Water Journal : Water Journal March 2011
conference reviews 48 MARCH 2011 water regular features PHOTO COURTESY OF ANNA ROMANOVA, UNIVERSITY OF BRADFORD, UK Taking sewers seriously: SPN6 November 7--10, 2010 E A (Bob) Swinton This IWA International conference, Sewer Processes and Networks, 6 (SPN6), was hosted by the Advanced Water Management Centre at the University of Queensland and attracted some 150 delegates from Australia and overseas. For the social occasion the overseas delegates (as well as the locals) were thrilled by an exciting dinner at Sea World watching the dolphins perform -- with two of the overseas keynote speakers invited into the water to stroke them. The Conference was held at the Holiday Inn, Surfers Paradise from 7-10 November 2010. Major sponsors were DHI, Sydney Water and Allconnex Water. The technical content was top-rate. Eighty-five international submissions were reduced to 48, with 13 posters. Contributions from Austria, Canada, China, the Czech Republic, Denmark, Egypt, France, Germany, Hong Kong, Korea, Luxembourg, the Netherlands, New Zealand, Portugal, South Africa, Spain, UAE, the UK and the US backed up the local papers. Inflow, Infiltration and Exfiltration After a welcome by Professor Zhiguo Yuan, Chairman of the conference organising committees, with grateful acknowledgement of the sponsors, the lead keynote address came from Professor Bryan Ellis of Middlesex University, UK, on the topic of inflow, infiltration and exfiltration. Despite the hopes and stipulations of regulators, there is no doubt that underground sewers will never be completely watertight. As we all know, age, cracks, joints, root intrusion and earth movement all combine to present us with a leaky system, usually (even our Australian separate sewers) yielding Peak Wet Weather flows in excess of three times the normal rate to treatment plants. In the more serious cases, 'pumping' in and out of breaks leads to void formation in the surrounding soil and eventual collapse, often with disastrous consequences. In the UK, some 5000 collapses occur every year, with a bill of some £8.5 billion over five years. Data from both the CSIRO and France shows that 50- 70% of problems stem from household connections, but mandatory inspection and repair seem to be politically and economically impossible. Infiltration from trenches below the water table can be estimated only with difficulty, since its hydrograph extends long after the rain event. Investigations are in progress in the EU to estimate leakage by using the consequent dilution of COD (corrected for the normal diurnal variation) as a tool, using submersible spectrophotometer probes, and the EU-funded APUSS project is using hydrogen and oxygen isotopes where there is a difference between the water supply and the local groundwater. Nonetheless, there are varied views on the cost benefits of rehabilitation of suspected lengths, since the problem may be merely exported downstream. Exfiltration is not so much of a problem, even though it can lead to local pollution. It has been tested in a full-scale rig at Dundee University in Scotland. They found that leakage from a simulated crack into the backfill gravel practically stopped after a few hours due to self-sealing by sediment, paper fibre and biofilm, though this could be washed away by flow surges and certainly by jetting. His full paper quotes ranges of infiltration and exfiltration from various global sources and a useful list of references. Corrosion and Odour Management The second keynote was presented by Professor Zhiguo Yuan, Deputy Director of the Advanced Water Management Centre at the University of Queensland, who reviewed recent advances in research and development on corrosion and odour management. A literature review of advances in Europe, the US and Australia has led to the identification of knowledge gaps and the focus for further research projects that encompass microbiology, physical chemistry, biotechnology, materials science and mathematical modelling, with a strong emphasis on collaboration with industry. These can be separated into the three zones of activity in a sewer: • Corrosion in the headspace above the wastewater, biofilm reactions on the sewer surface and protection against corrosion of concrete and mortars. • Liquid phase reactions, modelling of sulfide production and control of H2S by chemical agents. • Management of the gaseous phase and odours. The University of Queensland has concentrated on the liquid phase, starting with techniques for on-line measurement of the sulfide ion in the sewer environment. Samples for calibration must either be analysed immediately at an on-site laboratory Guests at the conference enjoyed a waterside dinner at Sea World at the Gold Coast.
Water Journal April 2011