Anaerobic Digestion

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As one of the leading industrial water and effluent treatment consultants, ARL Consulting are ideally placed to assist in the development of any Anaerobic Digestion (AD) projects being considered.

Anaerobic Digestion (AD) has become an increasingly important effluent treatment technique in recent years. Anaerobic digestion involves the breakdown and degradation of biodegradable organic material, ultimately producing methane gas – sometimes referred to as biogas.
 
The increasing prevalence of anaerobic digestion is due to a number of important issues, but particularly the financial incentives being offered by the UK Government for creating energy from renewable technologies – such as AD.
 
However there are a number of issues that need to be taken into consideration when considering AD technology:
 
When considering direct discharge to a controlled receiving water, it is very doubtful as to whether AD as a stand-alone process would reduce COD (and/or BOD) to a sufficiently low level to meet any imposed consent. AD is therefore frequently used as an ‘up-front’ pre-treatment process prior to an aerobic polish (such as MBR) to allow direct discharge.
 
A distinct advantage of the AD process, when compared with an equivalent aerobic process, is that there is a significant reduction in waste biomass created – typically referred to as ‘sludge’. This is due to a greater proportion of the organic material in the influent being broken down (in this case to methane gas) compared with the equivalent aerobic process.
 
It should be noted that anaerobic digestion is particularly suited to readily biodegradable feed stocks – often reflected in a closer COD:BOD ratio in the influent when compared with less biodegradable material. As such, anaerobic digestion is becoming increasingly common in the Food and Drink sector, particularly dairy, brewing, distilling and general food processing.
In addition to the Government financial waste to energy incentives as mentioned above, it is the direct use of the biogas that offers one of the most significant advantages to the AD process. The biogas produced can be utilised in a number of beneficial ways:
 Produce steam in an on-site boiler.Produce electricity and heat in a gas engine (CHP system). The electricity so produced can be used on site (displacing ‘bought in’ electricity produced from burning fossil fuels) or exported direct to the National Grid.

The biogas itself, following cleaning and calorific value enhancement, can be exported to the gas grid or used to power “green” vehicles.

The latest generation of anaerobic digestion (AD) reactors are based on the Continuous Stirred Tank Reactor (CSTR) which allows effective mixing of the influent with the anaerobic biomass. The separation of the treated effluent and the biomass (for return to the reactor or wastage as required) is then undertaken externally from the AD bioreactor. This separation can be achieved utilising membranes (in a similar way to the MBR process as described above) or utilising a physical solid-liquid separation process. These are then referred to as Anaerobic MBRs.

The advantage of this latest generation of reactors is two-fold:

(a)  They allow the inclusion of biodegradable fats, oils and greases (FOG) which historically would have been removed in a pre-treatment process before the AD process.

(b)  They allow a greater degree of COD removal compared with other AD techniques – typically greater than 90%. It should be noted that it is doubtful whether, even at this high removal rate, the quality of effluent will be sufficient to allow discharge direct to a receiving water course.

Other anaerobic digestion (AD) techniques that are commonly encountered include:
 
Internal Circulation (IC) reactor
Expanded Granular Sludge Blanket (EGSB) reactor
Upflow Anaerobic Sludge Blanket (UASB) reactor
Hybrid Anaerobic Reactor
 

Contact Us

For more information on any aspect of anaerobic digestion please call us now on 01244 344233 or just drop a note in the contact box on the left.

Latest Anaerobic Digestion Project

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Arla Foods Aylesbury

Effluent Plant Design & Project Management

ARL Consulting have worked closely alongside Arla Foods at Aylesbury as part of the team designing and building the UK’s largest dairy. ARL undertook extensive outline design, tender management and on-going project management and consultancy services relating to the waste water treatment plant. Arla required that the selected process should include a number of aspects which maximise sustainability as this has been a common theme across the whole dairy site.

ARL therefore proposed an advanced ‘state of the art’ anaerobic process which allows for the generation of biogas (methane) and subsequent usage in the on-site energy centre, to ensure all waste to energy aspects are maximised. In addition to waste water management, ARL also advised how clean process water streams could be treated using RO membrane systems and disinfection to allow re-use in the dairy.

ARL have also undertaken extensive negotiation with Thames Water to ensure that the waste water discharged into the Thames Water trade effluent sewer meets the most stringent quality requirements.

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Glenmorangie Distillery

AD plant design and project management

ARL Consulting were commissioned to evaluate technical and commercial options for effluent treatment at both Glenmorangie whisky distilleries at Tain and Ardbeg on Islay.

This initial feasibility study resulted in the selection of the Tain distillery as being the site for a state of the art anaerobic digestion plant.

ARL Consulting undertook detailed design for the effluent plant and prepared a detailed specification and contract documentation to allow the project to be tendered on the open market.

ARL undertook detailed negotiation with SEPA to determine the required effluent quality to allow discharge of high quality treated effluent to the Dornoch Firth. The AD plant included beneficial use of the methane in a dedicated biogas boiler to allow displacement of heavy fuel oil.

To view the full Glenmorangie Distillery project details please Click Here.

Anaerobic Digestion FAQ's

The technical and commercial benefits of the anaerobic digestion (AD) process can be further explained as follows:

Anaerobic Digestion (AD) has become an increasingly important effluent treatment technique in recent years. Anaerobic digestion involves the breakdown and degradation of biodegradable organic material, ultimately producing methane gas – sometimes referred to as biogas.

It should be noted that anaerobic digestion is particularly suited to readily biodegradable feed stocks – often reflected in a closer COD:BOD ratio in the influent when compared with less biodegradable material. As such, anaerobic digestion is becoming increasingly common in the Food and Drink sector, particularly dairy, brewing, distilling and general food processing.

When considering direct discharge to a controlled receiving water, it is very doubtful as to whether AD as a stand-alone process would reduce COD (and/or BOD) to a sufficiently low level to meet any imposed consent. AD is therefore frequently used as an ‘up-front’ pre-treatment process prior to an aerobic polish (such as MBR) to allow direct discharge.

A distinct advantage of the AD process, when compared with an equivalent aerobic process, is that there is a significant reduction in waste biomass created – typically referred to as ‘sludge’. This is due to a greater proportion of the organic material in the influent being broken down (in this case to methane gas) compared with the equivalent aerobic process.