Is Alkaline Hydrolysis An Effective Treatment Method For Hatchery Waste?

Article by Piet Kruger

Ever wondered what happens to the egg shell after the egg hatches? To be truthful, neither did I until recently when I received two separate requests from two different provinces in the same week asking if hatchery waste could be treated using our alkaline hydrolysis technology.

Broken chicken eggs at the start of the hydrolysis process

Normally I would be able to provide an answer, or at the very least give an educated guess immediately, but to my utter embarrassment, this time I was stumped.

The problem as outlined was as follows. Hatcheries deal with eggs (duhh!)- actually quite a lot of eggs – and as can be expected some of these eggs are either rotten or not viable and therefore will never hatch. In addition, mortalities should be fairly common, and as such the hatchery will have to deal with these two potential waste streams. That part was fairly obvious; however I never really gave much thought to what happened to the egg shells of the eggs that did hatch.

30 minutes into the hydrolysis process. Hydrolysis is almost complete except for the shells.

For some reason I just never pictured this as a problem until it was pointed out to me that egg shells damage the pressure cookers employed at rendering plants. I was told that the egg shells act as a very effective grinding paste that causes significant wear and tear on the inside of these pressure vessels that costs well over a million rand each.

It irked me that I didn’t have a clue as to what exactly would happen to egg shells in our tissue processor so I set out to find an answer. To do this, I set up a series of experiments and subjected any and every kind of egg I could lay my hands on to various protocols applicable to alkaline hydrolysis of animal matter.

It quickly became apparent that no matter how many times I replicated the trials, the answer stayed the same – egg shells are more resistant to MAAHP degradation than any type of bone material I’ve ever encountered.

The end of the hydrolysis process – 60 minutes later. Egg shells are really tenacious!

All the other components of the eggs digested beautifully except for the shells. The egg shells remained intact regardless of the temperature, agitation, chemical concentration and time parameters employed. I thought that the egg shells will eventually soften and disappear much like bone does in a tissue processor but the fact of the matter is that I could not have been more wrong if I tried!

Fully Hydrolyzed – Chinese Trick 73434

On the upside, I eventually did manage to beat the dreaded egg shells into submission with Chinese trick 73434 but unfortunately I cannot divulge the exact nature of the additional processes involved at this time

Because one tends to associate eggs with fragility almost by default, it was surprising to find that in some ways the egg shells were more resistant to alkaline hydrolysis than most other animal parts – skulls and teeth included.

The conclusion that I draw from all of this is that alkaline hydrolysis is, in my opinion, still a better answer for egg shells in hatchery waste than rendering plants but it is important to understand that neither process is capable of hydrolyzing the egg shells completely.

The advantage that I see is with the alkaline hydrolysis process itself. The hydrolyzing vessel is not pressurized, nor is it subjected to dry mechanical agitation as with the pressure vessels is the case in a rendering plant and therefore the grinding paste issue and the resulting wear and tear is entirely avoided.

Undigested solids will only be a small fraction of the original batch and will primarily be comprised of the mineral constituents of the eggs which can be recovered as a separate sterile product at the end of the process.

There is certainly a cost and logistical advantage if dealing with a significantly reduced volume of product should one wish to fully hydrolyze the remaining fraction utilizing a different process. It would also be feasible to simply dry the sterile egg shells and take advantage of the mineral content as a soil conditioner or compost additive.

By separating the hatchery waste from the regular feedstock stream that goes to the rendering facility, not only can the capacity be used to produce higher value by-products, but the simultaneous reduction in wear and tear on the pressure vessels will definitely make commercial sense and should offset the cost of a separate non-pressurized hydrolysis process entirely.

Till next time then…