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With the introduction of the European Landfill Directive (implemented in the UK by the Landfill Regulations), the off site disposal of liquid waste bentonite muds from piling, diaphragm walling, tunnelling and horizontal directional drilling operations is becoming increasingly difficult. In the UK, it is no longer acceptable to send liquid waste to landfill, now it must either be treated on site or sent to one of a few processing points around the UK. Transport costs associated with tankering liquid waste mud off site to a processing point are becoming more expensive given the travelling distances involved and often the best option is to use an on site processing system.
A flocculation system and centrifuge from PSD can usually convert liquid waste mud into a partially dewatered solids phase and a near clear fluid phase. Normally, the solids phase can be transported in a sealed back tipper truck to a local landfill site and the fluid phase can be discharged to the public sewer.
THE LAW
· European Landfill Directive (EC 2003/33)
· The Landfill (England and Wales) Regulations 2002
· The Landfill (Scotland) Regulations 2003
· The Landfill (England and Wales) (Amendment) Regulations 2004
THE TECHNOLOGY
Bentonite is a natural clay, which when mixed with water and used as a drilling fluid, provides beneficial rheological properties. When properly mixed, the clay particles disperse such that they are not large enough to be separated from the fluid by traditional mechanical means such as screens, hydrocyclones or centrifuges. These colloidal clay particles can be treated by a process called flocculation to bind them together using anionic or cationic charges, which enables them to be removed from the mud. The flocculated particles, or flocs, are large enough to be mechanically separated by centrifuge, belt press or filter press.
In some cases the mud must be pre-treated to enable successful flocculation to occur. This may be by the addition of a primary coagulant or a pH modifier.
There are many different flocculant products with differing characteristics which are suitable for use with different types of waste fluids. Products are available with varying degrees of anionic or cationic charge, different molecular masses and in solid or liquid forms. The type of products required will depend upon the bentonite, the type of excavated ground, the type of water and any other additives or contaminants.
PSD has an in house laboratory for testing waste drilling fluids to assess what products are effective for its treatment. PSD holds stocks of a wide range of products and has access to products from many first tier manufacturers so you can rest assured that suitable products can be found and sourced. PSD will carry out testing free of charge to clients who rent a PSD flocculation and centrifuge system.
This technology is used across many industries including potable water and waste water treatment.
 THE PROCESS
PSD has a wide range of centrifuges from low flow units, to the largest easily portable centrifuges in Europe and can provide flocculation and centrifuge systems to handle flowrates from 3m3/hr to 70m3/hr. A complete system can often be transported to site on one 40’ articulated trailer. PSD can supply an operator to supervise the running of the equipment or to train your own staff.
In a typical system from PSD, the flocculant is mixed with water in an agitator tank to form a dilute solution, from where it is dosed by a positive displacement variable speed pump in to the feed hose to the centrifuge, at a point some distance upstream from the inlet to the centrifuge.
After partial dewatering by the centrifuge, the solids are ejected from the centrifuge in to a skip supplied by others or to the ground for uplifting and transport to a licensed tip. The fluid centrate from the centrifuge is usually a practically solids free liquid, which can normally be re-used for flocculant dilution or disposed of to the public sewer system (subject to you obtaining the appropriate consents).
The whole process is easily controlled and provides a neat, cost effective and environmentally responsible solution to the disposal of liquid waste material.
KEY POINTS
· No longer possible to dispose of liquid waste to landfill.
· Liquid waste must be processed before disposal, which is likely to result in increased off site treatment costs.
· Very few liquid waste processing sites in the UK, which is likely to result in increased cost to transport liquid waste.
· On-site treatment of liquid waste with portable equipment will normally significantly reduce disposal costs.
WHAT TO DO NEXT
For an assessment of how PSD can help reduce your liquid waste disposal costs, or just to find out more, contact us via the website or phone Adam Beeby on 01772 690076 or email him at adam@psdmud.co.uk
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