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Increased biogas production (POME to biogas) and reduction of struvite

Process improvement study in anaerobic ponds of a palm oil mill in Malaysia

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In a process improvement study in anaerobic ponds of a palm oil mill in Malaysia, ACTI-Mag increases the volume of biogas produced and thus the financial returns from its conversion into heat or electricity.

 

case study summary

Challenges
  • Low palm oil mill effluent (POME) flow from a palm oil mill
  • Low POME flow was leading to poor biotreater efficiency and biogas production
  • Blockages from the formation of magnesium / ammonium / phosphate (“struvite”) crystals
Objectives
  •  Increase biogas production in anaerobic ponds
  • Eliminate blockages by stopping struvite
    formation on critical infrastructure
Solution

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Solution

ACTI-Mag, with its unique high surface area and high localised pH surface, is able to break down complex organic matter by hydrolysis into smaller units. This allows the biological system to convert organic matter into biogas more quickly, and improve the quality.

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Benefits of ACTI-Mag

Increased biogas production

Increased power generation

Less hard scum in the mixing pit

Reduction of pipe blockages due to struvite

INTRODUCTION

Biogas is formed naturally when palm oil mill effluent (POME) decomposes in the absence of oxygen. Unharnessed, this gas is an unwanted, potentially hazardous contributor to global climate change.

Biogas is typically composed of 50–75% methane (CH4), 25–45% carbon dioxide (CO2), and trace amounts of other gases. When POME collection is uncontrolled, methane is released directly into the atmosphere. As a greenhouse gas (GHG), methane is 21 times more powerful than CO2.

Biogas plants, on the other hand, take advantage of this natural decomposition process to generate electricity. Organic liquid wastes generated during palm oil production represent a major untapped source of energy. So converting POME emissions to biogas for combustion can produce energy, as well as significantly reduce the climate change impacts of palm oil production.

Palm oil production is vital for the economy of Malaysia, which is the world’s second largest producer of the commodity after Indonesia. Grown over 4.2 million hectares and traded in 160 different countries, palm oil growth and production provides jobs to more than half a million people in Malaysia. Forty percent of palm oil cultivation in Malaysia is owned by nearly 640,000 small land holders, also helping to alleviate poverty.

The large and rapidly growing palm oil industry demands better agricultural, industrial and sustainability practices. Capturing and converting biogas to energy, offers one way for palm oil mills to reduce their environmental impact and create renewable energy at the same time.

In this trial, Calix demonstrated that the dosing of ACTI-Mag not only improves the quality and quantity of biogas produced from POME, but can also alleviate the formation of struvite. Struvite forms in anaerobic digesters and, if left untreated, can turn into rock like formations and heavily restrict flow through pipes and can clog equipment.

PALM OIL MILL EFFLUENT (POME)

Processing fresh fruit bunches (FFB) from palm trees for palm oil production generates several types of waste. Oil extraction, washing, and cleaning processes generate liquid waste we call palm oil mill effluent (POME).

For every ton of fresh fruit bunches processed, the mill discharges from 0.7 to 1.0 m3 of POME. Fresh POME is a hot (temperature 60–80°C), acidic (pH of 3.3–4.6), thick, brownish liquid with high solids, oil and grease, chemical oxygen demand (COD), and biological oxygen demand (BOD) values.

The relation of POME and biogas Biogas is formed when microorganisms, especially bacteria, degrade organic material in the absence of oxygen. Methane, which makes up the bulk of biogas, can combust with oxygen. The energy release from combustion makes biogas a potential fuel, that can be converted into electricity or heat.

One of the main attractions of biogas technology is its ability to generate biogas from abundant, inexpensive organic wastes such as POME.

POME-to-energy applications typically use the anaerobic process.

The importance of pH and its buffering in anaerobic processes

Each of the microbial groups involved in anaerobic digestion has a specific pH region for optimal growth. Anaerobic systems must have adequate pH buffering capacity to accommodate the production of volatile acids and carbon dioxide.

To guard against the accumulation of excess volatile acids, system operators must prevent pH from becoming too acidic, which is why they typically need to dose a source of alkali – such as ACTI-Mag. A 60% concentrated stabilised suspension of magnesium hydroxide, ACTI-Mag buffers at pH ~8.5 – 9 when dosed, which makes it a more soluble and stable alkali when compared to caustic (pH 14) or lime (pH 12.5).

OBSERVATIONS

COD and impact of POME on power generation

Chemical oxygen demand (COD) covers both biologically available and inert organic matter, and it is a measure of the total quantity of oxygen required to oxidize all organic material into carbon dioxide and water.

COD values indicate the amount of organic matter that exists in POME and can be accessible to produce biogas. Put simply, the COD value is usually the basis of the renewable energy (ie. biogas) potential calculation.

 

 

During this trial we can observe that ACTI-Mag increased power generation even at a lower input of COD loading, which indicated it had a strong impact on the amount of biogas produced.

The kW generated per unit of COD loading was 1.38 during the ACTI-Mag dosing and 1.0 or less in March and April, prior to dosing ACTI-Mag.

 

COD and impact of POME on biogas volume

Calculating the potential energy generated from biogas uses several key parameters. One way to demonstrate the impact of ACTI-Mag on the volume of biogas produced is to look at the biogas/COD loading and POME/biogas ratios.

This is basically the theoritical volume of methane produced per kg of COD removed from the wastewater.

After only 5 days of dosing, we had already achieved a 20% increase on the POME/biogas ratio. This 20% boost in biogas volume was due to ACTI-Mag helping digest the undigested feedstock left in the system.

After 5 days, the biogas/COD loading ratio dropped as the undigested feedstock was digested. The organic loading rate at 0.5 shows the system was underfeeding. The low COD loading in July can also be explained by it being in the middle of the rainy season.

Before

 

 

After

A small part of the tank was scraped off. After only a few weeks, we can see the tank still did not show much struvite formation on the tank walls.

Before

Chunks of hardened scum can been seen on the mixing pit

After

Obvious improvement observed on the mixing pit after using
ACTI-Mag

ACTI-Mag for biogas management

Energy and cost efficiency

ACTI-Mag should be dosed at 200 ppm per day every alternative week with the intervening weeks allowing the available COD in the lagoon to build up. This dosing rate can optimize the production of biogas, while reducing chemical usage costs.

When conditions allow more COD into the system, the optimized dosing rate for ACTI-Mag should be 200 ppm per day, in order to maximize the power potential of biogas production.

Biogas Volume up by 20%

Increased power generated from biogas

Conclusion

CONCLUSION

ACTI-Mag can increase the volume of biogas produced and thus the financial returns from its conversion into heat or electricity.

In this project, we observed a quick and significant increase in energy generation per unit of COD.

Initial improvement in struvite formation was also observed during the trial.

ACTI-Mag for Biogas Management

Calix ACTI-Mag can increase the quality and quantity of the biogas coming from anaerobic systems, and provide a significant economic boost for food processing plants and water utilities.

Find out more

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