Water and Effluent Treatment Magazine
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12 WET NEWS AUGUST 2016 Conventional treatment are effective at removing Cryptosporidium but there are inherent weaknesses in the technologies. atg's Barry Hopton reveals all. The challenge: Tackling the problem of micro- organisms and pesticides INSIGHT Water treatment " The disinfection of public water supplies is a statutory requirement in England and Wales. Water supplied for domestic or food production purposes must not contain any micro-organism or parasite at a concentration which could constitute a potential danger to human health." So says the Drinking Water Inspectorate's (DWI) Guidance on UV disinfectioni. The phrase "micro-organism or parasite" includes, of course, Cryptosporidium which is still a major challenge to the water industry. There are several reasons for this, not least of which is the notorious resistance of the protozoan to the most widely used disinfectant, chlorine. The situation is not helped by the fact that monitoring Crypto- sporidium is not easy and, even if it were, the Water Supply (Water Quality) Regulations give little guidance on THE CONCEPT • Atg's ultra-efficient 800W Amalgam UV lamps offer guaranteed lamp life of 16,000 hours • The 800W Amalgam UV lamps reduces the number of lamps, quartz and seals by more than 50% • The first UV systems in the water supply industry were installed on good quality borehole sources • The technology is increasingly replacing traditional chemical systems on surface water sources NEED TO KNOW 1 Protozoans, which include Cryptosporidium, are resistant to the widely used disinfectant, chlorine 2 The average number of Cryptosporidium oocysts per 10 litres of water is less than one 3 UV disinfection has been used for water supply in the US for more than ten years 4 Membrane filtration is an effective, if very expensive, barrier THE VERDICT "The future looks good for ultraviolet disinfection but manufacturers are far from complacent" Barry Hopton,, atg Three installed 30 lamp UVLW systems featuring the very latest in ultra-high output, low pressure Amalgam UV lamp technology and optimised chamber design acceptable levels. Regulation 29 of the 2000 Regulations required that "the average number of Cryptosporidium oocysts per 10 litres of water is less than one". This required a physical barrier. Conventional treatment pro- cesses – coagulation, floccula- tion, clarification and filtration – are effective at removing Cryptosporidium but there are inherent weaknesses in these technologies. Membrane filtra- tion is an effective, if very expensive, barrier and was installed by a number of water companies. Regulation 29 was revoked in the 2007 Regulations and current Regulationsii require simply that "a water under- taker… shall disinfect the water…". This places the onus on the water supplier to ensure that the water put into supply is subjected to disinfection which it defines as "a process of water treatment to remove or render harmless to human health every pathogenic micro-organism and pathogenic parasite that would otherwise be present..." This relaxation opened the door to the use of alternative technologies and, for the first time, DWI allowed the use of ultraviolet (UV) irradiation as a means of controlling Crypto- sporidium and similar patho- genic protozoans. UV had long been proven to inactivate proto- zoans. A 2004 WHO reportiii summarises research that has demonstrated a 3-log (99.9%) inactivation of Cryptosporidium and Giardia at a UV dose of less than 10mJ/cm2 – a significantly lower dose than is required to inactivate most bacteria. But, given the difficulty of monitoring, how is it possible to be certain that protozoans are inactivated to a safe level? The DWI Guidance on the use of UV irradiation for the Disinfection of Public Water Supplies states that water suppliers "must pre-treat waters… the turbidity of waters to be disinfected should be maintained below 1NTU. In addition, the recommendations … summarised in the Badenoch and Bouchier reports, are still relevant and considered as good operational practice". It also advises that "chlorine and chloramine used to provide a residual chemical disinfectant concentration into supply should be dosed a§er UV processes". So UV, at an adequate dose, is an effective primary disinfect- ant, inactivating bacteria and protozoans, including Crypto- sporidium. It produces no dan- gerous disinfection by-products and involves no hazardous chemicals. The one requirement that UV cannot meet is protecting water in the distribution system but, with the microbiological burden removed, residual chlorination is all that is needed. •