Using Phoslock (applying)
Once a the pre-treatment assessment is completed and a decision to proceed to an application has been made, preparations for the treatment can begin.
From a practical point of view, one of the first issues that needs to be considered is the delivery of the product to the application site.
Phoslock Europe GmbH generally maintains inventory of between 300 and 400 tonnes of Phoslock at a centralised warehouse in Belgium, close to the port of Antwerp through which the product is imported. Depending on our forward project planning, smaller volumes of inventory are also maintained at other locations across Europe.
From Antwerp, product can generally be delivered to an application site in Europe with a lead time of 3-4 days. Depending on the size of the lake to be treated and the application equipment used (see below), product is either shipped in one tonne bulk bags or in 25kg bags (on pallets containing 42 bags, or 1.05 tonnes).
Most applications of Phoslock that have been undertaken to date in Europe have been undertaken by Phoslock Europe or Bentophos using our own application systems.
These systems generally consist of a venturi mixing system mounted on a motorized barge that is fed with material from a hopper.
Lake water is pumped into the system to allow continuous mixing and the resulting slurry is dispersed onto the lake from a spray boom mounted on the back of the barge.
A GPS system is also installed to ensure that the slurry is applied evenly and to the correct location.
Application barge systems can be created in various configurations using between two and six coupling pontoons.
Large scale projects involving the application of more than one hundred tonnes of Phoslock are undertaken using product in one tonne bulk bags. Up to ten tonnes of material can be placed on the barge at one time and these bags are lifted by a small on board crane. Up to 50 tonnes of material can be applied to a lake per day using these large systems, with even higher daily application rates possible through the concurrent use of multiple systems.
Product can be loaded onto the barge by a number of methods, including a telescopic loader, conveyor belt, or, for large-scale applications, a crane.
For small scale applications, a variety of simple systems are available in which product is mixed into a slurry and sprayed onto the surface of the water body from the shore.
Application strategies can be tailored to the particular characteristics of the water body. GPS and depth detection systems are used at all times and it is therefore possible to apply higher dosages of Phoslock to areas of a water body where concentrations of phosphorus in the water or sediment are known to be particularly high.
It is also possible to apply Phoslock either directly onto the surface of the water body or directly into the hypolimnion, or deeper water. The latter approach may be taken when most of the phosphorus in a water body is either in the sediment or the hypolimnion.
Following an application, a comprehensive monitoring program is implemented to confirm that the outcome of the application is consistent with the pre-treatment prognosis.
Post-treatment monitoring generally includes measurement of the same parameters that have been measured during the pre-treatment assessment of the water body. These include chemical parameters such total and soluble nutrients, metals and carbon as well as biological indicators such as chlorophyll a. A variety of on site measurements are also taken, including dissolved oxygen, pH, redox, temperature and conductivity.
Samples are collected regularly during the 12 months following the application so that a complete picture of the limnological development of the lake can be obtained. Depending on the size and the depth of the lake, samples are also collected from multiple locations and multiple depths.
Sediment samples are also collected on at least one occasion following the treatment so that changes that have occurred in sediment composition as a result of the application can be measured.
Following the conclusion of the post-treatment monitoring program, treatment reports are generally prepared and submitted to the water body owner (and water authorities if required).