Using Phoslock (pre-treatment assessment)

An application of Phoslock to a water body should be planned carefully and involves several key steps. These include a pre-treatment assessment of the lake's current condition, the application itself and post-treatment monitoring to measure the effects of the application.

Pre-treatment assessment

sampling-water1.jpg Before any treatment of a water body with Phoslock is undertaken, it is of course very important to undertake an assessment of the chemical, physical and biological characteristics of the water body, its sediment and its catchment . This should provide a clear understanding of the problems facing the water body, the causes of those problems and whether or not Phoslock is an appropriate restoration measure that should be considered.

sampling-water2b.jpgIn particular, it is important to understand whether or not elevated levels of phosphorus in a lake are caused primarily from internal or external sources. Phoslock is an effective tool to reduce both sources of phosphorus, however continued inputs of phosphorus from external sources such as inflows rich in phosphorus will naturally decrease the longevity of a Phoslock application. In these cases, follow up applications after an initial treatment may be required until inputs of phosphorus from external sources are brought under control.

Phoslock Europe's team of technically trained staff are able to visit potential application sites to make such an assessment. In many instances, this service is provided without charge. Comprehensive pre-and post treatment assessment of application sites forms an integral component of Phoslock Europe's Quality Control Program.

Although the components of a Pre-treatment Assessment vary according to the type of lake and its size, most Pre-treatment Assessment Programs consist of a desk top review of existing data on the lake, site visits to measure a variety of water quality parameters and collect water and sediment samples for analysis in the laboratory and preparation of an application and dosage plan based on the collected data.

Bathymetric-Map.jpgReview of existing data

The first step in assessing a lake is to undertake a desk top review of existing data on the lake. Many lakes are regularly monitored for a variety of parameters by environmental authorities and if this data is publically available it can provide a good starting point for assessing the lake's condition.

Bathymetric data is also important as this is required to calculate water volume and depth profiles. The overall residence time of the water in the lake is also required and this can be calculated by dividing the volume of water in the lake by the volume of water discharged from the lake. If bathymetric data and discharge volumes are not available, they can also be also be acquired during pre-treatment monitoring.

Sampling and testing of water and sediment quality

Following the completion of the desk top review of existing data, one or more site visits are generally required to undertake a number of on site tests and collect water and sediment samples from the lake.

Both water quality and water volume can vary substantially according to season, location and depth and therefore it is usually necessary to collect multiple samples from a lake at different times of the year.

A number of important water quality parameters such as pH, dissolved oxygen, conductivity and redox can be easily measured on site, however other key parameters such as total and soluble nutrients, DOC, TOC and TC need to be analysed in the laboratory. Consequently, water samples are generally collected during site visits and then delivered to the laboratory for testing. Depending on the parameter to be measured, samples will be either filtered on site or left unfiltered.

sampling-sediment1.jpgIn most water bodies, phosphorus contained in the sediment accounts for the highest percentage of the total load of phosphorus that can be considered to be potentially available for algal growth. As a result, collection of sediment samples is an important component in all pre-treatment assessment.

Sediment samples are usually collected using a Ekmann Birge bottom sampler (ref photo above), however sediment cores using a core sampler are also collected in certain situations. Sediment samples are generally analysed for their dry weight, organic content, nutrients (nitrogen, phosphorus) and metal concentrations (calcium, aluminium, iron, etc).

In some cases, fractionation of the sediment using methods such as Psenner is also undertaken in order to make an accurate assessment of the percentage of phosphorus in the sediment that can be considered to be potentially releasable.

Calculating dosage and preparing application plans

sampling-water3.jpgFollowing the collection and analysis of data relating to water and sediment quality in the lake, an assessment of the lake's current condition and the suitability of Phoslock as a potential restoration measure can be made. If it is determined that the lake can be expected to benefit from a treatment with Phoslock, a costed treatment proposal is developed and submitted to the customer.

Included in this proposal is the required Phoslock dosage and the proposed application strategy for the treatment, outlining the optimal timing of an application as well as recommended application methods. Depending on the water quality data that has been collected, Phoslock can either be sprayed onto the surface of a water body or injected directly into the hypolimnion (if most phosphorus is concentrated there or in the sediments).

While procedures for application are relatively simple, all applications should be undertaken carefully and responsibly to ensure maximum contact time between the Phoslock particles and phosphate ions, both in the water column and sediment pore water.

Following the collection and assessment of this data, a treatment proposal is developed and submitted to the owner or manager of the water body.