Intake protection system designed by PPM
Pollution and Process Monitoring (PPM) has completed the design and installation of a new intake protection system at Anglian Water's Heigham WTW.
PPM had already supplied intake monitoring instrumentation at a number of neighbouring Anglian Water sites, including Stoke Ferry and Mareham WTW. Heigham WTW already had an intake protection system in place, but the company was keen to take advantage of new technology and improve its performance. PPM was asked to bid for the job and was successful, based on its previous track record of providing reliable systems to Anglian Water.
The system was designed to monitor direct abstraction from the River Wensum at the Costessey intake, which is situated approximately two miles upstream of Heigham WTW.
An additional monitoring system is in place at the works to analyse the pumped, raw water, and PPM was also asked to provide ammonia, pH and turbidity instrumentation for process control as part of an extension to the existing 60M/l capacity.
PPM worked in consultation with a number of Anglian Water personnel on site, including the site operational scientist and instrument technician, to ensure that the new system met specific requirements.
These included, for example, ensuring that the power supplies to individual monitors could easily be isolated to simplify maintenance.
The new Heigham intake protection system comprises individual monitors for turbidity, ammonia, pH, conductivity and dissolved oxygen. These are mounted on two PVC back panels, in addition to an existing nitrate monitor.
The instruments used were chosen as they feature highly reliable, accurate sensors as well as rugged construction.
Anglian Water also stressed the need for simplicity of operation, calibration and maintenance.
The HF Micro200BW Turbidity instrument and the Ecoline DO monitor were chosen to fulfil these criteria.
The Micro200BW is calibrated using three polymer liquid standards at 0.02, 4.00 and 10.00 NTU - or 40.00 and 100.00 NTU for high ranges.
The Ecoline DO was one of three WTW instruments installed. A TriOxmatic sensor was added to indicate any calibration drift.
A Contronic ion selective ammonia monitor was also installed which reports from 0 to 5.00 mgl NH3-N.
To minimise the time it spends off-line, the instrument has been set to auto-calibrate during the wallboard cleaning cycle. This instrument is particularly important for detecting the presence of any farm waste and is used as a 'primary measurement' to automatically close the intake.
The new instrumentation will operate alongside the existing nitrate monitor, a KOWA unit which is of the same design as the WTW nitrate monitor used at Stoke Ferry.
The KOWA unit employs UV determination of nitrate and features its own automatic cleaning cycle which uses 10% HCL.
The monitor plays an important role in detecting the ingress of any fertiliser from agricultural run-off, which may occur during periods of high rainfall. Any other dissolved chemicals are indicated by either DO reduction, increased conductivity or pH fluctuation.
Physical characteristics are indicated by continuous turbidity measurement. This can be set to trigger a sampling device to provide samples for laboratory checks on content such as Cryptosporidium ooysts.
The instruments' sensors and pipework are automatically cleaned daily, using biocidal additives with a subsequent air/water scouring routine.
A simple panel, housing a PLC, provides rotary switches to select cleaning intervals and a visual indication of the system's status.
A common signal box, with individual power supply and ball-valve sample isolation system (with blanking plugs for each sensor) was installed to complete the installation.