Phoslock FAQs #2

Part #2 of our Frequently Asked Questions series. Look out for Part#1 published earlier

What are the benefits of Phoslock

Phoslock offers a wide range of benefits over other methods for reducing phosphorus concentrations in waterbodies. Some of the most important benefits are

• Reduction of phosphate | The ability of Phoslock to reduce phosphate to levels close to or below standard detection limits (< 10 μg/L) has been well demonstrated in a large number of both laboratory and field applications. ?Importantly, dosages can also be adjusted to achieve phosphorus concentrations that fall within a particular target range (e.g. 20-30 μg/L). ?This approach is used when it is necessary to reduce phosphorus concentrations.
• Rapid uptake of phosphate | The kinetic uptake of phosphate by Phoslock varies to some degree according to water chemistry, however in most situations, more than 90% of available phosphate is bound within three hours of an application of Phoslock.
• Eco-toxicity safety | available to view or download at petwatersolutions.com.au
• Stability under varying conditions | Unlike other methods that could be used to immobilise phosphorus in water and sediments, Phoslock is insensitive to the range of redox, temperature and pH conditions that are naturally found in lakes and reservoirs. ?Furthermore, buffering is not required prior to an application.
• Resistance to resuspension | Several studies have been conducted to determine the resistance of a Phoslock sediment capping to resuspension at different flow velocities. All studies have shown that Phoslock has substantially higher resistance to resuspension than aluminium or iron salts, which can also be used to immobilise phosphorus in sediments. This is not surprising given that the density of Phoslock is much higher than flocculants and highlights the suitability of Phoslock for use, even in shallow lakes.
• Long-term effects | Following the application of Phoslock to a water body, any phosphate that has reacted with the lanthanum in the clay will remain permanently bound. ?Furthermore, any lanthanum sites in the clay matrix that have not reacted with phosphate remain active and will continue to bind phosphate (from both external and internal sources) until saturated. ?This means that an application of Phoslock can be designed to achieve a sustained reduction in phosphate levels. The combination of these benefits makes Phoslock a unique and innovative solution to eutrophication control.

Use and Application

How is Phoslock applied to a water body

When used in lake restoration, Phoslock is usually added to a water body as a slurry, in some circumstances it can be cast dry. Phoslock as a slurry is mixed with in-situ lake water and sprayed over the water’s surface.

As Phoslock sinks, it strips phosphate from the water column. Once settled on the sediment, Phoslock continues to bind phosphate released from the sediment, until the lanthanum binding sites are saturated, at which point no further binding will take place.?

See also: What is Phoslock

When is the best time of year

The best time to apply Phoslock is between late Autumn and early Spring in Europe. This is because during these periods the majority of the available phosphate is not bound in biomass such as algae or aquatic plants but mainly in the sediment.?

An application of Phoslock strips the water column of phosphate and then ‘caps’ the bed sediments, and this targets much of the phosphate in the system

How much Phoslock will be applied to my water body

Every water body is unique and a water body-specific Phoslock dose would need to be calculated for each potential treatment but typically, 2 – 3 tonnes/hectare of Phoslock are applied but this can vary considerably for individual waterbodies as dosage is based on how much phosphate is in the water column, bound in the sediments and any external sources of phosphorus still entering the waterbody.

How much will it cost

The cost of an application is something we get asked all the time, and will vary considerably for a waterbody depending on size, depth and amount of phosphate that would need to be bound to Phoslock. Another cost is application, this is an area we are able to offer, but also assist in helping our clients self apply, reducing costs and saving budgets.

As the cost varies considerably from waterbody to waterbody, it is necessary to have a certain amount of information available to allow an accurate cost to be estimated. This information forms part of Phoslock's water body questionnaire that is completed upon each enquiry received. Phoslock is not an expensive solution, solutions are only expensive when they are not effective. ?

If you are interested in applying Phoslock to your waterbody or understanding cost, please contact [email protected] and we would be happy to provide an estimated quote.

What information is needed to asses if Phoslock is suitable for my water body

Every lake is different and a range of information about the lake needs to be understood when considering a Phoslock treatment. For instance, it is important to determine the sources of excess nutrients to your water body; i.e. are the nutrients coming largely from internal sources (e.g. from phosphorus release from sediments) or from external sources (e.g. from diffuse or point sources in the catchment). This is critical to know as continued high external loads could impact the effectiveness of a Phoslock application. These need to be understood to ensure we allow for these inputs in our calculations.

Water quality data is key to understanding each water body's unique story. Long-term water quality monitoring data is unfortunately rare for many water bodies but regular or adhoc monitoring helps us better understand what management options may be best if nutrient pollution and symptoms of eutrophication have become a problem. Water quality monitoring data is also vital to help us understand if Phoslock is a suitable product to control nutrient pollution in a water body as there are many aspects that need to be considered before an application.?

In addition to water quality sampling, sediment sampling is often needed to estimate how much phosphorus is potentially releasable under normal lake conditions. This information, along with other nutrient calculations is used to make an informed dose calculation for a Phoslock application. Sediment analysis is not required on all lakes, but some larger water bodies and those classified as Sites of Special Scientific Interest (SSSI) may be required to undertake sediment analysis for permitting applications. ?

Please do get in touch if you are considering Phoslock to treat your water body or if you need further information.

We can offer advice and create a pre-treatment assessment, estimated dose calculations and costings for your water body.

How long does Pholsock last for

Phoslock will continue to bind phosphorus until all lanthanum binding sites are saturated. Although the bond formed by lanthanum and phosphate is permanent and will not be broken under naturally occurring conditions in water bodies, the effects of a Phoslock application will depend on if any high external nutrient loads are entering the waterbody.?

If high loads are entering a water body following a Phoslock application, then repeated, usually much smaller Phoslock doses, may need to be applied every 18 month to uptake the Phosphates within the water column and not naturally taken up.?

Sometimes the presence of benthic feeding fish in high densities can impact a Phoslock application through continued sediment disturbance and potentially releasing phosphorus deeper than the Phoslock layer. High biomass of water birds at a water body can also have an impact of Phoslock efficiency through continued high nutrient concentrations after an application. All these impacts are taken into account when calculating a dose and treatment assessments.

Background & Additional Information

What is Phosphate

Phosphate is an inorganic nutrient.

What is Lanthanum

Lanthanum is a rare earth element that occurs naturally in the environment in low concentrations.?

Lanthanum forms a very strong bond with oxidized anions, such as phosphates, carbonates and silicates, forming lanthanum salts. The bond between lanthanum and ortho-phosphate (LaPO4) is particularly strong and stable under many environmental conditions.?Once bound Phosphates are removed from the water system and remain bound.

What is Bentonite

Bentonite is a clay consisting of smectite minerals, the most common of which is usually montmorillonite.?

Bentonite is characterised by exchangeable sodium, calcium or magnesium cations which greatly influence the properties and commercial uses of the clay. Bentonite is often called the mineral of 1000 uses due to its wide range of applications. The major worldwide applications of bentonite are as an additive in foundry sands and drilling muds, as cat litter, as an additive to stock feed to aid digestion, as a binder in iron, as pelletisation processes and as a clarifying agent in wine making and edible oil refining. Bentonite is also commonly used in the paper industry and as an efficient material to line a seal dams and landfill sites.

For more information and support please contact [email protected] or [email protected]