ICRISAT develops sweet sorghum for ethanol production (12 August 2004)

 

Encouraged by the positive response from the Andhra Pradesh Chief Minister YS Rajasekhar Reddy, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is strengthening its collaboration with partners to promote sweet sorghum varieties, hybrids and technologies to extract alcohol from the crop.

Dr William Dar, Director General of ICRISAT, said that the sweet sorghum varieties, hybrids and technologies developed by the Institute hold high promise for the farmer of the semi-arid tropics. The ICRISAT varieties can grow with less water and thus can be grown in the drylands of the world. In addition to the grain, the crop can be used to produce alcohol (ethanol) in a more environment friendly manner compared to sugarcane. The ethanol can be used to blend with petrol and diesel for producing Gasohol.

“ICRISAT's strategy is two-pronged,” Dr Dar said. “Using our sorghum breeding skills we are developing hybrid parents and varieties that are good for ethanol production. We are also helping in the incubation of the production technology for ethanol from sweet sorghum.”

ICRISAT initiated a program for the identification and development of sweet-stalked and high-biomass sorghum hybrid parents and varieties in 2002. Promising lines such as ICSB 631 and ICSB 264 among the seed parents; and Seredo, ICSR 93034, S 35, ICSV 700, ICSV 93046, E 36-1, NTJ 2 and Entry 64 DTN among the varieties/male parents were identified for their high stalk sugar content. The sugar percentage in these seed parents and varieties ranged from 16.8% to 21.6%. Four of these lines, S 35, ICSV 700, ICSR 93034 and Entry 64 DTN are being evaluated in All India Coordinated Sorghum Improvement Program (AICSIP).

A Special/Sweet Sorghum Hybrid (SSH) 104 developed from ICSA 38, an ICRISAT-bred male-sterile (seed) parent and SSV 84, a male parent bred in India is being recommended for release for commercial cultivation. The national sorghum program, through extensive testing in AICSIP, released a sweet-stalk sorghum variety SSV 84 in 1992/93 for general cultivation. The wide variability available in germplasm and hybrid parents for the traits related to ethanol production such as percentage of sugar, sucrose and Brix (a measure for sugar content in liquids) and high stalk yield offers bright scope for the development of high stalk yielding sugar-rich varieties and hybrids.

The Agri-Business Incubator (ABI) at ICRISAT has signed a Memorandum of Agreement (MOA) with Rusni Distilleries Pvt. Ltd. of Hyderabad to incubate the ethanol production technology using these sweet-stalk sorghum lines. ICRISAT signed another MOA with Vasanthadada Sugar Institute (VSI), Pune, for identification/development of improved sweet sorghum varieties, characterizing the juice, ethanol quality and quantity, and also providing process technology to Rusni Distilleries through ABI.

ICRISAT is hopeful that private seed companies in India would complement the efforts of the national program in the development of location-specific hybrids with sugar-rich high stalk yield (using hybrid parents developed in ICRISAT and the national program) to meet the expected increased demand for raw material for ethanol production in the years to come.

Multiple benefits

Sweet sorghum ( Sorghum bicolor ) is similar to grain sorghum with a sugar-rich stalk, almost similar to sugarcane. Besides having wide adaptability, rapid growth and high sugar accumulation and biomass production potential, sweet sorghum, is tolerant to drought, water logging, soil salinity and acidity toxicity. It has great potential for jaggery, syrup and alcohol (most importantly Gasohol, which is ethanol blended with petrol) production. The sugar content in the juice extracted from sweet sorghum varies from 16-23% Brix.

In recent years, there is increased interest in the utilization of sweet sorghum for ethanol production in India as its growing period of about four months, and water requirement of 8,000 cubic meters (cu m) over two crops are one-fourth that of sugarcane, which has a growing period of 12 to 16 months and a water requirement of 36,000 cu m per crop. In addition, sweet sorghum is better suited for mechanized crop production and seed propagation.

According to a pilot study conducted by VSI, sweet sorghum is the best alternative raw material, which can supplement the use of sugarcane in ethanol production. At 5,600 liters per hectare per year (over two crops, at 70 tons per hectare of millable stalk per crop at 40 liters per ton), the ethanol production from sweet sorghum compares well with the 6,500 liters per ha per crop for sugarcane (at 85-90 tons per hectare of millable cane per crop at 75 liters per ton).

According to estimates made by National Research Center for Sorghum (NRCS), Hyderabad, the per liter cost of production of ethanol from sweet sorghum is Rs 13.11 (at Rs 500 per ton of stalk), when compared to Rs 12.55 (at Rs 1,600 per ton of stalk) from sugarcane molasses. However, the increased cost of production of ethanol from sweet sorghum is more than compensated by grain yield of 1 ton per hectare (which can be used as food or feed) and the superior quality of ethanol. The really significant advantage is that the production of ethanol from sweet sorghum is environment friendly since it uses the non-molasses route.

Further, the stillage from sweet sorghum after the extraction of juice has a higher biological value than the bagasse from sugarcane when used as fodder for animals, as it is rich in micronutrients and minerals. It could also be processed as a feed for ruminant animals. Apart from these, stillage contains similar levels of cellulose as sugarcane bagasse, therefore has a good prospect as a raw material for pulp product.

In India, the estimated requirement for ethanol to blend with petrol (at 10%) is about 1000 million liters, and for blending with diesel (at 5%) another 3000 million liters. Total ethanol requirement including other purposes is 5000 million liters. The possible ethanol production from available sugarcane molasses (8.2 million tones) and other sources is 2000 million liters. This leaves a gap of 3000 million liters of ethanol. The deficit of ethanol can be made good if sweet sorghum cultivation is promoted for ethanol production.

For more information, contact Dr Belum V Subba Reddy at b.reddy@cgiar.org .