Scottish Water, Ballachulish WTW & Glenachullish WTW


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Introduction

ACWA was awarded a contract for the design, supply, installation and commissioning of the mechanical and electrical equipment associated with a new water treatment works at Ballachulish and upgrading of the existing WTW at Glenachulish.

The scope of supply for Ballachulish WTW included sand / anthracite filtration, carbon contactors, limestone contactors, sodium hypochlorite dosing, chlorine monitoring and control equipment, turbidity and flow monitoring and MCC.

The scope of supply for Glenachulish WTW included new carbon contactors, limestone contactors, sodium hypochlorite dosing, monitoring equipment and MCC.

The raw water source for both WTW ’s is from a local river. At times of high flow the raw river water is high in turbidity and solids. Treated water from the WTW’s is to Scottish Water potable water standards.

Description

Ballachulish WTW
Raw water from the river is delivered to the water treatment works via flow monitoring. The raw water is pumped to two skid mounted fully automatic multimedia filters, operating duty / duty. The water enters the filters via distributors at the top of the vessels, passes down through the filtration media and out though a nozzle plate installed at the lower tangent. The filter bed comprises a layer of filtration sand and anthracite. Backwashing of the filters takes place on a timed basis or on detection of high turbidity at the filter outlet.

The filtered water is transferred to two GAC (granular activated carbon) vessels operating duty / duty. The filtered water enters the contactors via two distributors at the top of the vessels, passes down through the carbon media and out through a nozzle plate installed at the lower tangent. The outlet flow from the carbon contactors is monitored prior to the addition of sodium hypochlorite solution.

The sodium hypochlorite dosing system is a proprietary unit consisting of a storage tank and duty/standby dosing pumps. The hypochlorite solution is dosed to the filtered water (post GAC vessels) at the inlet of a static mixer prior to entry to a chlorine contact tank. The chlorinated water is measured before and after the contact tank, and a PID loop used to control the chlorine dose requirements.

The chlorinated water enters a limestone contactor via a nozzle plate installed at the lower tangent and passes upwards through the limestone chips and out through a collector at the top of the vessel. The chlorinated, pH corrected water is directed to clear water storage tanks.

A flow of filtered water from the multimedia filters is directed to a backwashing tank, which then supplies the required water for backwashing of the filters. The dirty backwash water is sent to a simple sand filter prior to discharge.

Glenachulish WTW
Raw water from the river is delivered to the water treatment works via flow monitoring, and passes through the existing pressure sand filters. The filtered water is transferred to two new GAC contactors operating duty / duty. Filtered water from the carbon contactors will be dosed with sodium hypochlorite solution prior to entry to a chlorine contact tank. The new sodium hypochlorite dosing system is a proprietary unit consisting of a storage tank and duty / standby dosing pumps. Chlorine monitors pre- and post- chlorine contact tank monitor the level of chlorination, and a PID loop is used to control the chlorine dose requirements.

Chlorinated water enters a new limestone contactor via a bottom distribution system. In order to control the pH a manual valve arrangement allows the inlet water to bypass the limestone bed. The pH corrected water is directed to existing clear water storage tanks.

Backwashing of the existing filters is either on a timed basis or initiated on detection of high turbidity of the filter outlet.

Project Details

Client: Scottish Water, Ballachulish WTW & Glenachullish WTW, Scotland

Industry: Water Treatment

Application: Sand Filtration & Granular Activated Carbon

Technologies