By Edgar Mendoza on November 8, 2023
Category: Blog

Sludge disposal — challenges and solutions

Sludge is a solid byproduct produced during wastewater treatment. It contains a mixture of water, nontoxic organic compounds, toxic pollutants (heavy metals and chemicals), inorganic compounds, pathogens and other microbial pollutants. It is typically classified into two types:

Additionally, tertiary sludge is produced during further wastewater treatment, such as adding a flocculation agent. It is worth noting the sludge composition may significantly vary depending on the type of wastewater and the treatment processes applied.

Sewage sludge poses risks to environmental and human health, and sludge disposal is always a challenge for wastewater treatment plants because of the high treatment costs. While technological developments in wastewater treatment have enabled safe and sustainable sludge disposal, municipalities require the expertise of wastewater engineers to determine the most suitable and cost-effective sludge disposal method for publicly owned treatment works (POTWs).

Common challenges associated with sludge disposal

The chart below depicts common methods of biosolid reuse and disposal, including land applications (in agriculture, home gardens, etc.), landfilling, incineration, deep-well injection and more.

Source: U.S. EPAWastewater treatment plants have conventionally disposed of sludge on land through landfilling or composting. Burning the sludge (incineration) is another common method of sludge disposal to reduce volume and eliminate pathogens. However, these methods pose environmental challenges.
 

Challenges of common sludge disposal methods

Sludge disposal 

Challenge

Landfilling

The most common and relatively inexpensive sludge disposal method. Landfilling involves containing and isolating the sludge in designated landfill sites. However, landfilling sludge results in the production of greenhouse gases and potential leachate contamination. 

Incineration

Sewage sludge combustion is an effective method to convert sludge into a predominantly inorganic solid product. However, incineration is more expensive than landfilling and may cause air pollution if not properly controlled.   

Land application 

Reusing sludge as a fertilizer, soil amendment or feedstock for anaerobic digestion makes it a reusable resource instead of a waste byproduct. However, sludge should be properly treated and disinfected before being used on land.  

Sustainable sludge management addresses the challenges of conventional sludge disposal methods and involves minimizing the potential adverse effects of sewage sludge. The following are six common approaches to sustainable sludge management:The effective disinfection and stabilization of sewage sludge is critical to producing a stable biosolid product for land application and protecting the environment and human health.

 Different types of sludge disinfection methods

The 40 CFR Part 503, Standards for the Use or Disposal of Sewage Sludge under the Clean Water Act establishes the requirements and management practices for the use and disposal of sewage sludge (biosolids). The U.S. Environment Protection Agency (EPA) has divided biosolids into Class A and Class B based on their pathogen reduction requirements. The following are some key sludge disinfection technologies used to produce clean biosolids.
 

Types of sludge disinfection methods

Method

Description

Physical 

Physical stressors (temperature, pressure, irradiation, desiccation and others) solubilize organics, destroy cell membranes and break other critical cellular structures. Using physical stressors helps eliminate pathogens from biosolids. 

 

Some standard physical sludge disinfection methods include:

 
  • Thermal treatment.

  • Heat treatment.

  • Pasteurization.

  • Heat drying.

  • Air drying.

Chemical 

Chemicals stressors, including oxidants, pH and noncharged disinfectants, are directly added to the sludge or produced through chemical reactions during treatment to stabilize and disinfect sludge. 

Commonly used chemical sludge disinfection methods include:

  • Alkaline treatment.

  • Lime stabilization.

  • Ferrate oxidation.

  • Ozone.

  • Chlorine dioxide.

  • Hydrogen peroxide.

Biological 

Biological sludge treatment methods include:

These methods make use of noncharged disinfectants, such as ammonia and organic acids, to encourage microbial degradation in sludge. Biological methods are effective in stabilizing sludge and limiting chances of future putrification and odor production. 


Sludge disinfection methods implemented across a majority of wastewater treatment plants involve:  

Under 40 CFR Part 503, all POTWs should implement sludge disinfection methods to comply with the pollutant limits, pathogen and vector attraction reduction requirements and more. Failure to adhere to the requirements may result in enforcement action against the concerned wastewater treatment plant.

Partnering with water engineers for effective sludge disposal

At Fehr Graham, we are an experienced team of wastewater engineers committed to improving the efficiency of wastewater treatment plants and minimizing negative environmental effects. From developing innovative wastewater designs and planning upgrades to testing and sampling biosolids for routine land application and landfill disposal, we are your one-stop resource for wastewater treatment.

To learn more about how Fehr Graham can help your local POTW with effective sludge disposal, contact us or call 815.235.7643.

Edgar Mendoza is a Water and Wastewater Operations Specialist. He specializes in process control of wastewater and water treatment facilities, wastewater collection sewer systems, pump stations, water distribution and storage systems. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it..