Sugarcane is one of the most important cash crops in the tropics & subtropics. It is the 3rd most-produced crop globally, spanning more than 90 countries. With five million-hectare cultivation and 352 million tonne cane production, India is the 2nd largest producer of sugarcane, after Brazil. It is common knowledge that the teaspoon of sugar that sweetens our tea and coffee comes from sugarcane. What many do not know is that ethanol or ethyl alcohol produced from sugarcane is an important biofuel that is growing in popularity.

Sugarcane based alcohol distilleries generate 8-15 litres of effluent (spent wash/vinasse) for each litre of ethanol produced. The spent wash is slightly viscous, dark brown coloured liquid with an unpleasant odour and very high pollutant loading. It is for this particular effluent that the Central Pollution Control Board (CPCB) has designated alcohol distilleries under the ‘Red’ category, i.e. industrial Sectors having a Pollution Index score of 60 and above.

Globally practised spent wash management methods are (i) ferti-irrigation, (ii) bio-composting, (iii) incineration etc. (frequently with bio-methanation as an intermediate step). Among these, ferti-irrigation & bio-composting have been widely practised across the sugarcane producing countries with the aim to take advantage of the nutrient value of constituent K, N and P. However, concerns related to groundwater contamination & soil degradation over long exposure have resulted in stringent regulations /altogether discontinuation of these practices.

Ministry of Environment, Forest and Climate Change, Government of India, is implementing the “Zero Liquid Discharge” (ZLD) norm for alcohol distilleries through evaporation—incineration route. This approach requires high financial investments and suffers from various operational issues viz., scaling, refractory furnace failure, boiler choking & corrosion, frequent stoppages/ shutdowns for descaling & maintenance etc.

Transforming problem into opportunity - technology solution from CSIR-CSMCRI

The spent wash contains appreciable amounts of potassium – an important agri-nutrient. India imports the entire requirement of potash fertilizer – ca. 2.96 million t K2O in 2017-18 (MoP only), whereas domestic molasses-based alcohol distilleries discharge about 0.29 million t K2O annually through the effluent.

In 2015, under CSIR’s K-TEN project, CSIR-Central Salt and Marine Chemicals Research Institute (Bhavnagar, Gujarat) started to explore the possibility for utilization of distillery effluent (spent wash) as a potential resource for potash fertilizer and developed process know-how for the production of fertilizer grade potash from spent wash along with recovery of residual organics. In the course of further collaboration with M/s. Chem Process Systems Private Limited (Sanand, Gujarat), the know-how has been integrated into a complete technological solution for the valorization of spent wash while complying with the statutory ‘Zero Liquid Discharge’ norm.

The first 1st commercial unit, based on CSIR-CSMCRI’s Spent Wash Management (SWM) technology, has been installed at Aurangabad Distillery Limited (60 klpd distillery at Walchandnagar, Maharashtra).

This IPR protected technology [granted patents: IN 318659; US 10683211; US 10793480] can produce FCO grade potash fertilizers of choice (K2SO4, KNO3, KH2PO4 etc.).

Broad product profile is:

1. Indigenous Potash fertilizer (FCO) – critical agro-input, partial self-reliance in terms of national potash requirement, import substitution.
2. Desalted Spent Wash Organics – binder for cattle feed formulation as an alternative to molasses. Efficacy, palatability, animal physiology & productivity evaluation and feed plant trial – National Dairy Research Institute, Karnal (HR); National Dairy Development Board, Anand (GJ); Sabar Dairy, Himmatnagar (GJ).
3. Water – suitable for recycling in process, would eliminate the possibility of groundwater table contamination and riverine eco-system damage.

Likely benefits to the stakeholders:

• Distilleries – more revenue & profit (payback < 3 y); enhancement of ethanol production capacity due to delinking of distilleries from sugar mills, since the former would no longer require any press-mud for spent wash management,
• Farmers – faster & enhanced income realization, since sugar mills/distilleries would be able to clear cane arrears more quickly due to improved cash flow and profitability,
• GoI/ Policy - augmented ethanol production will help in addressing the fuel blending target,
• GoI/ Fiscal - additional revenue for government exchequer by way of taxes realized from the sale of additional products

Honours & Recognitions

Honourable Prime Minister of India issued a message of appreciation for CSIR-CSMCRI’s ‘Zero Waste’ spent wash management technology. This technology has been selected for the ‘CSIR Technology Award for Innovation – 2019’ & the award was given away by the Honourable President of India on 26th September 2019. This technology has also been awarded by IGCW-2019 (Knowledge Community – Researcher) and Gujarat Innovation Society (Hercules). NRDC has selected this technology for National Innovation Award – 2019.

This W2W technology is unique and unrivalled, as it not only achieves Zero Liquid Discharge (ZLD) for the distilleries but also generates valuable by-products which are import substitute and earn high profits. This innovative solution also addresses the issues and limitations of the currently prevailing technologies viz., bio-composting, bio-methanation and incineration.

Adoption of this globally unique technology will significantly improve the operational, financial and ecological sustainability of alcohol distilleries.

Pratyush Maiti
Senior Principal Scientist, CSIR-CSMCRI