Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Department of Chemical and Process Engineering

First Advisor

Mr. John O'Shea

Second Advisor

Dr. Aisling O'Gorman


The SBR process is a discontinuous, unsteady state process and has developed popularity in many countries assisted by reliable control technology for example programmable logic control. A typical SBR installation achieves equalisation, aeration and clarification of batches of wastewater on a timed sequence in one basin. This is in contrast to a volume sequenced process such as the conventional continuous stirred tank reactor where individual treatment objectives are met in separate basins. Advantages include, flexability, minimum energy input, consistent effluent quality and inhibition of filament organism growth by properly controlling substrate concentration and aeration sequences. Nitrification, denitrification and Bio-P removal can be achieved by altering the SBR cycle times.

SBRs are particularly suited to highly variable waste loads, a characteristic of vegetable processing. A pilot scale treatability study was carried out on the 1995 processing campaign effluent generated at Universal Dehydrates, Midleton, Ireland. Objectives included assessing the extent of COD and TSS removal, nutrient requirements, assessment of design criteria such as the Food to Micro-organism ratio (F/M) and determining the settling characteristics of the biomass with particular attention to variations in the waste load. The SBR reactors used in this study were 57 litres at maximum working capacity and operated at room temperature. Reactor pH, temperature and dissolved oxygen concentration was continuously monitored.

A typical SBR timed sequence is often termed a "cycle". Carbonaceous substrate removal is largely completed during the initial phases of the cycle - Fill and React. The time ratio of Fill and React can affect supernatant (or decant) quality and the setting performance of the biomass with a higher FilkReact ratio resulting in poorer decant quality and a diminished settling performance. This hypothesis was tested on the Pilot plant at Midleton. In addition, kinetic models describing the React phase were tested in order to compare and contrast with models cited in literature. The study also examines the rate of total COD removal during the unaerated part of the Fill phase (Mixed Fill) and the rate of oxygen uptake under varying FilkReact ratios.

One of the disadvantages of most wastewater treatment systems, particularly activated sludge systems, is the production of excess sludge. Land application was considered the most viable option for Universal Dehydrates. However, land application has its constraints52 and so close attention had to be paid to the potential yield of sludge from the proposed full scale Sequencing Batch Reactor treatment plant at Midleton. Chapter 4 describes how sludge yields from the pilot plant were calculated and how these results were used to predict sludge production on a full scale. Also, a correlation between sludge yield and reactor F/M was derived which can be incorporated into a land application management system.

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