Acid-Resistant Sewer Rehabilitation with Spin-Cast Technology

Biogenic sulphuric acid corrosion (BSC) is a microbiological deterioration process unique to sewers and wastewater infrastructure. In the anaerobic conditions of slow-moving or backed-up sewage, sulphate-reducing bacteria produce hydrogen sulphide (H₂S) which enters the sewer atmosphere. Aerobic Thiobacillus bacteria on the concrete surface above the waterline oxidise H₂S to sulphuric acid (H₂SO₄), which attacks the calcium compounds in Portland cement. Attack rates of 3-15mm/year of concrete surface dissolution are documented in high-H₂S conditions. Standard OPC concrete has essentially no resistance to BSC - Gemite's specialist Spin-Cast mortars resist this attack at pH values as low as 1.

Spin-Cast production rates depend on pipe diameter and access. Typical rates are 80-200 metres of pipe per day for access-from-manhole work. A standard urban sewer rehabilitation project of 1 kilometre can be completed in 5-10 working days from access point to access point. During rehabilitation, the sewer must be diverted or flow controlled - typically managed by sewer bypass pumping around the rehabilitation section, with minimal surface impact. Our project team manages the complete sewer bypass design and installation as part of the rehabilitation programme.

Spin-Cast relining is applicable to concrete sewers (the most common material requiring rehabilitation), vitrified clay pipes, ductile iron force mains, and steel pipes. The host pipe must be sufficiently intact to maintain its structural shape during the spinning operation and to provide support for the new lining. Oval deformation or structural collapse of the existing pipe requires pre-lining repair before Spin-Cast can be applied. Ovality assessment is part of the pre-lining CCTV survey. Our technical team reviews the survey results and specifies any pre-lining repairs required.