Enzymatic Treatment of Abattoir Waste Tissue

Is it just my imagination or are there a growing number of increasingly disillusioned business owners that have one thing in common - they all dabbled with small waste disposal processes that make use of proteolytic enzymes to digest animal carcasses and condemned abattoir waste tissue?

At first glance, using enzymes seems like such a logical way to get rid of all those smelly waste tissue, yet the concept in practice just does not seem to work properly on any kind of single-user scale.

Despite the fact that the science behind the use of digestive enzymes is very solid, it appears as if the practical execution is more complex than most people care to admit.

When considering an enzymatic process, take into consideration that you are dealing with a water process. Most of the waste process designers that I know get somewhat jittery at the mere mention of protein submerged into water, and with good reason.

The reality is that unless you really know what you are doing, it is virtually guaranteed that you will end up with a horrifically malodorous broth that is an enormous pollutant. More than anything else, you will also realize that the small amount of tissue initially added to your enzymatic digestor has now increased in volume due to additional water that is essential to make the process functional.

The three most important design criteria for any organic waste disposal system are :

Affordability
Consistency
Manageability

Unscrupulous consultants will often tell you in highly scientific lingo that enzymatic digestion is a process unique to whatever intellectual property it is that they are trying to sell you. The truth is that most so-called "enzymatic digestors" are really nothing more than stock-standard anaerobic digestors that require you to add enzymes to boost or mask what can otherwise only be described as an extremely poor performing septic tank.

So what exactly is enzymatic digestion anyway?

In the simplest possible terminology, enzymes are produced by biological organisms as “tools” to slice off a piece of their favourite food.

If you had to ask a scientist, you would probably hear that enzymes are proteinacious bio-molecules that catalyze a substrate-specific reaction through the reduction of the activation energy required, demonstrating extraordinary levels of regioselectivity, stereospecificity and also chemoselectivity without altering the equilibrium of the specific reaction.

Proteases (also known as proteinases or proteolytic enzymes, ) are part of the main enzyme class – hydrolases -, which catalyze the reaction of hydrolysis of various bonds with the participation of a water molecule – or in normal speak - the enzyme produced by the relevant bacteria is specific to whatever it is that the little critter wants to eat – almost like making a key that will unlock a lock of a very specific lunchbox - and this happens best when the substrate is mixed with water.

To make a long story short, using proteolytic enzymes will most definately increase the tempo of hydrolysis of the proteinacious waste dramatically compared to a non-catalyzed hydrolysis reaction – but this will all come at an equally impressive cost - especially once you realize that the proteolytic enzymes are but one of a multitude of different enzymes required to fully, safely and completely digest animal carcasses or abattoir waste .

Enzymes are not cheap by any stretch of the imagination and they happen to be very sensitive to operational parameters such as pH, temperature, minimum concentration, substrate and the presence of inhibitors in that substrate to mention just a few. Furthermore they do their job and then tend to degrade or deactivate, which in turn means that you have to buy more every time you run out of the miracle powder.

Frequently, inexperienced operators tend to overdose rather than risk an incomplete digestion, thereby even further increasing the digestion cost per kilogram. It would probably also be useful to know that in most practical applications that I have seen, the rotting animal tissue will take around 10 – 14 days to fully digest under optimal conditions.

The industrial uses of enzymes are numerous, but for this specific application, my advice to anybody would be to first set up a very small trial plant before spending any kind of serious money on a full fledged plant. Hopefully the reality of the intensive management issues, large capital expenditure required and the cost per kilogram tissue digested will not cause too severe a cardiac episode.

If, after the first round of trials, you still think enzymatic decomposition of animal tissue waste is a viable proposition, proceed to have the resulting effluent screened for pathogens and also tested by your local water utility (after all, you have to dispose of the effluent somewhere). If the effluent is pathogen free (don't bet the farm just yet), and the water utility is willing to accept it into their treatment plant without imposing serious surcharges, bear in mind that processing animal tissue for non-human consumption is considered a listed activity in South Africa.

That being said, prepare yourself for an even bigger shock once you realize that under South African NEMA act, your benign and environmentally friendly alternative is subject to a full scoping and environmental impact assesment process. The scoping and EIA process alone will set you back a few hundred thousand Rand and probably take between one and two years to conclude.

I would love to write about at least one small commercial enzymatic tissue disposal project that actually works in South Africa. If you have any feedback or comments regarding enzymatic decomposition of abattoir waste tissue, please contact us and let us know your experiences or advice.

Till next time then…

Enzymatic Treatment of Abattoir Waste Tissue

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