Waste Management
Keeping Sludge AD Working
Aug 19 2009
Southern Water has an important routine; every single day it checks the health of its sewage sludge anaerobic digesters on eighteen sites. There, each day Southern Water treats and recycles 1,400 million litres of wastewater from nearly two million households at 373 treatment works from its 21,500-kilometre sewer network. With that huge responsibility this utility company, like any other, needs to ensure the security of its sewage sludge digesters working at their optimum. Central to achieving that is Southern Water’s ‘Best Practice for the Operation of Sludge Digesters’. It produced this document to ensure industry best practice operating routines are carried out at each site. They include daily analysis of pH/alkalinity, volatile fatty acids (VFAs) and biogas composition.
For biogas analysis Southern Water uses fourteen Biogas Check portable biogas analysers from Geotech (UK). They measure methane (CH4), hydrogen sulphide (H2S), oxygen (02) and carbon dioxide (CO2) – as the balance gas. Southern Water checks each digester is healthy, producing over sixty percent CH4, the minimum for its CHP engines to run and generate electricity. The CHPs have a 1000ppm maximum for H2S. Above that, H2S may damage CHP engines. Southern Water selected the simple-to-operate Biogas Check as their field instrument for anaerobic digester biogas gas analysis for which it was designed. ATEX certified for use in potentially explosive atmospheres, the field-proven technology enables consistent collection of data for improved analysis and accurate reporting. User-configurable operation measures concentrations of CH4, CO2, O2 and H2S. An optional temperature probe measures gas temperatures. All readings are stored including, in-field calibration results. On-board rechargeable batteries last ten hours.
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