Engineering Hub: get this sized for your plant
Describe your goal, effluent limit or sludge volume and receive a technology shortlist plus a sizing proposal – by email, no phone call required.
When the dewatering unit stops, the clock starts
A dewatering unit failure is one of the few wastewater plant events that creates an immediate, visible problem: sludge accumulates in storage tanks, lagoons fill, and disposal costs escalate by the hour. The instinct is to call a rental supplier and ask for the fastest available unit. That instinct is right — but the specification conversation that follows determines whether the rental unit actually solves the problem or creates a new one.
This article sets out the technical information a rental supplier needs to match equipment to your situation, and the site conditions that must be confirmed before delivery.
Key Facts: Rental Dewatering Specification
- Parameter
- What to confirm before ordering
- Sludge type and origin
- Municipal, industrial, mixed — affects polymer selection
- Sludge solids content (TS %)
- Determines throughput and press sizing
- Target dry solids content
- Sets performance expectation for the rental period
- Available power supply
- 3-phase voltage, amperage, connection point location
- Available water supply
- Polymer make-up water flow and pressure
- Discharge point for filtrate
- Gravity or pumped, distance from unit
- Access for delivery vehicle
- Width, height, ground bearing capacity
The four most common rental mismatches
Rental failures almost always trace back to one of four mismatches identified after delivery rather than before it.
Flow rate mismatch: The rental unit is sized for a peak flow that the site cannot sustain, or the sludge pump feeding it cannot match the press throughput. Confirm the actual sludge production rate in m³/h — not the design figure, but the current measured rate — and the pump capacity available to feed the unit.
Polymer incompatibility: The rental unit arrives with a polymer make-up system configured for a different polymer type or concentration than what is available on site. Confirm whether the site has liquid emulsion polymer or powder polymer, the storage volume available, and the make-up water flow rate.
Power supply shortfall: Rental screw presses typically require 15–45 kW depending on size. Confirm the available amperage at the nearest distribution board and the cable run distance. A generator may be needed if the site supply is insufficient.
Filtrate disposal: The filtrate from dewatering must go somewhere. Confirm whether the existing filtrate return line can accept the additional flow, or whether a temporary pump and hose run to a collection point is needed.
Confirm site access before confirming delivery date
Rental units on skids or in containers are typically delivered by articulated lorry. Confirm the access route width (minimum 3.5 m clear), overhead clearance, and ground bearing capacity at the intended installation point. A delivery that cannot reach the site adds days to the outage.
Information to gather before calling the supplier
The faster you can provide the following data, the faster a supplier can confirm equipment availability and suitability.
Technical data to gather before the rental call
- Current sludge production rate (m³/h or m³/day)
- Sludge solids content (TS %) — measured or estimated
- Sludge origin (primary, secondary, mixed, industrial)
- Polymer type available on site (liquid emulsion or powder)
- Available power: voltage, phases, maximum amperage
- Water supply: flow rate and pressure at connection point
- Filtrate discharge: gravity drain available or pump required
- Site access: vehicle dimensions, ground conditions, distance from road
- Target dry solids content and acceptable range
- Duration of rental requirement (weeks or months)
Sizing logic for a rental screw press
A rental supplier will use your sludge flow rate and solids content to select a press size. As a rough guide, a single-shaft screw press handling municipal secondary sludge at 2–4 % TS can process 2–8 m³/h depending on press diameter. Multi-disc presses cover a wider range and are more tolerant of variable feed consistency.
| Sludge flow (m³/h) | TS content (%) | Indicative press size |
|---|---|---|
| 1–3 | 2–4 | Small single-shaft (75–110 mm shaft) |
| 3–8 | 2–5 | Medium single-shaft or multi-disc |
| 8–20 | 1–4 | Large multi-disc or twin-shaft |
These figures are indicative only. Actual sizing requires the supplier to review your specific sludge characteristics, including viscosity, fibre content, and polymer response.
Managing the rental period
Once the unit is on site and commissioned, a few operational practices reduce the risk of secondary problems during the rental period.
How long does it take to commission a rental dewatering unit after delivery?+
For a skid-mounted screw press with a pre-configured polymer make-up system, commissioning typically takes 4–8 hours once power, water and sludge connections are made. Allow a further 4–12 hours for polymer dose optimisation to reach target dry solids content. Plan for a full working day from delivery to stable operation.
What happens if the rental unit does not achieve the target dry solids content?+
The most common causes are polymer dose or dilution water rate outside the optimum range, feed sludge consistency different from the specification, or a press speed setting that needs adjustment. A supplier technician should be available for remote or on-site support during the first 24 hours of operation. Document the actual feed TS and filtrate quality to support any performance discussion.
Can a rental unit handle industrial sludge with high grease or fibre content?+
Some rental units are better suited to industrial sludge than others. Screw presses with wider pitch screws and larger drainage gaps handle fibrous sludge more reliably. High-grease sludge may require a different polymer chemistry and a higher dose rate. Disclose the sludge origin and any known contaminants to the supplier before equipment selection — this is the single most important step in avoiding a mismatch.
After the emergency: planning the permanent replacement
A rental period is also an opportunity to gather performance data that informs the specification of the permanent replacement unit. Record daily throughput, polymer consumption per tonne of dry solids, energy consumption, and achieved dry solids content. This data set gives a supplier the information needed to size the permanent unit correctly and to compare equipment options on a like-for-like basis.
Contact: [email protected]
Equipment we supply for this
Engineering Hub: get this sized for your plant
Describe your goal, effluent limit or sludge volume and receive a technology shortlist plus a sizing proposal – by email, no phone call required.