Don’t Let Sludge Weigh You Down

Sludge is the semi-solid matter produced from various industrial processes within the utilities sector. In this article, we look at some of the treatment solutions that your waste provider should be offering to your facilities to keep your costs in check.

Advantages of Sludge Treatment

Effective treatment of sludge provides tangible benefits for utilities facilities:

  • Reducing the volume of sludge
  • Recovering water for potential reuse
  • Reducing or eradicating the associated health risks
  • Potential for creating an agricultural fertilizer
  • Reducing sludge disposal costs

Sludge Treatment Processes

There’s a wide range of treatment processes that can transform what was once considered simply a waste stream into a valuable resource. Common sludge treatment methods include dewatering, thermal hydrolysis with biological treatment, and incineration.

Sludge treatment technologies, such as anaerobic digestion can cope with all kinds of organic sludge, reducing the volume of dry matter and maximising the production of renewable biogas.

The two main purposes of sludge dewatering are waste minimization and achieving cost efficiencies in disposal. Stabilized sludge can be handled more safely and often has fewer associated health hazards. Some sludges then have potential for beneficial reuse and can be land applied.

Sludge dewatering typically focuses on reducing the weight and volume of the sludge so that disposal costs – including transportation – are kept to a minimum. Water removal is the primary means of volume reduction before sludge waste can be treated or disposed of in the most economical manner.

The first step that any waste manager should build into sludge waste management is dewatering, before any container is hauled to a treatment site. This also ensures that container weights don’t exceed DOT limits. Your waste management partner should consider solutions such as staging containers for drying, and weights should be actively monitored to prevent compliance issues.

Additional dewatering technologies include:

  • High pressure filter pressing (225psi) for sludge where the solids are disposed of as a hazardous waste and the highest volume reduction is desired. Produces a filter cake 40-70% solids by weight
  • Low pressure filter pressing (100psi) for non-hazardous sludges where transportation and disposal or recycling costs are not as high as for hazardous waste streams. Produces a filter cake 25- 50% solids by weight
  • Geomembranes, for applications where a high volume of water and low volume of solids need to be effectively treated such as:
    • Water filtration plant residuals
    • Biosolids
    • Wastewater residuals
    • Ash residuals
    • Settling pond residuals
  • Centrifuges for oily sludges where oil recovery is a priority and the residual solids are not a major concern
  • Belt presses where a higher moisture content is acceptable in the filter cake (18-25% solids by weight)

Incineration, or Waste to Energy (WtE) plants are growing in prominence in the U.S. There are now 86 WtE facilities in 25 states. WtE technology is an energy recovery process that converts chemicals from waste residues into practical forms of energy like electricity, heat or steam. For sludge treatment, thermal conversion techniques are the most viable option.

Incineration works more efficiently on sludge if it has been pre-treated by dewatering. The thermal treatment process then generates stable and recyclable by products in the form of ash and dust. Ash can potentially be used in road construction, concrete production or discharged as an inert material to landfill.

As most utilities are subject to sustainability targets, WtE is an attractive disposal option. Not only does it divert heavy waste from landfill, but modern WtE facilities produce a renewable form of electricity while generating two-thirds less CO2 compared to traditional coal-fired power plants.

If your business completes ESG reporting, then diverting as much waste as possible from landfill is an important step to make. Switching the destination of your waste to a WtE facility rather than a landfill site requires no alteration to an organization’s waste operations, and as such can make an instantaneous impact alongside other resource minimization strategies.

Where WtE plants are available, a conscientious waste management provider will identify the haulers that are able to send the greatest proportion of your waste to these facilities. To take advantage of this opportunity, choosing a waste provider who is agnostic to disposal sites is key. A waste management provider who has no affiliation to disposal sites will be more willing to send your waste to sites that maximize your sustainability goals rather than what is most lucrative for the operator.

Anaerobic Digestion
For utilities to achieve a more sustainable resource recovery and to reduce their overall carbon footprint, organic sludges can be treated in an anaerobic digestion (AD) facility.

Anaerobic digestion is the biological degradation of organic matter, in the absence of oxygen. The process converts the chemical energy stored within organic carbon to biogas (methane), that can be combusted to generate energy. The process also creates a liquid by-product, otherwise known as digestate, that is high in nutrients and can be used as a crop fertilizer and soil enhancer.

Very few waste management companies operate AD facilities, and would instead seek to process your organic sludge waste using less sustainable methodologies. NWA has relationships with independent haulers who don’t own landfill sites and so are free to haul your waste materials to whichever treatment facility is best suited to your waste stream. Our experts will review the viability of AD for your sludges and then assess the availability of AD plants around your facilities. If facilities are available, we’ll source a hauler who is able to transport to them.

Thermal hydrolysis
Thermal hydrolysis fundamentally changes the properties of sludge by heating it to more than 300°F. In doing so, it improves water extraction potential, increases biogas production, and lowers operating costs.

Sludge can suffer from mass-transfer limitations, which slow down the rate at which biogas is produced. The often-gelatinous nature of the material also means that it retains more water, limiting the potential for water extraction, which is needed for efficient use or processing of the end biosolids product.

By destroying these gelatinous materials, thermal hydrolysis improves the performance of both digestion and dewatering. Digestion performance can improve by 15-50%, and biogas yields increase by approximately 390-430m3 biogas/tonne dry solids, compared with plants with no pre-treatment. Dewatering improves by up to 10%.

This pre-treatment methodology is usually built into the facilities, before the sludge is treated by sending to an anaerobic digester.

Sustainable Sludge Treatment with NWA

NWA has no affiliations with landfill sites, unlike the national haulers who also own landfill facilities. Instead, our model is to work with haulers who are truly independent and agnostic to which disposal sites they utilize. This is a key differentiator that enables our customers to capitalize on sustainable waste treatment opportunities such as incineration (WtE) and anaerobic digestion.

It also enables us to focus on helping your facilities to develop cost avoidance strategies. Our waste management experts work proactively with our clients to create tailored cost-reduction solutions. We will actively propose solutions such as staging containers to reduce the water content, so that you’re never paying more than you should for waste management.

Find out how NWA can improve your waste management operations.
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