Sludge management in wastewater treatment explained

A belt filter press is commonly used for dewatering sludge.

Sewage sludge is a wastewater treatment byproduct, a semi-solid slurry of organic matter, trace chemicals and inorganic solids. The effective management, treatment and disposal of sewage sludge is a major challenge. Wastewater treatment plants (WWTPs) protect public health, surface waters and the surrounding environment by focusing on the three Rs of sludge management:

  • Reduce the amount of sludge produced.
  • Recover nutrients from the sludge.
  • Reuse the stabilized sludge as a biosolid for land application.

Poorly designed sludge treatment and management systems lead to high maintenance and operational costs, penalties and plant shutdowns. Sludge management is at the core of the design and operation of all WWTPs.

Partnering with an experienced team of wastewater engineers can help municipalities devise custom and cost-effective sludge treatment strategies.

Sludge management in conventional wastewater treatment

The goal of sludge management is to reduce the volume of sludge and stabilize its organic matter. However, reaching this goal proves difficult because there are two sources of sludge in conventional municipal wastewater treatment.

  • Primary sludge accumulates during the primary treatment of wastewater. This sludge contains a high concentration of decomposing microbes and inorganic matter.

Lowering sludge volumes reduces the cost of pumping and storage, and stabilization eliminates the toxic components and offensive odors from this unavoidable byproduct of wastewater treatment. The table below outlines how municipalities manage their sewage sludge.

Processes for sewage sludge management

Consolidation processes

Sludge volume is reduced by removing the water and dissolved solids. Consolidation methods fall into two categories:

  • Thickening. Thickened sludge retains the free-flowing liquid-like properties of sludge. The thickening process aims to separate the solid and liquid phases of the sludge.  

Common methods include gravity thickening, centrifugal thickening, dissolved air floatation thickener, and rotary drum and gravity belt thickener.  

  • Dewatering. Dewatered sludge has a higher concentration of suspended solids and does not flow like a liquid. It is transformed into high-solids filter cakes for easy and cost-effective disposal. 

Common processes include belt filter presses, screw presses, filter presses, rotary presses, thermal drying, and drying beds and lagoons. 

Stabilization methods

Stabilization sludge reduces the odor, putrescence (decay) and pathogens. Sludge stabilization methods fall into two categories:

  • Chemical stabilization. Chemical or alkaline stabilization uses reagents such as lime to increase the pH level of the sludge and break down the organic matter. However, lime dosing does not reduce the sludge volume.   

  • Biological stabilization. This uses microorganisms to degrade the organic matter in the sludge biochemically. Depending on oxygen conditions, biological stabilization can be categorized into anaerobic and aerobic digestion. 

Additionally, thermochemical treatments are carried out by applying intense heat, either in the presence or absence of oxygen, to substantially reduce the water content and stabilize the sludge. 

Thermochemical methods include the oxidative processes of incineration, wet oxidation, supercritical water oxidation and nonoxidative gasification methods , pyrolysis and hydrothermal treatment.   

Sludge management is a big job with high stakes. That's why municipalities often partner with experienced wastewater engineers who can design custom processes and determine cost-effective methods for sludge management.

Partnering with Fehr Graham for effective sludge management in wastewater treatment

At Fehr Graham, we are committed to enhancing the efficiency of WWTPs and protecting public health and the environment. Our team of wastewater engineers and other licensed professionals help communities across the Midwest upgrade their wastewater infrastructure. From developing custom wastewater designs and sludge management strategies to testing and sampling biosolids for landfill disposal and land application, we are the one-stop solution for wastewater engineering.

To learn how Fehr Graham can help you with sludge management in wastewater treatment in your community, contact us or give us a call at 563.927.2060.

Portrait of Lucas Elsbernd Lucas Elsbernd, a Professional Engineer and Senior Project Manager, finds innovative solutions to challenging water and wastewater projects. He manages municipal, commercial and industrial planning and design projects in the water resources environment. He fosters a positive client experience and collaborates with leaders throughout the firm on project pursuits and technical issues. Lucas is one of the firm’s water and wastewater experts. He has a strong technical knowledge of water and wastewater treatment design and construction engineering. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it.. or 563.927.2060.