Category Archives: Biogas

Biogas Upgradation Methods

  By | |
8 Comments

Upgradation of biogas is primarily achieved by carbon dioxide removal which then enhances the energy value of the gas to give longer, driving distances with a fixed gas storage volume. Removal of carbon dioxide also provides a consistent gas quality with respect to energy value. The latter is regarded to be of great importance from the vehicle manufacturers in order to reach low emissions of nitrogen oxide.

biogas-enrichment

At present four different biogas upgradation methods are generally used for removal of carbon dioxide from biogas, either to reach vehicle fuel standard or to reach natural gas quality for injection to the natural gas grid. These methods are:

  • Water absorption
  • Polyethylene glycol absorption
  • Carbon molecular sieves
  • Membrane separation

Water Scrubbing

Water scrubbing is used to remove carbon dioxide but also hydrogen sulphide from biogas since these gases is more soluble in water than methane. The absorption process is purely physical. Usually the biogas is pressurized and fed to the bottom of a packed column where water is fed on the top and so the absorption process is operated counter-currently.

Polyethylene Glycol Scrubbing

Polyethylene glycol scrubbing is a physical absorption process. Selexol is one of the trade names used for a solvent. In this solvent, like in water, both carbon dioxide and hydrogen sulphide are more soluble than methane.

The big difference between water and Selexol is that carbon dioxide and hydrogen sulphide are more soluble in Selexol which results in a lower solvent demand and reduced pumping. In addition, water and halogenated hydrocarbons (contaminants in biogas from landfills) are removed when scrubbing biogas with Selexol.

Carbon Molecular Sieves

Molecular sieves are excellent products to separate specifically a number of different gaseous compounds in biogas. Thereby the molecules are usually loosely adsorbed in the cavities of the carbon sieve but not irreversibly bound. The selectivity of adsorption is achieved by different mesh sizes and/or application of different gas pressures.

When the pressure is released the compounds extracted from the biogas are desorbed. The process is therefore often called “pressure swing adsorption” (PSA). To enrich methane from biogas the molecular sieve is applied which is produced from coke rich in pores in the micrometer range. The pores are then further reduced by cracking of the hydrocarbons. In order to reduce the energy consumption for gas compression, a series of vessels are linked together.

Pressure swing adsoprtion process for biogas upgradation

The gas pressure released from one vessel is subsequently used by the others. Usually four vessels in a row are used filled with molecular sieve which removes at the same time CO2 and water vapour.

Membrane Purification

There are two basic systems of biogas purification with membranes: a high pressure gas separation with gas phases on both sides of the membrane, and a low-pressure gas liquid absorption separation where a liquid absorbs the molecules diffusing through the membrane.

  • High pressure gas separation

Pressurized gas (36 bar) is first cleaned over for example an activated carbon bed to remove (halogenated) hydrocarbons and hydrogen sulphide from the raw gas as well as oil vapour from the compressors. The carbon bed is followed by a particle filter and a heater. The raw gas is upgraded in 3 stages to a clean gas with 96 % methane or more.

The waste gas from the first two stages is recycled and the methane can be recovered. The waste gas from stage 3 (and in part of stage 2) is flared or used in a steam boiler as it still contains 10 to 20 % methane.

  • Gas-liquid absorption membranes

Gas-liquid absorption using membranes is a separation technique which was developed for biogas upgrading in the recent past. The essential element is a micro-porous hydrophobic membrane separating the gaseous from the liquid phase. The molecules from the gas stream, flowing in one direction, which are able to diffuse through the membrane will be absorbed on the other side by the liquid flowing in counter current.

The absorption membranes work at approx. atmospheric pressure (1 bar) which allows low-cost construction. The removal of gaseous components is very efficient. At a temperature of 25 to 35°C the H2S concentration in the raw gas of 2 % is reduced to less than 250 ppm.

POME as a Source of Biomethane

  By | | , , ,
6 Comments

During the production of crude palm oil, large amount of waste and by-products are generated. The solid waste streams consist of empty fruit bunch (EFB), mesocarp fruit fibers (MF) and palm kernel shells (PKS). Reuse of these waste streams in applications for heat, steam, compost and to lesser extent power generation are practised widely across Southeast Asia.

POME or Palm Oil Mill Effluent is an underutilized liquid waste stream from palm oil mills which is generated during the palm oil extraction/decanting process and often seen as a serious environmental issue but it is a very good source for biomethane production. Therefore, discharge of POME is subject to increasingly stringent regulations in many palm oil-producing nations.

POME-Biogas

Anaerobic Digestion of POME

POME is an attractive feedstock for biomethane production and is abundantly available in all palm oil mills. Hence, it ensures continuous supply of substrates at no or low cost for biogas production, positioning it as a great potential source for biomethane production. (Chin May Ji, 2013).

Palm oil mill effluent is a colloidal suspension containing 95-96% water, 0.6-0.7% oil and 4-5% total solids, which include 2-4% suspended solids. Biological Oxygen Demand (BOD) generally ranges between 25,000 and 65,714 mg/L, Chemical Oxygen Demand (COD) ranges between 44,300 and 102,696 mg/L.

Most palm oil mills and refineries have their own treatment systems for POME, which is easily amenable to biodegradation due to its high organic content. The treatment system usually consists of anaerobic and aerobic ponds. (Sulaiman, 2013).

Open pond systems are still commonly applied. Although relatively cheap to install, these system often fail to meet discharge requirements (due to lack of operational control, long retention time, silting and short circuiting issues).

Moreover, the biogas produced during the anaerobic decomposition of POME in open pond systems is not recovered for utilization. The produced gas dissipates into the atmosphere where it causes adverse environment effects (due to the fact that CH4 is a twenty times stronger greenhouse gas then CO2 (Chin May Ji, 2013).

Biogas from POME can be carried out using a number of various technologies ranging in cost and complexity. The closed-tank anaerobic digester system with continuous stirred-tank reactor (CSTR), the methane fermentation system employing special microorganisms and the reversible flow anaerobic baffled reactor (RABR) system are among the technologies offered by technology providers. (Malaysian Palm Oil Board, 2015).

Biogas production largely depends on the method deployed for biomass conversion and capture of the biogas, and can, therefore, approximately range from 5.8 to 12.75 kg of CH4 per cubic meter of POME. Application of enclosed anaerobic digestion will significantly increase the quality of the effluent/ discharge stream as well as the biogas composition, as mentioned in table below.

 Table: Performance comparison between open and closed digester systems

Parameters Open digester system Closed anaerobic digester
COD removal efficiency (%) 81% 97%
HRT (days) 20 10
Methane utilization Released to atmosphere Recoverable
Methane yield (kg CH4/kg COD removed) 0.11 0.2
Methane content (%) 36 55
Solid discharge (g/L) 20 8

*This table has been reproduced from (Alawi Sulaiman, 2007)

A closed anaerobic system is capable of producing and collecting consistently high quality of methane rich biogas from POME. Typical raw biogas composition will be: 50-60 % CH4, 40-50 % CO2, saturated with water and with trace amounts of contaminants (H2S, NH3, volatiles, etc.).

Biomethane Potential in Southeast Asia

The amount of biomethane (defined as methane produced from biomass, with properties close to natural gas) that can be potentially produced from POME (within the Southeast Asian region) exceeds 2.25 billion cubic meter of biomethane (on a yearly basis).

Especially Indonesia and Malaysia, as key producers within the palm oil industry, could generate significant quantities of biomethane. An impression of the biomethane potential of these countries including other feedstock sources is being highlighted below (VIV Asia, 2015).

Indonesia (4.35 billion m3 of biomethane):

  • 25 billion m3 of biomethane from Palm Oil Mill Effluent (POME).
  • 2 billion m3 of bio-methane from Sewage Treatment Plant (STP).
  • 9 billion m3 of bio-methane from Municipal Solid Waste (MSW).

Malaysia (3 billion m3 of biomethane):

  • 1 billion m3 of biomethane from Palm Oil Mill Effluent (POME).
  • 2 billion m3 of biomethane from Sewage Treatment Plant (STP).
  • 8 billion m3 of biomethane from Municipal Solid Waste (MSW).

The Asian Pacific Biogas Alliance estimates that the potential of conversion of biomass to biomethane is sufficient to replace 25 percent of the natural gas demand by renewable biogas (Asian Pacific Biogas Alliance, 2015).

To sum up, due to the high fraction of organic materials, POME has a large energetic potential. By unlocking the energetic potential of these streams through conversion/ digesting and capture of biomethane, plant owners have the opportunity to combine waste management with a profitable business model.

Co-Authors: H. Dekker and E.H.M. Dirkse (DMT Environmental Technology)

References

Alawi Sulaiman, Z. B. (2007). Biomethane production from pal oil mill effluent (POME) in a semi-commercial closed anaerobic digester. Seminar on Sustainable Palm Biomass initiatives. Japan Society on Promotion of Science (JSPS).

Asia Biogas Group. (2015, 08 15). Retrieved from Asia Biogas : http://www.asiabiogas.com

Asian Pacific Biogas Alliance. (2015). Biogas Opportunities in South East Asia. Asian Pacific Biogas Alliance/ICESN.

Chin May Ji, P. P. (2013). Biogas from palm oil mill effluent (POME): Opportunities and challenges from Malysia’s perspective. Renewable and Sustainable Energy Reviews , 717-726.

Malaysian Palm Oil Board. (2015, 08 26). Biogas capture and CMD project implementation for palm oil mills. Retrieved from Official Portal Of Malaysian Palm Oild Board:

Sulaiman, N. A. (2013). The Oil Palm Wastes in Malaysia. In M. D. Matovic, “Biomass Now – Sustainable Growth and Use”. InTech.

VIV Asia. (2015, 08 26). The international platform from feed to food in Asia. Retrieved from http://www.vivasia.nl

Note: This is the first article in the special series on ‘Sustainable Utilization of POME-based Biomethane’ by Langerak et al of DMT Environmental Technology (Holland)

The Role of Biomass Energy in Net-Zero Buildings

  By | | , , , , ,
Leave a comment

The concept of biomass energy is still in its infancy in most parts of the world, but nevertheless, it does have an important role to play in terms of sustainability in general and net-zero buildings in particular. Once processed, biomass is a renewable source of energy that has amazing potential. But there is a lot of work to be done to exploit even a fraction of the possibilities that would play a significant role in providing our homes and commercial buildings with renewable energy.

According to the U.S. Energy Information Administration (EIA), only about 5% of the total primary energy usage in the U.S. comes from biomass fuels. So there really is a way to go.

The Concept of Biomass Energy

Generally regarded as any carbon-based material including plants, food waste, industrial waste, reclaimed woody materials, algae, and even human and animal waste, biomass is processed to produce effective organic fuels.

The main sources of biomass include wood mills and furniture factories, landfill sites, horticultural centers, wastewater treatment plants, and areas where invasive and alien tree and grass species grow.

Whether converted into biogas or liquid biofuels, or burned as is, the biomass releases its chemical energy in the form of heat. Of course, it depends on what kind of material the biomass is. For instance, solid types including wood and suitable garbage can be burned without any need for processing. This makes up more than half the biomass fuels used in the U.S. Other types can be converted into biodiesel and ethanol.

Generally:

  • Biogas forms naturally in landfills when yard waste, food scraps, paper and so on decompose. It is composed mainly of carbon dioxide
  • Biogas can also be produced by processing animal manure and human sewage in digesters.
  • Biodiesel is produced from animal fats and vegetable oils including soybeans and palm oil.
  • Ethanol is made from various crops including sugar cane and corn that are fermented.

How Biomass Fuels Are Used

Ethanol has been used in vehicles for decades and ethanol-gasoline blends are now quite common. In fact, some racing drivers opt for high ethanol blends because they lower costs and improve quality. While the percentage of ethanol is substantially lower, it is now found in most gasoline sold in the U.S. Biodiesel can also be used in vehicles and it is also used as heating oil.

But in terms of their role in net-zero buildings:

  • Biomass waste is burned to heat buildings and to generate electricity.
  • In addition to being converted to liquid biofuels, various waste materials including some crops like sugar cane and corn can also be burned as fuel.
  • Garbage, in the form of yard, food, and wood waste, can be converted to biogas in landfills and anaerobic digesters. It can also be burned to generate electricity.
  • Human sewage and animal manure can be converted to biogas and burned as heating fuel.

Biomass as a Viable Clean Energy Source for Net-Zero Energy Buildings

Don’t rely on what I say, let’s look at some research, specifically, a study published just last year (2018) that deals with the development of net-zero energy buildings in Florida. It looked at the capacity of biomass, geothermal, hydrokinetic, hydropower, marine, solar, and wind power (in alphabetical order) to deliver renewable energy resources. More specifically, the study evaluated Florida’s potential to utilize various renewable energy resources.

Generating electricity from wind isn’t feasible in Florida because the average wind speeds are slow. The topography and hydrology requirements are inadequate and both hydrokinetic and marine energy resources are limited. But both solar and biomass offer “abundant resources” in Florida. Unlike most other renewable resources, the infrastructure and equipment required are minimal and suitable for use within building areas, and they are both compatible with the needs of net-zero energy.

The concept of net-zero buildings has, of course, been established by the World Green Building Council (GBC), which has set timelines of 2030 and 2050 respectively for new and all buildings to achieve net-zero carbon goals. Simplistically, what this means is that buildings, including our homes, will need to become carbon neutral, using only as much renewable energy as they can produce on site.

But nothing is simplistic when it comes to net-zero energy buildings (ZEB) ). Rather, different categories offer different boundaries in terms of how renewable energy strategies are utilized. These show that net-zero energy buildings are not all the same:

  • ZEB A buildings utilize strategies within the building footprint
  • ZEB B within the site of the property
  • ZEB C within the site but from off-site resources
  • ZEB D generate renewable energy off-site

While solar works for ZEB A and both solar and wind work for ZEB B buildings, biomass and biofuels are suitable for ZEB C and D buildings, particularly in Florida.

Even though this particular study is Florida-specific, it indicates the probability that the role of biomass energy will ultimately be limited, but that it can certainly help buildings reach a net-zero status.

There will be different requirements and benefits in different areas, but certainly professionals offering engineering solutions in Chicago, New York, London (Canada and the UK), and all the other large cities in the world will be in a position to advise whether it is feasible to use biomass rather than other forms of eco-friendly energy for specific buildings.

Biomass might offer a more powerful solution than many people imagine.

Food Waste Management

  By | | , ,
7 Comments

The waste management hierarchy suggests that reduce, reuse and recycling should always be given preference in a typical waste management system. However, these options cannot be applied uniformly for all kinds of wastes. For examples, food waste is quite difficult to deal with using the conventional 3R strategy.

food_waste

Of the different types of organic wastes available, food waste holds the highest potential in terms of economic exploitation as it contains high amount of carbon and can be efficiently converted into biogas and organic fertilizer.

There are numerous places which are the sources of large amounts of food waste and hence a proper food waste management strategy needs to be devised for them to make sure that either they are disposed off in a safe manner or utilized efficiently. These places include hotels, restaurants, malls, residential societies, college/school/office canteens, religious mass cooking places, communal kitchens, airline caterers, food and meat processing industries and vegetable markets which generate food residuals of considerable quantum on a daily basis.

anaerobic_digestion_plant

The anaerobic digestion technology is highly apt in dealing with the chronic problem of food waste management in urban societies. Although the technology is commercially viable in the longer run, the high initial capital cost is a major hurdle towards its proliferation.

The onus is on the governments to create awareness and promote such technologies in a sustainable manner. At the same time, entrepreneurs, non-governmental organizations and environmental agencies should also take inspiration from successful food waste-to-energy projects in Western countries and try to set up such facilities in cities and towns.

Synthetic Biology – A Catalyst to Revolutionize Biogas Industry

  By | | ,
16 Comments

Essentially a process operating by living organisms, the biogas industry is a natural target for synthetic biology. Synthetic biology combines biology and engineering to design and construct biological devices. Contrary to traditional genetic engineering that only alters an already existing DNA sequence, synthetic biology allows us to build entirely new sequences of DNA and put them to work in cells. This allows us to build novel biological devices that would never exist in nature.

synthetic-biology-biogas

Constructions and operations of devices that do not exist in nature, such as tools, vehicles, computers and the internet, have crafted modern civilization. Now, it is synthetic biology that is challenging nature’s limitations and advancing civilization to a higher level.

Generating biogas via anaerobic digestion of biomass and organic waste is one of the few proven, cost-effective, scalable biomass energy strategies. Biogas consists of mainly methane and carbon dioxide, and combustion of methane with air generates energy which can be used for many purposes such as cooking, heating, producing electricity and vehicle fuel. As a result, countless biogas plants are operating around the globe helping to clean up waste and generate energy. With more plants being built, they come in all sizes ranging from household to factory scales.

Anaerobic digestion is a process where extremely complex microbial communities degrade organic matter, such as sugars, fats and proteins, resulting in biogas as the primary end-product. Such inherent complexity makes this process very difficult to optimize. Mechanical engineers have made tremendous progress to optimize this process, but in many places it still requires government subsidies to be profitable.

Synthetic Biology and Biogas Industry

Essentially a process operating by living organisms, the biogas industry is a natural target for synthetic biology. In terms of their genetic content, organisms are classified into three natural groups, Archaea, Bacteria and Eukarya. Most microbes are Archaea and Bacteria, while humans are Eukarya.

In an anaerobic digester, many different types of Bacteria convert the complex organic matter in waste or biomass to hydrogen gas, carbon dioxide, formate and acetate. A unique group of methanogenic Archaea then produces the invaluable part of biogas, methane, by eating hydrogen and carbon dioxide, formate or acetate.

One can imagine creating a super microbe to convert the complex organic matter directly into biogas, thus making anaerobic digestion faster, more efficient and easier-to-manipulate. Making a synthetic microbial community by reprogramming key microbes may also help them work together when a tough job (i.e., eating extremely complex waste) needs to be done.

Among numerous microbes in anaerobic digester, methanogenic Archaea are one of a few microbial groups that have been extensively studied, and a number of genetic tools are available for engineering via synthetic biology. Therefore, scientists have begun to reprogram methanogenic archaea, allowing them to eat organic matter such as sugars and directly produce methane. If they succeed, they may engineer a super microbe that never existed in nature and revolutionize the biogas industry by making anaerobic digestion much simpler and more efficient.

There is also the possibility of more applications downstream. For instance, upgrading biogas by removal of carbon dioxide improves its combustibility. A super microbe could be made to upgrade biogas using hydrogen gas or even electricity to form more methane from carbon dioxide.

Conceptualized super cell that converts idealized organic matter (2CH2O) directly into biogas.

Grand Challenges

However promising, grand challenges remain when it comes to the use of synthetic biology in biogas industry. About 10,000 moving parts are needed to make an automobile, millions of parts for an airplane, and all the parts are standardized.

Similar to those engineering sectors, synthetic biology also needs many standardized genetic parts and modules to be able to create biological devices that can really revolutionize an industry. Sophisticated genetic tools are needed as well to assemble these parts and put them to work. However, few such parts, modules and tools are at disposal for engineering microbes in an anaerobic digester.

Take methanogenic Archaea for example, only three parts are available in the iGEM registry, the world largest collection of biological parts for synthetic biology. Another challenge is an apparent neglect of synthetic biology by the biogas industry. Symposiums bringing professionals from biogas industry and synthetic biology together for discussions are rare, as are major investments for promoting synthetic biology.

As a result, few research groups are developing synthetic tools and parts for the biogas industry. For example, the aforementioned three iGEM parts were all contributed by only one group, the UGA-iGEM team at the University of Georgia.

Future Perspectives

Synthetic biology is developing faster than ever, and its cost continues to fall. Thanks to prompt actions of many industrial pioneers in embracing and supporting synthetic biology, it is already starting to revolutionize a few fields.

Synthetic biology holds great potentials to revolutionize the biogas industry. To achieve this goal, joint efforts between the biogas industry and academia must be made. The former side needs to understand what synthetic biology can achieve, while the latter side should identify which parts of the process in the biogas industry can be re-designed and optimized by synthetic biology.

Once the two sides start to work together, novel synthetic parts and tools are bound to be invented, and they will make anaerobic digestion a better process for the biogas industry.