Other Biomass Resources

OTHER BIOMASS SOURCE

There are other biomass resources potentially available for biomass source in Sarawak such as landfill gas, sewage sludge, and some agricultural wastes such as cocoa husk and sago wastewater.
 

LANDFILL GAS OF BIOMASS

Municipal solid waste (MSW) can be directly combusted in waste-to-energy facilities as a fuel with minimal processing, known as mass burn; it can undergo moderate to extensive processing before being directly combusted as refuse-derived fuel (RDF); or it can be gasified using pyrolysis or thermal gasification techniques. Each of these technologies presents the opportunity for both electricity production as well as an alternative to land filling or composting the MSW. Another MSW-to-electricity technology, landfill gas recovery, permits electricity production from existing landfills via the natural degradation of MSW by anaerobic fermentation (digestion) into landfill gas.

In contrast with some countries that have constrain to require lands for landfills purpose, "landfilling" could be an effective method for disposal of municipal and household solid wastes or refuses in the state since there are enough landfill areas can be provided in the state for landfill purpose. Although maintained in an oxygen-free environment and relatively dry conditions, landfill waste produces significant amounts of landfill gas, mostly methane. With the whole state of Sarawak dumping about 2,000 tons of waste per day, the total amount of landfill gases could be produced in Sarawak is estimated only about 2.3 MW.

Landfill gas (LFG) is generated by the natural degradation of MSW by anaerobic (without oxygen) microorganisms. The following Table shows the composition of landfill gas (LFG) obtained in average value by Department of Environment (1989).

 

Component

Composition (% by volume)

 

Average in UK

Typical value in Malaysia

Methane

63.8

45 - 60

Carbon Dioxide

33.6

40 - 60

Nitrogen

2.4

2 - 5

Oxygen

0.16

0.1 - 1.0

Hydrogen

0.05

0.0 - 0.2

Ethane

0.018

-

Unsaturated Hydrocarbons

0.009

-

Acetaldehyde

0.005

-

Ethane

0.005

-

Butanes

0.003

-

Propane

0.002

-

Carbon Monoxide

0.001

0.0 - 0.2

Helium

0.00005

-

Halogenated Compounds

0.00002

-

Alcohols

0.00001

-

Higher Alkanes

<0.05

-

Sulphides, disulphides, mercaptans

0.00001

0 - 1.0

Others

0.00005

0.01 - 0.6

Table: Landfill Gas Component Analysis

Once the gas is produced, the gas can be collected by a collection system, which typically consists of a series of wells drilled into the landfill and connected by a plastic piping system. The gas entering the gas collection system is saturated with water, and that water must be removed prior to further processing. The typical dry composition of the low-Btu gas is 57 % methane, 42 % carbon dioxide, 0.5 % nitrogen, 0.2 % hydrogen, and 0.2 % oxygen. In addition, a significant number of other compounds are found in trace quantities. These include alkanes, aromatics, chlorocarbons, oxygenated compounds, other hydrocarbons and sulfur dioxide. After dewatering, the LFG can be used directly in reciprocating engines.

It can also be further processed into a higher-British thermal unit (Btu) gas (suitable for use in boilers for manufacturing processes, as well as for electricity generation via gas turbines.) The gas is also suitable for electricity generation applications such as gas turbines and fuel cells. Figure below simplifies the treatment of LFG before being used to generate electricity. The power generation method is optional whether to use steam turbine or gas engine.

Figure: Single line diagram of production of electricity from landfill gas

Table A below shows the rate of waste generation per capita in each division according to NREB (2007). The average rate is 1.19 kg/ca/d. Table B shows the prediction of power potential that can be obtained from LFG based on some data from Trienekens. They claimed that their landfill in Mambong Landfill releases LFG and the volume is gradually increase over the time. The highest forecast volumetric flow rate is 800 m3 LFG/hr. Besides, they also claimed that the calorific value of the gases is 25 MJ/m3. As a comparison, the last column represents the power potential if methane is extracted from the LFG in which the composition of methane is assumed as 55 % and the calorific value is 36 MJ/m3. To put in the nutshell, utilizing the LFG directly into gas engine has higher power potential compared to that of utilizing methane from LFG because of the volume is higher.

Division

Waste Capacity
(ton/d)

Population (person)

Generation Rate
(kg/ca/d)

Kuching

496.0

632,679

0.78

Samarahan

190.0

37,775

5.03

Sri Aman

88.0

17,100

5.15

Betong

65.0

57,000

1.14

Sarikei

94.0

45,500

2.07

Sibu

260.0

269,045

0.97

Mukah

66.0

53,983

1.22

Kapit

40.0

25,000

1.60

Bintulu

433.0

204,167

2.12

Miri

206.2

281,120

0.73

Limbang

50.0

52,959

0.94

TOTAL

1988.2

1,676,328

1.19

Table A: Waste generation rate in the State

 

Volumetric Flow Rate (m3 LFG/hr)

Potential Power (MW)

Using LFGivision

Using Extracted CH4

100

0.69

0.55

200

1.39

1.10

300

2.08

1.65

400

2.78

2.20

500

3.47

2.75

600

4.17

3.30

700

4.86

3.85

800

5.56

4.40

Table B: Potential power output

 


According to NREB (2007), Mambong Landfill site received 450 ton/d, and according to Trienekens their landfill is currently generate more than 200 m3/h of LFG. By assuming these are true for this current state, 1 ton/d of solid waste could generate 0.444 m3 LFG/h and prediction for power potential for each division is made in the following Table.

By taking the lowest engine efficiency of 38 %, the total power potential in Sarawak is 2.3 MW but Trienekens claimed that there are 10 MW power potential from all waste in Sarawak. This may be due to the technology they are using has higher efficiency than 38 %. The power potential from LFG is still unattractive but the state can improve the solid waste management for future utilization of such green technology. However, developers should see this path as environmental perspective instead of investment return.

Division

Volumetric Flow
Rate (m3 LFG/hr)

Potentia
Power (kW)

Potential Electricity,
38% efficiency (kW)

Kuching

220.2

1529.3

581

Samarahan

84.4

585.8

223

Sri Aman

39.1

271.3

103

Betong

28.9

200.4

76

Sarikei

41.7

289.8

110

Sibu

115.4

801.7

305

Mukah

29.3

203.5

77

Kapit

17.8

123.3

47

Bintulu

192.3

1335.1

507

Miri

91.6

635.8

242

Limbang

22.2

154.2

59

TOTAL

882.8

6130.3

2330

Table: Potential power output in the State

 

SEWAGE SLUDGE

Sewage sludge in Sarawak can be classified into black water that came from the toilets, and grey water that came from wash areas like the kitchens. Grey water is disposed into drains that will eventually reached the rivers while the black water treatment involves primary treatment in septic tank, screening chamber, sedimentation tanks and aeration tank before released to the rivers.


There are three sewerage treatment plants in Sarawak located in Kuching, Miri and Sibu. The current treatment system of sewage sludge in Sarawak is illustrated in the following figure.



Figure: Current sewage sludge treatment in Sarawak

The deterioration of river pollution in Sarawak as being indicated by Malaysian Surface Water Quality in the following Table shows that the current sewage treatment is inefficient and requires a better and more organized system. One of the problems in the system is septic tanks. Tankers will only collect the sludge in the septic tanks once in 4 years or when requested by owners which means the treatment is not fully continuous. The untreated sludge that overflows between the collection periods is released to drains which will eventually be sent to rivers. This bypass occurred severely in the system especially for the undersized septic tanks.

Location

Physio-chemical

Bacteriological

Sg Sarawak Kanan

IIA/IIB

-

Sg Sarawak Kiri

IIA/IIB

-

Batu-Kawa Satok

IIA/IIB

III (Polluted)

Satok-downstream Barrage

III (Polluted)

V (Very Polluted)

Tributaries in Kuching

IV/V (Very Polluted)

V (Very Polluted)

Table: Sarawak Water Quality Classification

 

It is claimed that until 2008, there are 338,671 numbers of septic tank located in Sarawak that occupies for 182,374 Population Equivalent (PE) where 1 PE is equivalent to the capacity of 5 houses. Sewage treatment plant in Matang, Kuching receive 44 m3/day of sewage sludge from tankers collection. This capacity is not capable of treating sewage sludge in the whole region. Thus, Sewerage Services Department Sarawak is proposing a centralized sewerage system for the state to mitigate the problems of existing treatment system. The new concept is visualized in Figure below. This system channels both black and grey water into treatment plant through a network underground pipes and sewers. Wastewater is treated to Grad A before being discharged into the rivers.

Figure: Proposed centralized sewerage system

 

The sources of sewage sludge can be the residual semi-solid material left from industrial or wastewater treatment process and storm water flowing in drainage system. 75 – 90 % of the weight is water in which make it inefficient and not economical to convert to electricity. However, some technology has been used by different countries to utilize sewage sludge effectively, as shown in following Table.

Country

Method

End-product

Drawback

New Zealand

Alga is grown in sewage treatment process.

Biodiesel to energy

Time consuming

California, USA

Digested sludge is exposed to extreme heat and pressure so the cellular structures of solid are ruptured and easy to gasify.

Biosolid to energy

High operational cost due to high temperature and pressure

Lulu Island, UAE

Biogas from anaerobic digester is used in micro-turbines and fuel cells.

Biogas to electricity

-

United Kingdom

Heat from gasification of digested sludge is used to dry the sewage sludge before it can be gasified.

Biogas to electricity

-

Canada

Uses pyrolysis instead of gasification.

Biofuel to energy

-

Japan

Uses ultrasonic pre-treatment on the sludge so that solid present became more soluble. Ozone reforming refractory is used to reduce sludge volume and increase digestion gas production in methane fermentation. Sewage sludge is combined with garbage and other biomass.

Biogas to electricity

High installation cost of ultrasonic and ozone process

Illinois, USA

Combined anaerobic digestion and gasification process to optimize biogas recovery.

Biogas to electricity

-

Table: Methods of utilizing sewage sludge in different places

 

Figure below shows a concept of biological and chemical technologies combination to convert sewage sludge into electricity. Depending on composition of sewage sludge, the anaerobic digestion process will degrade 40 – 60 % by weight of the carbonaceous material which produces biogas of 65 % methane and 35 % carbon dioxide. The digested sludge can be dried out using conventional dryer or filter press to reduce the water content to 10 – 20 % before it can be gasified. Gasification at 1,700 - 2,800 o F can produce syngas of this constituent:

Carbon Monoxide

13 – 25 %

Hydrogen

10 – 28 %

Carbon Dioxide

8 – 17 %

Nitrogen

2 – 55 %

Water Vapor

11 – 41 %

 


 

 


 

 

 

Figure: Conceptual diagram of digester-gasifier hybrid system

 

COCOA AND SAGO

90 % of the cocoa pod weight is left as pulp, mucilage, sweatings and husk. Both pulp and mucilage are used for food and beverage production such as juice and jam while sweatings is used in acetic acid, ester and alcohol production. This makes only cocoa husk an available biomass from cocoa processing, which weights ten times that of cocoa bean. For sago which is the 3rd important agriculture product in Sarawak, the wastewater of sago processing plant can be used to generate electricity. Approximately, 5 m3 of wastewater is generated for the procession of 1 tonne of sago. Other waste of sago, which is coarse and fine hampas from starch extraction process, is not appropriate for electricity generation as it is more viable for synthetic polymer production. The usage of sago starch itself also does not appropriate because of the rising price of food worldwide. The potential energy that can be derived from these wastes is shown as per following Table.

 

Biomass

Production Rate

Moisture Content (%)

Lower Heating Value (kJ/kg)

Energy Available (GJ)

Cocoa
Cocoa Husk

 

18,600 tpa

 

9

 

13,000

 

240

Sago
Sago Wastewater

 

200,000 m3/annum

 

95

 

22

 

11.1

Table: Potential energy available from cocoa and sago waste


It can be seen that cocoa husk has slightly lower LHV compared to rice husk but higher than some of POB like EFB and fiber. However the potential energy is low because of the low production rate which made it less favorable for investors to utilize this biomass as electricity source. The same situation falls for sago wastewater where the production rate is much lower if compared to POME though LHV is identical.

 

ALGAE

Micro algae have a very fast specific growth rate as compared to other photosynthetic organisms. Like other plants, they use photosynthesis to harness sunlight and carbon dioxide. Energy is stored inside the cell as lipids (the source for oil) and carbohydrates. Algae can be converted into biodiesel, ethanol, biocrude and aviation fuels. Tailored algae within a highly controlled environment and fermentation of biomass can also be used to produce hydrogen. In some approaches, energy, food, and pharmaceuticals can be produced simultaneously. Microalgae have been demonstrated to capture over 80 percent of the daytime CO2 emissions from power plants and can be used to produce up to 10,000 gallons of liquid fuel per acre per year.
Among biofuels projects, algae are commonly grown in two scenarios; in ponds and in translucent containers called photobioreactors. In both cases the growth of algae requires a source of carbon, light, nutrients, and warm water. The ability to ingest CO2 and produce oxygen through photosynthesis is particularly attractive as a means to curb carbon emissions . The high cost of algae production remains an obstacle. The major conclusion is that there is little prospect for any alternatives to the open pond designs, given the low cost requirements associated with fuel production. The factors that most influence cost are biological, and not engineering-related. These analyses point to the need for highly productive organisms capable of near-theoretical levels of conversion of sunlight to biomass. Even with aggressive assumptions about biological productivity, the costs for biodiesel were projected two times higher than current petroleum diesel fuel costs.

There are efforts made to establish the feasibility of large-scale algae production in open pond systems. Study proved that outdoor ponds could be run with extremely high efficiency of CO2 utilization. Careful control of pH and other physical conditions for introducing CO2 into the ponds allowed greater than 90% utilization of injected CO2. Of essential concerns are ways to achieve consistently high productivities with conducive conditions at the site, ample sunlight and right temperature.
Cultivation methods for microalgae in open ponds have been developed to a point where media specification and unit designs are fairly standard, but there remain many technical, engineering and economic questions that stand between the desired productivity and the present available data to produce algal biofuels.

Tremendous advances were made in the science of manipulating the metabolism of algae and the engineering of microalgae algae production systems; particularly in the production of biodiesel from high lipid content algae grown in the ponds, utilizing CO2 emission from coal fired power plant.

Carbon capture and displacement fossil fuels are likely the roles for growing algae to produce oil. Many industries are seeking to develop costly and elaborate technologies and system to capture, concentrate and sequester CO2 generated in fossil fuel power plant in the earth or in the oceans. In fact algae can perform an equivalent sequestration by utilizing captured and using sunlight as the source of energy.

Commercialization to produce specialty chemical products is well advanced (nutritional supplements, primarily spirulina (Arthrospira plateasis). However, commercialization to produce high volume biofuels faces extensive challenges with regard to biological, engineering and economic factors.
The fact of the matter, the estimated capital cost (excluding operation cost) could not be justified with a currently achievable yield of oil content biomass for biodiesel. Thus, this requires a major productivity improvement of such systems and increases tremendously the outputs of what is currently possible. The possible pathway is to envisage the possibilities in succeeding commercial scale of biofuels production via microalgae together with the value chain as income streams to support and make it viable such as co-production of higher value specialty products and carbon capture monetization.

Hence, as present, we shall keep abreast with the development and emergence of promising technology, significant genetic breakthrough and economic viability so that we will be able to grasp these advantages to curtail carbon emission in future as well as an absolute option to produce sustainable biofuels, particularly for biodiesel.