Liquid purification or separation – Processes – Treatment by living organism
Patent
1995-08-09
1998-01-06
McCarthy, Neil
Liquid purification or separation
Processes
Treatment by living organism
210769, 210928, C02F 1102, C02F 1110
Patent
active
057050732
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for disposing of excess sludge produced during waste water treatment in biological waste water treatment plants of paper or paper pulp manufacturing plants, with waste water neutralization takes place preferably on basis of a digestion method with magnesium oxide (MgO), whereby the waste water is neutralized with a base before entering the activation facility and whereby the excess sludge that is produced is incinerated wither directly or is mixed with another liquid fuel and is then incinerated in a furnace.
A method to lower the adhesion of the combustion chamber dust by which alkaline earth oxides or hydroxides and/or carbonates are mixed into the water lye is known from European Patent Publication No. 0 171 093. However, this method does not solve the excess sludge problem of biological sewage treatment plants for acid waste water, in particular with exhaust vapor condensates.
U.S. Pat. No. 3,740,363 describes a biological waste water treatment method for the bleaching of waste water by means of salts, in which the sludge from the settling basin and that from the biological process steps is filtered jointly, is de-watered and reduced to ashes. The ashes are mixed with the tiltrate and the fresh waste water after separation of a valuable substance. This method used in the paper pulp industry shows no connection with chemicals recovery and is therefore independent of same.
At present, the excess sludge produced in biological waste water treatment is either dumped or incinerated in a dedicated unit. In either case, the waste water is neutralized, whereby the mostly acid waste water is mixed with milk of lime for neutralization before its biological cleaning. In this situation, a significant portion of the neutralization product and/or flocculent (lime) is incorporated into the biological mass produced and appears during the combustion of the excess sludge in form of fly ash which must be disposed of, thus being an environmental pollutant. The lower heating value of the pre-dried sludge is so low, due to the relatively high water contents, that in general additional fuels are required.
Conventional incineration plants are expensive because of their special construction and the additionally required complicated exhaust-gas processing equipment but even sludge dumping is not a satisfactory solution because of the environmental pollution which is produced and also because of the cost involved, with the necessary dumping volume being very limited in most cases.
JP-A-01-109 305 describes a method by which the chemicals, such as for example MgO or CaO used pulp disintegration are recovered from the exhaust gas cleaning unit following the incineration of the used-up chemicals in that the combustion ashes are suspended in water and in that the waste gas going to the SO.sub.2 absorption unit is washed with the suspension. This method has no connection with a waste water treatment plant.
The latter two methods are used together in similar form in paper pulp manufacturing plants. Since the chemicals are reclaimed where possible and since purity, in particular when recovering boiling lye, is highly prized, a consolidation is out of the question. Thereby two separate circuits with two independent incineration plants are created for different chemicals, namely a waste water treatment circuit and a waste lye treatment circuit.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the existing difficulties in the prior art and to use sludge utilization in combination with the reclamation of chemicals.
In the invention, sludge together with lye is incinerated in a lye incineration furnace and dust entrained in the combustion gas is separated and the neutralization product contained in the dust is used at least in part for the neutralization of the waste water and for the pulp disintegration. In particular, the SO.sub.2 contained in the exhaust gas is absorbed by alkali or alkaline earth additions. The sludge mixture
REFERENCES:
patent: 3377271 (1968-04-01), Cann
patent: 3561922 (1971-02-01), Allen et al.
patent: 3740363 (1973-06-01), Fuller
Glaser Wolfgang
Loquenz Heinz
Tamandl Kurt
Yaldez Peter
Austrian Energy & Environment SGP/Waagner-BIRO GmbH
McCarthy Neil
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