frequently asked questions

Surveys

Common Questions

A lagoon survey’s primary purpose is to provide a measurement of the volume (in m3) of sludge, biosolids or residuals in each cell. The survey will also provide information on sludge blanket thickness, depth from water level to top of sludge, an analysis of the in-situ percent solids and specific gravity of the sludge, and a calculation of the Bone-Dry Tonnes (BDT) of sludge. Cell information such as total depth of the cell, cell area, total cell capacity, and elevations are provided, as well as qualitative observations on cell conditions. Additional sludge analysis to determine if sludge meets land application criteria can also be provided as requested.

A lagoon survey can help quantify the amount of desludging to be done in a cell and provide the owner with the information necessary to determine whether any work should be pursued. The lagoon survey can also assist in determining what disposal or beneficial reuse options exist for the sludge. A good lagoon survey provides suppliers with the appropriate information to provide an accurate price for work offered by the owner. A pre and post desludging survey can help to verify the amount of work performed by a vendor. The survey can assist in identifying potential infrastructure issues at the lagoon site.

A lagoon survey is not necessary if a cell is essentially full of sludge (i.e., portions of the sludge blanket are visible throughout the cell), and the cell dimensions and volume are known. If a cell requires regular desludging due to the volume of sludge inflows, a lagoon survey may not be as beneficial.

A survey is an estimate of the sludge volumes in a cell. Proper calibration of survey equipment, and a large amount of survey points helps to minimize errors in volume estimates. Measurements of sludge in-situ percent solids and specific gravity, which is information that is used to calculate the Bone-Dry Tonnes of sludge, is prone to sampling errors. This is due to only a couple of litres of sludge being taken as a sample in what is generally several hundred or thousand m3 of sludge in a cell.

desludging

Common Questions

A lagoon can be desludged using either a floating dredge, or a PTO powered lagoon agitator pump. A floating dredge sits on top of the cell water. The dredge has a ladder that reaches down to the sludge blanket. A pump at the end of the ladder will pump sludge to the surface, where it is transported through a floating pipeline to the shore. The dredge traverses the lagoon, pumping the accumulated sludge volumes. The dredge requires a minimum quantity of water in the lagoon in order to float (about 1m). A floating dredge is appropriate for desludging larger cells (over 36m wide) or cells that need to stay in service while desludging occurs. A PTO powered lagoon agitator pump will reach about 50’ into a cell. The pump will first remove effluent water sitting on top of the sludge blanket, pumping it to an adjacent cell. The pump will mix the sludge blanket into a homogenous mixture and then pump the sludge out of the cell. Larger cells being desludged by a lagoon agitator pump can have the sludge mixed by a lagoon crawler prior to pumping the sludge out of the cell.

A flowmeter is used to measure the volume of sludge pumped from the cell. Flowmeters are calibrated each year to minimize errors in readings. The flowmeter readings are recorded throughout the day by the project team. Samples of the sludge being pumped through the flowmeters are taken multiple times per day. The sludge samples are analysed in a lab quality moisture analyser to determine the percent solids of the material being pumped. The sample results are recorded and used to calculate an estimate of the Bone Dry Tonnes of material removed. Independent samples can be taken and tested by the owner to verify the reasonableness of the samples taken in the field.

  A floating dredge will typically leave about 20 – 30 cm of sludge behind. This is due to the guards on the cutterhead and because there is no direct visibility to the sludge blanket. A lagoon agitator pump will also leave about 20 – 30 cm of sludge behind, however, as there is visibility of the sludge layer, and because water is typically added to the lower layers of the sludge to make them easier to pump, more of the sludge is typically removed. Leaving some sludge behind is generally good as it allows for the biological processes important for the health of the lagoon to continue.

The floating dredge and the lagoon agitator pump both have guards around the pumping mechanisms that prevent contact of the pump or dredge cutterhead with the lagoon liner. For poly lined lagoons, the dredge is placed in the lagoon by a crane. For clay lined lagoons the dredge, or the lagoon agitator pumps, are backed into the cell. Depending on the softness of the clay liner, some rutting should be expected. Lagoon agitator pump mixing nozzles are moved continually during desludging in order to prevent erosion of the liner by the flow of sludge through the pump. Poly lined lagoons can sometimes experience bubbles in the liner (typically due to air or water table issues underneath the cell). Desludging these cells increases significantly the risk of damage to the liner as the liner bubbles can move into the pumping mechanisms and result in liner tears. If this situation exists, the owner should be aware of and accept the risks of a liner tear prior to desludging proceeding.

 A complete cell cleanout of a cell will follow the typical method employed in desludging until the typical limits of the desludging equipment is reached. If a dredge was used in the initial desludging, the water would then be pumped off the cell. A piece of equipment, such as a wide path dozer, a skid steer with a blade, or a side by side with a blade, is then placed in the cell. The equipment will then push the remaining sludge to a lagoon agitator pump. Ideally the cell has an existing area that can act as a natural sump, otherwise a sump may need to be dug into the cell to facilitate the pushing and pumping of the remnants of the sludge. A vac truck can also be used to remove any sludge remnants. Due to the placement of equipment into the cell bottom, the owner should expect that there may be some damage to the cell liner when performing a complete cell cleanout.

land application

Common Questions

Land application of sludges is typically reserved for biosolids that will provide beneficial nutrients (nitrogen and phosphorus) to the soil. Land application of materials that provide little value to the soil, or that could damage soil (i.e. sands, clays, silts, hydrocarbon impacted sludges, etc.) is generally not allowed. Biosolids must meet the applicable land application regulations for the province where the work is being done, and should be clean of debris.

Biosolids are a rich source of nitrogen, phosphorus and organic material. These nutrients help significantly in the growth and yield of crops. The organic material provided through biosolids helps to amend weak soil conditions. These benefits are compounded by the contribution of biosolids to a circular economy where the waste from food consumption is used to assist in food production. Many recipients of our biosolids applications request yearly applications to different sections of land owned.

The amount of biosolids that can be spread, as measured in Dry Tonnes (DT) per hectare, is determined by the processing methodology and nutrient contents of the biosolids, and the soil characteristics of the land being applied on. Lab analysis of the sludge and soil characteristics are put into a model to calculate the appropriate application rate. The intent is to spread the biosolids at a rate that allows for nutrient uptake into the crop, and prevents nutrients from penetrating deeper into the earth where they could eventually reach aquifers.

Biosolids land application has been a well researched and analysed method of beneficial reuse of wastewater solids for over 50 years, on a global scale. Guidelines, based on the scientific evidence of this ongoing research, are developed and implemented by regulatory bodies. Emerging issues are identified as part of this process and guidelines are updated accordingly. The overwhelming majority of communities in Canada will produce biosolids that are safe and beneficial to use. When issues arise it is typically through industry pollution of the wastewater stream. When this occurs the biosolids will require additional treatment and will likely need alternate disposal to a landfill.

dewatering

Common Questions

Dewatering of sludges is primarily done mechanically using centrifuges, screw presses and belt presses, or passively using Geotubes and drying beds. Each method has its relative strengths and weaknesses. Dewatering is achieved quicker by mechanical means, but it has reached its maximum dewatered state after its initial dewatering. Mechanically dewatered material needs to be sent to its final disposal location quickly, otherwise it risks getting rehydrated by weather events. Passive dewatering takes longer to achieve, but is able to reach a much drier state. Usually it will take 6 months to achieve a dewatered state similar to the mechanically dewatered process, after which it will continue to dry. Geotubes protect the sludge from rehydrating in the elements and contain odors. The drier state that can be achieved through passive dewatering will result in less hauling and disposal costs.

Mechanical dewatering is generally preferable in situations where the dewatered sludge needs to be disposed of quickly, there is limited space available on site for storage of dewatered product, the final disposal location is relatively close to the dewatering site, and tipping fees are not a significant part of the disposal cost. Geotubes are generally preferable where there is sufficient space on site for placing the Geotubes, the Geotubes can remain in place for a longer period of time (one or more years), the distance to disposal site is relatively far, and tipping fees are a significant part of the disposal cost. The Geotubes can attain a drier state, resulting in less volume and weight, if they are allowed to remain on site for a long period of time.

 Dewatering should be performed when; the biosolids do not pass land application criteria, there is no land available within a reasonable distance to spread biosolids on, or land that would otherwise be available is not due to poor weather or crops actively growing.

Polymer is critical to successful dewatering of biosolids. To work appropriately the biosolids should be tested against a range of polymers to identify which polymer provides the best dewatering results. Polymers should be appropriately measured, mixed, and aged prior to coming into contact with the biosolids. Appropriate dosing, static mixing, and reaction time of the polymer with the biosolids should occur prior to the sludge entering the mechanical or passive dewatering process. Having a good polymerization process allows for the solids within the sludge to flocculate and coagulate with the polymer, and water to be released in the dewatering process.

costs

Common Questions

The cost of a survey will depend on; the distance to site, the number of cells being surveyed, the size of the cells being surveyed, the ease of access to the cells, and the lab analysis that needs to be performed on the sludge. A detailed quote can be provided once these factors are known.

Factors that impact the cost of a land application project include; the distance to site from Red Deer, the proximity of land to the lagoon site, the size of the cells being desludged, the thickness of the sludge blanket, the ease of access to the site, and the existence of debris within the sludge.

Factors that impact the cost of a dewatering project include; the distance to site from Red Deer, the size of the cells being desludged, the thickness of the sludge blanket, the in-situ percent solids of the sludge, the ease of access to the site, the existence of debris within the sludge, and the topography of the lagoon site for construction of a Geotube laydown area.

Mobilization and Demobilization costs are generally charged as a lump sum. Sludge removal and land application or dewatering, can be charged as a day rate, per m3, or per Dry Tonne. We typically charge day rates for complex situations, such as complete lagoon cleanouts, or where sludge quantities or characteristics are unknown. Charging per Dry Tonne is generally preferable to charging by m3. Charging by volume can result in higher charges as the volume pumped can be inflated by pumping a more dilute slurry. Charging by Dry Tonnes creates an incentive for the desludging contractor to work more efficiently. Supplies such as Geotubes, polymer, liner, and services such as land procurement, sampling and reporting, are generally charged on a per item (materials used) basis.

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Questions about how our biosolids removal, dewatering services, and sludge management benefits the environment? Ask us.

Contact
Phone: 1-403-348-8298
Toll Free: 1-877-340-8298
Fax: 1-403-348-8290

51 Belich Crescent
Red Deer County, AB
T4S 2K5

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