Anaerobic Digestion

Anaerobic digestion (AD) is the breakdown of organic material by micro-organisms in the absence of oxygen. AD produces biogas, a methane-rich gas that can be used as a fuel, and digestate, a source of nutrients that can be used as a fertiliser. Increasingly AD is being used to make the most of our waste by turning it into renewable energy.

Devoting attention to safety

Biogas is primarily comprised of methane and carbon dioxide but may also contain concentrations of hydrogen sulphide, moisture, VOCs, oxygen, siloxanes, and other species. With regards to safety, the two major constituents of concern are methane and hydrogen sulphide. Significant attention must be devoted to safety provisions to ensure the successful operation of an AD facility.

Methane, a colourless gas, is flammable in air between concentrations of 5-15%, and may explode if ignited in an enclosed area. The inhalation of methane will cause dizziness, breathing difficulties and loss of consciousness. Hydrogen sulphide is also a flammable, colourless gas. However, it is also toxic and produces a strong rotten egg odour at low concentrations. More importantly, it is odourless at poisonous, and fatal, concentrations and is flammable in air at 4.3 to 43% concentrations. Exposure to hydrogen sulphide at low levels will cause irritation, dizziness, nausea, and coughing. At higher concentrations, hydrogen sulphide will burn out the nasal receptors, causing a loss of smell, unconsciousness and shock, while greater concentrations will cause respiratory failure and death.

Providing an engineered ventilation solution

To avoid the hazards posed by these two gases consideration to a correctly designed ventilation system must be considered.  Any enclosed space must be designed with suitable ventilation provisions to prevent the build-up of hazardous gases and provide safe ambient air conditions.

We provide ventilation systems for AD facilities to ensure the containment and control of odour by means of imposing a negative pressure environment within the building envelope.  Contaminated air removed from the building is treated via either a Bio-Filter System or Chemical Scrubber, or both in some cases dependent on the entrained air stream, to ensure clean air is dispersed to external atmosphere.

An assured service in a challenging environment

We always work with our clients to assess project requirements from which we offer recommendations and provide proposals and quotations prepared to meet the challenging regulatory requirements of an AD facility and importantly within available budgets.  We can offer a full service package from initial design through to installation and commissioning including documentation, ensuring compliance of current UK Legislation.
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