When Should you Complete a Sludge Survey?
Introduction
We often get asked how often our clients need to complete sludge assessments of their wastewater lagoon. There are several factors that impact our recommendation; however, generally we recommend conducting a sludge survey every one or two years. This paper explains how annual sludge surveys can help reduce operational/maintenance costs at your lagoon.
First, lets look at the negative effects that excessive sludge build-up can cause. Wastewater lagoons are designed on the basis of average daily wastewater in-flows and are sized to provide a specific volume, which results in a desired retention time for these daily flows. This hydraulic retention time is crucial to allow the lagoon biological system time to properly treat the influent wastewater. When there is excessive sludge build-up in a lagoon, it can “short-circuit” the overall treatment process by effectively reducing the design volume. This sludge build-up sludge is effectively making your lagoon smaller. This reduction in hydraulic retention time and increase in sludge levels can have several negative consequences such as:
Elevated TSS & BOD Effluents - A reduction of treatment time can result in an increase in effluent concentrations of BOD and TSS.
Offensive Odours – Excessive sludge means that biological breakdown will start to happen anaerobically. This will result in a much slower treatment process and a release of noxious gases. These noxious gases have offensive odours.
Ammonia Spike – In some cases anaerobically digesting sludge can actually release ammonia into the water. This situation can lead to effluent ammonia concentrations being higher than influent.
Reduced Aeration Efficiency – Having sufficient levels of dissolved oxygen (DO) in your lagoon is critical to facilitate nitrification. If you are using an aeration system to add DO, excessive sludge could be choking individual aerators from supplying this DO.
Lagoon Turnover – The sludge and water from the bottom of the lagoon rises to the top. This can eventually cover the entire lagoon causing a whole host of other problems.
Visible sludge beaches reducing treatment capacity
Keeping these problems at bay is paramount for lagoon operators and other environmental stakeholders. Thankfully, there is a way to help see these negative situations approaching, giving you time to act and get prepared. A comprehensive sludge survey can provide valuable information regarding the amount of sludge accumulation you currently have in your lagoon and the amount of retention time you have lost. The lagoon snapshot included in your comprehensive sludge survey provides the following benefits to stakeholders and operators:
Is Dredging Required? – A sludge survey informs you about your sludge accumulation, and whether or not dredging is necessary. This information can eliminate one variable if you are having effluent quality problems.
Sludge Distribution – The sludge maps provided in a comprehensive sludge survey report show the distribution of the sludge blanket across the entire lagoon. Some areas may have a greater sludge build-up than others. This information allows you (and your dredging contractor) to plan resources accordingly to dredge the lagoon efficiently.
Reduced Dredging Costs – If there is uneven distribution of sludge in a lagoon, these effected areas can be targeted by dredging contractors, which reduces dredging project costs. The efficiency of the contractor results in a direct cost savings for the project.
Accurate Sludge Volume – An accurate sludge volume in a tender package allows all dredging contractors to bid on the same volume (and corresponding dry tons of sludge) so that you can compare apples-to-apples when reviewing bids.
Sludge Composition – During a comprehensive sludge survey sludge is sampled and analyzed to determine its composition. Lagoon operators can now assess which methods of sludge disposal are available to them such as geobagging on site, hauling to landfill or agricultural land application of the biosolids. This allows for straightforward project planning and significantly reduces the risk that project budgets will be exceeded while ensuring that the lagoon is cleaned entirely.
3D Sludge Map included in a Comprehensive Sludge Survey Report
A snapshot of the current sludge situation in a lagoon provides a vast amount of information. Sludge surveys conducted yearly or every two years, can provide advanced warning which allows for accurate planning and budgeting. Operators and other stakeholders will be prepared and not surprised by potential effluent problems and large costs associated with sludge dredging and disposal.
Some of the benefits of yearly lagoon surveys are:
Sludge Accumulation Rate – By comparing the sludge volumes year over year, you can determine accumulation rates. These accumulation rates can be used to accurately predict when a lagoon should be dredged, well before negative consequences are experienced.
Forecast for Dredging – Being able to predict when a lagoon needs to be dredged, potentially years into the future, provides the opportunity to tender and award a quality dredging contract, which ultimately reduces project costs and the stress associated with managing a poorly prepared dredging contract.
Reduced Survey Cost – While the initial cost of a comprehensive survey can provide good value, the cost of frequent surveys is reduced. Some of the required data collection and processing only needs to be done once. This savings is then passed on to the client, thus increasing the value of subsequent surveys.
Comprehensive sludge surveys provide crucial information about a lagoon’s operation. These surveys are like going to the doctor, frequent checkups help keep things healthy, and if something is detected early, they can provide you time to implement corrective action. The further out you can detect a threat, the lower the cost will be to eliminate it in terms of time, money, and stress. Has your lagoon had its checkup?
Top of Sludge Change Map
