Design of a hybrid reed bed system to achieve complete nitrification and denitrification of domestic sewage

The design of vertical-flow (VF) reed beds is reviewed and the performance of the few worldwide existing hybrid systems, combining both horizontal- and vertical-flow beds, is assessed. Horizontal-flow (HF) beds are good for suspended solids removal and will remove BOD5 up to a set loading. Vertical-flow beds can achieve BOD5 removal at much higher loading rates and they are capable of complete nitrification as tertiary or secondary treatment systems. It is possible to achieve biological denitrification in horizontal-flow beds. By combining horizontal- and vertical-flow systems in the appropriate process sequence it is thus possible to produce a system which removes BOD5, TSS and achieves complete nitrification as well as substantial removal of nitrate and hence a lowered Total N. The paper discusses the possible process options for combining horizontal- and vertical-flow systems. One example of these systems will be described in more detail. This is a flexible hybrid system being built by Severn Trent Water. Designed to treat the flow for a small village with a population of 129 it will have vertical-flow beds followed by horizontal-flow beds. The design allows for flexibility such that the size of the vertical-flow and horizontal-flow stages can be altered (for experimental purposes) to allow the design arrangement to be stressed and performance evaluated with the intention of defining the optimum loading rates for each of the stages. The same site also has sludge drying reed beds for treating the primary sludge.

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A comparison of different concepts of the running-in of nitrification and denitrification in activated sludge plants

Water Science & Technology ◽

10.2166/wst.1999.0259 ◽

1999 ◽

Vol 39 (6) ◽

pp. 53-60 ◽

Cited By ~ 2

Author(s):

O. Nowak ◽

V. Kühn ◽

V. Müller

Keyword(s):

Activated Sludge ◽

Pilot Plant ◽

The Other ◽

Aeration Tank ◽

Reduction Step ◽

Gaseous Nitrogen ◽

Nitrification And Denitrification ◽

Anoxic Zones ◽

Complete Nitrification ◽

Heterotrophic Biomass

Two different concepts of the running-in (without inoculation) of activated sludge plants for nitrification and denitrification have been tested on two pilot plants for the extension of a municipal WWTP. During the running-in period, the aeration tank of one pilot plant was fully aerated, whereas the other pilot plant was operated with an anoxic section of 20%. It could be shown that the installation of anoxic zones during the running-in period leads to a higher nitrite peak as compared to complete aeration of the whole volume of the aeration tank. Hence, it is highly recommended to aerate the whole biological reactor, until complete nitrification is achieved. Furthermore, it was found that the activated sludge of the fully aerated pilot plant was not capable of the reduction step of nitrite to gaseous nitrogen. This indicates that for ‘full’ denitrification the heterotrophic biomass has to be adapted to ‘regular’ anoxic conditions at first.

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