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Contenido archivado el 2022-11-21

Further investigation of technical and economic benefits associated with the use of pure oxygen in the biological treatment of carbonization effluents

Objetivo

i) To examine the stability of biological treatment with pure oxygen injection at increased influent strengths and biological loadings;

ii) To examine the ability of biological treatment with pure oxygen injection to produce a treated effluent with a more generally acceptable, low level of suspended solids;

iii) To examine the influence of aeration tank pH regulation on the performance of both pure-oxygen and air-based activated-sludge systems.
Overall, it was concluded that pure oxygen injection provided a very versatile means of oxygen transfer enabling higher organic loads to be accommodated than would be possible with many conventional aeration systems. Pure oxygen injection also provided benefits in terms of eliminating foam production minimizing heat losses, and providing favourable conditions for nitrification.

The study did not corroborate claims that the use of pure oxygen reduces excess sludge production or treated effluent suspended solids concentrations.

By operating the activated-sludge process at different aeration tank pH levels over the range 5.9-8.0 it was concluded that the pH within this range had no significant effect on chemical oxygen demand removal. With regard to treated effluent suspended solids concentration, however, the aeration tank pH did appear to exert an influence although the optimum pH varied from one effluent to the other.

Scale-up of the laboratory-scale data to full-scale BET plant operation was found to be extremely good thereby confirming the accuracy and validity of the laboratory-scale approach.
In January 1987 The Monckton Coke and Chemical Co Ltd (M. C & CC) commenced an 18 month research study to investigate impartially the technical and economic merits of using the BOC Vitox pure-oxygen injection system in the biological treatment of carbonization effluents.

Although pure oxygen injection has allowed a higher COD removal to be achieved at a given biological loading than that achieved in a conventional air-based system, it has yet to be demonstrated that treatment can remain stable at the much higher influent strength and biological loadings that have been maintained successfully in a conventional air-based system during the previous 18 month research period. When considering the capital cost of an effluent plant, the maximum biological loading that can be maintained, and therefore the plant size, is obviously of great importance. The relative merits of pure oxygen and air in this respect must therefore be quantified.

In addition, the high COD removal obtained at MC & CC with pure oxygen injection (based on filtered samples) has been achieved at the expense of a fairly high concentration of suspended solids in the final effluent. It is doubtful whether this level of suspended solids in the final effluent would be consistent with the discharge consent conditions imposed on some coking works within the European Community.

It is especially interesting to note the very substantial and consistent difference in aeration tank pH levels recorded between the pure oxygen and air-based treatment systems over the 18 month research programme. This observation must lead one to question whether the differences in COD removal and final effluent colour recorded between the pure oxygen injection and the conventionally aerated systems might be due simply to an aeration tank pH effect. In other words, could some of the benefits of pure oxygen injection be achieved perhaps more cost-effectively and perhaps even more strikingly via automatic pH regulation of a conventional air-based system.

Convocatoria de propuestas

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Régimen de financiación

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Coordinador

BCRA Scientific and Technical Services Ltd
Aportación de la UE
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Dirección
Mill Lane Wingerworth
S42 6NG Chesterfield
Reino Unido

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Coste total
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