Alkaline Hydrolysis As A Precursory Process To Anaerobic Digestion Of Abattoir Condemned Waste

Introduction

There has been a lot of talk lately about the effectiveness of anaerobic digestion as a disposal method for abattoir waste streams. The principle of turning abattoir waste streams into electricity, fertilizer and hot water is certainly attractive and provided that disease control can be effectively incorporated into this process, it is difficult to find a more suitable and comprehensive way to dispose of the total waste stream generated by abattoirs on a daily basis.

The anaerobic digestion process by itself does not provide adequate pathogen removal for specific risk material or diseased carcasses. Until recently this shortcoming was a major hurdle in safe processing of all abattoir waste using only anaerobic digestion.

This is where alkaline hydrolysis can play an integral part of the waste treatment regime for abattoirs. Alkaline hydrolysis of the condemned meat waste and specific risk items provides a sterile effluent with exceptional biogas generation potential. Even if biogas generation is not the main objective, the use of alkaline hydrolysis as a precursory treatment of condemned meat and tissue provides a safe and reliable method that ensures extreme levels of pathogen destruction that far exceeds that of any other means of specific risk material or bio-hazardous carcass disposal.

The utilization of the hydrolysis effluent as a feedstock for an anaerobic digestor makes sense as the effluent is totally bio-available and serves as instant nutrients for the anaerobic micro flora, and as an additional benefit, provides an effective means of cost recovery through electricity generation and hot water production – both of which are in high demand in abattoirs.

The concept of anaerobic digestion is by no means new and is being successfully utilized worldwide as a disposal method for various types of waste such as municipal sewerage treatment, diary and pig manure sludge etc.

Anaerobic digestion is a very effective tool in dealing with abattoir waste streams because of its ability to utilize such a wide variety of feed materials. Blood and rumen content are the two largest waste streams that a normal abattoir has to contend with every day. These two items also have the biggest pollution potential and are rarely accepted by the majority of waste water treatment plants due to the high organic and chemical oxygen demand. This, at first glance, seems in itself somewhat peculiar as most wastewater treatment facilities also utilize anaerobic digestion as part of the treatment process. So what seems to be the problem. The short answer is nutrient value.

Any waste water treatment plant will have design features incorporated that enables the system to process a waste material that conforms to a “typical / expected” chemical and biological composition. Bear in mind that what goes in eventually must come out. The form of the waste that is being processed will change, but ultimately the chemical composition of the entire waste matrix will still include, amongst others, the nitrogen and phosphate contents of the various constituents of the original feedstock. This brings us back to retention time and process design.

All waste water treatment facilities have to conform to legislation that strictly governs the maximum load levels of the effluent (in this instance the effluent is the treated water) discharged into water streams and dams. High nitrogen and phosphate levels will dramatically increase the availability of nutrients in the stream or dam that receives the inflow from the water treatment plant. If the organic and chemical oxygen demand is too high or the treated water contains high nutrient levels, the knock-on effect will be to drastically reduce the oxygen available to all aquatic life forms inhabiting that dam or stream. This can cause a major shift in the eco-balance, and could render the entire water source hostile to its usual inhabitants and humans alike.

It is a generally accepted and well known fact that the effluent and sludge from an anaerobic digestor have excellent fertilizer properties. If the effluent is utilized as a liquid fertilizer, plants and other soil organisms can use the “unwanted” nutrients Nitrogen (N) and Phosphates (P) as two of the three main nutrient bases of NPK fertilizers. The sludge is very similar to peat moss and numerous growth trials have proven its value to plants.

So far we have only touched on the process effluent rather than the process emissions of an anaerobic digestor. The main emission from an anaerobic digestor is methane. Methane is a serious greenhouse gas and one of the biggest and most dangerous environmental pollutants. It is considered to be thirty times more harmful to the atmosphere than carbon dioxide. Methane is odorless and colorless and is produced whenever organic material is broken down in the absence of oxygen. This would account for the huge international outcry concerning poorly managed landfills. By burying organic material in a landfill, methane will be produced once the oxygen levels have been depleted and the anaerobic process kicks in.

There are several commendable projects that already utilize the methane emissions from landfills to generate electricity and thereby not only turn a major environmental pollutant into a more environmentally friendly form, but also reduce the need for fossil fuel based electricity generation. It is definitely a win-win situation.

The basic principle behind biogas electricity is to capture the methane and feed it to a generator that has been adapted to run on gas. Whilst efficiencies of these generators vary, they do normally produce electricity at a lower cost than can be purchased from the grid. As a standard addition, hot water is also produced by fitting a heat exchanger to the combustion chamber and circulating water through the heat exchanger.

If one considers that heat is a byproduct of this process, it would be very easy to utilize some of this heat to further pasteurize both the liquid and the solids before using them as fertilizer and soil improvers if required.

Alkaline hydrolysis is also not a new concept. Alkaline hydrolysis as a process was first utilized for the digestion of low level radio-active tissue in the early 90’s. Since then the technology has gone through a rapid growth cycle, and is currently one of the very few non-incinerator technologies that are internationally recognized as valid method of prion destruction.

The technology has traditionally been horrifically expensive, and has only very recently become more affordable as a commercial tissue digestion alternative. Although the process itself is cheap to run, the equipment used to be extremely expensive and very difficult and technical to operate unless skilled staff members were properly trained and the installation housed in purpose built buildings.

By default the price tag of the equipment and the intricacies of the process made the process very unattractive to commercial entities and the use of these installations were limited to a few exceptionally well-funded universities, laboratories and research facilities.

This has all changed when products like the Bioliquidator Carcass Disposal system and the MAAHP processes were introduced in 2008. The cost of the digestor units came down to a fraction of the original price and due to the ease of operation, commercial interest is rapidly increasing.

Convertech Biological Conversion Technology was the first company in Africa to incorporate alkaline hydrolysis into their abattoir condemned meat waste disposal and mortality composting technology and also the first to roll out the process on a commercial basis to clients in Southern Africa.

Through smart partnerships with both local and international businesses and specialists, Convertech BCT has been able to put together a formidable range of waste disposal alternatives specifically focused on abattoirs and meat processors in Southern Africa.

By introducing alkaline hydrolysis as a precursory process to anaerobic digestion of abattoir condemned waste, it has become possible to ensure safe and effective disposal of all types of abattoir waste and produce several end products that allow owners of these technologies to not only comply with all relevant legislation, but also to recover costs by treating their own waste streams in a responsible and environmentally friendly manner.

6 comment(s) for this article

Please leave a comment

The Bioliquidator

The BioLiquidator Carcass Disposal System is now available in South Africa! Convertech is proud to be the distributor for this amazing product in Southern Africa

For more information please contact us