Tunnel Refineries


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Introduction

Tunnel Refineries are one of the UKÕs leading producers of sugars for the food, drinks and pharmaceutical industries. The original plant consisted of an anaerobic plant plus associated equipment. ACWA Services Ltd. obtained a contract worth £1 million to extend and modify the existing effluent treatment plant at the Greenwich glucose refinery in order to improve the discharge quality of the effluent for direct discharge to river.

This turnkey project included construction of a new anaerobic treatment system and the conversion of the existing anaerobic plant to a second stage aerobic treatment plant. Both systems included all associated mechanical and electrical equipment.

Design Information

The following table indicates the influent quality and the final effluent quality achieved from this plant.

Description Influent
Characteristics
Average
Effluent
Quality
Requirements
Flow m³/day (avg) 3500  
Flow m³/day (max) 5100  
COD mg/l 4100  
COD kg/day (avg) 1400  
BOD mg/l   30
SS mg/l 600  
Ammoniacal Nitrogen mg/l 30 10
Temperature ?C 35 - 45 35
pH 6.0 7.0

Description

The raw effluent from the processing plant is transferred via a run-down screen to the existing balance tank where sodium hydroxide is added for pH correction and supplemental alkalinity and a nutrient solution added to ensure optimal growth and function of the downstream biological processes. As the temperature from the balance tank is often in excess of the required operating temperature for the anaerobic treatment processes, the effluent is transferred via pumps through a cooling system to provide a constant effluent temperature of 35 Ð 37?C. A cooling system bypass operates if the effluent temperature is within the required range.

The effluent is transferred to the new anaerobic reactor for the first stage of biological treatment. The anaerobic reactor used is a hybrid anaerobic reactor comprising of a lower section containing the biomass, a media section which acts as a solid / liquid / gas separator and a central degassing chamber. The effluent enters the anaerobic reactor through a series of valves that distributes the effluent throughout the reactor. The effluent flows upwards through the sludge blanket where treatment of the carbonaceous load occurs. Typical removal rates for a reactor of this type are 70 Ð 80% of the incoming COD loads. The biogas produced under anaerobic conditions is sent to flare for safe disposal or re-circulated through a gas compressor back into the anaerobic reactor to assist with mixing of the reactor contents.

The new anaerobic reactor was seeded using the contents of the original anaerobic reactor. On optimum operation of the new anaerobic reactor the original reactor was decommissioned and refurbished with a fine bubble diffused air system in order to utilise the tank as an activated sludge plant. The activated sludge tank was seeded using locally sourced activated sludge.

The partially treated effluent is transferred from the anaerobic reactor to an anoxic tank from where it flows to the activated sludge tank. A fine bubble diffused air system and air compressors deliver the required oxygen to the activated sludge in order to provide the second stage of biological treatment. Typical removal rates are in excess of 85% of the BOD entering the activated sludge plant. The treated effluent is fed to a final settlement tank, where the clarified effluent is directed to the discharge point. A proportion of the settled sludge is returned to the activated sludge plant (RAS), with the remainder removed from site as surplus activated sludge (SAS).

Project Details

Client: Tunnel Refineries, Greenwich

Industry: Industrial Wastewater Treatment

Application: Anaerobic plus Aerobic Treatment

Technologies

Wastewater Treatment
Anaerobic Treatment