ANAEROBIC DIGESTION

Anaerobic Digestion is a natural process where organic matter (animal or food waste) is broken down to produce Biogas and Biofertiliser (Digestate).

This happens in a sealed, heated, oxygen-free tank called an Anaerobic Digester.

Digestate contains all the nutrients and micronutrients necessary for modern farming including nitrogen, phosphorus, and potassium in an organic form to promote healthier soils.

ENERGY FROM WASTE

Anaerobic Digestion (A.D.) has been shown on a commercial scale to lead to odour reduction, waste stabilization, pathogen reduction, and GHG emission reductions.

Beyond these benefits, the Anaerobic Digestion process is also of interest to dairy operations because of the methane (CH4) rich Biogas it produces, which can be used to generate electricity and heat.

A PROMISING SOLUTION – ANAEROBIC DIGESTION
TECHNOLOGY

Anaerobic Digestion is one of the few manure treatment options that reduces the environmental impact of manure and other organic waste, whilst producing savings and revenues.

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HOW DOES IT WORK?

Several times throughout the day a fixed amount of effluent, or effluent with organic industrial wastes or food wastes in it, is pumped into the reactor (Anaerobic Digester tank).

The reactor is a huge (often 1.5m litre) insulated tank that is heated to around 38 degrees with stirrers attached to assist with the suspension of solids in the tank.

Over a 21–25 day cycle the structure of the effluent is modified into a potent organic Biofertiliser we call Digestate. Digestate is our “Hero” product.

Once fully operational, as we feed into the tank, an almost equal amount of Digestate is naturally pumped out. We then have the option to send the Digestate to a screw press for solids separation, or directly to storage. Separated solids can be used for bedding or sold to nurseries, and liquids are sent to storage to be applied to paddocks or crop fields as Biofertiliser.

This Digestate has a much greater uptake into the soils than raw effluent. Furthermore, Digestate is virtually odourless and 99% free of pathogens.

Through this Mesophilic Digestion process inside the reactor, biogas is also being formed through anaerobic fermentation, resulting in methane-rich biogas. We capture this Biogas inside the upper area and flexible dome lid of the Tank.

This bio-methane is then cleaned (H2S removed) and burnt via our highly efficient internal combustion engines attached to a generator (CHP unit), converting the Biogas into significant volumes of valuable heat and energy – i.e. electricity and hot water.

About 20% of the hot water generated is used to heat the Anaerobic Digester tank. What electricity is not used on the farm, can be sent to the grid.

This CHP unit helps offset the cost of the A.D. plant and all the good work we are doing for the environment.

 

GENERAL EFFECT OF DIGESTION ON BOD, NUTRIENT, PATHOGEN, AND WEED SEED

Anaerobic Digestion in a digester will reduce BOD and TSS by 80-90%. Odour is virtually eliminated. The Digester will have minimal effect on the nutrient content of the digested manure. Pathogen reduction is greater than 99% in a 20-day HRT mesophilic digester (37 C). Half or more of the organic nitrogen (Org-N) is mineralized to ammonia (NH3-N). A small amount of the P and K will settle as sludge in most digesters. 30 – 40 % of P and K are retained in covered lagoon digesters. Digesters are very effective in killing weed seeds.