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Improving Biogas Production

Ta Chana, Thailand

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ACTI-Mag improves organics digestion, Chemical Oxygen Demand (COD) reduction and pH stability but also increases biogas production in Ta Chana, Thailand.

case study summary

Challenges
  • Low biogas production
  • High Hydrogen Sulfide (H2S) levels
  • Low Chemical Oxygen Demand (COD) reduction
  • High instability
Objective
  • Generate more biogas
  • Generate more power
  • Improve Chemical Oxygen Demand (COD)
  • Improve stability
Solution

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Calix presented their product ACTI-Mag to improve organics digestion, Chemical Oxygen Demand (COD) reduction, and pH stability and increases the biogas production to Ta Chana.

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Benefits of ACTI-Mag

Improved biogas production

Improved pH stability

Improved COD percentage reduction

Improved system stability

Wastewater Process

Following the lab testing, wastewater treatment at the palm oil mill commenced. The wastewater from the plant arrived at the balancing pond at 80 + degrees celsius and the optimum temperature for a mesophilic anaerobic system is 37.5 degrees celsius. The second application at the balancing pond was to balance the flow to the anaerobic ponds each day as the plant wastewater stream can vary per day per hour. From the balancing ponds the wastewater goes into the dosing channels and into the anaerobic lagoon. On average the hydraulic retention time in the lagoon was 21 days.

The biogas produced from the anaerobic process was collected in the lagoon balloons and then sent to the H2S bio scrubbers. The limits of the H2S bio scrubbers was 5000 ppm. After the biogas is scrubbed and dewatered it goes to the biogas generators. The effluent from the anaerobic lagoon then goes to aerobic ponds to be further treated.

Introduction

Biogas production from wastewater streams is an ideal way to increase bioenergy production while reducing odours and CO2. The effluent load in untreated wastewater includes carbon, which can be converted into methane and burned to provide power. This makes biogas a viable source of renewable energy, especially for the agricultural sector.

With palm oil accounting for approximately 36% of global vegetable oil production in 2015 and only one tonne of palm oil produced for every six tonnes processed means there is a large amount of waste and wastewater.

The palm oil industry in Thailand processes more than 13 million tonnes of palm oil material in more than 90 processing plants. Many of these treat their wastewater streams through an anaerobic process which produces biogas energy and treats their wastewater simultaneously, providing a significant economic boost.

Three of the key parameters in maximising the economics of biogas generation from anaerobic systems are the management of hydrogen sulphide (H2S) formation, the quantity, and the quality of the biogas produced. The addition of an alkali is a critical part of maintaining pH and alkalinity, stability and ensure that the anaerobic system, performs at its optimum rate.

This case study was done on a Palm oil plant in Thailand that processed around 40 tonnes of palm oil per day and had a waste stream of 1000 – 500 m3 per day, treated by four anaerobic reactors. The effluent stream was turning it into power to run the plant, while also supplying electricity back onto the grid. The plant had a quota it needed to supply back onto the grid and was looking for ways to increase power generation and biogas quantity from its anaerobic reactors.

BALLOON TESTING

Each alkali was added to provide equivalent hydroxide levels to the effluent after accounting for the different strengths of each product. The test procedure involved taking 2.5 litre of the anaerobic effluent and 2.5 litres of the input influents. The caps on the bottles were sealed to a tube and left to balloon for two days before a visual observation was taken. In all test runs a control was used and compared. In all the tests with caustic soda, lime, and standard magnesium hydroxide the balloon size did not exceeds the control.

ACTI-Mag at a dose rate of 100 + showed improvement over the control and in all the balloon tests 300 mg/L and above gave a minimum 30% increase in biogas compared to the control with no ACTI-Mag. In the field trial it was decided to use 300kg/ML.

TESTING EQUIPMENT

 

During and prior to the trial the wastewater was tested for COD level, pH and temperature on a daily basis.

The biogas was also tested daily for H2S, CH4 and CO2

RESULTS

The anaerobic lagoon used in this trial was a 6,000m³ lagoon with a target input volume of 250 m³ per day. The targeted HRT was 21 days. In the trial, ACTI-Mag pushed the bio-gas volume from the historic volume of 4,127 m³ to 5,221 m³ per day. 

 

This changed the ratio of waste-water to bio-gas from 16.51 to 20.88, which was a. 26% increase.

One of the reasons for the increase in biogas is that ACTI-Mag helps in the hydrolysis step in the anaerobic process. This step is the breaking down of complex particulate matter into lower molecular weight compounds, which can be more easily broken down by biological means.

The hydrolysis step has been seen to be one of the rate-limiting steps in the digestion process in anaerobic systems. ACTI-Mag was dosed into the last point before the anaerobic lagoon, which gives it good contact time with the new wastewater stream at the right pH. This allowsed breakdown of the complex organic chain in the wastewater, including proteins, carbohydrates and lipids, which are hydrolysed into smaller units such as amino acids, sugars and long chain fatty acids.

FIELD TRIAL

The first part of the field trial is to acquire historical data.

The typical input levels into the anaerobic lagoon were:

 

*********************

 

The typical output figures coming out of the anaerobic lagoon were:

The waste-water flow temperature from the palm oil factory comes in at 80 degrees celsius and required the flow to be cooled before entering the anaerobic ponds. There was two methods to cool the wastewater. One was the use of a cooling tower.

 

*********************

 

The second method was the use of a cooling pond.

ACTI-Mag’s high surface and solubility give it a very unique property in that the localised pH close to the surface of the ACTI-mag particle has a significantly higher pH than the surrounding bulk wastewater. This property lets ACTI-Mag hydrolysis the complex soluble organic compounds without affecting the biological environment in the system.

The yield value in the trial increased 28% from 0.167 to 0.215 because ACTI-Mag sped up the hydrolysis process and increased the sludge hydraulic retention time. Due to an increase in the CH4 level and biogas production.

The increase in the biogas volume to COD was 29.6%, which showed the anaerobic system was more efficient with the carbon load being fed into it and increasing the conversion rate to biogas.

One of the reasons for the increase in yield and biogas volume to COD loading efficiency is because ACTI-Mag has a mild flocculation effect due to the magnesium ion, which bridges the biopolymers together. This mild effect increases the sludge hydraulic retention time to increase the biological breakdown of the organic solids in the wastewater stream.

Increase in Biogas

 

With the increase in biogas this site was able to grow its earnings per month by $322,500 baht making the wastewater process of the business more profitable to the plant.

 

This trial showed that ACTI-Mag increased the conversion of carbon into bio-gas by 29.6% and improved the yield value by 28%. It also showed a 23.5% improvement in the conversion of wastewater to bio-gas. Ultimately, this trial gave the plant an increased return of $322,500 baht per month, which was a key goal for the plant operators. The unique properties of ACTI-Mag that allow mild flocculation and improved hydrolysation were the reason for this.

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.

Download the Solution Spec Sheet

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