Math For Wastewater Treatment Operators Grades 3 & 4	Operation And Maintenance Of Wastewater Collection Systems - Vol 1	Operation And Maintenance Of Wastewater Collection Systems - Vol 2
Operation of Nutrient Removal Facilities	Operation Of Wastewater Treatment Plants - Vol 1	Operation Of Wastewater Treatment Plants - Vol 1, 7th ed.
Operation Of Wastewater Treatment Plants - Vol 2, 7th ed.	Pumps and Pumping	Sludge Engineering