With rising maintenance costs and outdated equipment, Timaru District Council implemented a locally built screening solution that improved safety and reduced manual handling and disposal.

Effective waste management is crucial for cost savings, operator safety, and environmental sustainability, particularly where ageing or inadequate screening systems can lead to high maintenance costs and downstream network issues. Timaru District Council recently addressed a long-standing issue at the Geraldine Wastewater Treatment Plant, where an old screw/auger inlet screen was no longer fit for purpose.

Old System Clogged Weekly

The council’s original screening system, a standard product originally designed decades ago for a very different waste stream, struggled with modern loads. Back then, rags were burned and non-biodegradable materials such as wipes or nappies weren’t commonly flushed. Today, hundreds of similar outdated screen units remain in use across New Zealand, potentially struggling to cope with modern wastewater loads.

At the Geraldine Wastewater Treatment Plant, the system clogged up to three times a week as fibrous material bound at the top of the auger. Operators were forced to manually cut tangled rags using serrated blades, then manually dispose of them by hand into a wheelie bin. This was not only a time-consuming task but it also presented significant health and safety risks. The auger tube had also failed more than once due to mechanical strain.

Cleaner Output with Reduced Disposal Frequency

To modernise the inlet, a fully automated escalator screen was locally fabricated, sized, and installed to suit the site’s requirements. Its 5mm retractable perforated plates lift and separate solids from the incoming flow, feeding them into a hopper tank. From there, a Haigh macerator pump transfers the material to a Haigh Liquid Separator and Compactor (Lisep) unit.

Inside the Lisep unit, macerated screenings enter a rotating centrifugal sieve with 3mm perforations, which remove 98% of organics and return them to the process flow via a decant line downstream of the Escalator screen. Remaining solids are transferred into the integral compactor, producing a relatively dry, low-odour plug suitable for landfill or incineration.

Disposal frequency is also expected to reduce significantly due to the cleaner output and reduced moisture content. The on-site wheelie bin, previously emptied frequently, is now expected to require clearance only once every two to three months.

The Escalator screen was designed for safe, low maintenance operation. With all moving parts mounted above the waterline, there are no components in the flow path, reducing wear and eliminating the need for confined space entry. Features such as quick-release perforated panels, cartridge rollers with easy-to-remove inspection covers, and a deluge backwash system allow all servicing to be carried out easily at ground level. By keeping mechanical components above slab level, the design also avoids motor flooding and further improves operator safety.

The New Zealand manufactured proprietary control panel has a user-friendly HMI screen complete with telemetry signals suitable for SCADA integration. This allows adjustments and controls to be managed remotely by the council.

With a high average screening capture ratio of 79% at 5mm, low headloss via VFD controlled Escalator drive motor, and compatibility with channels up to 3 metres wide and 10 metres deep, the system provides a future-ready alternative to outdated screening technologies.

The system was designed to fit the existing 500mm-wide by 1200mm-deep concrete channel on site, with no structural changes required. A key benefit of the project was the local fabrication of the escalator screen, avoiding import and supply chain delays. With strict end-of-year budgeting constraints in place, the entire solution was designed, built, installed, and commissioned in under six weeks.

The result is a safer, cleaner, and far more efficient inlet works - purpose-built for the realities of today’s wastewater environment.

Features & Benefits

• High capture rate: 79% average screening efficiency at 5mm.
• Flow-responsive: VFD-controlled motor adjusts speed to match inflow.
• Low-maintenance design: No flow-contacting parts; all mechanics mounted above coping level.
• Optimised screening: 45° installation angle with tines to prevent rag rolling and lift larger matter.

Find out more about The Haigh Lisep Unit here.