Ice pigging

Ice Pigging is the process in which an ice slurry is pumped into a pipe and forced along inside in order to remove sediment and other unwanted deposits to leave the pipe clean. It has many applications in the water, sewage and food industries. Ice pigging was invented and first patented by Professor Joe Quarini of the University of Bristol. Since 2010 Ice Pigging has been undertaken exclusively by SUEZ and its partners, who own the patent on the technology. 
The Process.
Ice Pigging has the benefits of solid conventional pigging, but without the associated drawbacks; the Ice Pig can flow like a liquid through obstructions such as changes in diameter and valves, and it can be inserted and ejected from the pipe using small diameter fittings. If an Ice Pig does become stuck it can be left to melt and flushed out after a few hours.
The process can be undertaken on all pipe materials, on diameters from 8mm to 600mm, and on lengths of several kilometres. The ice pigging process takes less time than traditional pigging methods for underground pipes and can be operated by fewer people reducing labour costs.
Minimal enabling works are required to insert the ice and remove it, this gives the benefits of not only less water supply disruption but also less traffic disruption for enabling works
Any water flushing methods (such as uni-directional flushing, air/water flushing or closed loop with sidestream filtration) are limited by the fact that as water flows through pipework, a boundary layer of slower flow occurs at the pipe surface, so the wall shear generated is small, even at flushing velocities of several metres per second. Because the ice pig moves through the pipework like a solid object, movement is concentrated at the pipe wall generating high wall shear even at velocities as low as 0.2m/sec.
Environmental impacts.
Ice pigging uses less water and requires less cleanup than traditional flushing or underground pipe pigging techniques. A significant amount of energy is required in the manufacture of the ice slurry, however this can be mitigated by using a renewable power source. 
Research and development.
The University of Bristol have produced a paper entitled "Investigation and development of an innovative pigging technique for the water supply industry." in which they have detailed the research that they have carried out. It looks particularly at how the properties of the ice pig behave with different ice fractions and varied levels of particulate loading as well as looking into the effects of shear strength, viscosity and heat transfer characteristics.
References.
www.ice-pigging.com