Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2001-04-05
2003-10-07
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S624000, C210S631000, C210S205000, C210S207000, C210S208000
Reexamination Certificate
active
06630070
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of treating wastewater and a wastewater treatment equipment, in particular, for recycling reactants and unreacted chemicals to reduce genesis sludge capacity and consumption of chemicals.
In an era of reducing waste, various methods of reducing sludge generated in a wastewater treatment equipment are being studied.
Also, a method of treating wastewater of regenerating and recycling sludge generated from chemicals in use such as a coagulant and the like is being examined with the objective of reducing treatment costs.
For example, with regard to sludge containing unreacted chemicals, a method of reusing the unreacted chemicals is employed. The unreacted chemicals include unreacted calcium hydroxide, unreacted aluminium hydroxide and so on. When aluminium hydroxide sludge is generated, aluminium is eluted from the sludge to reuse the aluminium. These unreacted chemicals are reused for the purpose of reducing a genesis sludge capacity and consumption of chemicals.
FIG. 17
shows an example of these conventional wastewater treatment equipment. In this conventional equipment, wastewater flows into a first water tank
101
used as a raw water tank. After the wastewater stored in the first water tank
101
for a certain period of time, the wastewater is introduced into a conventional reaction tank
134
by a raw water pump
102
.
This reaction tank
134
is provided with a rapid reaction tank agitator
105
and a pH meter
106
. Returned sludge containing reactants and unreacted chemicals is introduced into the reaction tank
134
and an acid or alkali is added to the returned sludge. As a more specific example, returned sludge in a wastewater treatment equipment for treating fluorine contains aluminium fluoride as a reactant and aluminium hydroxide as an unreacted chemical. The pH in the reaction tank
134
needs to be eleven or higher to reliably elute aluminium from aluminium fluoride and aluminium hydroxide in the returned sludge.
However, a large amount of alkali such as calcium hydroxide or the like is required to adjust to pH 11 or higher in the reaction tank
134
. Therefore, particularly when calcium hydroxide is added, not only running costs are increased since the consumption of chemicals added into the reaction tank is increased, but also sludge is generated by calcium hydroxide.
In general, poly aluminium chloride, aluminium sulfate or the like is excessively added as a coagulant in wastewater treatment. Therefore, various methods of regenerating and recycling the above aluminum compounds are being studied.
Such prior art includes the one disclosed in Japanese Patent Laid-Open Publication HEI 9-276875. This prior art is a method of treating wastewater for reducing the quantity of generated sludge and chemicals used for fluorine wastewater treatment. Specifically, aluminium sulfate is added to fluorine-containing wastewater as a coagulant to generate precipitates in a first reaction tank with pH 6.5. Subsequently, after the precipitates are separated by a precipitating tank, water and sulfuric acid are added to the precipitates in a separate second reaction tank and adjust to pH 4.0 so that coprecipitated fluorine is eluted. Then, after a solution containing fluorine is separated in a precipitating tank, the remaining precipitates are returned to the first reaction tank and recycled as a coagulant.
In these reactions, aluminium sulfate sludge is precipitated in a neutral region while containing fluorine and the fluorine is introduced from the precipitate (elution of fluorine) into an acidic or alkaline region. Aluminium sulfate is recycled as a coagulant containing no fluorine in the precipitate in the acidic or alkaline region. Consequently, the quantity of generated sludge and aluminium sulfate as a coagulant chemical are reduced by recycling aluminium sulfate.
Another prior art is disclosed in Japanese Patent Laid-Open Publication HEI 6-262170. In this prior art, after aluminium hydroxide is used to adsorb fluorine contained in wastewater in a first reaction tank, calcium chloride is allowed to act on fluorine-adsorbed aluminium hydroxide in a second reaction tank with pH 8. Subsequently, wastewater is introduced into a precipitating tank so as to allow calcium chloride to act on the fluorine-adsorbed aluminium hydroxide. Calcium fluoride formed thereby is precipitated and separated.
In a supernatant separated by this precipitation, aluminium hydroxide is regenerated to produce an aluminate solution. Furthermore, the aluminate becomes aluminium hydroxide by adjusting to pH 7 in a third separate reaction tank. Thus, aluminium hydroxide is regenerated as a coagulant. This aluminium hydroxide is returned to the first reaction tank and thus a recycling is completed. As a result of this prior art, the consumption of aluminum as a coagulant and the quantity of aluminium hydroxide sludge can be reduced.
Furthermore, another prior art is disclosed in Japanese Patent Laid-Open Publication HEI 9-19681. In this prior art, after fluorine contained in wastewater is adsorbed to aluminium hydroxide in the first reaction tank, wastewater is introduced into the precipitating tank to be separated into supernatant and aluminium hydroxide as precipitate. Subsequently, excessive calcium sulfate is added into a second separate reaction tank to generate calcium fluoride. Consequently, fluorine adsorbed to aluminium hydroxide is desorbed.
By fixing a surplus calcium ingredient as hardly soluble calcium sulfate, aluminium hydroxide is generated with a strong alkali in a third separate reaction tank (dissolving tank). This generated aluminium hydroxide is returned to the first reaction tank and thus a recycling is completed. As a result of this prior art, the consumption of aluminum as a coagulant and the quantity of aluminium hydroxide sludge can be reduced.
As shown in
FIG. 17
, a common reaction tank used in the above-described prior art is a usual water tank in which a rapid reaction tank agitator
105
and a pH meter
106
are installed in a conventional reaction tank
134
.
First of all, it is required to solve problems related to a recycling in a conventional reaction tank
134
by constructing a reaction tank in which, for example, aluminium contained in returned sludge as an active ingredient is easily eluted and recycled.
In the above-described prior art disclosed in Japanese Patent Laid-Open Publication HEI 9-276875, 6-262170 and 9-19681, a reaction tank and a precipitating tank are required in any case when aluminium hydroxide is regenerated. Consequently, a problem arises that costs for constructing a system including equipment related to a reaction tank and a precipitating tank are high.
Specifically, for example, it is required to clarify conditions of regenerating aluminium hydroxide, aluminium fluoride or the like and examining the conditions in detail so that a wastewater treatment system achieving an object of regeneration can be constructed with little equipment investment.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method of treating wastewater and a wastewater treatment equipment with reduced waste at low cost and, furthermore, to provide a method of treating wastewater and a wastewater treatment equipment which can regenerate objective substances for use in wastewater treatment with little equipment investment.
In order to achieve the above object, the present invention provides a method of treating wastewater comprising the steps of: introducing wastewater into a reaction tank; introducing returned sludge into a separate reaction unit installed in the reaction tank to obtain a separate reactant by carrying out a separate reaction from a reaction in the reaction tank; and introducing the separate reactant from the separate reaction unit into the reaction tank.
According to this invention, a predetermined reaction is carried out in a reaction tank while a separate reaction is carried out in a separate reaction tank. Separate reactants generated from returne
Chujou Kazumi
Sawai Norio
Yamasaki Kazuyuki
Barry Chester T.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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