Student:	Tuğçe KOÇ
Supervisor:	Prof. Dr. Mehmet BERKÜN
Department:	İnşaat Mühendisliği
Institution:	Graduate School of Natural and Applied Sciences
University:	Karadeniz Technical University, Turkey

Title of the Thesis:	DETERMINATION OF T90 AND INVESTIGATION OF ITS EFFECTS ON THE OUTFALL DESIGN
Level:	M.Sc.
Acceptance Date:	6/8/2008
Number of Pages:	151
Registration Number:	i1954

Summary:

For the evaluation of outfall systems according to the wastewater discharge standarts,

dilution criteria should be obtained. Because; the dilution level of wastewater and its

organic matter content are important for the decrease of coliforms.

The parameter T90 used in the 3rd. level dilution expresses the time in which the

concentration of a determined indicator bacteria reduced by 90 %. The estimation of the

bacterial die-off period (T90) is one of the most important aspects in the design of outfalls.

The objective of this study is to determine the variability of T90 values depending on

the different environmental conditions and the type of chosen indicator bacteria. The

effects of these variations on the dilution and the design of the outfall system are

investigated.

Key Words: T90 ,wastewater, outfalls, dilution, bacterial die-off, water quality indicators,

Blacksea