FAQs

Does the system work with any reactor configuration (plug-flow, oxidation ditch, etc.)?

Many of our installations are plug-flow however we are working with customers that have oxidation ditches. In particular we think that there may be a good opportunity with SBR’s where, rather than running aeration for a fixed period of time, we could report on the current demand and if appropriate, reduce the processing time.

How are the graphs plotted? Is it a continuous measurement over the 60 min or is a final BOD value at the end of each 60 min interval?

Pressure / Time graphs are plotted on the control panel as a continuous measurement during the course of the 60 minutes. The BOD is produced at the end of the 60 minute cycle and the dashboard is updated at this time.  Dependant on plant characteristics this processing time can be shortened in many instances.

How does the system detect abnormalities/toxic events and what kind of alert does it create?

The core of the Shepherd measurement is a pressure time graph. We extract 7 data characteristics from the graph either as a static entity or as a composition over time of multiple graphs so we can analyse properties such as BOD drift. These characteristics are weighted according to significance but in practice we have observed that in combination, multiple triggers lead to an abnormality. Once identified the event is communicated via an email to all registered subscribers of the service and also on the cabinet display.

Does it have a connection with a PLC/SCADA?

Shepherd has a 4-20Ma output as well as a serial RS232 ModusRTU output and an RJ45 ModbusTCP output. Since Shepherd is only sending 4 values the comms is fairly basic and these values can be programmed by SCADA/Telemetry connected computers.

Does the sensor need calibration & if so how often?

Pressure sensors are calibrated at the factory however complex calibration is not required once Shepherd is deployed because differential pressure readings are used for calculations not absolute measurements. 

What maintenance is required & at what intervals?

A six monthly maintenance cycle includes a deep clean, examination and replacement of service items such as gaskets and membranes. Shepherd is designed as a low maintenance system with approximate service costs of £1000 pa.

What are Bactest’s proposals on monitoring multi-lane installations?

Single lane installation is sufficient for many sites however site calibration work will identify anomalies and the need to employ multiple Shepherd systems.

What is the size and weight of Shepherd for handling purposes?

The control cabinet (60kg) is a fixed installation that can split into two parts and be mounted vertically or horizontally. The sensor head (25kg), measures 750mm in length and 200mm in diameter, this floats in the AS lane and requires 2-person installation or removal for maintenance. 

Can shepherd be used on non-nitrifying tanks or sites?

Shepherd is well suited to non-nitrifying sites and can advise aeration control volumes or F/M ratio.

How does Shepherd deal with high load situations?

Shepherd’s algorithm is correlated to the load experienced. Testing has been completed on a range of 500 mg/l MLSS to 10000 mg/l MLSS in the laboratory and up to 7000 mg/l in situ on site.

Is shepherd measuring both load and biological activity?

Yes, Shepherd measures both biological activity and load so both contribute to the calculations for recommended aeration level.  

How does Shepherd recommend an aeration flow rate?

Shepherd uses the oxygen demand and calculates total airflow required for the BOD loading based on known design parameters and taking into account the air delivery characteristics, apportioning zonal flowrate to design specifications or individual plant calibration.

What is Shepherd measuring? Is it Carbonaceous BOD?

Yes, the algorithm has been correlated to BOD(ATU)

Where is Shepherd sited in the AS lane?

Shepherd’s sensor head is sited in the first aerobic zone immediately after the anoxic zone (if present) and the control cabinet is positioned alongside the lane as close as practically possible to the sensor head.

Will Shepherd be affected by foaming?

Shepherd operation is not affected by foaming.

What type of activated sludge processes are suitable for Shepherd?

Shepherd has been tested and calibrated on plug flow nitrifying works however Shepherd will also have applications in other designs such as Oxidation Ditches, Sludge Batch Reactors and fixed film systems. Each site is different so Shepherd undergoes a review period to check applicability plus a calibration period once installed.