POME as a Source of Biomethane

POME-BiogasDuring 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.

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).

POME 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 capture 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)

Biogas from Slaughterhouse Wastes

slaughterhouse-wasteSlaughterhouse waste (or abattoir waste) disposal has been a major environmental challenge in all parts of the world. The chemical properties of slaughterhouse wastes are similar to that of municipal sewage, however the former is highly concentrated wastewater with 45% soluble and 55% suspended organic composition. Blood has a very high COD of around 375,000 mg/L and is one of the major dissolved pollutants in slaughterhouse wastewater.

In most of the developing countries, there is no organized strategy for disposal of solid as well as liquid wastes generated in abattoirs. The solid slaughterhouse waste is collected and dumped in landfills or open areas while the liquid waste is sent to municipal sewerage system or water bodies, thus endangering public health as well as terrestrial and aquatic life. Wastewater from slaughterhouses is known to cause an increase in the BOD, COD, total solids, pH, temperature and turbidity, and may even cause deoxygenation of water bodies.

Anaerobic Digestion of Slaughterhouse Wastes

There are several methods for beneficial use of slaughterhouse wastes including biogas generation, fertilizer production and utilization as animal feed. Anaerobic digestion is one of the best options for slaughterhouse waste management which will lead to production of energy-rich biogas, reduction in GHGs emissions and effective pollution control in abattoirs. Anaerobic digestion can achieve a high degree of COD and BOD removal from slaughterhouse effluent at a significantly lower cost than comparable aerobic systems. The biogas potential of slaughterhouse waste is higher than animal manure, and reported to be in the range of 120-160 m3 biogas per ton of wastes. However the C:N ratio of slaughterhouse waste is quite low (4:1) which demands its co-digestion with high C:N substrates like animal manure, food waste, crop residues, poultry litter etc.

Slaughterhouse effluent has high COD, high BOD, and high moisture content which make it well-suited to anaerobic digestion process. Slaughterhouse wastewater also contains high concentrations of suspended organic solids including pieces of fat, grease, hair, feathers, manure, grit, and undigested feed which will contribute the slowly biodegradable of organic matter. Amongst anaerobic treatment processes, the up-flow anaerobic sludge blanket (UASB) process is widely used in developing countries for biogas production from abattoir wastes.

Slaughterhouse waste is a protein-rich substrate and may result in sulfide formation during anaerobic degradation. The increased concentration of sulfides in the digester can lead to higher concentrations of hydrogen sulfide in the biogas which may inhibit methanogens. In addition to sulfides, ammonia is also formed during the anaerobic digestion process which may increase the pH in the digester (>8.0) which can be growth limiting for some VFA-consuming methanogens.