Wednesday, June 25, 2014

How to Stop Water Pollution Risks Leading to Water Pollution from Biogas and AD Plants

There was recently quite a serious UK biogas plant digestate tank failure at Harper Adams University recently, which we reported on in our last post. It led to digestate leaking into a bunded area, and because the right precautions were taken with containment it is extremely unlikely that any pollution has occurred.

That led us to consider what we could do to help those people who are responsible for Anaerobic Digestion and Biogas Plants to understand the UK legislation on watercourse and groundwater protection. Most will be familiar through their site environmental permitting arrangements anyway, but we wanted to provide an accessible reminder which would also be useful to our international readers who might view it as "good practice" worth following, even if similar local regulations don't exist in their location. 

The idea is that a better appreciation of the law in this area, and what causes most spillages, should help to ensure that those responsible, such as site managers and plant operators carry out what is in fact their legal duty (in the UK). That is to assess risks from their liquid storage installations and reduce all such risks to their minimum which in most cases (as for anaerobic digestion plants) means providing suitable containment.

The answer, we thought, would be to post the infographic image below which is based upon a UK Chartered Institute of Waste Management Fact File.

It provides the legal basis for compliance by owners/ operators of factories and other potentially polluting sites, making sure that they appreciate their legal liability should they fail to follow the guidance. It then provides a summary of some of the most important requirements for minimizing pollution risks from processes like anaerobic digestion, where collapse or even a leak can harm large areas of groundwater, or long stretches of rivers if either the mixed-liquor, stored digestate, or even uncontrolled maturation slab run-off reaches rivers, or soaks into the ground and into the groundwater.

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Here, in text, is what the CIWM said in their Fact File:

OPERATORS OF permitted facilities are responsible for complying with their environmental permit and for preventing pollution of air, land and water.
Waste management facilities have the potential to cause significant environmental harm, which could threaten water supplies, public health and wild life in the event of an environmental incident such as fire, explosion or spillage.
 A facility found guilty of causing a pollution incident could face a fine of up to £50000 in the Magistrates Court.
In order to prevent environmental harm you should be aware of the following:
The source of the contaminant;
  • the most common pollutant in the UK is oil 

The pathway 
  • this could be the site's surface water drainage system or via off-site surface drainage, direct run-off, foul drainage system or into the atmosphere 
The receptor
  • ie a river, groundwater, the local population. 

Potential causes of environmental incidents include: 
  • delivery and use of materials 
  • plant or equipment failure 
  • containment failure 
  • fire, explosion or failure to contain fire fighting water 
  • wrong connections of sewers and pipes 
  • discharge of partially-treated or raw effluent 
  • vandalism 
  • flooding of part or all of your site.

Those operating waste facilities need to assess the risk from every one of the above listed potential causes, in the context of the source (degree and nature of pollution), the pathway to the permeable ground, river, ditch or stream which would become the receptor

Tuesday, June 03, 2014

Harper Adams University Biogas Plant Explosion and Tank Collapse Produces 2nd Spill of Liquor at Troubled Green Power Facility

This is appalling news for a flagship UK anaerobic digestion plant which was put into operation less than 3 years ago.

As far as can be seen from the Shropshire Star report referenced below, there was an explosion which resulted in a digester tank collapse and that led to the contents of the tank being dropped on the ground around the plant.

We found the short video below on YouTube, briefly showing the clean-up:

There was also previous spill at the plant last year, which appears to be beset by incident.

Thankfully, we don't think there were any injuries on either occasion, but there may have been some of the biomass which entered the local stream, again the articles referenced below don't make it clear just what the effect was on the local water quality. Hopefully, there would not be expected have been any significant loss of liquor outside of the bunded area for the plant, and therefore the clean up will adequately remove any future risk of pollution.

Sludge power plant collapses in Shropshire

"A power plant using farm waste today exploded at Harper Adams University, spilling tonnes of slurry. A 200-metre exclusion zone was today put in place by police, who described it as a “chemical incident”."
The incident took place on Friday 30 May, and the following further article was published on Monday 2 June:
"The clean-up operation continues at the HarperAdams University anaerobic digestion plant today. The access road to the AD plant was fully cleared over the weekend. Digestate is now [contained]."

 Credits: Clean-up continues at Harper Adams anaerobic digestion plant - (press release)

Today the Farmers Guardian had more to say, as the staff worked on at the clean-up:
THE clean-up at the Harper Adams anaerobic digestion (AD) plant is continuing today (Tuesday) with specialist contractors working on limiting the impact of the spill on the environment. The university has been working to tackle the major leak since one ...

 Credits: Harper AD plant clean-up continues after major spill - Farmers Guardian

It is clear that this was a major explosion to cause this degree of damage, and from the articles the presence of watercourse pollution remains unknown while tests are carried out:
"A Harper Adams spokesman said: “The Environment Agency is also conducting routine monitoring of the local watercourse. No release of pollution has been detected so far.”
I would predict that the University will carry out an inquiry into the cause, and that in due course there will be lessons to be learnt for the UK biogas industry.
We have previously highlighted the potential for explosions at Anaerobic Digestion Plants on this blog, and the need for this to be heeded at all times both during design and construction, and throughout biogas plant operation.
In this case there does not appear to have been anyone present at the automatically operated plant when the incident took place simply because there is no mention of a staff, or maintenance contractor's presence at the time, so we would guess that an equipment failure of some sort is the most likely cause.
In the video below we see the biogas plant in happier times, on opening day in 2012:

Wednesday, May 07, 2014

Poo Power Infographic Taps Into Public Sensitivities About Biogas from Waste in Our Latest AD Blog Post

This post is about another web page, which we hope that you will want to visit. Read-on and you will discover why that is.

Here is the top part of the new infographic from that other page, which we have been given permission to use by Lanes for Drains – Drainage Contractor, through the embedding code they provide below this interesting infographic image, in its original location, on their website.

 From Poo to Power - Via Anaerobic Digestion!

The way the subject is handled won't meet the approval of some people (we apologize if that is you...) as the source of this very clean and environmentally sustainable "energy from poo" is something most of us would rather not dwell upon. 

However, the reason that "Lanes for Drains" commissioned this informational artwork in the way they have done, was very much one of publicizing anaerobic digestion to a new audience by using a novel way to communicate what most would otherwise consider to be a very dry subject.

If you visit our web page at you can see the full infographic which is unfortunately simply too large for us to embed it here on this blog page!

Below the infographic which tells the story of the growing number of (sewage sludge waste fed) Anaerobic Digestion Plants around the world, we have added a YouTube video which we really liked because it shows an experiment which demonstrates just how well a digestate culture can produce biogas in a simplified biogas reactor system.

It is just the sort of "hands-on" chemistry experiment which inspired me when I was at school and hopefully it will inspire many youngsters to consider studying science.

More and more schools are teaching children about how anaerobic digestion produces biogas and indeed GCSE teaching in the UK about biogas includes a course-unit in which it is explained. So we hope that this page will help continue that trend. More and more demonstrations of the unique combination of chemistry and biology which creates this useful, mostly methane (biogas) power source can only mean that the take-up of AD will grow further.

We are hoping that our page at the Anaerobic Digestion blog (see link above) will be seen very widely, so any help you can give when you go and check the infographic out. by "Liking" or "Sharing" the page using the buttons that we have provided, would be greatly appreciated. Now if you visit I'll see you there!

Thursday, April 24, 2014

Recent Biogas and Sewer Methane Explosion Incidents Worldwide

Thankfully, as far as we are aware, there have been few methane explosions reported recently worldwide, which is good news because there have been deaths in the past when biogas has exploded.

There was an explosion in India at the start of 2013 which caused at least one death, which was reported as follows:

Two labourers killed in Maharashtra gas explosion

Solapur (Maharashtra) : Two labourers were injured, one critically, in an explosion at a biogas factory while it was being constructed on the outskirts of the city, police said.
"Some labourers had undertaken drilling and welding work near a cement tank at the upcoming biogas plant Solapur Bio Energy Pvt. Ltd. However, they did not know of the gas in the tank," an official from Solapur's Jodbhave police station told IANS.
"An explosion took place after the gas leaked out due to drilling and welding near the tank. Two labourers have died and one is critically injured with severe burns," the official added.
Read more here.

There has also been an explosion in China, which was reported on March 30 2014, as follows:

Biogas explosion erupts in Xiamen sewer, no casualties reported

“The food stall was burning coals to cook soup in a pottery jar by the door at that time. Maybe its coal fire splashed into the sewer and caused the explosion,” he explained. However, the cause of the biogas explosion has not been confirmed. The case ...
A sewage gas explosion erupted in a sewer on Siming South Road in Xiamen on Friday morning, terrifying many residents around the site after hearing a loud bang caused by the explosion.

The explosion that occurred at 9:30 am has been brought under control. No casualties were reported, but the glass door of one nearby store and a section of the street was heavily damaged.

According to the work safety supervision bureau, the area of Siming South Road near the explosion is filled with food stalls. These stalls often dump their sewage and waster into the closed sewer, which easily produces a large quantity of highly flammable methane gas. 
Credits: Biogas explosion erupts in Xiamen sewer, no casualties reported - What's on Xiamen

Then there was our own report, on our sister blog, of on anaerobic digestion plant biogas explosion back in March of last year, which we wrote about :

Anaerobic Digester Plant Explosion

Nobody was hurt by this biogas incident...
Credits: Anaerobic Digester Plant Explosion Blamed on Gas Storage EPDM ...

Of course, if we look back in time a little further, there were the following biogas explosion incidents:

Four die in biogas plant explosion in Ernakulam

Aug 27 2009: By Staff Correspondent,. Kochi: Four people were killed and several others injured when a biogas plant exploded at Aluva in Ernakulam yesterday. About six people are reported to be missing. The explosion ... 
Credits: Four die in biogas plant explosion in Ernakulam |

And finally:
Investigators believe the powerful explosion that rocked Kirinyaga Road on Sunday was caused by biogas from an underground room of a petrol station.
Credits: Biogas in room likely cause of city explosion, say ... - The Standard
If any of our readers know of other recent biogas explosion incidents, please use our comments facility below to tell us what you know. These incidents need publicizing so that the both biogas businesses and the health and safety authorities responsible globally, never forget of this danger.

Friday, March 28, 2014

Removing CO2 from Biogas - Carbon Dioxide Scrubbing Methods and the Eco Benefits from Upgrading to Eliminate CO2 from Biogas/53357d78cfee7
Biogas can be upgraded (purified) to natural gas distribution pipeline quality for use as a renewable natural gas, but as part of the upgrading process it will be necessary to remove the carbon dioxide (CO2) from the biogas. 

This upgraded gas may also be used for residential heating and as vehicle fuel, so there are many good reasons for removing the CO2. CO2 will always be found in biogas due to the fact that during anaerobic digestion, (i.e. degradation in the absence of oxygen), organic material is decomposed by bacteria forming a mixture of CO2 and CH4 with trace amounts of H2S and water vapour at saturation pressure. 

Common methods used to eliminate CO2 from biogas are: - water scrubbing - membrane systems - pressure swing adsorption (PSA) - chemical CO2 absorption - amine gas treatment - CO2 by cooling and recovering dry ice. These systems also generally reduce the H2S and H2O content. Biogas treatment systems, also need to include feed compression on the un-pressurized raw biogas.

Trace components that are often present in biogas are water vapor, hydrogen sulfide, siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide, and nitrogen. Pressure swing adsorption (PSA) systems, can be thought of as being molecular-sieves for carbon. PSA has been described are the second most commonly used biogas upgrading technology in Europe, after water scrubbing which is most likely the most popular. A typical system is composed of four vessels in series that are filled with adsorbent media which is capable of removing not only the CO2 but also water vapour, N2, and O2 from the biogas flow. 

Typically the PSA upgrading takes place over 4 phases: pressure build-up, adsorption, depressurization and regeneration. The pressure build-up occurs by equilibriating pressure with a vessel that is at depressurization stage. Final pressure build up occurs by injecting raw biogas. During adsorption, CO2, N2, and O2 are adsorbed by the media and the purified gas discharges as pure methane to a quality which will be far less corrosive and has a higher calorific value.

Recently developed gas-liquid membranes have been introduced, which operate at atmospheric pressures thereby reducing the energy consumption of compression. The use of specific solvent solutions allows the separation and recovery of the H2S and CO2.

 Another approach to improving the economics of gas upgrading has been to recover the CO2 by cooling and recovering dry ice. This can then be sold as an industrial gas whilst the biogas is either used in its more concentrated form (80-90% CH4) or further refined to vehicle quality standard (>96% CH4).

 An example of membrane use for the elimination of CO2 from Biogas follows:
"Silicone (PDMS) has a very high permeability to CO2 compared to methane. This difference in permeability facilitates the transfer of CO2 preferentially over methane, thus enabling the removal of CO2 from a natural gas stream.
Similarly other contaminants such as hydrogen sulfide (H2S) and water (H2O) can be readily removed from methane. The separation factor for CO2/CH4 is approximately 3 for a 50/50 gas mix, indicating that the ratio of the mass fraction of CO2 to CH4 in the feed/retentate is three times smaller than the ratio in the permeate.
Natural Gas purification is simple and straightforward. The feed gas is supplied to one side of the membrane though the feed port, and depending on the feed pressure, a vacuum supply to the opposite side of the membrane may be necessary at the permeate ports.
The contaminants with higher permeability than natural gas will permeate the membrane much faster than the methane, thereby stripping the feed from these contaminants. The high purity natural gas will exit at the permeate port. The permeate can be vented or flared as necessary."
Mongabay News, Pre Combustion CO2 Capture

Why It Is Green to Eliminate CO2 from Biogas?

The purification of biogas for higher value applications, such as vehicle use or pipeline-quality, is established to be in general a more sustainable and environmentally friendly option than conversion of the energy to electricity as the energy losses from power generation and the transmission losses for electricity are in general higher than for direct uses of the gas as fuel.

Also, the AD Process is uniquely able to produce transport fuels, whereas other renewable energy sources such as wind turbine, and hydro-power don't, which suggests that it is best utilized to meet the demand for transport fuels.

The energy efficiency for transport fuel use of upgraded biogas is particularly good where the upgraded gas is used to fuel vehicles working on the came facility, or operating from the same facility. The technology for biogas upgrading is relatively new and improvements to the upgrading processes are ongoing to reduce methane losses and improve energy efficiency.

Thursday, March 20, 2014

Cory’s First Anaerobic Digestion Plant Uses Landia GasMix System a Load of Rubbish! A Plea for sustainable waste disposal./532ac7a2e794a

Cory Environmental, who with over 40 sites are one of the UK's leading recycling, waste management and energy recovery companies, has unveiled its first anaerobic digestion facility, with Landia’s acclaimed GasMix system at the heart of the process.

 Generating up to 500kw of energy per hour for on-site use and export to the National Grid, Cory’s inaugural digester at Weston-Super-Mare has the capacity to handle 12,000 tonnes of food waste pa. Around 7,500 tonnes of this is part of a seven year waste treatment contract with North Somerset Council. Alistair Holl, Cory’s Director of Resource Management, said:
“We are very proud of our first AD facility, for which our team were main contractors, as well as plant and site designers, achieving energy production just 18 months after planning consent was gained. This includes us recognising the importance of a highly effective and ultra-reliable mixing system, which is why we’ve chosen Landia’s GasMix. It mixes the digester throughout at a consistent temperature, which will optimise our gas generation”.
He added:
“GasMix is mounted externally on the digester so routine maintenance can be carried out with no interruptions, and from our past experience with Landia, we also have peace of mind in the back up service that they provide”.
Sustainable waste management servicesFor over a decade, Landia’s Chopper Pumps have been installed at other Cory sites – and at Weston-super-Mare, they are also in use in eight other process and storage tanks, where they perform a combination of process mixing and transfer functions. Paul Davies, Landia’s UK & Eire Sales Manager commented:
“Our relationship with Cory has grown steadily over the years as we’ve worked together to adapt the best possible pumping and aeration solutions for their wastewater needs. We are very pleased to see the faith placed in us and our equipment, with our GasMix system set to play a long-term role in the success of this impressive new facility”. Alistair Holl continued: “Initially, we’ll be producing enough energy to power around 1,000 homes, and will soon be working towards the second phase of the development, which will see an upgrade of the plant to a minimum of 1MW. This will double the volume of our green energy generation at Weston-super-Mare”.

Comprising three 18.5kW chopper pumps and a self-aspirating system that reduces solids to produce more methane in a much shorter time period, Landia’s GasMix (designed specifically for AD/biogas) has no mechanical equipment inside the digester. Simple to regulate, GasMix also offers significant energy savings because it only has to run for a maximum of 30 per cent of the installed capacity.

 +44 (0) 1948 661 200

Saturday, February 08, 2014

The Anaerobic Digestion Processes Used For Municipal Solid Waste Diversion Away From Landfill And Biogas

Increasingly Anaerobic Digestion Processes are being Applied To Municipal Solid Waste (MSW) for the production of biogas as a renewable energy source, and also for Waste Diversion. Waste Diversion in this context means the diversion of waste (especially organic waste) away form landfill.

Anaerobic Digestion Processes
The Anaerobic Digestion Process Flow Diagram – Material and Energy

Anaerobic digestion (AD) of MSW is often part of an MBT Plant (Mechanical Biological Treatment Plant) and the AD process is applied to the organic fraction of the waste which is separated from the mixed residual waste which the householders place in their “black bag” and is known as residual waste. To start with the municipal solid waste feedstock is macerated (chopped up in specialized knifing equipment) with the addition of a large proportion of process water to provide either a dilute thin (‘wet’), or thick (‘dry’), slurry that can be fed into a digester tank. This stage also normally includes a useful decontamination stage to remove heavy and light contaminants through wet gravimetric (gravity based) separation.

The digestion process takes place in sealed tanks (digesters) that are normally mixed thoroughly using externally mounted pumps which pull the liquor out into the pump, which while returning it ejects it at speed again into the tank, or stiring blades, to maximise contact between microbes and waste. Mixing can also be achieved using the methane gas by pumping it out from the reservoir above the digestor reactor into the tank, and allowing it to bubble up to the surface to create a mixing effect.

The AD process can be operated at mesophilic (typically 30 – 40°C) or thermophilic (typically 50 – 60°C) temperatures (see Table). Dry Anaerobic Digestion processes work well in the thermophilic range of temperatures. Wet processes can be either mesophilic or thermophilic with the first being the most commonly adopted for MSW AD. The EU Animal By-Products Regulations (ABPR) (current at time of writing but in case of changes readers must check for themselves) require the pasteurization of MSW which is classed as a mixed source AD waste, to a standard method which ensures a temperature of 70°C for one hour. UK legislation has an alternative option which (at the time of writing) requires treatment for 57°C for 5 hours.
AD processes can be single step processes where all the waste is placed into a single digestion stage (biogas reactor tank) or multiple step processes.

Multiple step processes usually include a separate hydrolysis stage, which can be either aerobic or anaerobic. Hydrolysis (heating to a high temperature and raising the pressure) is used to optimize the breakdown of complex organic material into soluble compounds. This is most often followed by a high-rate AD process for biogas production. The AD process can take place in a number of vessels, or just one, but normally two are employed, one as a hydrolysis vessel and the second as the digester.

An example would be to use thermal hydrolysis of the organic content of MSW followed by anaerobic digestion to produce a biogas that is burnt in an engine electricity generator set. The reason for using a hydrolyser, is the addition of this process stage results in more of the degradable material in the feed being converted into biogas, rather than just passing through and emerging in the digestate.

The key process stages which would be seen in the waste processing plant (MBT Plant or MRF) include an MSW reception area, shredding, and a form of wet separator, where the biodegradable material is separated from the inert and reject (sometimes called “contrary”) material. A thermal hydrolysis stage is a feature of many MSW biogas process systems, followed by a one stage anaerobic digestion process.

The AD plant utilizes the biogas produced is often used to power an engine, which powers a generator, with waste heat recovery that delivers the steam and heat to the hydrolyser and digesters.

Anaerobic Digestion Processes – Commonly Considered Process Options

Anaerobic Digestion Process Option Diagram - Anaerobic Digestion Processes
Anaerobic Digestion Process Option Diagram

It is accepted by many AD professionals that the rate-controlling step in the anaerobic digestion of MSW is the hydrolysis of complex materials such as cellulose, in paper and leaves etc. in the waste. The process converts the waste into small soluble molecules such as glucose, which can then be easily digested by the biogas producing microbes. In the commercially available process this conversion is accelerated by heating the material under pressure to around 150°C. This results in substantially more of the biodegradable material being made available for conversion into gas and ensures the feed material is also sterilized, as required by the EU Animal By-Products Regulations.

After this initial anaerobic composting period (when there is biogas production) the raw compost is placed in windrows (often out in the open) to mature for an additional 5-6 weeks, in the same way as for aerobic composting treatment. The matured compost is then passed through a trommell screen to remove any plastics.

In a final processing step to produce a digestate product for sale, the compost can be blended with additives (e.g. sand, brick dust). Plus, Nitrogen, Phosphorus and Potassium) can be added to meet different specifications from wholesale and retail sellers, and bagged if required.