Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1998-03-10
2001-06-05
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S739000, C210S749000, C210S631000, C210S906000
Reexamination Certificate
active
06241888
ABSTRACT:
DESCRIPTION
Method of controlling the phosphorus concentration in biological wastewater purification plants.
The invention relates to a method of controlling a biological wastewater purification plant, in which the wastewater is aerated in an activation tank in the presence of an activated sludge and, to influence the properties of the activated sludge, phosphorus is added under controlled concentration.
According to knowledge to date in the field of biological wastewater purification plants, phosphorus is an element which has an influence on the degradation performance and the sedimentation properties of the activated sludge, more precisely in such a manner that both properties change adversely with decreasing phosphorus concentration. According to prevailing opinion, a phosphorus concentration in the mixed liquor of about 1% by weight (P), based on the biological oxygen demand (BOD5), is the optimum, in which case this optimum concentration may depend on the wastewater and the sludge. However, at the same time, the phosphorus concentration in the plant effluent, i.e. after the secondary clarification stage, which is downstream of the activation stage, must not exceed the limits prescribed by the authorities. Therefore, in the known processes, the phosphorus concentration in the activation tank is adjusted by measuring the phosphorus concentration in the plant effluent and using this value as a basis for controlling the phosphorus addition, usually as aqueous H
3
PO
4
solution. This control is intended to keep the phosphorus concentration in the effluent constant to an extent.
This known process has the disadvantage that the phosphorus concentration in the effluent fluctuates very greatly, with the risk that the limit value prescribed by the authorities is exceeded.
The object therefore underlying the invention was to improve the known process in such a manner that the fluctuations are at least decreased.
It has now surprisingly been found that this object may be achieved by measuring the phosphorus concentration in the activated sludge for the control of the phosphorus addition and controlling the phosphorus addition in such a manner that the phosphorus concentration in the activated sludge is greater than or equal to a lower limit and is less than or equal to an upper limit.
By means of the method according to the invention, the effluent values of a biological wastewater purification plant can be optimized and the limit values in the effluent of a wastewater purification plant prescribed by the authorities can be complied with better than hitherto.
The invention therefore relates to a method of controlling a biological wastewater purification plant, in which the wastewater is aerated in an activation tank in the presence of an activated sludge and, to influence the properties of the activated sludge, phosphorus is added under controlled concentration, which comprises measuring the phosphorus concentration in the activated sludge for the control of the phosphorus addition and controlling the phosphorus addition in such a manner that the phosphorus concentration in the activated sludge is greater than or equal to a lower limit and is less than or equal to an upper limit.
Preferred embodiments result from the subclaims.
To determine the phosphorus concentration, the method as specified in DIN 38 405 can expediently be used. In this method, the phosphorus concentration is determined in a homogenized mixed liquor and the phosphorus concentration measured in the effluent is subtracted therefrom. This result is divided by the dry matter concentration (dry matter (DM)=dried activated sludge) giving the phosphorus concentration in the activated sludge (P/DM, weight of P/weight of DM) as a result. In a preferred embodiment, the measurement is performed on line, i.e. continuously.
The invention is described in more detail by the experiments described below. This is not intended to restrict the invention in any way.
REFERENCES:
patent: 5076928 (1991-12-01), Ballnus
patent: 5908555 (1999-06-01), Reinsel
Water Science Technology, vol. 33, No. 1, 1997, pp. 165-173, XP002069450 entitled Experiences with Automatic N and P Measurements of an Activated Sludge Process in a Research Environment.
Patent Abstracts of Japan, vol. 015, No. 496, Dec. 16, 1991.
Barry Chester T.
Frommer & Lawrence & Haug LLP
Hoechst Aktiengesellschaft
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