United Sludge-Free Alliance

Alternative Uses for Sewage Sludge

The Ocean Dumping Ban signed into law in 1988 outlawed the dumping of sewage sludge into the ocean after December 31, 1991. At the same time that municipalities had to come up with alternative methods to dispose of the highly concentrated waste product solids that remain after water extraction, many of them were also confronted with growing populations helping to create increasing amounts of it to dispose of. Landfilling, incineration, and land application became the most common disposal methods, but with increasing concerns over the safety of those methods, researchers around the world have been exploring other ways to manage sludge. In this section, you’ll find samples of that research. Some of the most promising has looked at sludge as a renewable energy source. The renewable part comes as no surprise, but the fact that sludge can be used in a variety of ways to generate energy and fuel may. As exciting a prospect as that may be at a time when we feel an increasing urgency to find alternative energy sources, it’s important to note that this is an emerging technology and that many of the concerning heavy metals, pathogens, and other pollutants found in sludge still need to be addressed. It’s also fair to say that there will be no "one size fits all" solution; no one method will work for every municipality. Finally, it’s critically important to approach the management of sludge in a deliberate, thoughtful manner, as in the following example from Sweden.

Sweden’s Sustainable Waste Management System

The Swedish system of Sustainable Waste Management is highly regarded around the globe. As the Swedes put it, "Waste and refuse are resources in the wrong place," and so they've spent decades finding ways to make the most of sewage sludge. According to Stephen J. Salter, an engineer from Victoria, British Columbia, who has written extensively about his travels in Sweden to study their methods, sewage sludge is used to fuel vehicles and heat homes. But it's not just that the Swedes have turned sludge into energy that makes their system so special. It's that they've developed an integrated approach to dealing with waste that sets them apart from so many other nations, including the United States. In "Powered by the People: Victoria Engineer Discovers Swedes View Sewage as a Valuable Resource" from Victoria's Times Colonist newspaper, Salter says, "I went [to Sweden] expecting to see really cutting-edge technology, and instead what I found was a lot of common sense applied to community planning," he said. "Instead of just looking at liquid waste separately, they look at liquid waste, solid waste, energy, transportation and environment. They look at all of those five areas as one plan."

We can learn a lot from the Swedes.

1. Their integrated approach to managing waste and converting it into a resource is one that has evolved over decades. Their first treatment plants were built in the 1930s. Over time, they have upgraded to tertiary plants, meaning that physical, chemical, and biological methods are used in the treatment process.
2. Municipalities have control over their waste management systems, as each city owns its own companies for managing sewage, solid waste, energy and transportation.
3. Treatment plants are often built within communities, even under an apartment building in one case, so that residents are mindful that the waste we generate doesn’t just go away when we flush the toilet.
4. The entire matter of waste management is carefully thought out, so that resources from waste are used to best advantage in each community.
5. All of their efforts have resulted in reduced costs for sewage treatment per household , whereas costs in the U.S. continue to rise dramatically and don’t take into account the cost of rebuilding the crumbling sewage infrastructure . By the way, the Swedes also get subsidies for filling their tanks with bio-fuel.

As a means of making use of waste, applying sewage sludge to land as a fertilizer isn't a terrible idea. It's an idea carried out in a terrible way in this country. In fact, it's a great example of how not to manage sewage sludge. In order to use sewage sludge safely as a fertilizer, you would need to know where it's from, what’s in it, and how to clean it so it doesn't cause contamination. When sludge is imported from other municipalities and even states, when it's not sufficiently tested to know what it contains, and when adequate resources aren’t dedicated to cleaning it, it's impossible to safeguard the soil and the food supply. Instead of making our standards and testing requirements more stringent over time, we have made ours less so. And since "sewage contains 10 times the energy needed to treat it ," we may be overlooking more efficient ways of using even the cleanest sludge.

To Download the Alternative Uses for Sludge chart Click Here

Stephen J. Salter – Treating Waste as a Resource: Inspiration from Sweden

(video and pdf versions + related article from Georgia Strait Alliance site)

• Watch Video
• PDF Version
• Georgia Strait Alliance

Waste Not

Great chart by Salter providing an overview of how sludge can be utilized based on the Swedish model.

• PDF Version

Survey Sewage Sludge Research

The avenues of research into alternative uses of sewage sludge are as diverse as the locations of the research facilities themselves. It would be impossible to provide a comprehensive list of studies, so here is a sampling. The accompanying chart provides a more orderly look at some of the more interesting uses being investigated.

General

This is a more general list, but contains several great examples specific to sewage sludge. It was compiled by Stephen Salter, who was cited in the discussion on Sweden.

• Resource Recovery Examples

Worldwide

The SUSAN Project is a consortium created by the EU to find safe ways of recovering nutrients, primarily phosphorous, from sludge by using a two-part process of mono-incineration followed by a thermochemical treatment. Members of the consortium are listed in this document.

• SUSAN Project

USA

The United States has lagged behind many other countries in its exploration into alternative uses for sewage sludge. In the past year, a number of projects have sprung up around the country. Several are summarized here . 

European Union:

• Council Directive 86/278/EEC of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture
• Evaluation of sludge treatments for pathogen reduction

Germany:

Hosted by Hans Huber AG, a German company that supplies sewage treatment equipment and operates a sludge division. There are many case studies on the site of applications of their technology.

• 1st Sewage Sludge Symposium held in Berching / Germany on 9th September 2003
• Hans Huber AG Home Page

"IWEtec (Innovative Water and Environmental Technologies, Germany) and Dirk European Holdings, Ltd. (United Kingdom) have developed the "DIRK Power Ultrasound" treatment. Full-scale application of this treatment in Germany has shown that the use of this patented split-flow disintegration by means of high-powered ultrasound offers a reliable and cost-effective means to treat wastewater treatment sludge. The treatment results in a decrease in sludge quantity (volume and mass) and increases the biogas yield. It also results in a higher dry solids output and a lower requirement for polymer/additives in the dewatering process."

• Ultrasound Disintegration of Sewage Sludge: An Innovative Wastewater Treatment Technology
• Eisenmann Pyrobuster

Greece:

Explores use of dried sewage sludge as an additive in construction materials.

• Solidification of Dried Activated Sludge in Ceramic Materials

Japan:

Japan has been using ash or slag resulting from the incineration of sludge as backfill for civil engineering projects, raw material for brick and tiles, etc., but supply has exceeded demand, so this paper discusses methods of supplying sludge to Portland Cement plants.

• Reuse of Sewage Sludge as Raw Material for Portland Cement in Japan

Netherlands:

• Recovery of Phosphorous from Sewage

Scotland:

The specific page in the link contains pdf files for each of Scotland’s Waste Recovery Technologies. They provide nice overviews of the technologies.

• Scottish Environmental Protection Agency

United Kingdom:

Anaerobic digestion refers to a process that takes place in the absence of oxygen. It is a bacterial process that occurs during the fermentation of the sludge and leads to methane production.

• Anaerobic Digestion

This is a great UK-based website for learning about Anaerobic Digestion. Among the many resources are downloadable documents including the following:

Biogas Methane Explained & Other Articles

The Magic of Combined Anaerobic Digestion with Composting of Municipal Solid Waste

The site also provides information on the German company, Schmack.

• Schmack