Water Journal : Water Journal November 2012-1
odour management refereed paper technical features 56 NOVEMBER 2012 water • Odour is a complex mixture of organic and inorganic substances and Photoionisation treats all of them; • Both highly complex odours and single compounds are treated effectively; • The process handles peaks (spikes) through its inbuilt buffer function; • It has minimal requirements regarding inlet temperature and/or humidity; and • Its small compact units may be located in a decentralised manner, directly at odour source(s). Because of these advantages, Photoionisation is often applied to control of odours at sewage pumping stations. For EMTP, however, another advantage was important: the Photoionisation units were placed directly at their odour sources by short and direct duct connections. This configuration provided more operational flexibility, since not all tanks are used all the time, whereas the former biofilter was permanently connected to all the four odour sources through a central underground ducting network. This decentralisation allows for flexible use of the installed units and provides considerable energy savings. Due to the short duct connections and the low-pressure loss of the Photoionisation units themselves, overall system pressure loss is reduced considerably, which in turn reduces the installed and operation electrical power. Furthermore, the flexible use of the tanks allows shutting down single Photoionisation units if they are not required to run, which further reduces the energy consumption. The process of Photoionisation does not require a start-up time; full performance is available directly after start-up of the odour treatment unit. Methodology Besides installation costs, the operation demand and costs for the different odour control technologies have been studied in detail. Maintenance records of the former biofilter were available. The operation of the Photoionisation units at the EMTP was also well documented. Regarding operation, the following aspects have been studied: • Electricity demand; • Demand for other consumables; • Necessary personnel input; and • Odour monitoring. Operational and investment costs have been studied based on the German standard VDI 2067. This standard allows for comparison of all relevant costs on an annualised basis, the results of which are shown in Figure 5. Investment costs are considered using an interest rate and minimum of 15 years (equipment) and 30 years (structures) operation time respectively. Operational costs for Photoionisation are mainly based on exchanging consumables about once per year. These consumables are UV-lamps, catalysts and dust filters. On the biofilter side, the main consumables are the biofilter material, which had to be replaced at least every three years. Operational costs for the biofilter were dominated by high electricity demand. The difference in energy costs is caused by the different airflow rates required for the two different systems based on their different pressure losses. The biofilter was designed for treatment of QBF = 25,000m3/hr. This airflow rate was required to minimise concentration of odour substances in the raw off-gas. Regarding airflow, the operator stated “the more the better”. The dilution taking place through this high airflow rate helped the biofilter to stay operational. The high- pressure loss of the biofilter is twofold; caused by both the extensive central piping network and the pressure loss of the filter bed itself. Photoionisation, in contrast, accepts highly concentrated odours allowing for lower airflow rates to be used. The total airflow rate of the four installed Photoionisation units amounts to only QPI = 7,500 m3/hr. Furthermore, due to the direct installation of the units at the odour sources much less piping is required and hence reduced pressure loss results. It should be noted that the biofilter design was not oversized, but the technology of biofiltration requires high dilution rates for its function. Photoionisation accepts high contaminant concentrations and does not require dilution in this range. The comparison of biofiltration and Photoionisation is therefore valid, as it is based on “function” not “flowrate”. Chemical scrubbers were not considered, due to expectations of high control and maintenance requirements. Odour monitoring has been done on the basis of taking grab samples by gas detection tubes and periodical online H2S measurement by ODALOGs. Odour monitoring still continues; however, most important for the EMTP Plant Management is that the odour complaints have decreased to a minimum and are not now linked to the sludge reception facility. Results Operational costs have been analysed and are presented according to VDI 2067 as annualised results (see Figure 5). The comparison shows that the Photoionisation process is extremely competitive in regard to these costs. The technology provides large savings in energy consumption and personnel input. Furthermore, the decentralised approach provides considerable operation flexibility. Before installation of the full-scale Photoionisation units, testing was carried out with a mobile demonstration unit. The demonstration unit was made available by Neutralox Umwelttechnik GmbH. The test was carried out for two reasons: to demonstrate the effectiveness and suitability of the process under real operation conditions; and to collect design data. Figure 4. PI unit at the reception station, EMTP.
Water Journal December 2012
Water Journal September 2012-1