Croda Chemicals

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A large scale extension to an existing wastewater treatment plant was designed, installed and successfully commissioned by ACWA Services Ltd. The extensions at the Humberside works of Croda Chemicals, one of the UK’s leading producers of lanolin; lanolin derivatives and other fatty chemicals used in the production of for personal care preparations. Whilst all these compounds are known to be biodegradable, ACWA’s process designers had to take into consideration the presence of detergents, water insoluble fatty materials and warm temperatures – all factors which tend to reduce efficiency of the process. Odour control, using an ACWA AIR scrubbing system, also forms an important part of the process.


The plant which combines both Bio-filtration and Activated Sludge processes, comprises Coarse and Fine pH Adjustment, Dissolved Air Flotation, Biofiltration, Aeration, Settlement, Thickening and Odour Control, and is capable of testing a maximum influent flow of 1600m³/day at a rate of 50m³/hour, with a COD loading of up to 8500kg/day. The average flow rates are in the region of 1200m³/day with a COD loading of 3800kg/day and 200mg/L suspended solids.

Incoming effluent to the treatment plant is received in a coarse pH Correction Tank, where acid/alkali is added to achieve effluent pH correction prior to the flotation process.

Air Flotation
Suspended solids are removed by the injection of high pressure water at the inlet, and the addition of Polymer solution in an in-line Flocculator. Floating solids are automatically removed from the surface by a scraper and discharged into a sludge hopper, whilst clear effluent leaves the tank, via an infusion pipe, to an adjacent Level Tank.

Part of the clarified effluent is then mixed with compressed air in a high pressure manifold before being returned to the flotation tank.

Remaining clarified effluent from the process is then discharged into a Fine pH Adjustment tank where it is dosed with acid/alkali solutions in preparation for the next stage of treatment.

High Rate Bio-Filtration
From the fine pH adjustment stage, effluent gravitates to a recirculation sump, from where it is transferred to two high rate Bio-towers, operating in parallel. The recirculation sump comprises three chambers and the biotowers are capable of removing up to 75% of the effluent organic loading.

In the biofilters, effluent is spread over the upper surface of packing media by a specialised distribution system. As it passes down through the media, biomass growing on the surface adsorb and absorb the soluble organic material, converting it to further cellular matter, or the eventual breakdown products of carbon dioxide and water. Excess cellular matter is continuously shed from the filter and passes into the recirculation sump.

Activated Sludge Process
Filtered effluent from the Bio-towers is pumped into an Anoxic tank, which allows sufficient residence time for the dentrification to occur. Treated effluent then overflows a peripheral weir into an aeration tank, where helixors supply oxygen required to allow micro-organisms to bio-degrade the remaining organic matter. After passing through the aeration tank, mixed
liquor is discharged to a final settlement tank where activated sludge settles to the bottom and is pumped away and returned to the inlet of the anoxic tank.

Excess activated sludge is returned to a thickening tank which is fitted with a picket fence thickening mechanism which rotates slowly to consolidate solid particles. Thickened sludge falls to the floor of the tank and gravitates to a central hopper, from which it is pumped away for dewatering.

Final Treated effluent from the settlement tank overflows into a collection sump and is discharged by submersible pumps into the River Humber.

Odour Control
To provide strict control of odour, the bio-towers are totally enclosed with purpose built roofs, to contain contaminated air above the effluent. Contaminated air is exhausted by fan to the inlet of a chemical absorption scrubbing system, utilising caustic soda and hypochlorite as cleaning agents, before it is vented to atmosphere.

Project Details

Client: Croda Chemicals

Industry: Effluent Treatment