Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2001-03-30
2003-08-05
Upton, Christopher (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S624000, C210S625000, C210S626000, C210S903000
Reexamination Certificate
active
06602417
ABSTRACT:
The invention relates to a process for the combined biological treatment of waste water containing one or more specific components in a pre-treatment reactor and waste water containing non-specific COD in a main reactor. The specific component can in particular be an organic substance or ammonia.
A process for the treatment of waste water containing ammonia by nitrifying bacteria, wherein ammonia is predominantly oxidised to nitrite, is disclosed in EP-A-826639. According to this known process, the waste water is treated in a continuously stirred tank reactor (CSTR) without sludge retention, with adjustment of the hydraulic retention time at about 1½ days. Under such conditions the bacteria which convert ammonia to nitrite, including e.g. the genus Nitrosomonas, have a sufficient growth rate to compensate for the sludge loss from the reactor, while the bacteria which convert nitrite to nitrate, including e.g. the genus Nitrobacter, do not have a sufficient growth rate to be maintained in the reactor. As a result, conversion of nitrite to nitrate is suppressed, which has the advantages of reduced oxygen consumption and reduced electron donor (COD) demand in a downstream denitrification process. This process is also referred to as Single reactor for High activity Ammonia Removal Over Nitrite (SHARON) process.
A drawback of this known process is that the required hydraulic retention time of 1-2 days necessitates the use of large reactors, which are loaded to a low level only. This is especially disadvantageous in the treatment of relatively diluted waste water.
Another approach is the use of selected microorganisms (EP-A-562466). In this process specific mixtures of micro-organisms (such as Pseudomonas, Acinetobacter, Moraxella, Corynebacterium, Micrococcus, Flavobacterium and Bacillus) are grown in separate reactors (so called propagators) and continuously or discontinuously dosed from these reactors into the waste water treatment plant. Drawbacks of such a process are the laborious (and therefore costly) cultivation of the selected micro-organisms and the relatively ineffective use of the bioreactors.
EP-A-503546 describes a process characterised in that a waste water containing a high concentration of nitrogen (i.e. reject water) is stored in a tank in which subsequently nitrification/denitrification takes place. The produced biomass is continuously or periodically transferred to the waste water treatment plant. The setbacks are comparable to the setbacks of the SHARON process referred to above, i.e. low sludge concentration, relatively large reactor volume and poor settling characteristics.
WO 98/00370 describes a nitrification process for the treatment of ammonia, in which a concentrated ammonia-containing side stream, e.g. reject water of the main stream, is treated in a conventional high loaded unit for producing nitrifiers. The nitrifiers are fed to the main stream in order to enhance the nitrification in the main stream. As in the process of EP-826639, the nitrifiers will be sensitive to preferential grazing by higher organisms in the main process.
A process has been found now which overcomes this drawback. In the process of the invention, surplus sludge from an activated sludge plant is used in a pre-treatment reactor in which higher levels of the specific component(s) are treated than in the activated sludge plant. The reactivated sludge is recycled to the activated sludge process.
In the process of the invention, the hydraulic retention time in the pre-treatment reactor can be shorter than the sludge retention time and the sludge age is controlled. In case of nitrification, the sludge age is preferably shorter than the doubling period of the nitrate-producing bacteria. The desired retention times are effected by settling and separating part of the sludge from the pre-treatment reactor, either together with the treated waste water or separately, and returning part of the sludge to the pre-treatment reactor.
Preferably, the pre-treatment reactor is operated batch-wise, and part of the sludge separated from the pre-treatment reactor is fed to the activated sludge plant treating organic waste containing non-specific COD and lower concentrations of the specific component(s). Non-specific COD is understood to comprise regular waste, for example municipal waste, exclusively or predominantly consisting of non-aromatic biodegradable organic material such as alcohols, fatty acids, fats, carbohydrates, proteinaceous material and the like. The configuration of the invention is referred to as a Bio Augmentation Batch Enhanced configuration, and the pre-treatment reactor will be referred to as the BABE reactor or bio-augmentation reactor.
An important feature of the process of the invention is that a limited amount of surplus sludge from the main (activated sludge) process is used in the BABE reactor, allowing the growth of specific micro-organisms and incorporation thereof in the added floc-forming sludge from the main process. In this way, the sludge is reactivated and, together with the effluent form the BABE reactor, recycled to the activated sludge plant. Thus, the removal capacity of the activated sludge plant for the specific component(s) is enhanced. Preferably, 0.01 to 0.25 part, especially 0.05 to 0.2 part per weight per part of the sludge from the activated sludge reactor returned to the activated sludge reactor is added to the bio-augmentation reactor. Without this sludge control of the invention, the specific micro-organisms would not sufficiently survive the selection pressure by the non-specific micro-organisms in the main process.
An advantage of the process of the invention is that the sludge retention time in the pre-treatment (bioaugmentation) reactor can be controlled independently from the hydraulic retention time, by separating sludge from the reactor effluent continuously or, preferably, discontinuously, and retaining part of the sludge in the reactor. As a result, the hydraulic retention time can be much shorter than the sludge retention time, and thus the reactor dimensions can be reduced and the productivity of the reactor increased.
The part of the sludge that is retained is preferably between 10 and 90 wt. % of the total sludge content of the reactor, especially between 20 and 80 wt. %. The sludge retention time in the pre-treatment reactor is usually between 1 and 5 days and the hydraulic retention time is generally less than 2 days, especially from 2 h to 12 h, depending on the nature of the specific component and of the micro-organism which converts the specific component. The sludge concentration in the pre-treatment reactor is generally between 1 and 30 g/l.
The specific component to be treated can be any organic or inorganic component, which requires particular organisms to be degraded or which are xenobiotic or inhibitory chemicals not sufficiently degraded in a normal activated sludge plant. Examples are organic substances like phenolic compounds, organic nitrogen compounds such as aromatic amines, especially phenylenediamines, organohalogen compounds and inorganic substances, such as thiocyanate and especially ammonia. Degradation of thiocyanate can take place by bacteria of the genus Thiobacillus, while phenol can be removed by Pseudomonas bacteria. Ammonia is degraded by nitrifying bacteria including the genus Nitrosomonas. Breakdown of o-phenylenediamine in a conventional nitrifying sludge system by yet unidentified, but commonly available, species was confirmed.
The bacteria capable of specifically converting these components are usually present in normal waste water treatment sludge, and will grow and become sufficiently active in the pre-treatment reactor as a result of the higher relative concentration of the specific component. For this purpose, it is important that the level of non-specific COD in the pre-treatment (bioaugmentation) reactor is lower than in the main reactor, while the level of specific component(s) is higher than in the main reactor. In particular, the level of non-specific COD in the pre-treatment reactor is le
DHV Water B.V.
Handal & Morofsky
Upton Christopher
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