Chemistry of the Alkaline Hydrolysis Process

Alkaline hydrolysis is a process whereby chemical bonds are broken by the insertion of water between the atoms in the bond. Alkaline hydrolysis can be catalyzed by enzymes, metal salts, acids, or bases. Bases are typically water solutions of alkali metal hydroxides such as sodium hydroxide (NaOH) or potassium hydroxide (KOH). Heating the reactants dramatically accelerates the hydrolysis reaction.

The process thus destroys all of these classes of compounds, reducing them to their building blocks and, in some cases, degrading them even further into smaller molecules. All proteins, regardless of their origin, are destroyed during the alkaline hydrolysis process.

Alkaline Hydrolysis Process

Amino acids are linked to each other in a peptide (amide) bond in which the carboxyl group of one amino acid is condensed to the amino group of another amino acid with the elimination of water. The resulting polymer is called a polypeptide or protein. All polypeptides consist primarily of the elements carbon, hydrogen, nitrogen, and oxygen, along with smaller amounts of other elements, mainly sulfur and phosphorous. Alkaline hydrolysis reverses the condensation of amino acids into proteins by the acid- or alkali-catalyzed breaking of the peptide bonds and the addition of water at the break.

Infectious Waste

The process destroys all pathogens listed as index organisms by the State and Territorial Association on Alternative Treatment Technologies (see STAATT I [April 1994] and STAATT II [December 1998] reports) and to be recommended in the new STAATT III Guidelines [2006]. The STAATT guidelines call for a system to be able to prove efficacy in the destruction of infectious agents by producing a 6 log10 reduction in vegetative infectious agents and a 4 log10 reduction in spore-forming agents. While each state has its own regulations for approving alternative treatment technologies for regulated medical waste, most of them are derived from or equivalent to the STAATT guidelines.

In the case of one category of disease agents – prions (which are proteins that do not consist of living cells) – the alkaline hydrolysis process has been specifically approved in EU legislation for the treatment of Mad Cow disease and other “Category 1” (TSE transmissible spongiform encephalopathy) wastes, in addition to approval for use with Categories 2 and 3 wastes in Europe.

The same process has been used for years for prion waste as laboratory waste decontamination systems for USDA laboratories and has been cited as an acceptable method of prion waste treatment in USDA and EPA regulations. Recently the US EPA determined that prions were to be treated as “pests” under the Federal Insecticide Fungicide and Rodenticide Act (FIFRA); our systems are registered under FIFRA.

Indigestible Materials

Paper, string, undigested plant fibers and wood shavings (bedding) are among the cellulose-based items that may be associated with animal carcasses but are not digestible by alkaline hydrolysis. Rubber, most plastics, ceramics and stainless steel (catheters, needles, clips, and staples) also cannot be digested by alkaline hydrolysis, although silk and collagen sutures, which are protein in nature are rapidly digested. However, the indigestible materials are completely sterilized by the BioSAFE Engineering process. They can be removed from the basket of the Tissue Digester and disposed of as ordinary waste at a sanitary landfill, with appropriate treatment of any sharps.

Radioactive Materials

Among the most difficult biological wastes to deal with are tissues and carcasses that have been generated in biomedical and pharmaceutical research and contain minute amounts of radioactive isotopes that had been injected into animals to study cell and tissue function, drug localization and metabolism, and toxin localization.

To meet Federal and state regulations for disposal of solid LLRBW, whole carcasses of small animals must be packed in lime and an adsorbent, then sealed in a 30-gallon can. The 30-gallon cans hold approximately 25 kg of animal carcasses. Each 30-gallon can must then be packed in a 55-gallon drum, also filled with adsorbent, and shipped to a licensed low-level radioactive waste (LLRW) burial site. There are only two such sites currently operating in the United States. The cost of shipping and burying each 55-gallon drum containing the can of radioactive carcasses is currently nearly $200 per kilogram.

In contrast, to the disposal process described above, our process converts animal tissues and carcasses from solid low-level radioactive biological waste (LLRBW) to an aqueous solution that is suitable for release to a sanitary sewer under 10CFR20 and derivative state regulations and does so at a cost of $0.07-$0.13 per kilogram.

Operating Costs

The operating costs per pound of material processed can range due to local input factors. The process requires operator labor, electricity, chemical, steam, water, amortized maintenance, and disposal fees. For up-front investigation and planning purposes, we recommend that clients use $0.10 to $0.20 per pound as an operating cost estimate.

Depending upon the nature of the material being processed, this amount compares favorably with incineration and special landfill operating disposal. These alternative costs can range anywhere from $0.25 to greater than $1.00 per pound. At a client’s request, our engineers are happy to help construct very exacting operating cost estimates based on the size of the machine to be employed and local utility factors.