Greencore Grocery


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Introduction

Greencore Grocery at Selby produces a wide range of branded and retail branded products. The major product lines include: cooking sauces, pickles, salad dressings, table sauces and soft drinks.

Previously in 1996, ACWA Services Ltd designed, built and commissioned the effluent treatment plant consisting of screening, pH control, balancing, primary clarification, secondary biological treatment (biofilter) and secondary clarification to permit discharge of treated effluent to the River Ouse.

Due to an increase in production, resulting in an increase in flow and load of factory effluent to the treatment plant, the existing plant was unable to meet the required standards for discharge to river. ACWA were contracted to upgrade the existing plant to accommodate the increase in flow and load and to ensure that the more stringent river discharge consent, could be met.

Design Information

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

Description Influent Characteristics Effluent Quality Achieved
Flow m3/day 2500 2500
Suspended Solids kg/day 7000 750
BOD kg/day Max 7200 750
COD kg/day Max - -
Ammoniacal Nitrogen mg/l - -
Phosphorus - -
pH 4-11 5-9
Temperature oC 20 <35

Plant Description

This project included the design, construction and commissioning of additional biological treatment, whilst incorporating as much of the existing plant as was viable.
The upgrading of the effluent treatment plant included the installation of a new rotary drum screen, new balancing facilities, new primary clarification, heat exchangers, a new anaerobic reactor for biological treatment, new secondary clarifier, new sludge storage tanks and new SCADA control system. From the existing system, the inlet sump, biofilter, secondary clarifier and sludge treatment process were retained. Due to the close proximity of a local housing estate a full odour control and scrubber system was supplied by ACWA Air.

Effluent from the factory enters the existing inlet sump from where it is pumped through a rotary drum screen to the primary clarification stage. The screening process consists of a 2mm wedge wire screen and screening compactor. Liquor from the compactor is re-processed through the plant, and the compacted screenings are removed from site. Due to space limitations the screened effluent flows by gravity to a Swirl-Flo clarifier that removes the readily settleable solids from the effluent.

The primary treated effluent flows by gravity to the balancing tank. This tank has sufficient volume to provide 4 hours balancing at peak flows. For occasions where the effluent may be outside of influent specification a separate aerated calamity tank was installed. Although a manual process, effluent from the Swirl-Flo clarifier can be diverted to the calamity tank, where it can be held until such a time when it can be passed through the treatment plant without causing any detriment to the biological processes.

Effluent from the balance tank is pumped to the Anaerobic Reactor through two stages of heat transfer. Prior to passage through the heat exchangers the effluent undergoes pH correction using caustic soda to maintain a pH of 7- 8 and nutrient addition. Both chemical additions are required to ensure that the optimum conditions for anaerobic treatment are maintained within the reactor.

The Anaerobic Reactor operates most efficiently at 35 – 37 oC. The first stage of heat exchange uses recovered heat from the anaerobically treated effluent to partially heat the effluent feed to the reactor. This stage will raise the temperature to approximately 30oC. The second stage will heat the partially heated effluent, using a hot water heat exchange, to the required temperature before it enters the reactor.

The reactor 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 an upper degassing zone. Heated effluent enters the anaerobic reactor through a series of valves that distributes the effluent throughout the reactor. The effluent flows upwards through a sludge blanket where treatment of the carbonaceous load occurs. A reactor of this type can typically remove 80% of the incoming COD load. The biogas produced under anaerobic conditions can be used within the dual fuel boiler to heat the hot water required for the second stage heat exchange. Excess biogas is directed to a flare stack for safe disposal.

The treated effluent is transferred from the anaerobic reactor to the existing Biofilter. The Biofilter contains random packed media. The effluent is distributed evenly over the upper surface of the packing media. As the effluent passes down through the filter, further biological treatment of the remaining carbonaceous load occurs. The treated effluent is collected in a sump from where it is pumped to the Secondary Clarification Stage.

The treated effluent is manually split (25%:75%) between the existing clarifier and the new clarifier. The clarified effluent overflows to the final effluent buffer tank, from where it is discharged to the River Ouse.

Primary sludge from the Swirl-Flo clarifier and secondary sludges from the secondary clarifiers are pumped on a timer basis to two sludge storage tanks. Sludge from these tanks is removed by tanker for off-site disposal.

The major process units – swirl-flo clarifier, balance tank, calamity tank, biofilter and sludge storage tanks - are fitted with covers and odour extraction equipment. All the sumps have covers. The gases from these units are ducted to the odour control scrubber. The scrubber is a column packed with proprietary random packing. Chemical solutions absorb the odorous compounds before discharge to atmosphere through a stack.

Project Details

Client: Greencore Grocery, Selby

Industry: Industrial Effluent (Food Waste)

Application: Anaerobic Digestion