Sludge Dewatering in Durban — Ten 7 m × 20 m Tubes — Case Study

Case Study Brief

The Durban project required large-scale sludge dewatering using ten custom tubes, each 7 m × 20 m. Geosynthetics Africa manufactured the monofilament tubes and supplied the supporting lining materials. The working area used approximately 2,300 m² of 1.5 mm HDPE geomembrane and 2,500 m² of MIRAFI® S51 protection geotextile. The tubes provided a filtration enclosure for the pumped sludge, while the lined area managed collected drainage. The project reported operation without flocculant addition for the sludge treated. That result is specific to the material and operating conditions; polymer requirements for other sludge streams need separate assessment. Dewatering performance depends on sludge characteristics, pumping rate and the tube arrangement. Any discharge or reuse acceptance must follow the project’s water-quality requirements and relevant test results.

Waterproofing of Drain Pad with GSE HDPE Geomembrane

Dewatering Tubes on Site Ready for Installtion

Installed Dewatering Tubes

The Installation Challenge

The project needed large tubes with suitable seam strength and filtration characteristics, plus a lined arrangement for collecting filtrate. Sludge retention, flow and chemical-conditioning requirements depended on the material being treated.

Ten 7 m × 20 m monofilament tubes were manufactured in-house and installed with a geomembrane-lined working area and protection geotextile. The graded platform and collection arrangement managed drainage from the tubes. Reported operation without flocculants applies to this project’s sludge and conditions.

Installation Sequence

Prepare the dewatering platform

Establish the supporting surface, falls, perimeter containment and filtrate collection arrangement.

Install the protection and lining layers

Place the protection geotextile and HDPE geomembrane, complete seams and details, and inspect the lined platform.

Position and connect the tubes

Arrange the ten custom 7 m × 20 m tubes and connect the pumping system in accordance with the project layout.

Manage filling and drainage

Control pumping and filling, monitor the tubes and drainage, and assess the filtrate against the project’s water-quality requirements.

Field Quality Assurance (QA/QC) Checklist

Quality checks recorded on this installation.

Geomembrane trial welds performed at the start of each shift and on any change of welding conditions, with peel and shear specimens tested to destruction on site and results logged against ambient temperature, machine speed and operator before production welding commenced.

All geomembrane seams on the waterproofed drainage platform subjected to non-destructive testing across their full length — air pressure testing of dual-track fusion welds and vacuum box testing of extrusion welds - with any failed sections cut out, re-welded and re-tested.

Factory seam samples from each production run of dewatering tubes tested to ASTM D4884 and verified to retain more than 70% of parent fabric strength, with certificates issued per tube batch and cross-referenced to the mill certificate for the delivered fabric.

Each fabricated tube visually inspected on deployment for fabric damage, seam continuity and inlet port integrity, and the flat-laid alignment confirmed against the collection channel before slurry lines were connected.

Products Used in Project

Products supplied and installed on this project.

Geomembranes

Specification Conformity & Lab Verification

Key properties compared with the project specification.

Property	Test Method	Specification Minimum	Delivered Value (Average)	Margin Above Spec
Wide-Width Tensile Strength (MD)	ASTM D4595	105 kN/m	105 kN/m	Meet
Wide-Width Tensile Strength (CD)	ASTM D4595	105 kN/m	105 kN/m	Meet
Apparent Opening Size (O95)	ASTM D4751	≤ 200 µm	180 µm	Exceed
Factory Seam Strength	ASTM D4884	≥ 70% parent	75% parent	Exceed
Water Flow Rate	ASTM D4491	client spec	mill cert	Meet

“In-house project comment: The tubes were only one part of the Durban dewatering system. Bringing custom manufacture, platform lining and installation together helped the project manage both the sludge and the filtrate collection arrangement.

Ivan M

Project Manager · Geosynthetics Africa — internal project team

Sludge Dewatering in Durban — Ten 7 m × 20 m Tubes — 50,000 m³ sludge volume