INTRODUCTION

As it becomes recognized that water resources protection will require integrated regulations for wastewater effluents discharges, accomplishing the disinfect ion process by use of an appropriate disinfectant has been considered to be an essential task for preventing health risks of direct or indirect wastewater reuse applications, particularly in water-limited regions (Emerick et al., 2003; Goosen and Shayya, 2000). But by use of conventional process of chlorination problems such as producing toxic by-products and questionable efficiency on high turbid and ammonia-rich effluents are often reported. On the other hand, high free chlorine concentration (beyond the breakpoint) is required to inactivate cysts and viruses of concern (Emerick et al., 2003; Metcalf and Eddy., 2003). Thus, a number of facilities in advanced countries are in the stage of substituting chlorine by other disinfection operations. Ultraviolet (UV) as a completely chemical-free process is a proven technology that enables wastewater to be disinfected and reused economically and safety (Masschelein., 2002). While technologies using Low-pressure (LP) lamps are still more common, the new guidelines also address new types of UV systems and now technologies using Medium-pressure (MP) lamps are considered to be a solution for better disinfecting wastewaters of poor quality and for flow rates greater than 140 mgd, so trend globally is more towards MP system (Cairns and Wright, 2000; Swift et al., 2002). Of course, MP systems are more energy consumptive but have fewer components to replace, thus in terms of objective choice comparing the higher power cost for the MP system with the higher component cost (Sleeves, ballasts and lamps) for the LP option is essential. Indeed, each has merit and the total cost of the project is being used to determine the successful vendor (Cairns and Wright, 2000; Stedman., 2004). The purpose of this study was to determine the feasibility of MPUV lamp in disinfect ion of a highly polluted industrial wastewater and the extent to which this lamp type can be used in these applications. This study has been performed in 2004 and all the wastewater analyses had been accomplished in the laboratory of Environmental Health Department of TUMS.

MATERIALS AND METHODS

UV equipment: The UV system source was a medium pressure mercury lamp. The lamp’s characteristics are presented in Table 1. In contrast to the low-pressure lamps, which can be precisely monitored with a calibrated photo detector, the irradiance of the MP lamps cannot easily determined by similar available apparatus. This being the case, the data was confined to the determination made by the lamp manufacturer, which was reported to be 90 μW cm^–1 UV irradiance in 1 M from the new lamp. For running the experiments by this lamp, a lab scale UV submerged system was arranged with 3 L effective volume and 10 cm ID. This single-lamp reactor was adjusted to operate at the flows of 18 and 6 L min^–1 in the equivalent contact times of 10 and 30 sec. Figure 1 shows the used UV reactor. The MP lamp was enclosed within a quartz jacket in order to prevent the direct contact of lamp with wastewater.

Wastewater samples: The samples were collected from Pegah Milk Factory in Tehran. It should be noted that food processing in Iran produces the highest volume of industrial wastewater. Sampling of the secondary effluent of this factory was performed (totally 13) on grab basis in the spring and summer of 2004. The characteristics of these samples are presented in Table 2.

Fig. 1:	Medium pressure UV reactor for wastewater disinfection

Table 1:	The UV lamp specifications*
*Technical information report from the lamp manufacturer (Arda Inc. France-1995)

Table 2:	Characteristics of Pegah Secondary Effluent Samples in the period of the study

All the analyses have been performed according to the procedures described in Standard Methods (APHA., 1998). Comparison of disinfect ion results of various samples has been accomplished by determination of coliform group (using 15 tube test) (APHA., 1998).