 In the 1980s the capacity was increased again with the addition of another activated sludge treatment train, using course bubble diffusion.The last expansion occurred in the 1990s when an Modified Ludzack-Ettinger activated sludge train was constructed, bringing the permitted capacity up to 27.5 MGD.TPS recently underwent a major facility upgrade in treatment ability that coincided with a decrease in capacity by 1 MGD.