The largest methane gas collection programme in the world has begun at a huge sewage treatment plant at Werribee near Melbourne, Australia. The plant is expected to generate 800 KW of electricity. Sewage at the plant is treated in ponds in a two- phased process. The first is by an aerobic bacteria which breaks down sewage and generates methane, carbon dioxide and odorous gases. In the second process, mechanical aerators introduce oxygen into the sewage. Gas is collected from the ponds by a system of plastic pipes which are up to 500 mm in diameter.