Enhancement of Ultraviolet Disinfection of Wastewater by Low Pressure Water Jet Pretreatment: Effectiveness and Impacts on Bacteria

• Published in: Journal of environmental engineering (New York, N.Y.) Vol. 138; no. 7; pp. 796 - 803
• Main Authors: He, Cheng, McFadyen, Renée, Rochfort, Quintin
• Format: Journal Article
• Language: English
• Published: Reston, VA American Society of Civil Engineers 01.07.2012
• Subjects: Applied sciences; Case Studies; Case Study; Exact sciences and technology; General purification processes; Pollution; Wastewaters; Water treatment and pollution; Water pressure; Energy consumption; Particle size; High and low pressure water jet; Water jet; Wastewater management; Disinfection; Particle break up; Overflow; Waste water; Ultraviolet radiation; Indirect method; Bacteria; UV disinfection; Pretreatment; E. coli; Ultrasonic method
• ISSN: 0733-9372; 1943-7870
• DOI: 10.1061/(ASCE)EE.1943-7870.0000534

AbstractIt has been proven that the concept of using a high pressure water jet (HPWJ) to pretreat wastewater for the enhancement of ultraviolet (UV) disinfection of wastewater is an effective and cost-efficient alternative compared with the widely studied ultrasonic method. This study addresses: (1) the effectiveness of the pretreatment with a low pressure water jet (LPWJ) under similar experimental settings to the previous HPWJ study, (2) the water pressure impacts on bacteria in the treated wastewater, and (3) the difference in electrical energy consumption under treatment with different pressures. The results show that with the tested primary clarifier overflow (PCO), there were no real differences in enhancement of UV disinfection with LPWJ pretreatment operating under a tested pressure range from 0.97 to 6.80 MPa. More than 1 log unit improvement of UV disinfection efficiency can be achieved under all the tested pressures compared with treatment by UV irradiation alone when the UV dose is in the 20∼30  mJ/cm2 range. The general hypothesis for the enhancement of UV disinfection using a water jet is attributable to two factors: (1) reduction in the particle shield/shadow effects by breaking up the larger particles and (2) reduction in the resistance to UV irradiation by weakening the bacteria. Unfortunately, there is no easy and reliable way to test bacterial viability. In this study, an indirect method was proposed, and corresponding experiments were conducted for an investigation of the impact of water jet force on the bacteria. Results show that for the tested pressure range from 0.97 to 6.80 MPa, there was no confirmation that the bacteria in PCO were weakened after being treated by the water jet. The main function of the water jet pretreatment was to affect a reduction of particle size in the treated water, instead of weakening the bacteria themselves.