What is Dewatering?

Dewatering in its simplest definition is the removal of water. This process is used in many industries but commonly referred to in construction and wastewater when water is separated from solids through a variety of different pumping or filtering processes.  Construction dewatering is often referred to as dewatering, unwatering, or water control. It involves pumping from wells or sumps to temporarily lower groundwater levels, to allow excavations to be made in dry and stable conditions below natural groundwater level.

In wastewater treatment, dewatering is the part of the process whereby sludges are reduced in volume and converted from a liquid to a solid product. Biosolids dewatering typically occurs when transportation and storage costs for large volumes can be reduced or when the material is destined for landfill.  The biosolids dewatering  process not only effects the volume but also the nutrient and odour levels of the material.

Dewatering Techniques

  1. Centrifuge: The centrifuge works in a similar nature to a front loading washing machine. The spinning action causes a separation of water from the solids.  This process typically requires a large power input and polymer addition.  The system works best with a consistent slurry or feed sludge and provides a dewatered product between 16-35% solids.
  2. Belt press: If a centrifuge can be compared to a front loading washing machine then the belt press can be compared to a wringer on an old washing machine. The method of separation is primarily obtained by passing a pair of filtering cloths or belts through a system of rollers. The system takes a sludge or slurry as a feed, and separates it into a filtrate and a dewatered product between 12-35% solids.
  3. Geo-textile: High strength permeable fabrics are woven into dewatering bags that can be filled with slurry. The water permeates from the dewatering bag through the small pores in the geo-textiles resulting in effective dewatering and volume reduction of the contained solid material. Although somewhat slower than mechanical dewatering options, geo-textile dewatering is an excellent dewatering option, reducing costs, and energy inputs.  This method can produce material from 15-45% solids.
  4. Rotary Vacuum: This method of dewatering involves the suction of liquid through a filter.  Because the filter itself can be changed depending on the project needs, the solids capture rate is very high. Material can be filtered down to 0.5 micron producing unparalleled effluent quality.  This process while slower than other mechanical dewatering options provides material with 20-45% solids.

Dewatering and Waste Management

Dewatering is used by large wastewater treatment plants to separate sludge into a liquid and solid. The principle methods in wastewater are belt filter presses and centrifuges.These systems are high maintenance and require a high degree of supervision and operator training. They are usually only implemented at larger facilities and are not cost efficient to be used on a small scale. This is only one part of the process of wastewater becoming treated water and biosolids.  Primary treatment is essential prior to the dewatering. The filtrate or centrate liquid which is separated during the dewatering process must also be treated. This typically involves circulation to the headworks of the wastewater treatment plant.

Not sure what the optimal solution is for you? Download the Waste Audit worksheet.

Making the Right Choice for Dewatering of Sludge

Is there a “right choice” for dewatering of sludge?

Many manufacturers will be quick to highlight the features and benefits of their technology over a competitor’s. Whether it is % solids achievable, polymer dosage required, throughput available, automation, ease of maintenance, energy costs, odor capture or a plethora of other options. It is easy to focus in on one benefit or feature and lose the sight of the big picture.

The truth is there is no right choice for the dewatering of sludge. Instead there is a right process for determining what dewatering technology or technologies will work best for your needs and it starts not with the technology, but with the sludge itself.

Dewatering of Sludge Trends vs. Individual Sludge Assessment and Solutions

It is true that trends exist in the industry like those highlighted in the article How Do I Choose the Best Option for Sludge Dewatering? Those trends exist for a reason. Facilities with similar types of sludge and related needs will tend to required similar solutions.

The overview provided in the article isn’t wrong but starting with a trend to determine the sludge dewatering process required can yield poor results. Your dewatering solution may require more than just the selection of a dewatering technology but may also involve sludge pre-treatment or other changes to your sludge collection and management process.

The Ideal Process for Dewatering of Sludge

The best process for dewatering sludge involves a few steps:

  1. Assess sludge characteristics
  2. Establish dewatering goals and factors affecting the desired outcome
  3. Identify and select the best techniques and technologies available to achieve goals
  4. Implement dewatering of sludge technologies and techniques
  5. Evaluate success of the dewatering implementation against goals

Each individual sludge situation will have different characteristics and understanding these characteristics is the first step to determine which technology you should choose. Once the sludge characteristics are known and understood, the next step is to clearly define the desired goals and factors affecting the goals. Some may suggest the goals should be defined first, but it is impossible to define realistic goals without knowing what you have in the first place. Often the goals may be the same from one facility to another but the factors affecting them such as volumes, disposal cost, energy cost, or maintenance capabilities will vary significantly. Knowing the sludge characteristics and the desired outcome(s) will ensure the big picture remains in sight while different technology features and benefits are being evaluated. The final steps in the process are to implement and gauge the success. Rolling these learnings into the future dewatering of sludge process will be key to improved success down the road.

The Right Choice for Dewatering of Sludge is All About the Process

So, in order to make the best choice for dewatering of sludge, it is important to focus on the process first and allow the technology and equipment choices to be informed by the sludge assessment and defined goals.

To find out more about how following the process delivers results, check out Wessuc’s Lagoon Dewatering Case Study or contact us.

Dewatering Best Practices to Optimize Efficiency, Cost and Environmental Impact

Best-in-Class Mechanical Dewatering Methods

Depending on what industry you’re in the term “dewatering” can mean different things. Construction site dewatering typically refers to the management of water on a site, whether it be pond water or ground water to allow construction activities to continue uninhibited.  In this context dewatering typically focuses on the removal of water from the site through pumping and its corresponding treatment and discharge.

In contrast wastewater dewatering typically focuses on slurry liquid solid separation to reduce waste volumes and provide waste management options. The wastewater dewatering process is one step in the operation of a wastewater treatment system. Optimization of wastewater dewatering then typically involves maximizing throughput, minimizing costs and maximizing separation.

Optimizing the Dewatering Process

Mechanical dewatering is a common method to reduce and manage liquid waste streams. Factors to consider in choosing and optimizing your dewatering process include:

  • Polymer dosage
  • Equipment maintenance
  • Ease of operation
  • Sludge Feed
  • Effluent characteristic requirements
  • Volumes to be processed
  • End use

Best-in-Class Mechanical Dewatering Canada Methods

The number of dewatering methods are as varied as the number of liquid waste streams they treat. As one component of a treatment system, variation in implementation is limitless. The three most common methods of wastewater dewatering are centrifuge, belt press and geo-textile bags.


The centrifuge spins the polymerized sludge feed at a high speed to separate the solids and liquid.  They have a high power requirement and polymer dosage rate. They benefit from a smaller foot print, low maintenance and ease of operation when used with a consistent sludge feed. Centrifuge units are common place in many large wastewater treatment facilities and achieve solids concentrations anywhere from 18-30%.


Belt presses come in a variety of designs but all work on the principal of squeezing the polymerized sludge feed to separate the water from the solids. The belt is permeable to water but not solids allowing their separation.  They benefit from lower power requirements and dosage rates. They have higher maintenance and require more operational oversight. They work well with consistent sludge feed.  Belt presses are common in many small to mid-size wastewater treatment facility and achieve solids concentrations anywhere from 18-28%.

Geo-textile Bags

Geo-textile bags provide a unique dewatering option.  They work by trapping the solids inside the bag and allowing the water to permeate through the geo-textile.  This method typically requires a large footprint to setup, although some unit have been setup in a standard waste bin.  The bags allow for large volumes to be dewatered quickly and have been used in the past during lagoon clean outs.  The bags are a one-time use and once full are disposed of increasing the cost of the operation for larger steady sludge feed flows.  They are able to handle fluctuations in solids content rather well and benefit from lower polymer dosage rates. They also can provide storage for the captured solids (which will continue to desiccate) while awaiting final disposal or reuse.  Because the dewatered sludge can be left to desiccate for any amount of time this method can achieve solids concentrations anywhere from 18-55%.

Rotary drum

Rotary drum dewatering units while used throughout the world are a newer entrant into the dewatering arena and perhaps serve a niche in the market. Wessuc first started using rotary units in 2010 when we used a vacuum unit. Since then we have switched to a rotary fill unit which works in much the same principal as a geo-textile bag.  The rotary drum is filled to capacity while the liquid permeates through the outer shell.  Once the unit is filled, the material is rotated for a number of hours to expedite the drying process. This method benefits from low polymer usage, low energy requirements and simple operation. The units can handle high solids fluctuations in the sludge feed and produce a high quality effluent (less than 100 mg/L TSS). The higher solids found in a digester clean out project result in dewatered solids concentration of 25-50%.

3 Important Best Practices in Detwatering

1. Testing and Evaluation

Polymer dosage rates will vary greatly depending on the dewatering method being used and the liquid waste characteristics. Liquids with higher solids concentrations will require higher dosage rates. Different dewatering methods will require different dosage rates to achieve equal solids dryness results which related directly to the overall dewatering cost. Polymer cost are often more than 50% of the input cost required for a treatment system and as such require testing and evaluation to determine the optimal type and dosage.

2. Automating Methods

Ease of operation is a key factor in the overall cost of the equipment. The more automated the equipment the less man hours required to supervise, trouble shoot, restart, and clean up the equipment. Therefore, the more a method can be automated, the more time operators can spend optimizing other areas of the wastewater treatment process.

3. Achieving High Quality Effluent

Effluent quality required from the dewatering operation will directly impact the available options. High quality effluent while achievable often requires a slower process with solids higher capture rates.  For most wastewater treatment plants, the effluent quality is not the determining factor as it is typically returned to the plant for reprocessing and not directly discharged to the environment.

Wessuc has experience completing projects with each of these best practices and has been working to improve the dewatering process in Canada for over 10 years to achieve efficiency and reduce cost and environmental impact. Contact us for more information on dewatering Canada.


Three Key Benefits of Solid Capturing

The process of solids capture is a cornerstone of waste management productivity for innumerable reasons. Some people within the agricultural and environmental industries may already be aware of capturing solids and its various advantages. For those that do not know, solid capturing or dewatering is essentially the process of wastewater being divided into its liquid and solid constituents. In other words, the not-so-useful sludge we call wastewater is converted into two resources that possess much more utility: freshly treated water and nutrient-rich biosolids. Read ahead to discover how this by-product of water treatment is an economic, environmental, and agricultural asset.

Economic Benefits

Biosolids that are sifted from wastewater would normally be a nuisance that would be expensive to dispose of; however, biosolids have been found greatly beneficial when it comes to agriculture, forestry, lawn maintenance, and home gardening. As well, a lack of solid capture would be more costly for water treatment facilities as it would lead to more frequent maintenance and the breakdown of certain mechanical processes over time. Those that use biosolids on their soil will see economic benefits in their crop yields and overall soil quality. Furthermore, these people will save money as this valuable resource reduces the need for chemical fertilizers.

Environmental Benefits

Since biosolids are a recycled commodity, they are helping the environment simply by reducing what needs to go to the landfill. For farmers, gardeners, and foresters that fertilize with biosolids, they can avoid using chemical fertilizers that have adverse effects on the surrounding environment. Even the process of isolating biosolids from wastewater through dewatering is an eco-friendly act since it improves overall water quality. This means safer drinking and swimming water for us as well as for fish habitats. The suspended solids that biosolids are eventually removed from a can actually harbour a variety of viruses and damage a fish’s respiratory system. To sum it up, biosolids promote more environmentally conscious soil and water maintenance while reducing the impact of our ever-growing landfills.

Agricultural Benefits

In addition to being economically and environmentally viable, biosolids have also proven a precious resource for the agricultural industry. As previously mentioned, biosolids reduce the need for chemical fertilizers; this makes for safer, more natural land while removing a notable expense. The high-quality composition of biosolids is worth mentioning as well. They contain nutrients that are vital to plant growth like phosphorus, nitrogen, and potassium. Besides these valuable nutrients, biosolids also offer a variety of heavy metals that are considered invaluable micronutrients for plant life. These micronutrients include but are not limited to zinc, nickel, copper, molybdenum, cobalt, and selenium. The presence of these key nutrients equates to greater crop growth and yields and further enriched soil. There is a reason why biosolids are being used in similar areas of expertise ranging from forestry to mine reclamation.

In short, solid capturing has allowed us to create a revolutionary commodity. Biosolids are an opportunity to improve the quality of our fields and the environmental quality of our world as a whole. If you are ever in need of an eco-friendly compost or fertilizer, biosolids are certainly worthy of your consideration.