Could Biomass Be The Answer To South Africa’s Energy Problem?

South Africa is experiencing a mammoth energy crisis with its debt-laden national power utility, Eskom, being unable to meet the electricity needs of the nation. After extensive periods of load shedding in 2018 and again earlier this year, it is becoming increasingly important to find an alternative source of energy. According to Marko Nokkala, senior sales manager at VTT Technical Research Centre of Finland, South Africa is in the perfect position to utilize biomass as an alternative source of energy.

Things to Consider

Should South Africa choose to delve deeper into biomass energy production, there are a few things that need to be considered. At present, a lot of biomass (such as fruit and vegetables) is utilized as food. It will, therefore, be necessary to identify alternative biomass sources that are not typically used as food, so that a food shortage is never created in the process.

biomass-sustainability

One alternative would be to use municipal solid waste from landfills and dumpsites as well as the wood waste from the very large and lucrative forestry industry in the country. It is also essential to keep in mind that an enormous amount of biomass will be needed to replace even a portion of the 90 million tons of coal that Eskom utilizes every year at its various power stations.

Potential Biomass Conversion Routes

There are a number of processing technologies that South Africans can utilize to turn their biomass into a sustainable energy source. Biochemical conversion involving technology such as anaerobic digestion and fermentation makes use of enzymes, microorganisms, and bacteria to breakdown the biomass into a variety of liquid or vaporous fuels.

WTE_Pathways

Fermentation is especially suitable when the biomass waste boasts a high sugar or water content, as is the case with a variety of agricultural wastes. By placing some focus on microbial fermentation process development, a system can effectively be created that will allow for large-scale biofuel production. Other technologies to consider include thermal methods like co-firing, pyrolysis, and gasification.

Future of biomass energy in South Africa

Despite the various obstacles that may slow down the introduction of large-scale biomass energy production in the country, it still promises to be a viable solution to the pressing energy concern. Biomass energy production does not require any of the major infrastructures that Eskom is currently relying on.

Although the initial setup will require a substantial amount of electricity, running a biomass conversion plant will cost significantly less than a coal-powered power plant in the long run. With the unemployment rate hovering around 27.1% in South Africa at present, any jobs created through the implementation of biomass energy conversion will be of great benefit to the nation.

Conclusion

Without speedy intervention, South Africa may very soon be left in the dark. Although there are already a number of wind farms in operation in the country, the addition of biomass conversion facilities will undoubtedly be of great benefit to Africa’s southernmost country.

Biomass Storage Methods

Sufficient storage for biomass is necessary to accommodate seasonality of production and ensure regular supply to the biomass utilization plant. The type of storage will depend on the properties of the biomass, especially moisture content. For high moisture biomass intended to be used wet, such as in fermentation and anaerobic digestion systems, wet storage systems can be used, with storage times closely controlled to avoid excessive degradation of feedstock. Storage systems typically used with dry agricultural residues should be protected against spontaneous combustion and excess decomposition, and the maximum storage moisture depends on the type of storage employed.

Moisture limits must be observed to avoid spontaneous combustion and the emission of regulated compounds. Cost of storage is important to the overall feasibility of the biomass enterprise. In some cases, the storage can be on the same site as the source of the feedstock. In others, necessary volumes can only be achieved by combining the feedstock from a number of relatively close sources. Typically, delivery within about 50 miles is economic, but longer range transport is sometimes acceptable, especially when disposal fees can be reduced.

Storage of biomass fuels is expensive and increases with capacity.

Agricultural residues such as wheat straw, rice husk, rice straw and corn stover are usually spread or windrowed behind the grain harvesters for later baling. Typically these residues are left in the field to air dry to moisture levels below about 14% preferred for bales in stacks or large piles of loose material. After collection, biomass may be stored in the open or protected from the elements by tarps or various structures. Biomass pelletization may be employed to increase bulk density and reduce storage and transport volume and cost.

Biomass Storage Options

  • Feedstock is hauled directly to the plant with no storage at the production site.
  • Feedstock is stored at the production site and then transported to the plant as needed.
  • Feedstock is stored at a collective storage facility and then transported to the plant from the intermediate storage location.

Biomass Storage Systems

The type of biomass storage system used at the production site, intermediate site, or plant can greatly affect the cost and the quality of the fuel. The most expensive storage systems, no doubt, are the most efficient in terms of maintaining the high fuel quality. Typical storage systems, ranked from highest cost to lowest cost, include:

  • Enclosed structure with crushed rock floor
  • Open structure with crushed rock floor
  • Reusable tarp on crushed rock
  • Outside unprotected on crushed rock
  • Outside unprotected on ground
  • Subterranean

The storage of biomass is often necessary due to its seasonal production versus the need to produce energy all year round. Therefore to provide a constant and regular supply of fuel for the plant requires either storage or multi-feedstocks to be used, both of which tend to add cost to the system.

Reducing the cost of handling and stable storage of biomass feedstocks are both critical to developing a sustainable infrastructure capable of supplying large quantities of biomass to biomass processing plants. Storage and handling of biomass fuels is expensive and increases with capacity. The most suitable type of fuel store for solid biomass fuel depends on space available and the physical characteristics of the fuel.

Energy Value of Agricultural Wastes

Large quantities of agricultural wastes, resulting from crop cultivation activities, are a promising source of energy supply for production, processing and domestic activities in the rural areas. The available agricultural residues are either being used inefficiently or burnt in the open to clear the fields for subsequent crop cultivation.

agricultural-wastes

On an average 1.5 tons of crop residue are generated for processing 1 ton of the main product. In addition, substantial quantities of secondary residues are produced in agro-industries processing farm produce such as paddy, sugarcane, coconut, fruits and vegetables.

Agricultural crop residues often have a disposal cost associated with them. Therefore, the “waste-to-energy” conversion processes for heat and power generation, and even in some cases for transport fuel production, can have good economic and market potential. They have value particularly in rural community applications, and are used widely in countries such as Sweden, Denmark, Netherlands, USA, Canada, Austria and Finland.

The energy density and physical properties of agricultural biomass wastes are critical factors for feedstock considerations and need to be understood in order to match a feedstock and processing technology.

There are six generic biomass processing technologies based on direct combustion (for power), anaerobic digestion (for methane-rich biogas), fermentation (of sugars for alcohols), oil exaction (for biodiesel), pyrolysis (for biochar, gas and oils) and gasification (for carbon monoxide and hydrogen-rich syngas). These technologies can then be followed by an array of secondary treatments (stabilization, dewatering, upgrading, refining) depending on specific final products.

It is well-known that power plants based on baled agricultural residues are efficient and cost-effective energy generators. Residues such as Rice Husks, Wheat Straw and Maize Cobs are already concentrated at a point where it is an easily exploitable source of energy, particularly if it can be utilized on-site to provide combined heat and power.

The selection of processing technologies needs to be aligned to the nature and structure of the biomass feedstock and the desired project outputs. It can be seen that direct combustion or gasification of biomass are appropriate when heat and power are required.

Anaerobic digestion, fermentation and oil extraction are suitable when specific biomass wastes are available that have easily extractable oils and sugars or high water contents. On the other hand, only thermal processing of biomass by pyrolysis can provide the platform for all of the above forms of product.

Many thermal processing technologies for agricultural wastes require the water content of biomass to be low (<15 per cent) for proper operation. For these technologies the energy cost of drying can represent a significant reduction in process efficiency.

Moisture content is of important interest since it corresponds to one of the main criteria for the selection of energy conversion process technology. Thermal conversion technology requires biomass fuels with low moisture content, while those with high moisture content are more appropriate for biological-based process such as fermentation or anaerobic digestion.

The ash content of biomass influences the expenses related to handling and processing to be included in the overall conversion cost. On the other hand, the chemical composition of ash is a determinant parameter in the consideration of a thermal conversion unit, since it gives rise to problems of slagging, fouling, sintering and corrosion.

A Glance at Woody Biomass Resources

Woody biomass resources range from corn kernels to corn stalks, from soybean and canola oils to animal fats, from prairie grasses to hardwoods, and even include algae. Woody biomass may be used for energy production at different scales, including large-scale power generation, CHP, or small-scale thermal heating projects. Some of the major sources of woody biomass are being discussed in the following paragraphs:

 

Pulp and Paper Industry Residues

The largest source of energy from wood is the waste product from the pulp and paper industry called black liquor. Logging and processing operations generate vast amounts of biomass residues. Wood processing produces sawdust and a collection of bark, branches and leaves/needles. A paper mill, which consumes vast amount of electricity, utilizes the pulp residues to create energy for in-house usage.

Forest Residues

Forest harvesting is a major source of biomass for energy. Harvesting may occur as thinning in young stands, or cutting in older stands for timber or pulp that also yields tops and branches usable for bioenergy.

Harvesting operations usually remove only 25 to 50 percent of the volume, leaving the residues available as biomass for energy. Stands damaged by insects, disease or fire are additional sources of biomass. Forest residues normally have low density and fuel values that keep transport costs high, and so it is economical to reduce the biomass density in the forest itself.

Agricultural or Crop Residues

Crop residues encompasses all agricultural wastes such as straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. which come from cereals (rice, wheat, maize or corn, sorghum, barley, millet), cotton, groundnut, jute, legumes (tomato, bean, soy) coffee, cacao, tea, fruits (banana, mango, coco, cashew) and palm oil.

Rice produces both straw and rice husks at the processing plant which can be conveniently and easily converted into energy. Significant quantities of biomass remain in the fields in the form of cob when maize is harvested which can be converted into energy. Sugar cane harvesting leads to harvest residues in the fields while processing produces fibrous bagasse, both of which are good sources of energy.

Energy Crops

Dedicated energy crops are another source of woody biomass for energy. These crops are fast-growing plants, trees or other herbaceous biomass which are harvested specifically for energy production. Rapidly-growing, pest-tolerant, site and soil-specific crops have been identified by making use of bioengineering. For example, operational yield in the northern hemisphere is 10-15 tonnes/ha annually. A typical 20 MW steam cycle power station using energy crops would require a land area of around 8,000 ha to supply energy on rotation.

Miscanthus-Elephant-Grass

Herbaceous energy crops are harvested annually after taking two to three years to reach full productivity. These include grasses such as switchgrass, elephant grass, bamboo, sweet sorghum, wheatgrass etc. Short rotation woody crops are fast growing hardwood trees harvested within five to eight years after planting. These include poplar, willow, silver maple, cottonwood, green ash, black walnut, sweetgum, and sycamore.

Industrial crops are grown to produce specific industrial chemicals or materials, e.g. kenaf and straws for fiber, and castor for ricinoleic acid. Agricultural crops include cornstarch and corn oil soybean oil and meal wheat starch, other vegetable oils etc. Aquatic resources such as algae, giant kelp, seaweed, and microflora also contribute to bioenergy feedstock.

Urban Wood Wastes

Such waste consists of lawn and tree trimmings, whole tree trunks, wood pallets and any other construction and demolition wastes made from lumber. The rejected woody material can be collected after a construction or demolition project and turned into mulch, compost or used to fuel bioenergy plants.

Biomass Energy in Indonesia

It is estimated that Indonesia produces 146.7 million tons of biomass per year, equivalent to about 470 GJ/y. Sources of biomass energy in Indonesia are scattered all over the country, but the biggest biomass energy potential in concentrated scale can be found in the Island of Kalimantan, Sumatera, Irian Jaya and Sulawesi.

Empty_fruit_bunches

Studies estimate the electricity generation potential from the roughly 150 Mt of biomass residues produced per year to be about 50 GW or equivalent to roughly 470 GJ/year. These studies assume that the main source of biomass energy in Indonesia will be rice residues with a technical energy potential of 150 GJ/year.

Other potential biomass sources are rubber wood residues (120 GJ/year), sugar mill residues (78 GJ/year), palm oil residues (67 GJ/year), and less than 20 GJ/year in total from plywood and veneer residues, logging residues, sawn timber residues, coconut residues, and other agricultural wastes.

Sustainable and renewable natural resources such as biomass can supply potential raw materials for energy conversion. In Indonesia, they comprise variable-sized wood from forests (i.e. natural forests, plantations and community forests that commonly produce small-diameter logs used as firewood by local people), woody residues from logging and wood industries, oil-palm shell waste from crude palm oil factories, coconut shell wastes from coconut plantations, as well as skimmed coconut oil and straw from rice cultivation.

The major crop residues to be considered for power generation in Indonesia are palm oil, sugar processing and rice processing residues. Currently, 67 sugar mills are in operation in Indonesia and eight more are under construction or planned. The mills range in size of milling capacity from less than 1,000 tons of cane per day to 12,000 tons of cane per day. Current sugar processing in Indonesia produces 8 millions MT bagasse and 11.5 millions MT canes top and leaves.

There are 39 palm oil plantations and mills currently operating in Indonesia, and at least eight new plantations are under construction. Most palm oil mills generate combined heat and power from fibres and palm kernel shells, making the operations energy self–efficient. However, the use of palm oil residues can still be optimized in more energy efficient systems.

Other potential source of biomass energy can also come from municipal wastes. The quantity of city or municipal wastes in Indonesia is comparable with other big cities of the world. Most of these wastes are originated from household in the form of organic wastes from the kitchen. At present the wastes are either burned at each household or collected by the municipalities and later to be dumped into a designated dumping ground or landfill.

Although the government is providing facilities to collect and clean all these wastes, however, due to the increasing number of populations coupled with inadequate number of waste treatment facilities in addition to inadequate amount of allocated budget for waste management, most of big cities in Indonesia had been suffering from the increasing problem of waste disposals.

With Indonesia’s recovery from the Asian financial crisis of 1998, energy consumption has grown rapidly in past decade. The priority of the Indonesian energy policy is to reduce oil consumption and to use renewable energy. For power generation, it is important to increase electricity power in order to meet national demand and to change fossil fuel consumption by utilization of biomass wastes. The development of renewable energy is one of priority targets in Indonesia.

The current pressure for cost savings and competitiveness in Indonesia’s most important biomass-based industries, along with the continually growing power demands of the country signal opportunities for increased exploitation of biomass wastes for power generation.

Agricultural Biomass in Malaysia

Malaysia is located in a region where biomass productivity is high which means that the country can capitalize on this renewable energy resource to supplements limited petroleum and coal reserves. Malaysia, as a major player in the palm oil and sago starch industries, produces a substantial amount of agricultural biomass waste which present a great opportunity for harnessing biomass energy in an eco-friendly and commercially-viable manner.

Peninsular Malaysia generates large amounts of wood and’ agricultural residues, the bulk of which are not being currently utilised for any further downstream operations. The major agricultural crops grown in Malaysia are rubber (39.67%), oil palm (34.56%), cocoa (6.75%), rice (12.68%) and coconut (6.34%). Out of the total quantity of residues generated, only 27.0% is used either as fuel for the kiln drying of timber, for the manufacture of bricks, the curing of tobacco leaves, the drying rubber-sheets and for the manufacture of products such as particleboard and fibreboard. The rest has to be disposed of by burning.

Palm Oil Industry

Oil palm is one of the world’s most important fruit crops. Malaysia is one of the largest producers and exporter of palm oil in the world, accounting for 30% of the world’s traded edible oils and fats supply. Palm oil industries in Malaysia have good potential for high pressure modern power plants and the annual power generation potential is about 8,000 GWh. Malaysia produced more than 20 million tonnes of palm oil in 2012 over 5 million hectares of land.

The palm oil industry is a significant branch in Malaysian agriculture. Almost 70% of the volume from the processing of fresh fruit bunch is removed as biomass waste in the form of empty fruit bunches (EFBs), fibers and shells, as well as liquid effluent. Fibres and shells are traditionally used as fuels to generate power and steam. Palm oil mill effluent, commonly known as POME, are sometimes converted into biogas that can be used in gas-fired gensets.

Sugar Industry

The cultivation of sugarcane in Malaysia is surprisingly small. Production is concentrated in the Northwest extremity of peninsular Malaysia in the states of Perlis and Kedah. This area has a distinct dry season needed for cost-efficient sugarcane production. Plantings in the states of Perak and Negri Sembilan were unsuccessful due to high unit costs as producing conditions were less suitable.

The lack of growth in cane areas largely reflects the higher remuneration received by farmers for other crops, especially oil palm. Over the past 20 years while the sugarcane area has remained at around 20000 hectares, that planted to oil palm has expanded from 600 000 hectares to 5 million hectares.

Other leading crops in terms of planted areas are rubber with 2.8 million hectares, rice with 670 000 hectares and cocoa with 380 000 hectares. Malaysia, the world’s third largest rubber producer, accounted for 1 million tons of natural rubber production in 2012. Like oil palm industry, the rubber industry produces a variety of biomass wastes whose energy potential is largely untapped until now.

Biogas from Agricultural Wastes

The main problem with anaerobic digestion of agricultural wastes is that most of the agricultural residues are lignocellulosic with low nitrogen content. To obtain biogas from agricultural wastes, pre-treatment methods like size reduction, electron irradiation, heat treatment, enzymatic action etc are necessary. For optimizing the C/N ratio of agricultural residues, co-digestion with sewage sludge, animal manure or poultry litter is recommended.

Agriculture_Waste_Biogas

Types of Agricultural Wastes

Several organic wastes from plants and animals have been exploited for biogas production as reported in the literature. Plant materials include agricultural crops such as sugar cane, cassava, corn etc, agricultural residues like rice straw, cassava rhizome, corn cobs etc, wood and wood residues (saw dust, pulp wastes, and paper mill waste)

Others include molasses and bagasse from sugar refineries, waste streams such as rice husk from rice mills and residues from palm oil extraction and municipal solid wastes, etc. However, plant materials such as crop residues are more difficult to digest than animal wastes (manures) because of difficulty in achieving hydrolysis of cellulosic and lignocellulosic constituents.

Codigestion of Crop Wastes

Crop residues can be digested either alone or in co-digestion with other materials, employing either wet or dry processes. In the agricultural sector one possible solution to processing crop biomass is co-digested together with animal manures, the largest agricultural waste stream.

In addition to the production of renewable energy, controlled anaerobic digestion of animal manures reduces emissions of greenhouse gases, nitrogen and odour from manure management, and intensifies the recycling of nutrients within agriculture.

In co-digestion of plant material and manures, manures provide buffering capacity and a wide range of nutrients, while the addition of plant material with high carbon content balances the carbon to nitrogen (C/N) ratio of the feedstock, thereby decreasing the risk of ammonia inhibition.

The gas production per digester volume can be increased by operating the digesters at a higher solids concentration. Batch high solids reactors, characterized by lower investment costs than those of continuously fed processes, but with comparable operational costs, are currently applied in the agricultural sector to a limited extent.

Codigestion offers good opportunity to farmers to treat their own waste together with other organic substrates. As a result, farmers can treat their own residues properly and also generate additional revenues by treating and managing organic waste from other sources and by selling and/or using the products viz heat, electrical power and stabilised biofertiliser.

Agricultural Wastes in the Philippines

The Philippines is mainly an agricultural country with a land area of 30 million hectares, 47 percent of which is agricultural. The total area devoted to agricultural crops is 13 million hectares distributed among food grains, food crops and non-food crops. Among the crops grown, rice, coconut and sugarcane are major contributors to biomass energy resources.

The most common agricultural wastes in the Philippines are rice husk, rice straw, coconut husk, coconut shell and bagasse. The country has good potential for biomass power plants as one-third of the country’s agricultural land produces rice, and consequently large volumes of rice straw and hulls are generated.

Rice is the staple food in the Philippines. The Filipinos are among the world’s biggest rice consumers. The average Filipino consumes about 100 kilograms per year of rice.  Though rice is produced throughout the country, the Central Luzon and Cagayan Valley are the major rice growing regions. With more than 1.2 million hectares of rain-fed rice-producing areas, the country produced around 16 million tons of rice in 2007. The estimated production of rice hull in the Philippines is more than 2 million tons per annum which is equivalent to approximately 5 million BOE (barrels of oil equivalent) in terms of energy. Rice straw is another important biomass resource with potential availability exceeding 5 million tons per year across the country.

With the passing of Biofuels Act of 2006, the sugar industry in the Philippines which is the major source of ethanol and domestic sugar will become a major thriving industry. Around 380,000 hectares of land is devoted to sugarcane cultivation. It is estimated that 1.17 million tonnes of sugarcane trash is recoverable as a biomass resource in the Philippines. In addition, 6.4 million tonnes of surplus bagasse is available from sugar mills. There are 29 operating sugar mills in the country with an average capacity of 6,900 tonnes of cane per day. Majority is located in Negros Island which provides about 46% of the country’s annual sugar production.

The Philippines has the largest number of coconut trees in the world as it produces most of the world market for coconut oil and copra meal. The major coconut wastes include coconut shell, coconut husks and coconut coir dust. Coconut shell is the most widely utilized but the reported utilization rate is very low.  Approximately 500 million coconut trees in the Philippines produce tremendous amounts of biomass as husk (4.1 million tonnes), shell (1.8 million tonnes), and frond (4.5 million tonnes annually).

Maize is a major crop in the Philippines that generates large amounts of agricultural residues. It is estimated that 4 million tonnes of grain maize and 0.96 million tonnes of maize cobs produced yearly in the Philippines. Maize cob burning is the main energy application of the crop, and is widely practiced by small farmers to supplement fuelwood for cooking.

Agricultural Wastes in the Middle East

Agriculture plays an important role in the economies of most of the countries in the Middle East.  The contribution of the agricultural sector to the overall economy varies significantly among countries in the region, ranging, for example, from about 3.2 percent in Saudi Arabia to 13.4 percent in Egypt.  Large scale irrigation is expanding, enabling intensive production of high value cash and export crops, including fruits, vegetables, cereals, and sugar.

The term ‘crop residues’ covers the whole range of biomass produced as by-products from growing and processing crops. Crop residues encompasses all agricultural wastes such as bagasse, straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. Wheat and barley are the major staple crops grown in the Middle East region. In addition, significant quantities of rice, maize, lentils, chickpeas, vegetables and fruits are produced throughout the region, mainly in Egypt, Syria, Saudi Arabia and Jordan.

Agricultural Wastes in the Middle East

Large quantities of agricultural wastes are produced annually in the Middle East, and are vastly underutilised. Current farming practice in the Middle East is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. These residues could be processed into liquid fuels or thermochemical processed to produce electricity and heat in rural areas.

Date palm is one of the principal agricultural products in the arid and semi-arid region of the world, especially Middle East and North Africa (MENA) region. The Arab world has more than 84 million date palm trees with the majority in Egypt, Iraq, Saudi Arabia, Iran, Algeria, Morocco, Tunisia and United Arab Emirates. Date palm trees produce huge amount of agricultural wastes in the form of dry leaves, stems, pits, seeds etc. A typical date tree can generate as much as 20 kilograms of dry leaves per annum while date pits account for almost 10 percent of date fruits. Some studies have reported that Saudi Arabia alone generates more than 200,000 tons of date palm biomass each year.

In Egypt, crop residues are considered to be the most important and traditional source of domestic fuel in rural areas. These crop residues are by-products of common crops such as cotton, wheat, maize and rice. The total amount of residues reaches about 16 million tons of dry matter per year. Cotton residues represent about 9% of the total amount of residues. These are materials comprising mainly cotton stalks, which present a disposal problem. The area of cotton crop cultivation accounts for about 5% of the cultivated area in Egypt.

A cotton field in Egypt

Energy crops, such as Jatropha, can be successfully grown in arid regions for biodiesel production. Infact, Jatropha is already grown at limited scale in some Middle East countries and tremendous potential exists for its commercial exploitation.

Technology Options

A wide range of thermal and biochemical technologies exists to convert the energy stored in agricultural wastes into useful forms of energy. Thermochemical conversion technologies like combustion, gasification and pyrolysis can yield steam, syngas, bio oil etc. On the other hand, the high volatile solids content in agro wastes can be transformed into biogas in anaerobic digestion plants, possibly by codigestion with MSW, sewage sludge, animal wastes and/and food wastes.

The cellulosic content in agricultural residues can be transformed into biofuel (bioethanol) by making use of the fermentation process. In addition, the highly organic nature of agricultural wastes makes it highly suitable for compost production which can be used to replace chemical fertilizers in agricultural farms. Thus, abundance of agro residues in the Middle East can catalyze the development of biomass energy sector in the region.

Biomass Harvesting

Biomass harvesting and collection is an important step involving gathering and removal of the biomass from field which is dependent on the state of biomass, i.e. grass, woody, or crop residue. The moisture content and the end use of biomass also affect the way biomass is collected. For crop residues, the operations should be organized in sync with the grain harvest as it occupies the centrestage in farming process.

biomass-harvesting

All of other operations such as residue management and collection take place after so-called grain is in the bin. On the other hand, the harvest and collection dedicated crops (grass and woody) can be staged for recovery of the biomass only. In agricultural processing, straw is the stems and leaves of small cereals while chaff is husks and glumes of seed removed during threshing.

Modern combine-harvesters generally deliver straw and chaff together; other threshing equipment separates them. Stover is the field residues of large cereals, such as maize and sorghum. Stubble is the stumps of the reaped crop, left in the field after harvest. Agro-industrial wastes are by-products of the primary processing of crops, including bran, milling offal, press-cakes and molasses. Bran from on-farm husking of cereals and pulses are fed to livestock or foraged directly by backyard fowls.

The proportion of straw, or stover, to grain varies from crop to crop and according to yield level (very low grain yields have a higher proportion of straw) but is usually slightly over half the harvestable biomass. The height of cutting will also affect how much stubble is left in the field: many combine-harvested crops are cut high; crops on small-scale farms where straw is scarce may be cut at ground level by sickle or uprooted by hand.

Modern combine-harvesters generally deliver straw and chaff together

Collection involves operations pertaining to gathering, packaging, and transporting biomass to a nearby site for temporary storage. The amount of a biomass resource that can be collected at a given time depends on a variety of factors. In case of agricultural residues, these considerations include the type and sequence of collection operations, the efficiency of collection equipment, tillage and crop management practices, and environmental restrictions, such as the need to control erosion, maintain soil productivity, and maintain soil carbon levels.