Potash from Spent Wash. Some observations on the CPCB directions of 19-01-2023

Potash from Spent Wash. Some observations on the CPCB directions of 19-01-2023
By Dr. Yashpal Singh

The Central Pollution Control Board has, through its orders issued vide no. P5-14099/4/2021-WQM-11-HO-CPCB-HO 87528755 dated 19-01-2023, directed the State Boards to consider the technology for recovery of FCO grade potash fertilizers from molasses based distillery spent wash as one of the options for achieving Zero Liquid discharge in molasses based distilleries. The order has also provided that such a permission would include also-

• That the sludge generated in the process may be used as cattle feed subject to its utility being certified by competent authority.
• Spent Liquor left after recovery of potash and inorganic salts may be used as a binder in cattle feed subject to its suitability.
• In case spent Liquor is not used as a bye product then the spent liquor has to be concentrated to minimum 60% solids and incinerated. It has been categorically stated that land application of spent liquor/spent wash shall not be considered.
• Other waste water streams such as spent lees, condensate, boilers/cooling tower blow down shall be treated through CPU for reuse in process.

The directions would indicate that the solid sludge generated during the process can be utilized as animal feed if found suitable and the spent liquors can be used as binder but in the absence of spent liquors being used as a binder, it has to be concentrated and incinerated.
The CPCB has referred to information available at www.csmcri.res.in/technologies/tech-details/8164 as a source of detailed technology. The said document contains a very sketchy treatment of the patented methodology but mentions that ‘Know how transfer of the process, license fee and other financial details would be made on specific request.” Full information on the technology is therefore not available and can be sourced only from the Central Salt and Marine Chemicals Research Institute. The CSMCRI however, provides that one commercial plant is operational at ADL’s 60 klpd distillery at Walchandnagar, Maharashtra and for a sixty KLPD distillery the cost would be between 25 to 30 crores towards plant and machinery with a payback period of less than 3 years. The process at Walchand nagar needs to be studied in details.

Through its order of 19-01-2023 as above, the CPCB has also once against reiterated that spent Liquor/spent wash shall not be used in land application. The CSMCRI may be asked to throw further light on the ways in which the sludge and spent Liquour could be utilized if not found suitable for cattle feed.

The process details have not been made available either by the CSMCRI or the CPCB but some information may be derived from the International Application published under the Patent cooperation Treaty (PCT). This document, in giving a detailed description of the invention, describes the following process steps.

1. Addition of lime in spent wash under stirring till pH of the slurry is greater than 12.
2. Centrifugation/filtration of the resultant slurry to obtain clear liquid and carbon rich slurry /sludge.
3. Purging of carbon dioxide gas in the supernatant/filtrate obtained from step-ii. pH is in the range of 8.0 to 9.0.
4. Centrifugation/filtration of the resultant slurry to obtain clear liquid and solid calcium carbonate.
5. Addition of sulphuric acid in the supernatant/filtrate obtained from step (iv) till a pH of less than 2.5 is achieved.
6. Centrifugation/filtration of the resultant slurry to obtain clear liquid and solid gypsum.
7. Addition of tartaric acid in the supernatant/filtrate obtained from step (vi) under stirring, followed by addition of sodium hydroxide to maintain pH in the range of 2.5 to 3.1.
8. Centrifugation/filtration of the resultant slurry to obtain a clear liquid and solid Potassium bitartartate.
9. Addition of calcium carbonate in the supernatant/filtrate obtained from step (viii) under stirring, till the pH in the range of 5 to 6 is achieved.
10. Centrifugation/filtration of the resultant slurry to obtain clear liquid and solid calcium tartarate.
11. Discharging the supernatant/effluent obtained from step (x) as process effluent for subsequent environmental remediation/water recovery/salt reclamation.
12. Addition of Calcium oxide/hydroxide/carbonate and Phosphoric acid in aqueous suspensious of the potassium bitartarate obtained from step (viii) under stirring.
13. Centrifugation/filtration of the resultant slurry to obtain clear liquid and solid calcium tartarate.
14. Evaporation/cooling of the supernatant/filtrate obtained from step (xiii) to produce solid non potassium phosphate crystals.
15. Addition of the calcium tartarate solids obtained from step (x) and step (xiii) to the aqueous solution of sodium carbonate, under stirring.
16. Centrifugation/filtration of the resultant slurry to obtain clear liquid and solid calcium carbonate.
17. Addition of disodium tartarate solution obtained as supernatairt/filtrate in step (xvi) to the reaclion in step (vii) in place of tartaric acid and adjusting pH with sulphuric acid.
18. Recycling the solid calcium carbonate obtained from step xvi in the reaction process of step (xii).

The water and energy requirements in the various step are not known. Significant quantities of sludges are likely to be generated. The quantity, nature and composition of sludges is not known and the process does not recommend use of sludges as cattle feed as directed by the CPCB. Sludge handling and disposal needs to be better understood. Details on the nature and quantity of effluents are also not available. The CPCB suggests that the lean spent wash shall be concentrated to more than 60% solid content to either produce de-potashed vinasses (65 to 70% solids content) or shall be disposed through composting /concentration incineration routes. The use to which De-Potashed vinasses could be put have not been suggested and may need to be looked into. The Fertilisation potential of De-potashed vinasses may also need to be examined by the CPCB.
The CPCB has again directed that land application of spent Liquour/spent wash shall not be considered. This may however need to be reexamined and the CPCB may be requested to examine and open itself to sustainable technologies. Individual industries may only have a right to appeal against these directions, once the State Board issues directions to individuals. The State Board, if it feels that the implementation of these orders causes undue hardship, refer this matter to the State Government and in case the State Government agrees with the State Board request the State Government to refer to the MoEF&CC. The directions of the MoEF and CC could be final.
While material recovery from wastes is a desirable and viable option and potash recovery from spent wash is an age old recommendation in handling spent wash, CPCB and CSMCRI may for a better understanding of the whole process wish to examine some of the following issues before implementation:

• The costing of indigenous potash from other technologies/imported potash vis a vis potash generated from spent wash.
• The rate of return expected in the investment. The Financial cost benefit analysis.
• The quantity and nature of sludges produced and possible disposal pathwasys. The acceptability of sludges as animal feed or manure.
• The nature and quantity of effluents discharged and their probable uses and disposal alternatives.
• The nature and quantity of de-potashed vinasses and its probable uses.
• The acceptability of spent liquors after recovery of potash as a binder in cattle feed and alternative uses if not suitable.
• The cost benefit of concentration incineration, environmental sustainability and green house impacts of the process as compared to other available technologies like fertigation, OTCLA, Sodic land reclamation based on a life cycle assessment analysis, energy, carbon and water foot prints.
• The price and marketing competitiveness the co-products .
• The specific technical reasons why land application of spent liquor/spent wash is not being allowed here.

It would also appear important that the existing facility at Walchandnagar be visited by industry representatives to get a better understanding of the processes and viability/sustainability.

Also See:

• Management of Spent Wash in Distilleries
• Using Distillery Spent Wash in Sodic Land Reclamation
• Using Distillery Spent Wash For One Time Controlled Land/Presown Land Application