Table 5.7.1 shows main materials usable in composting. Husk and woody materials have a

low biodegradable material index so their decomposition takes time but are effective for improving soil and can be used in combination with other materials to produce high quality compost. Raw garbage contains many materials impossible to ferment such as plastic, metal, and glass and also requires thorough sorting and the right preprocessing. Sludge may require special measures for dealing with heavy metals, etc.

Among the recycling technologies of composting, biogas, drying, carbonization, livestock feed, and incineration, composting can use vaious kinds of materials and offers significant advantages in terms of technology and distribution. However, amount and period of the product demand are limited, and some regions have excess compost stocks. Future production efforts will require elaborate quality control, composting of all material produced in a region, and regional consumption of the entire amount produced in those areas.

Further information

Japan Livestock Industry Association Ed., Composting Facility Design Manual(2003) (in Japanese) Japan Organics Recycling Association Ed., CompostingManual2004 (in Japanese)

Livestock Industry’s Environmental Improvement Organization Ed., Livestock Dung Process Facility — Machine Setup Guidebook (compost processing facility version) (2005) (in Japanese)

7.5.1 General scope

Brunei has large amount of fossil fuel resources such as oil and natural gas, and obtains half of its GDP by exporting these resources to enjoy good economy. Thus, they do not have interest in biofuel development so much.

Meanwhile, the land area is small (5,770 km2), and agricultural land is very small, thus most of the food is imported. National development plan always aims at improvement of self-supply rate of food. However, since its independence in 1984, governmental sector was developed and stable high-income jobs are available, which lead to the people’s removal from agriculture. In general, agriculture is stagnant, and its productivity within total GDP is only 2.7%.

Some of the typical implementations of large-scale anaerobic digestion systems are described below.

(a) Sewage Sludge

Sewage sludge is a waste biomass which is discharged in large quantities from sewage treatment facilities. For a long time, anaerobic digestion has been one of the treatments on sewage sludge to stabilize the sludge and reduce its volume. The reactor design usually applied to sewage sludge digestion is a completely mixed reactor design (Fig. 8.2.2). A contemporary anaerobic digester for sewage sludge is as large as 10,000 m3 in the effective volume. Typical design parameters include the operational temperatures of ambient (ca. 20 degC) to mesophilic (ca. 35 degC) range, and the relatively long retention time of 20 to 30 days.

(b) Industrial organic wastewater

Industrial wastewater containing readily biodegradable organic matters, but little solids, such as the wastewater discharge from a beer brewery, the UASB (up-flow, anaerobic sludge blanket) reactor design, which was originally developed in the Netherlands, is usually selected. The UASB reactor design maintains a high density of anaerobic microorganisms in the form of self-aggregated microbial "granules" that enables a high rate of anaerobic digestion.

(c) Organic wastes from food industries

Anaerobic digester designs which allow a high rate anaerobic digestion on readily biodegradable biomass containing high concentrations of organic solids are being developed, and some have already been in actual operation in recent years. An example of such a new design is the DAPR (down-flow anaerobic packed-bed reactor) design. Many high-rate anaerobic digestion facilities for food wastes and distillery wastes, incorporating the DAPR design, have been implemented in Japan. The largest facility as of writing has the design capacity of 400 tons/day (Fig. 8.2.3).

Further information

R. E.Speece: Anaerobic Biotechnology, Archae Press, pp.127, Tennessee (1996)

Japan Sewage Works Association: Sewage Facilities planning, policy and explanation (second part) 2001, pp.384, Japan (2001)

J. B.Lier: Current Trends in Anaerobic Digestion; Diversifying from waste(water) treatment to re-source oriented conversion techniques, 11th IWA World Congress on Anaerobic Digestion, 23-27 September

2007, Brisbane, Australia (2007)

Hisatomo Fukui and Motonobu Okabe: Distilled spirit processing waste recycling plant using thermophilic dawn-flow packed-bed reactor, Gas fuel manufacture from biomass and its energy utilization, NTS, pp.265-275, Japan (2007)

There is no established way of categorizing biomass, which is defined differently according to the field; categorization changes depending on the purpose and application. Generally there are two ways to categorize biomass: one is biological categorization based on types of existing biomass in nature (such as categorization according to ecology or type of vegetation), and the other is based on the use or application as resources. The latter is highly significant in terms of making effective use of energy (resources).

2.1.3 An example of biomass categorization (in terms of use and application)

An example of biomass categorization appears in Fig. 2.1.2. In this categorization, biomass includes not only the conventional product and waste from agriculture, forestry, and fisheries, but also plantation biomass. Categorization according to source is important for designing biomass usage systems.

Biomass

Conventional Biomass Resources

Agriculture, Forestry (Woody), Fishery, Livestock farming

Food, Materials, Medicine, Timber, Pulp, Chip, e. t.c

Biomass Wastes (Derivatives)

Agricultural, Forestry, Fishery, Livestock residues (wastes)

Rice straw, Cattle manure, Lumber mill, Sawdust, Sewage sludge Black liquor

Plantation Biomass

Forestry Eucalyptus, Poplar, Willow, Oil palm Herbaceous Sugarcane, Switchgrass, Sorghum, Corn, Rapeseed Aquatic Giantkelp, Water hyacinth, Algae

Fig. 2.1.2. Biomass categorization (in terms of use and application).

Moisture content is a major factor to consider when using biomass, especially as energy. Because moisture content is defined differently in each field, care is needed in reading indications of moisture content. In the energy field, moisture content is often defined as follows.

(moisture content) = (moisture weight) / (total weight) x 100 [%]

(total weight) = (biomass dry weight) + (moisture weight)

Using this definition, moisture content never exceeds 100%. In the forestry and ecology fields, moisture content is often defined as follows:

(moisture content) = (moisture weight) / (biomass dry weight) x 100 [%] (2.1.3)

As a rule, this handbook employs Eq. (2.1.1) for definition of the moisture content. Biomass comprises natural macromolecular compounds such as cellulose, lignin, and proteins, and many kinds of biomass have high moisture content, because the origin of biomass is living organisms. Fig. 2.1.3 shows the moisture content of various biomass types. There is a wide range, from biomass types like dry wood and paper waste with about 20% moisture content, to those with over 95% moisture content, such as microalgae, fermentation residue, and sludge. For the purpose of energy conversion, one must choose a process adapted to the moisture

content.

Fig. 2.1.3. Relation of moisture contents and heating value.

Further information

Ogi, T. in “Biomass Handbook”, Japan Institute of Energy Ed., Ohm-sha, 2002, pp.2-6 (in Japanese)

(a) Rice and wheat

Residues from rice and wheat are mainly exemplified by chaff and straw. Of these, chaff generally refers to those derived from rice. This is because wheat chaff never drops in harvesting, and it can be processed without being removed. Rice chaff is almost uniform in shape and size, and is suitable for processing and transportation. Rice chaff, however, has a hard structure and less suitable for fermentation, due to its large amounts of lignin and silica (SiO2). Most rice chaff is used as fuel for combustion. However, the silica contained in rice chaff as much as 10 to 20 wt%, which may damage incinerators during combustion, raising some considerations on its practical use. On the other hand, straw similarly contains lignin, silica and so forth, but may be more fermentable than the chaff, and it is used as energy sources both for combustion and fermentation.

(b) Corn and rhizomic crops

Corn residues are discharged not only as residues in fields (leaves, stems, etc.), but also as corncobs after processing. Kernels of corn are abundant in starch, and it is used for ethanol production through fermentation in the USA.

Rhizomic crops may have leaves and stems as residues.

(c) Sugarcane

All parts of sugarcane other than the stems, such as cane tops (top portion with only a low sugar content), leaves and roots, are removed before the stems are transported to the sugar mill, leaving them as residues in the fields.

Wood biomass includes bark, sawdust, and cut-offs from lumber, veneer, plywood, and engineered wood products. The total amount of woody biomass use in Japan was 10,782,000 m3 in 2006. Almost all of this (10,197,000 m3 (95%)) was used as a biomass resource, while the rest was discarded. Woody biomass is classified as: 1) wood chips, 4,408,000 m3 (43%); 2) fuel,

2.330.0 m3 (23%); 3) livestock bedding materials, 2,256,000 m3 (2 %); 4) compost or soil improvement materials, 580,000 m3 (5.7%); and 5) wood-based panels such as particleboard

258.0 m3 (2.5%). Fuel (2,330,000 m3) is classified as: 1) energy for operating drying kilns (1,550,000 m3), 2) electric power (595,000 m3), and 3) energy for manufacturing pellets (46,000 m3).

Starch is a polymer of glucose in which glucose units are linked with each other via a — 1,4 and a-1,6 linkages. Starchy materials are first hydrolyzed to glucose using amylase enzymes (Eq. (5.2.2)).

(CeHwO5)n + nH2O ^ nC6H12O6 (5.2.2)

molecular weight n(162.14) n(18.02) n(180.16)

100 g 11.11 g 111.11 g

Starchy materials are first cooked at temperatures between 100 and 130oC and then hydrolyzed to glucose by using a-amylase and gluco-amylase.

A large amount of ethanol is produced from corn in USA and from sweet potato in China.

Low temperature cooking procedure for ethanol production from sweet potato which was the practice in Japan until 1990’s is described below. Raw sweet potato is first crushed by hammer-mill, cooked at 80-90 oC for 60min, added with a-amylase to liquefy starch and to reduce viscosity, and then cooled to temperature of about 58oC. Liquefied starch is hydrolyzed to glucose in two hours of hydrolysis by gluco-amylase. Glucose concentration of mash is adjusted at about 15%. Fermented beer of about 8 vol% ethanol is obtained after four days of batch-wise fermentation at 30-34oC. When starch value of raw sweet potato is 24.3% (27% glucose equivalent), and fermentation yield is 92%, the amount of raw sweet potato required to produce 1 m3 (kL) of 95% ethanol is 6.03 t-wet.

Fuel ethanol is produced mostly from corn in USA. In a wet mill process corn is immersed in dilute sulfite solution, fractionated into starch, germ, gluten, and fiber. Starch fraction is hydrolyzed to glucose by the amylases after cooking and then fermented by yeast. One of the popular fermentation process is a continuous fermentation process with several fermentation tanks connected in series in which yeast cells are recycled via centrifuge resulting in high fermentation rate. Traditional batch-wise process is also the practice in some of ethanol plants. Final ethanol concentration of fermented beer is 8 to 11 vol% on average. Wet-mill process of corn to ethanol conversion is indicated in Figure 5.2.2. When starch value is 63% (70% glucose equivalent), and fermentation yield 90%, the amount of corn necessary to produce 1 m3 (kL) of 95% ethanol is about 2.4 t-wet.

CO2 emission has been focused on as only one environmental impact of biomass. But it is necessary to consider the emission of other greenhouse gases such as CH4 and N2O in biomass production. Land use of biomass production is also key effect to environment.

In addition, the competition with food might be considered as derivative environmental impact in the case of cultivation type of biomass.

Further information

Tahara, K. et al. “Evaluation of generation plant by LCA-Calculation of CO2 payback time “, Chemical Engineering, 23(1), pp.88-94, 1997 (in Japanese)

Uchiyama, Y. and H. Yamamoto, “Impact of Generation Plant on Global Warming”, Central Res. Inst. of Electric Power Industry report Y91005, 1992 (in Japanese)

Science and Technology Agency resource survey society, “Natural energy and generation technology”, Taisei Publishing co. Ltd, 1983 (in Japanese)

Tahara, K. et al., “Role of ocean thermal energy conversion in the issue of carbon dioxide”, Macro Review, 6, pp.35-43, 1993 (in Japanese)

Inaba, A, et al, “Life cycle assessment of photovoltaic power generation system, Energy and Resources”, 16(5), pp.525-531, 1995

Tahara, K., et al. “Life Cycle Assessment of Biomass power Generation with Sustainable Forestry System” 4th International Conference on Greenhouse Gas Control Technologies (GHGT-4) 1998, 9, Interlaken, Switzerland

Basically in Malaysia, there are only 2 out of 5 sugar factories, which use sugar cane as raw materials for refined sugar production. The other plants would use solely brown sugar as raw materials for sugar production. The main objectives of the industry are for food security supply, creation of jobs, development of industrial projects in rural areas and reducing foreign exchange.

Bagasse is the residue after sugarcane has been processed to remove the sugar juice. On average, about 32 % of bagasse is produced from every tonne of sugar cane processed. The amount of sugar cane processed in 2002 is about 1,111,500 tonnes. Thus, the amount of bagasse produced is 355,680 tonnes. This bagasse is not wasted as it acts as a biomass residue fuel to the boiler for its cogeneration plant. This saves the factory expenditure in boiler fuel oil and electricity expenses.

At the current rate of usage, all of the bagasse is used as fuel for its cogeneration plant. In fact there is insufficient bagasse for the sugar mills. Thus, they are buying other biomass residues such as rice husk, wood off cuts and palm oil residues to be used as fuel.

For the proper management of carbon budget in the future, land-ecosystem models that are truly useful for ecosystem monitoring and carbon budget evaluation are inevitably required. To extrapolate the results based on ground-observation data in a spatial and a temporal scale, more studies will be required to develop satellite remote sensing and statistical ecosystem models. Using a land-use model and land-ecosystem carbon cycle model, we can predict the fluctuations in carbon balance caused by human activities (i. e. terrestrial carbon management) and climate change in the future. And also, we can conduct the assessment of carbon management potential.

By Oikawa and Ito, a process-based carbon cycle model (Sim-CYCLE) was developed and validated with observational data at many measurement sites. The changes of carbon balances and stocks from present to future condition (after 70 years under twice time of CO2 atmospheric concentration and higher air temperature by 2,10C) was estimated using the Sim-CYCLE model. As shown in Fig.2.5.1 (T. Oikawa, 2002), carbon stocks in soil and vegetation of land-ecosystem will increase from 642.3, 1495.1 GtC at present to 835.1, 1559.0 GtC in the future, respectively.

Fig. 2.5.1. The changes of carbon balances and stocks from present to future condition (after 70 years under twice time of CO2 atmospheric concentration and higher air temperature by 2,1°C) estimate by Sim-CYCLE model. (T. Oikawa, 2002)

Further information

Dixson, R. K., Brown, S.A., Solomon, A. M., Trexler, M. C. and Wisniewski, J., Carbon pools and flux of grobal forest ecosystems. Science 263,185-190 (1994)

IPCC Fourth Assessment Report, 2007: A report of the Intergovernmental Panel on Climate Change. Oikawa, T. Land ecosystem response to global warming (in Japanese), Suuri-Kagaku, 2002, No.470, 78-83.