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Dirk mobile centrifuge feeding an Anglian Water liming plant at Kings Lynn sewage treatment works

Alkaline Sludge Stabilisation

The chapter "Sludge Stabilisation" highlights the requirements of the water industry. Alkaline stabilisation is one possible tool to meet those requirements and an approved process for the production of agricultural biosolids.

DIRK is a specialist in alkaline sludge stabilisation.

Beneficial biosolids are defined as Class A or Class B products. Both classes can be achieved by alkaline stabilisation.

Alkaline Stabilisation is an approved method to achieve Class A or B if operated to provide the listed minimum process criteria.

Biosolid Product Alkaline Stabilisation using Lime Alkaline Stabilisation using Rhenipal
Class A Sludge to be treated with sufficient quicklime (CaO), to achieve a minimum of 55oC for a continuous period of at least four hours and pH exceeding 12 for a period of at least two hours.*  
Class B (UK Code of Practice) pH exceeding 12 for 2 hours pH exceeding 12 for 2 hours

*The statutory definitions of the 1989 Code of Practice are still under revision, it is likely that the DETR will adopt the above proposed revision of definition for the effective autothermic sludge treatment process.

Lime is able to achieve Class A or B providing both temperature and the necessary pH requirements.
Rhenipal is able to achieve Class B by providing the necessary pH.
Lime consists of CaO (Calcium Oxide), which reacts with the water in the sludge to produce Ca(OH)2 (Calcium Hydroxide) and exothermic heat.

Rhenipal, a DIRK product based on Pulverised Fuel Ashes from coal fired power stations and other hydraulic binding additives reacts with the water in the sludge, also producing some Calcium Hydroxide and therefore inherits properties of lime stabilisation but with significant cost savings.

A secondary effect of both product applications is the release of ammonia. This is an important part of the process, which helps to increase the pH. Lime generates an instantaneous ammonia release, while the ammonia release caused by Rhenipal is lower and more controlled.

DIRK is offering both Lime and Rhenipal contract stabilisation.
Our alkaline stabilisation work includes constant quality monitoring and certification of the resulting biosolid product.

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