A Guide to Sludge Dewatering with Horizontal Vacuum Belt Filters

Sludge dewatering is one of the most critical treatment areas within a wastewater plant. Raw sludge is only 30–40% solids, while treated sludge has to be over 85% solids. There is a lot at stake in the final quality of treated sludge that needs to meet discharge limits and be rid of free oil and grease. This article will provide an overview of sludge dewatering.

What is Sludge Dewatering?

Sludge dewatering separates water and excess fluid from the sludge, either by settling or centrifugation. It is one of the critical steps during sludge treatment and is very important in maintaining the final product’s quality and reducing disposal costs.

Dewatering sludge is the first step to removing solids from wastewater. The main objective of dewatering is to separate concentrated suspensions of sludge into a thickened slurry and fluid by using gravity or centrifugal force. There are several different methods and specialized machines that can complete this task. Each method has its advantages and disadvantages that you must consider when deciding on the type of equipment to use for your facility.

The sludge dewatering process is accomplished through gravitational methods or with vacuum belt filters. The gravitational methods can be relatively simple but time-consuming. In contrast, belt filters allow for quicker dewatering and higher dry solids content of the final product.

Horizontal Vacuum Belt Filters

These machines use a rotating vacuum belt to filter sludge, remove water content, and leave dryer cake material behind. Sludge from water treatment plants is often dewatered with this method since it’s more environmentally friendly than incineration or landfills. Horizontal vacuum belt filters are also typically used for flue gas desulfurization (FGD), gypsum dewatering, and the filtration of industrial waste products or byproducts.

How Do Horizontal Belt Filters Work?

You have several options when looking for a dewatering solution for your sludge. One of the most popular is the horizontal vacuum belt filter. It’s known for handling a wide range of fluids, producing high product yields and cake solids, and being used in various ways depending on your needs. Here is the working principle of a vacuum belt filter:

The first part of the process is gravity drainage. The sludge is positioned on a porous material that allows the water to pass through while trapped between the filter’s belt and the feed end. This stage can reduce your overall costs because it requires little to no power or chemicals. You can even use this process alone if your main goal is to remove excess water from the sludge.

The next step is vacuum filtration, which is where the sludge moves along a vacuum belt filter cloth supported by a moving belt. At the same time, liquid and air are drawn through the fabric under vacuum pressure. This part of the process helps separate more moisture from the sludge and gives you more control over your final product’s solid content. The vacuum pressure also helps move it along faster than gravity drainage.

Which Sludge Types Can Be Dewatered Using Horizontal Vacuum Belt Filters?

The type of sludge you want to dewater will affect the best method for your situation. When it comes to sludge dewatering with horizontal vacuum belt filters, some types of sludge respond better than others.

Paper and Pulp Wastewater

Paper and pulp industry wastewater, for example, is often treated with a horizontal vacuum belt filter because it produces a high volume of suspended solids. The suspended solids in this type of sludge can be effectively separated and removed by the vacuum belt press.

Biological or Municipal Wastewater

A horizontal vacuum belt filter is still a good option when you need to dewater biological or municipal wastewater treatment plant sludge. These sludges generally have lower solids content than paper and pulp wastewater, but they can also be efficiently separated using the vacuum belt press with proper conditioning.

Metal Finishing Wastewater

Industrial wastewater from metal finishing processes—including aluminum anodizing, electroplating, and other metal plating operations—is another type of sludge compatible with horizontal vacuum belt filters. These sludges have high organic content and will generally require some conditioning before being processed on a vacuum belt press.

What Are the Benefits of the Horizontal Vacuum Belt Filter?

There are several reasons vacuum belt filters have become the go-to for processing wastewater:

Efficient

These filters are more efficient than traditional plate filters because they don’t require frequent cleaning. Less maintenance will reduce downtime and costs significantly. In addition, this filter design allows for more efficient drainage than other types of filters, such as rotary drum filters or plate and frame filters.

Versatile

The ability to operate at high pressures makes these filters ideal for applications where other types would be impractical or cost-prohibitive due to excessive head loss requirements, such as seawater treatment systems with high salinity levels.

High-Quality Cake

The horizontal sludge dewatering method separates liquid from solids through a porous filtration medium. Sludge is applied to the surface of the filter cloth and then conveyed under vacuum pressure while being squeezed by rollers. This process results in a solid cake automatically discharged at the end of each cycle.

Easy to Operate

Vacuum filter sludge dewatering machines can be automated, making them easy to integrate into existing processes and procedures. You can configure these systems with multiple zones that allow continuous operation with automatic cake discharge, reducing labor costs.

Durable

These industrial-grade filters are designed to withstand harsh environments and last longer than other filters. In addition to being durable, they are also effortless to clean and maintain.

Minimizes Sludge Disposal Costs

A vacuum belt filter helps reduce sludge disposal costs by minimizing the amount of water in the sludge that must be treated before being disposed of properly. This method reduces waste disposal costs by eliminating the need for expensive chemicals or other hazardous materials during treatment processes.

Delivers Continuous Filtration

Continuous filtration means a vacuum belt filter can be easily integrated into your current processes without significant changes or disruptions. It provides maximum flexibility during operation, allowing you to adjust process parameters to meet your needs.

How to Select the Right Horizontal Vacuum Belt Filters

Horizontal vacuum belt filters are an essential part of the sludge dewatering process. These filters can dewater a wide range of sludge types and consistencies, and they are more cost-effective than alternative filters. But how do you know which horizontal vacuum belt filter is right for you?

Here are five of the most important factors to consider when choosing your filter.

The Characteristics of Your Sludge

Whether you are dewatering municipal sewage sludge, lime softening sludge, or sludge from another process, your sludge’s consistency and composition will significantly impact the design of your filter.

• If your sludge has a high solids content, you might want to go with a wide belt filter. A wide belt will allow more filtration, resulting in more efficient dewatering.
• If the sludge is incredibly fragile and delicate, your best bet is to choose a filter with high back pressures. High back pressures will minimize any damage to the sludge during dewatering.
• If you have significant amounts of sludge (over 10 tons), you should opt for a horizontal vacuum belt filter with a high level of automation. This will reduce manual labor and make full-scale dewatering feasible without sacrificing efficiency.

Filter Media Type

The type of media used in your vacuum belt filter determines how effectively it will separate water from solids. Woven cloth is a good choice for thick sludges, while a mesh cloth is better suited to thinner ones. If you have both thick and thin sludges, you may consider using an adjustable system to accommodate different media types.The right filter media choice depends on your budget and how regularly you use your filter. If you’re operating your filter daily, synthetic would be a great choice because of its long-lasting durability. However, the woven wire might be better if you’re only filtering sludge occasionally.

Vacuum Source and Pumping System

How the sludge will be converted into filtrate (liquid) is a fundamental consideration when choosing a filter. Most sludge filtration systems use a liqui-vac pump, which uses a liquid ring to create a vacuum, but other options are available. The type of pump you choose will affect both the initial cost of your sludge filtration system and its operating costs down the line.

Chemical Addition System

Chemical addition systems add chemicals to sludge to improve filtration. Some materials are likely to clog the belt or otherwise interfere with the filtration process without additives. But it’s important to note that not every filter is equipped with a chemical addition system. If you’re processing a material that might clog the filter, make sure your vacuum belt filter includes one.

Belt Width and Size

Wider belts can process more sludge at once, but they also require more horsepower to run, which will increase your operational costs. Before choosing your belt width and size, think about how much sludge you need to handle in a single batch and choose accordingly. The right belt size will depend on your unique needs, but it should be large enough to process all of the sludge without being so large that it becomes difficult or expensive to operate.

Final Thoughts

Horizontal vacuum belt filters are a great tool to use in the dewatering process. They’re efficient and cost-effective, and they help preserve the structural integrity of your sludge.

But you don’t want to choose this tool haphazardly—you need to consider its size, material, and other specifications.

Are you looking for the right filter for your wastewater treatment? Contact filter holdings to find the best equipment for your filtration system.