How it works

We believe that on-site aerobic digestion of solid organic waste is the best method and should be used wherever practical.  This page describes how

  • aerobic digestion works,
  • our machines work
  • the economics work

and finally, describes some examples of aerobic digestion delivering value.

Aerobic Digestion

 

When organic materials decompose in the presence of oxygen, the process is called “aerobic.” The aerobic process is very common in nature. For example, it takes place on ground surfaces such as the forest floor, where droppings from trees and animals are converted into a relatively stable humus. There is no accompanying bad smell when there is adequate oxygen present.

shutterstock_356402933waste-ssDuring composting a great deal of energy is released in the form of heat in the oxidation of the carbon to C02. For example, if a gram-molecule of glucose is dissimilated under aerobic conditions, 484 to 674 kilo calories of heat may be released.

If the organic material is in a vessel, the temperature of the material during decomposition will rise to over 170°F.  Oxidation at these high temperatures takes place more rapidly than at room temperatures and, hence, a shorter time is required for decomposition. The high temperatures will destroy pathogenic bacteria, protozoa (microscopic one-celled animals), and weed seeds, which are detrimental to health or agriculture when the final compost is used.

Aerobic digestion requires a considerable amount of oxygen and produces none of the characteristic features of anaerobic putrefaction. In its modern sense, aerobic composting can be defined as a process in which, under suitable environmental conditions, aerobic organisms, principally thermophilic, utilize considerable amounts of oxygen in decomposing organic matter to nutrient rich biomass.

Advanced Organic Waste Digester Description

The primary purpose of our AOWD units is to create an optimum aerobic environment for thermophilic bacteria to produce biomass from organic waste.  It is an exothermic process so it generates heat.  The temperature controlled unit has an auger to turn the material to aerate it and to achieve optimal bacterial activity.

bed2000-debranded

Advanced Organic Waste Digester

Our AOWD units can process organic waste in 24-72 hours depending upon input.  This is very fast. Comparable open-air aerobic digestion can take many months to complete, and anaerobic digesters can take between 15 and 40 days to process such waste.

We have developed machines that automate traditional composting into a continuous process and we have developed ‘cocktails’ of bacteria to attack all common mixes of waste.  We can digest meat processing waste; and in many cases we have digested 90%+ in 24 hours to a sterile combustible waste product that retains the nutritional value of the waste digested.

Our constant management of the environment in the machine and our ability to provide essential trace elements and nutrient for the thermophilic bacteria, means we are able to operate bacteria at levels of 140ºF.  This means that the output from our machines have much lower levels of pathogens than the output from anaerobic digesters.

On site Solid Organic Waste Treatment – the Economics

Example 1 – Food Processing Factory

Let’s assume your unit creates around 6 tonnes of solid organic waste per week.  You could be paying up to £80 a tonne for collection and disposal of this waste either going to landfill or for reprocessing.  By using an onsite digester to avoid sending this waste off site, you are immediately saving over £1,900 per month.

Renting or leasing a machine for this volume of waste is likely to cost around £750 per month.

You can optimise the process to create up to 14 tonnes of biomass. This biomass has a similar energy value to coal and if you use a biomass boiler it saves you over £2,000 per month in fuel costs. Alternatively you could use the biomass as a soil improver saving the cost of buying compost.

Whichever way you look at it, you are saving money almost from day one!

Example 2 – Commercial Kitchen

There is a machine to cater for all requirements from around 200 kg of solid organic waste per day.

Let’s assume that a canteen is producing that amount of waste. An AOW Digester is likely to cost around £380 per month.

The small digester would reduce the weight of waste that is collected by over 80%.  That’s a saving of almost 5 tonnes per month, or over £500 collection costs per month.

Whichever way you look at it, you are saving money almost from day one!

Examples

Our AOWD’s can handle almost any organic waste.  Examples include:

  • Food waste from restaurants and canteens
  • Waste and surplus from the food processing industry
  • Agricultural waste such as sugar cane leaves, palm leaves, oil seed rape leaves & stems
  • Horticultural waste such as grass cuttings and hedge trimmings

Example 1 Food processing

shutterstock_grapesThe factory is packaging grapes, melon pieces and other fruits for supermarkets. They are producing waste from spoil and from trimmings. The waste is placed in a hopper where it passes through a shredder and a dewatering unit and into the digester.   24 hours later out comes biomass with a high calorific value, increased because of the high sugar content of the input, and this is fed automatically into a biomass furnace that provides some of the energy to power the air-conditioning units for the cool storage.

Example 2 Horticulture

shutterstock_74186974grayA nursery that forces plants in a greenhouse disposes of plants that fail to flourish as well as trimmings. These are placed in a digester adjacent to the greenhouse. Because most of the plants are small and tender there is no need for a shredder. Within 48 hours there is new biomass which can be mixed with extenders to create compost ready to grow the next batch of plants. In addition the digester is producing heat, carbon dioxide, and water vapour these are piped directly back into the greenhouses where they encourage plant growth. Plants thrive when exposed to warm, dioxide and water.

Example 3 Catering

buffet33sA large country hotel that hosts many weddings has to manage food prep waste and buffet leftovers. In addition, in order to keep the grounds and garden in tiptop condition, the ground staff are producing grass cuttings and plant trimmings.

The kitchen and garden  waste are placed in the digester and within a couple of days there is new biomass which is left for short time to mature and then applied to the gardens as nutritious compost.

 

  • The need to pay a contractor to collect the waste – gone!
  • The cost of buying compost – reduced!
  • The environment around the hotel – Greatly improved!