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Improve coagulant dose control on your water and wastewater treatment plants


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Compass is a predictive coagulant control system that continuously optimises dosing

Compass is a predictive coagulant dose control system that continuously optimizes dosing for both water and wastewater treatment plants.

Coagulant dose requirements are determined by characterizing and measuring the quality of the water to be treated. Measurement is by a turbidity meter and UV-Vis meter. The Compass algorithms run in either the UV-Vis meter or in a standalone controller depending on the model selected.

Compass reduces operating costs and improves treatment plant process reliability by determining the coagulant demand of raw water or treatment plant influent and reacting instantly to changes in raw water / influent quality. Thus, ensuring the correct coagulant dose at all times.

The basic Compass model is designed for turbidity removal in drinking water treatment. It requires a single UV-vis spectrophotometer and a turbidity meter on the raw water. This model controls coagulant dosing to meet filtered water turbidity targets at the lowest dose rate. The Compass software runs within a UV-Vis spectrophotometer controller.

The enhanced organics removal (EOR) model is designed for dissolved organics removal in drinking water treatment. It provides the optimum dose to meet filter turbidity targets plus maximizing dissolved organics removal at the lowest coagulant dose. It requires a UV-vis instrument and turbidity meter on the source water and a UV-Vis meter on the filtered water. The Compass algorithms run within a stand- alone controller.

The chemical phosphate removal (CPR) model is designed for P removal in wastewater treatment. It provides the optimum dose to meet P discharge targets at the lowest coagulant dose. It requires a single UV-vis instrument on the influent prior to coagulant dosing. The Compass algorithms run within the UV-Vis instrument controller.

The chemically enhanced pre-treatment (CEP) model is designed for pre-treatment in wastewater treatment. It provides the optimum dose to meet performance targets at the lowest coagulant dose. It requires a single UV-vis instrument on the influent prior to coagulant dosing. The Compass algorithms run within the UV-Vis instrument controller.




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Source water turbidity and the type and amount of dissolved natural organic matter (NOM) changes very rapidly, and trying to maintain an optimum coagulant dose using existing techniques, such as operator experience, jar testing and streaming current control, results in over-dosing of coagulant and frequent plant failures.

Meet filter turbidity targets under all conditions at the lowest coagulant cost.


Return on investment ranges from 6 to 24 months

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Eliminate under-dosing while reducing risk of plant failure.
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Eliminate over-dosing as well as reducing operating costs.
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Responds instantly to changing conditions, fine-tuning your treatment process.
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Award winning system in use on over 70 plants worldwide.

Learn how Kapiti Coast District Council are using Compass to improve their plant performance and eliminate overdosing.




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The removal of natural organic matter (NOM) in drinking water is important for health, aesthetic and operational reasons. The presence of NOM can lead to; colour, taste and odour issues, increased coagulant and chlorine demand,reduced efficiency of UV disinfection, membrane fouling, microbial growth in distribution systems and most importantly the formation of disinfection by-products (DBP’s).

Meet filter water NOM targets under all conditions at the lowest coagulant cost.


Compass has improved coagulant dose control for these organisations


Our Frequently Asked Questions.


If you want to know more about Compass, you can find our FAQ's below.
Does Compass work for large lakes or open reservoirs where the raw water variability and organics are generally low?
Lakes and open reservoirs may still experience high turbidity events during rain events. Where turbidity spikes occur rapidly in response to a rain event, then Compass will allow the plant to immediately respond to these events as they occur, without Operator intervention.
Can the Compass controller accept particle count in it dose algorithm?
No – the Compass controller does not accept particle count as a measurement parameter. It is noted that the particle count does not give a correct representation of the coagulant demand of particulate matter. For example, five tiny particles vs five huge particles will still show up as a count of five but will have a completely different coagulant demand.

Can the Compass system work down to temperatures of <1 degree Celsius?
Yes – the Compass system and recommended measurement systems can work reliably down to freezing level.
How is Compass different from a standard raw water organics (UV254 or colour) monitoring instrument?
Compass is a predictive coagulant dose control system that continuously optimizes dosing for both water and wastewater treatment plants. In drinking water treatment applications, Compass utilises on-line turbidity and UV-spectroscopy measurements to characterize natural organic material (NOM) in real time. This enables the system to continuously optimise coagulant dosing depending upon the nature of the organics. A feedback loop from a second UV- spectral sensor in the treated water provides a further dosage trim and information on disinfection by-product formation potential. Compass online disinfection by-product formation potential (DBPFP) parameters are used for source management and continuous plant optimisation, whereby removal of the trihalomethane formation potential (THMFP) can be optimised. This cannot be achieved with UV254 (or SCM) based coagulation control systems.

Is coagulation pH a factor in a Compass coagulation control system?
No. The UV-spectral and turbidity measurements are pH independent. Also, pH is not an input variable although it is of course recognised that pH control is important in coagulation performance. Ideally, pH should be controlled to an optimum setpoint in an independent control loop. In this way, pH is not driving the dose requirement. However, for some sites where flocculation pH control is not practiced Lutra can accommodate this within our site-specific calibration procedures. In situations where raw water pH is high (usually due to seasonal algae influence), the coagulant is sometimes used as a weak acid. This can be managed by modifying the dose control via the PLC whereby the Compass predicted dose is trimmed to maintain a pH below an upper limit.
How much variation in water quality do you need to see to optimise any algorithm or understand the nature of the NOM in the raw water? Do you need seasonal variation for example?
The NOM characterisation parameters integral to Compass do not need to be calibrated per se and therefore we do not need to see a years’ worth of data for example. We have a wider number of base versions of the Compass algorithms for different plants, which we then tune to the site. What we like to see is how the plant responds to transient conditions. There is typically a three-month evaluation period, which is normally sufficient to observe several “events”. If the source is stable and events are rare, a longer period may be required. Conversely, if the source is variable, it can be done faster. Our fastest evaluation period was 4 weeks from install to full plant control. The longest was over 12 months, as also capture of seasonal differences might be important.

How do Algal blooms effect the accuracy of the Compass predicted ideal coagulant dose?
Algae have an affinity to coagulant and thus will also consume coagulant which otherwise would have been consumed by the organics. As then not all dissolved organics might be coagulated and removed as predicted by the feed-forward loop, the UV spectral sensor in a Compass EOR system (feed-forward and feed-back control) picks up excess organics and adjusts the coagulant dose. However, algae blooms are mainly a polymer dose issue, and a case-by-case adjustment would be needed to manage loads. Here a feed forward component by additional data from algae and cyanobacteria sensors as part of the Compass system in the raw water stream can add on-line process control capability. Further, algae blooms have a strong effect on pH and as coagulation is pH dependent, pH control in the process is important. Lutra is also currently developing a Compass module for optimization of e.g. carbon dosing to remove potential cyanotoxins from treated water. In summary, Compass takes out some of the process control uncertainty added by infrequent algal blooms.
Does Compass need to be used in an automatic coagulation control system, or can this be modified so that manual or semi-manual control can still be maintained?
Compass can operate in an advisory mode or as a fully automatic control system. Compass will output an ideal coagulant dose based on the raw water quality at that time. Some plants only use this as a reference point and maintain manual control. Other sites allow Compass to work automatically within a band and then defer to manual if Compass starts predicting an ideal dose outside of that band. Some sites use Compass in fully automatic mode and the PLC controls the dose based on the output from Compass.
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Phosphorus removal is often achieved by dosing coagulant to treated effluent and allowing the flocculated particles to settle or be removed by filtration before discharging. The dose can be set manually by measuring influent and effluent phosphorous concentrations and carrying out jar testing. Compass CPR provides an alternative which will continuously adjust the dose to the optimum level, accounting for all components of the coagulant demand.

Meet P discharge targets under all conditions at the lowest coagulant cost.

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Chemically enhanced pre-treatment involves dosing coagulant to the primary clarifiers in order to increase the capacity of a wastewater treatment plant. Compass CEP predicts the coagulant demand in the influent, in order to achieve the required treatment quality in the primary effluent.

Meet pre-treatment performance targets under all conditions at the lowest coagulant cost.

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