Biosolids Lime Stabilization and Coal Ash

Our sisters and brothers in residuals management are doing resource recovery with panache. Coal ash, CKD/LKD, waste asphalt and concrete – each sector is developing new markets, reducing landfilling, improving quality, and introducing efficiencies. Are there lessons here for biosolids in the dusts of other industries?

Attracting me to the topic of residuals management was the article A New Life for Coal Ash, the cover story of the February 15 issue of Chemical & Engineering News of the ACS. It describes the initiatives underway to introduce efficiencies in coal-fired generators, thereby yielding improved ash, and developing markets for the improved ash, thereby diverting ash from landfills and scoring big on measures of sustainability. Some environmental groups are pushing back against the initiatives, despite EPA’s support, and, yes, the industry has had its bad news, as with the collapse of the TVA waste pond in 2008. But resource recovery is progressing.

This good work is brought about by the American Coal Ash Association. Established in 1968 as a trade association devoted to “recycling the materials created when we burn coal to generate electricity,” the ACAA has a program “Fly Ash – A Strong and Sustainable Future” to explain that “technologies to improve ash quality will increase the volume of ash available for beneficial use” and that “reclaiming fly ash from disposal facilities will increase supply significantly [its emphasis].”

The ACAA is not alone in transforming a waste into a resource.

The Portland Cement Association has a webpage called Sustainable Development with Concrete  featuring its 2008 publication Beneficial Uses of Cement Kiln Dust. These uses include, as we all probably know, the stabilization of biosolids, as in the N-Viro process.

The construction industry features the recycling of waste concrete back as a major sustainability goal.  The ASTM (American Society for Testing and Materials,) in its “Standardization News”, published The Greening of Civil Infrastructure. A key part of that program is its ASTM International: Standard Guide for Greener Cleanup calling for use of residuals in all aspects of public infrastructure. TheGreen Highways Partnership (the tagline for which is “Green Roads, Streets and Towns”) takes in not only the ACAA but also the National Asphalt Pavement Association (See NAPA’s downloadable document Black and Green: Sustainable Asphalt, Now and Tomorrow) in offering ways to reuse old pavements. I can’t help but hear in the sustainability commitments of these “civil infrastructure” groups the use of biosolids-derived products, as in landscaping and maintaining highway medians and rights-of-way.

What is more, ash and biosolids have been linked together for many years.

Ash, along with agricultural lime products, have been ingredients in lime-stabilization of sludge for many decades. Even before the 1993 Part 503 regulations, liming was a “process to significantly reduce pathogens,” and this process further evolved during the Part 503 rulemaking into standards for pathogen and vector attraction reduction.  If you want to refresh your memory,EPA Control of Pathogens and Vector Attraction in Sewage Sludge is the “White House” document, our  “bible” for this topic. You will recall that the VAR Option 6 calls for biosolids to hit pH 12 for 2 hours, followed by a pH at or above 11.5 for additional 22 hours. Processes to Significantly or to Further Reduce Pathogens (PSRP and PFRP) take off from there. To review how the CKD and ash fit into this, the EPA has Examples of Equivalent Processes: PFRP and PSRP.  WEF issued the  National Manual of Good Practice for Biosolids  to provide guidance for compliance with these and other performance standards.

Over the years I formed a personal bias against lime stabilization. This comes from several significant public relations issues in the mid-Atlantic region stemming from inadequate processing with lime. But now I return to stabilization with alkaline amendments, suspending my bias, and considering the possibility that lime and alkaline ash can, in fact, produce a high quality biosolids product?

Back in the early 2000s, DC Water was a force of good in providing practicable, scientifically-sound advice for making lime stabilization work. In particular, DC issued reports  Survey of Odor Emissions from Several Lime Stabilization Programs in the District of Columbia and Maryland and Mitigation of odors from lime stabilized biosolids.   Though DC Water has taken itself out of the lime stabilization business, it leaves a legacy of successful production and use of this type of biosolids. Recently, I have spoken with operators who provide persuasive examples that lime stabilization works. Further, I have heard from one regulator that farmers in his state love and need lime-rich biosolids.

Pittsburgh’s ALCOSAN is one place that lime stabilization is working. It is now the largest facility in the MABA region producing a lime-stabilized biosolids,ALCOSOIL, for recycling.  ALCOSAN reports that it is happy with the process, product and utilization program it is managing with lime stabilization, which takes 50% of its biosolids, the other half being incineration. In fact, ALCOSAN has returned recently to recycling facilities in Pennsylvania through Synagro, its contractor.

The mid-Atlantic region is also home to one of the more “out-of-the-box” alkaline stabilization programs. Middlesex County Utility Authority, in Sayreville, NJ, has been operating for several years a process that makes an ideal daily cover for that authority’s solid waste landfill. The process, described in “Processes and apparatus for treating sewage or like sludge,” uses a two-step dewatering system comprised of a belt filter press followed by a BUSS thin film dryer.  A thickened combined primary and WAS is brought to 50+% solids with this process train, after which the sludge is blended with a combination of quick lime and hydrated lime (8 percent on a wet weight basis) to produce a workable and low odor material for landfill cover. Anyone with a bent to agronomy would nearly salivate over the material’s soil amendment attributes, but MCUA has a good thing going at its landfill.

But beyond the objective of achieving lime stabilization, the combination of biosolids and ash has many other favorable attributes.

A dozen years ago I spent a lot of time with coal ash. I had reviewed a paper by Paul Rosenfeld on the West Coast. His work (“Effect of high carbon ash on biosolids odor emissions and microbial activity” ) had discovered a remarkable reduction in odorant emissions from digested biosolids when a certain kind of coal ash was amended, one with a high proportion of carbon.

In the early 2000s I searched through a large array of additives and agents for the holy grail of odor control. In 2006, I presented at WEF’s Residuals and Biosolids Conference a paper co-authored with Bucknell’s Matt Higgins on  “RESULTS OF TRIALS OF CHEMICALS, ENZYMES AND BIOLOGICAL AGENTS FOR REDUCING ODORANT INTENSITY OF BIOSOLIDS.”  Among the nearly dozen ingredients, high carbon coal ash topped the list for effectiveness.

Colleagues at American Green, a subsidiary of Reading Anthracite, helped with a field study of the coal ash for odor mitigation. Reading Anthracite has a lot of ash, and together we selected for evaluation a high carbon ash of the kind that Rosenfeld had used. This was from the Schuylkill Energy Resources, Inc. (SER), plant, a 100-megawatt anthracite culm-fired cogeneration facility located in Mahanoy Township, Schuylkill County. In laboratory and in field tests, a 50:50 mix (wet weight) of coal ash and biosolids was very effective.  With laboratory olfactometry, the odorant intensity of an ash-treated cake was less than 10% that of untreated cake; in the field, the Nasal Ranger required 4 times as much dilutions air for untreated cake than treated cake to achieve a detectable odor.  Coal ash may still prove to be an elixir for pathogen and vector attraction control in biosolids.

The work by ACAA, PCA and ASTM reminds us that the marketplace drives the reuse of recovered residuals. With biosolids, the landowner’s requirements for nutrients and for liming and the community’s concerns for odors, for low pathogen risk and for aesthetics are parameters for guiding innovations in lime-stabilization technologies, and all of our treatment processes, for that matter. This is the foundation of the WERF High Quality Biosolids Research Project that is now in full swing.

But we also need to sell our products, and in this respect these other residuals industries seem out ahead of us.

To aide in marketing biosolids re-use, a new tool has just been released.  It is a document authored by a European-based committee of biosolids land application professionals working through Global GAP (Good Agricultural Practices). I urge you to download and use this cogent rationale for committing to good biosolids product quality and to sound utilization practices.


All of this talk about food crops, biosolids and ash prompted my memory of a biblical passage in Genesis (3:19), “you will eat your food…. and to dust you will return.” I guess biosolids and ash have always been that kind of natural combination, and, so with biosolids, to Dust We Return.