Stormwater Turbidity

NEUTRA-MILL WATER TEATMENT SYSTEM – CASE STUDY

STORMWATER TURBIDITY – COAL MINE – KALIMANTAN, INDONESIA

• Turbidity lowered
• Ability to treat multiple ponds
• Portable unit for ease of transport
• Water quality improved for release or reuse onsite
• No extra infrastructure required at treatment location

LOCATION

This large mining site lies less than two hundred kilometres north of the equator on the east coast of Kalimantan, Indonesia.,/p>

SETTING AND CLIMATE

The region has a tropical climate with an annual rainfall of 2000-3000mm. The rainfall pattern is typified by localised short-lived cloud bursts. Much of Kalimantan has been affected by the spate of forest fires over the last several years, reducing the coverage of mature vegetation.

CLIENT

Multinational mining company.

BACKGROUND

The mining at this site exploits several gently dipping Tertiary coal seams that are one to five metres thick. Mining is conducted via three separate opencuts yielding coal of varying sulphur and moisture content. The coal is recovered and transported using ‘drill and blast’, and ‘excavator and truck’ methods for transport to the intermediate ROM stockpiles.

SITE ISSUES

Local topography and a high overburden to coal seam ratio result in large opencut areas and overburden piles. Some of the soils that are exposed during the mining process contain dispersive clays that are readily eroded during rainfall events.

The clays are transported with the surface run-off, resulting in high suspended solid loads in some water storage dams. The minesite environmental department wished to reduce the suspended solid load in these dams to enable discharge from the site.

REQUIREMENTS

The site was familiar with the Neutra-Mill Technology as other units were being used for the treatment of acid mine drainage. Previous work at the site had shown that alum (aluminium sulphate) was an efficient and cost effective method for reducing the suspended solid load.

Earth Systems was asked to design a Neutra-Mill system that could be used to efficiently dispense a flocculant (e.g. alum) to reduce the suspended solids in specific water storage dams.

Design criteria for the Neutra-Mill system included:

• self contained regarding power requirements,
• on-water mobility,
• ability to be transported easily between water bodies,
• simple to operate by site personnel,
• ability to also dispense lime for pH adjustment if required following addition of alum, and
• no extra infrastructure requirements.

TREATMENT OPERATION

The resultant Neutra-Mill system, called a Turbidity Mill, was powered by an on-board 5 KVA generator and propelled through the water with a 12V outboard motor. Reagent is continuously fed into the Turbidity -Mill as it is driven around the water body dispensing the flocculant.

Preliminary training and trials were conducted on a 180 ML dam with high suspended solid levels. Six hundred kilograms of alum were dispensed into the water body over a two hour period. Two personnel were required to operate the unit – one to drive and the other to load the reagent.

RESULTS

Dramatic visual improvement in the water quality was evident less than 18 hours after treatment had been conducted. It is anticipated that the Turbidity Mill will dispense 2-3 tonnes of alum per hour during routine treatment.

The results showed that the Turbidity Mill:

• required no extra infrastructure and only two personnel to effectively treat the waterbody,
• was a cost effective method for treating large bodies of water, and
• will be an important tool in water management at the site.