Today’s biocontainment community is evolving at record pace with expanding science and rapid discovery of new diseases. In the past few years, this increase in research has challenged the waste treatment industry to play a major role in development of new technology.

This new waste treatment industry, once limited to landfill and incineration, has expanded with microwave sterilization, rendering, and alkaline hydrolysis treatment methods. Not only are each of these technologies viable for consideration, but there are also multiple providers of each technology. One of the issues, given the expansion of technology and providers, is adequate testing and validation.

Over the next few months, a group of seasoned industry members, including a microbiologist, mechanical engineers and biosafety officers, will share some insight into the alkaline hydrolysis technology, which in today’s market is referred to as the “tissue digester” or “caustic digester.” This series of articles will provide a clear history of the technology and share a better understanding of the costs associated with the operation, design consideration, and compliance issues for each of these waste treatment technologies.

Considering the basic facts and developing an understanding of the each these solid waste treatment systems and how each works in the biocontainment market is critical. It also provides insight as to why more caustic digesters are being used to treat animal carcasses. Some critical elements might be inadequate coverage of local municipality issues, public perception, and guideline compliancy requirements. However, before discussion of today’s market, a review of the history of alkaline hydrolysis is appropriate.

The History of Alkaline Hydrolysis
In 1888, Amos Herbert was granted U.S. Patent 394,982 for alkaline hydrolysis. His patent summarized reads, “My invention relates to the treatment of bones and animal waste and the horns, hoofs, skins, cartilages, and meat of animals,” “If the bones be treated with from 5 to 10 per cent of their weight of caustic potash or its equivalent, the…matter of the bone is dissolved... especially if heated to or above boiling point.”

The similarity between Herbert’s patent and today’s caustic digesters is the “specified” mixture of the percent of caustic to carcass weight. A comparison between the 1888 patent and today’s mixture of caustic is the addition of caustic to achieve a pH 13. This aggressive pH, which breaks up the tissues in today’s digesters, is typically achieved with the addition of sodium or potassium hydroxide—measured to 7 ½ percent the weight of the animal carcass—at an elevated temperature.

In addition, the science of alkaline hydrolysis is identified in the U.S. Federal Register (44 FR 53460, September 13, 1979) under the Environmental Protection Agency, 40 CFR, Part 257 – Criteria for Classification of Solid Waste Disposal Facilities and Practices. Appendix II to Part 257 states:

A. Processes to Significantly Reduce Pathogens… “Lime Stabilization: Sufficient lime is added to produce a pHof 12 after 2 hours of contact.”

B. Processes to Further Reduce Pathogens… “Heat Treatment: Liquid sludge is heated to temperatures of 180 °C for 30 minutes.”

One important aspect about the Federal Register is it relates to a term often used in this industry, “reduce.” For instance, the biological testing protocol requires a pathogen death rate of a 6 log reduction.

So what is the significance? This technology actually dates back over 122 years as a documented method of treating carcasses as well as an acceptable method in the sterilization process. Other than being cased in a shiny stainless steel vessel, there is prior art which identifies the process.

The Process
Let us move forward now and discuss the chemical reaction that occurs and discuss some of the operational parameters of today’s caustic digesters. We will get back to some of the other technologies in future articles.

The chemical reaction creating hydrolysis is a fixed science. Variations include less caustic and longer exposure time, more caustic and less time, and less caustic with agitation.

These systems operate at an elevated temperature ranging from 250 ºF to over 300 ºF which is the process of sterilization, which will be presented in some test data in a future article. The heating method of these systems typically is steam heat, but the use of hot oil/electric can be used. In most cases, steam heat is not only the most economical approach, but also the most dependable.

To recap the road we have traveled so far, we now realize it is a 100 plus year old process, a heated water and chemical mixture with a pHof roughly 13, and it comes in a shiny vessel. Now let us get into some of the issues that you will need to address if you select a caustic digester.

Design and Selection
Interestingly enough, some animal facility projects do not select the technology or address the SOP for the treatment of animal carcasses until late in the project. This can cause major increases in costs when inserting a digester into the facility design when the design has reached a 50% or higher completion progress. It can also cause issues with the municipality and local public perception of acceptance of the technology. How is this avoided? Obviously it cannot always be avoided, but it can be addressed by having a good understanding of the technology early on.

One of the best methods to weed through this process is to contact select suppliers and have each team provide a presentation on their equipment. This should be a zero cost project (maybe your only zero cost) and have them go into detail about the technology, critical design elements, history of their company, and discuss their company’s after sales efforts. Please keep in mind that you may have to complete an early selection of the vendor to keep your team moving forward.

Early vendor selection also provides you an opportunity to interview the suppliers because in some cases, you may be faced with cast-in-place embed when the digester is penetrating the containment barrier. It is critical that the proper embed design is considered because a generic embed may not necessarily be adequate for all digesters.

Secondly, having your vendor onboard early on is critical because the team can help present the system to the municipality using actual test data for the system that will be installed. It is often difficult to promote a common BOD (biological oxygen demand) and suspended solids count when each supplier has conducted their own testing and these results may differ depending on the uniqueness of their system.This can prevent the technology from being accepted and cause a devastating impact to the expectation of facility operation and program research.

Planning the utility profile for the facility is also critical and when your team elects to use a digester for the treatment of their waste carcasses, one can see the importance to address the requirements early on. The most critical question you and your team will be faced with is to develop the proper size of the system and deal with the questions of material handling. But don’t think you are done yet, there are more questions you need to address. Some of these questions and issues include how do you move carcasses safely, what type of space is required (both vertical and horizontal), what do you do with the waste streams, do you need an embed, what will be the requirement for the bioseal if it is penetrating containment, what will be the cycle consistency (daily, weekly), redundancy requirements, cooling options, control logic, BAS interface (building automation system), HEPA requirements…. and the list could grow.

There is light at the end of the tunnel however, because once the design is perfected, the building is complete and the system is up and operational, the operational costs will vary slightly depending on local electrical costs and the cost of caustic, but the client now has the lowest cost method of treating animal carcasses. Not only are you using the lowest cost of operation, but also the “greenest” technology when comparing the environmental impacts.

More To Come
Over the next few months, we will lead you through alkaline hydrolysis in greater detail and as mentioned, using some brilliant minds to contribute on this subject and hopefully over the next few months provide proven data about the alkaline hydrolysis process as it relates to the current market.

Shanon Jones is the Bio Division General Manager at Progressive Recovery, Inc. PRI having been in business for over 25 years, provides Effluent Waste Decontamination systems worldwide and has been designing and manufacturing Caustic Digesters for several years. Shanon joined PRI after working with an engineering firm where he contributed on (5) BSL4 labs and many additional BSL3-Ag and BSL3 facilities.; Progressive Recovery, Inc. 700 Industrial Drive, Dupo, IL 62239; (618) 286-5000;