is desired in the effluent treated water30and when measured values are outside the ranges, the program logic controller50will adjust nutrients22dosing to correct the concentrations. This feed-forward, feed-backward nutrient22dose control70ensures that sufficient nutrients22are dosed to the system10while minimizing excess nutrients in the effluent treated water30of the anoxic-anaerobic bioreactor12.

Pressure sensors56,57,58may be used to measure pressure drop between the influent drinking water20and the effluent treated water30, and between the effluent treated water30and the treated effluent stream38. Turbidity sensors59,60may be used to measure turbidity of the effluent treated water30and treated effluent stream38. The measurements may be transmitted to the program logic controller50for calculating biomass conditions at each stage12,14to assess the slime growth, sloughing matter, clogging and the like that is detrimental to efficient system10operation. Based on the measurement data the program logic controller50will adjust the dosing of hydrogen peroxide24by control of a hydrogen peroxide dosing unit72in water flows26,30, and will control backwash pump40and air blower18to chemically scour and physical loosen and remove biomass accumulation in the system10. The measurement data may also be used to control and adjust dosing of the particle conditioning agent34by a particle condition unit74and of the liquid oxygen32by an oxygen dosing unit76.

While the invention has been particularly shown and described with respect to the illustrated embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.