Lochaline TTU Case Study

The Modular Water Treatment Experts

Project Overview

The Lochaline WTW was identified for replacement with a membrane treatment plant as part of the Scottish Water SR15 Water Quality Enhancement Intervention Programme due to the risk of water quality failures and growth in demand in the local supply zone.

Works location map

An effective cryptosporidium barrier was required at Lochaline WTW. To achieve this a Nanofiltration (NF) Membrane based process was installed adjacent to the existing plant. The maximum raw water flow to the works was 90m³/day during Phase 1 of this project, however the NF plant delivered during this phase, was sized to deliver the full Phase 2 (Growth) deployable output of up to 195m³/day.

Through Scottish Water’s Non-infrastructure Alliance with ESD, Ross-shire Engineering (RSE) was engaged to design, manufacture and install a 195m³/day Nanofiltration modular and Transportable Treatment Unit (TTU) membrane plant operating at 85% recovery, on the Lochaline site.

Phase 1a of the project included Inlet Strainers, Membrane Feed Pumps, Recirculation Pumps, Nanofiltration Membranes, CIP facility, Sodium Hypochlorite dosing, Chlorine Contact Pipe, Re-mineralisation Tank, Chemical Waste Tank, Site Motor Control Centre, Software and System Integration, Instrumentation, Telemetry and Welfare Facilities, all housed within the TTU. Other work included a new raw water main, dechlorination chamber, standby generator with power auto-changer panel, a treated water pumping station and a new water main.

Phase 1b of the project included a new 146.3m³ capacity Clear Water Tank (CWT-1)

Phase 2 (Growth) will involve the construction of a new Service Reservoir and changes to the Treated Water Pumping Station installed under Phase 1b.

Project Overview

RSE’s modular TTU product range allows us to facilitate a quick turnaround of our Client’s scope requirements, in to a detailed BIM design and through manufacture within our state of the art off-site modular assembly facilities.

RSE’s modular TTU product range allows us to facilitate a quick turnaround of our Client’s scope requirements, in to a detailed BIM design and through manufacture within our state of the art off-site modular assembly facilities.

An innovative design approach was required due to site topography and access constraints, this allowed for the incorporation of a modularised welfare unit to accommodate all of Scottish Water’s operational requirements and has been well received by our clients.

Utilising our group manufacturing capability ensures a collaborative approach for our clients. As Principal Contractor, RSE also manufactured and produced the TTU. Ross-shire Engineering’s specialist chemical dosing company PSI were engaged to design and manufacture a modular solution for Sodium Hypochlorite disinfection. PSI adopted a pioneering approach which led to them bringing the main process line within the dosing unit, negating the need for extensive pipework runs and reduced the installation and maintenance requirements.

The TTU was designed and assembled at Ross-shire Engineering’s Modular Facility of Excellence base in Muir of Ord, before undergoing comprehensive testing.

We offer a unique and unrivalled service for our clients with design, manufacturing, assembly and off-site testing all delivered within our Muir of Ord Modular facility of excellence. As our company has grown so has our facilities and our innovative thinking challenging convention of what can be delivered off-site. What would have been traditionally delivered as an in-situ civil solution - like the chemical contact pipe and bulk waste tank, have now been incorporated in to our off- site modular package. This enables the complete water treatment works to be manufactured and assembled in a controlled environment. Once off-site testing and commissioning is complete we separate the units, mobilise to site and complete final site testing and commissioning comfortable in the knowledge that this or the turn key solution will work first time and provide maximum customer satisfaction.

Fig 1 (top left) - Lochaline TTU Floorplan. Fig 2 (top right) - Lochaline WTW – 3D model. Fig 3 (bottom left) - Lochaline WTW – 3D Elevation. Fig 4 (bottom right) - Lochaline WTW – 3D Section.

Ross-shire Engineering’s in-house design team transforms a Water Treatment Works concept in to a detailed BIM Level 2 design. Our Design for Manufacture & Assembly (DfMA) process enables a seamless transition from design in to fabrication and modular assembly within our specialist facilities.

We have control over every aspect of the modular plant delivery process with design, fabrication and assembly within walking distance. Having all our facilities in the same location saves time compared to a traditional in-situ construction of a new water treatment works.

Our in-house BIM design capability and DfMA approach to Modular Off-site construction allows us to support our client’s internationally.

The units can be closed, fully clad, sealed and ready to be shipped by road or boat to anywhere in the world. This philosophy is scalable and is something that RSE are continuously developing.

Following testing and commissioning the Lochaline plant is separated into its four modules and carefully prepared for the 118 mile journey by road to its permanent home via the A9, the A82 and the Corran ferry crossing.

Water Quality Tables

The raw water treatment plant and in particular pre-treatment, NF membranes, CIP and post treatment remineralisation were selected based on suitability for operation to treat the following raw water quality envelope.

Note:- ‘<’ denotes laboratory detection limit.

Membrane Cleaning

  • Foam Ball Cleaning - Yes
  • Frequency - Daily (Every 4 hours; duration 10 minutes)
  • Frequency of CIP Cleaning - Every 3 months
  • Chemicals used for CIP cleaning - Citric Acid / Sodium Hypochlorite

Sodium Hypochlorite Dosing

PSI adopted a pioneering approach which led to bringing the main process line within the dosing unit, negating the need for extensive pipework runs and reduced the installation and maintenance requirements.

Chlorine Contact Pipe (CCP)

The Chlorinated Water flows through the Chlorine Contact Pipe (CCP) to ensure that there is the required contact time for disinfection. Incorporating the CCP within the modular construction has reduced the amount of civils work on site.

Waste Water Tank

The Waste Water Tank has been incorporated within the modular structure, which has allowed it to be constructed in steel and reduce the amount of civil work on site.

Laboratory and Welfare Facilities


The project was successfully completed on time, defect free with acceptance from Scottish Water. Scottish Waters Customer Service Delivery (CSD) operatives are pleased with the new plant’s performance, see post below from Douglas Millican, Scottish Water CEO, following a recent visit to the site.

Jeff Forrester - ESD, Delivery Project Manager

Challenges to a project like Lochaline are disruption to the local community which we want to keep to a minimum. The advantages of a Transportable Treatment Unit (TTU) is that the programme is reduced, management of traffic is reduced to a minimum and there is less disruption to the local community, this is very important as it allows them to be engaged and on board with the project. This has been very successful on the Lochaline project. Residents live very close to the site, keeping them engaged allows them to see the time scale for disruptions has been vastly reduced due to the method of constriction that was chosen."

Paul Gerard – ESD – Design Lead & Process Engineer

The Lochaline WTW was awarded to ESD from SW in May 2016. With the assistance from RSE, the design was agreed, developed and a full working solution was delivered to site within 8 months in January 2017. The project rocketed along at a very high speed and worked first time. This was only through the strong collaboration between ESD, SW and RSE Design and Delivery teams. The early engagement with RSE has allowed the innovative modular approach to water treatment and has transformed the industry, especially in more remote locations. Lochaline is a successful example of supply chain collaboration, working together to provide a positive and successful outcome for SW and their customers. The challenges on this project were the time frames due to the water quality at Lochaline, the site size and location."

Gavin Steel - Scottish Water’s Regional Communities Manager for the Highlands

This project is a great example of Scottish Water, ESD and Ross-Shire Engineering working together to deliver a positive result for our customers."

Scope Summary

An effective cryptosporidium barrier was installed at Lochaline WTW. To achieve this a Nanofiltration Membrane based process with a deployable output of up to 195 m³/day. Also included are provision for Welfare Facilities, Membrane Feed and Recirculation Pumps, new Clear Water Tank (CWT-1) of capacity 146.3m³, Remineralisation Tank, Chlorine Contact Pipe, Dechlorination Chamber, Standby Generator, Site Control System, Telemetry and new domestic waste Septic Tank.

  • Membrane Plant building including laboratory and welfare facilities
  • Membrane Filter Feed Pumps
  • Raw Water Feed Pumps
  • Strainers
  • Membrane Filtration Modules
  • Membrane Clean In Place (CIP) and Neutralisation facility
  • Permeate Tank
  • Membrane Filter Recirculation Pumps
  • Disinfection (Sodium Hypochlorite dosing and Chlorine Contact Pipe (CCP))
  • pH Correction (Limestone Contact Tank)
  • Re-lift Pumps
  • Final Water Flow Monitoring
  • Water Quality Sampling for control and Regulatory purposes
  • Waste Water Tank
  • Motor Control Centres
  • Local Control Panels
  • Telemetry

Additional Site scope included:

  • Dechlorination Chamber
  • Standby Generator
  • Septic Tank
  • Civil Groundworks & Drainage
  • TTU Building Foundations
  • Services
  • Clean Water Tank
  • Treated Water Pumping Station