The municipal water sector and many within the industrial sector, have progressively installed on-line water quality monitoring systems, to more effectively manage their processes, reduce operating costs and demonstrate compliance. Whilst the decision to implement continuous measurement for many, has been simply driven by the need to comply with ever tightening regulations, others have systematically installed instrumentation to reduce operational costs and improve process control.

The Environmental Permitting Regulations (introduced during 2009) have also promoted continual improvement and the installation of water quality instrumentation. A point scoring system called OMA-3, is used to assess permitted operators within industry and encourage self monitoring with the objective of optimising processes, reducing waste and demonstrating discharge compliance.

The importance of selecting the correct instrumentation which is deemed fit-for-purpose is crucially important. The MCERTS scheme, introduced by the Environmental Agency, takes a one-size-fits-all approach and ensures that certified instruments have passed the minimum performance standard, set by the Agency.

However, what is very apparent is that no two apparently similar applications, necessarily present the same challenges. Whilst a given instrument may satisfy the key monitoring requirements, many other considerations may need to be taken in to account.

The complete monitoring system including sample preparation, sample delivery and installation (mounting, protection and housing) may need to vary from site to site. A standard approach, where ever possible, has its merits, but can also be far too simplistic.

A site visit to take in to account all the various considerations may establish site-specific issues and help to minimise the risk of making the wrong installation. Only when all the factors, such as access, maintenance, running costs, suitability, installed cost et cetera, have been collectively considered can the level of automation, instrument type and final mounting detail be finalised.

Once decided, what is then equally important is to make a correct installation. Sometimes simple details can have significant impacts.

Probes mounted into final effluent tanks may need to be removed periodically for manual cleaning and calibration. If mounted below fixed chequer plate, sensor removal becomes very difficult and regular maintenance is unlikely to occur.

Specific sensors may also have specific requirements. Ion selective sensors, such as those used for pH, ammonium and nitrate, should remain immersed at all times. Flow regimes and resultant water depths must therefore be considered.

Analytical devices need suitable frost protection and specific services such as open gravity drains. The type of sample preparation may not only affect measurement reliability, but may also affect measurement performance and correlation to laboratory analysis. Ortho-phosphate measurement is one such case.

Where analytical methods need to be installed, pre-installation of analysers into bespoke GRP kiosks, including electrical and sample distribution, has many merits. This approach reduces time on site and minimise the risk of making a poor installation. A relatively small increase of expenditure may ultimately reduce the total delivery cost of the asset but most importantly, help to ensure that the best possible performance is achieved.

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