Blog-Technical
A Short History of Diffusers in Australia
Fine bubble diffusers have been used in Australia since the late 1960s, from a time when many new activated sludge plants were built and others converted from trickling filters. Their use increased greatly from about 1975 after the Arab oil crisis forced energy prices up and curtailed the use of less-efficient surface aerators.
The earliest plants used ceramic domes and discs in which aluminium oxide particles were bonded together in a fused glass matrix at high furnace temperatures. Later plants in Europe tended towards resin-bonded silica sand moulded into tubes and fired at much lower temperatures. Both types of porous diffuser were capable of generating fine bubbles of 2-5mm diameter and hence achieving high oxygen transfer efficiencies.
Porous diffusers have a low intrinsic head-loss when new, and hence risk uneven air distribution at low air flows. Moreover, they are vulnerable to backflow and clogging if uninterrupted air flow cannot be maintained. Largely because of this, a new generation of membrane diffusers was developed in Europe which could be operated intermittently.
The first membrane diffusers used in Australia were imported from the German company GVA in about 1985, and were in tubular form with fine-slit EPDM membranes. Disc-type diffusers became available soon afterwards. In both cases, early diffusers used EPDM membranes, and a wide variety of proprietary compound formulations has been used to maximise effective service life.
Because membrane diffusers can tolerate interruptions in air supply and have a very wide turn-down range, they have largely superseded porous diffusers for most new applications in recent times.
Tubular diffusers are generally supplied in pairs, mounted either side of supporting pipe laterals. These can be of square tube, or of plastic or stainless-steel pipe. The diffusers are typically mounted in pairs either side of their support laterals and are usually held in place by tie-rods.
Disc diffusers are commonly mounted atop plastic or stainless-steel laterals, and have a variety of fixing systems. Their membranes are typically held in place by locking rings which allow them to be quite simply replaced in-tank.
Tom Lawson (September 2020)