Technologies for the treatment of molasses based distillery effluents

Article Index

Code No: TMS062 Price: 1200 Category: Foods & Agriculture: Sugar Industry By Products

Table Of Contents :

  • Introduction,
  • Need for treating Distillery Effluent,
  • Effluent generation,
  • Effluent Characteristics,
  • Technologies for the treatment of Distillery Effluent,
  • New Processes for the treatment of Distillery Effluent,
  • World trends, Assessment of options,
  • observations and Recommendation.
  • Annexures Equipment,
  • know-how Suppliers for the treatment of Distillery Effluents,
  • List of organisations contacted during the survey, international organisations

 


 

 


 

1. Objectives

The primary objective of this report is to present the following aspects of the “Technologies for the Treatment of Molasses based Distillery Effluents”:

a. The relationship and the importance of the selected subset of technology to the broad one to which is belongs;
b. The current status of the technology in the World and our Country;
c. Assessment of the technology and options available to India;
d. The economic aspect of technologies along with their feasibilities which lead to the preferred options(s);
e. Impact of the preferred option by itself, its linkages to the broad area of technology and spin offs. And
f. Identification of agencies/group/individuals and suggested action plan.

2. Methodology

The report is based on the findings of mail survey and field visits and the information collected through desk research.

3. The Need for Treating Distillery Effluent

The Indian distillery industry produces alcohol from molasses, a by-product of sugar manufacture. During 1990-91, India produced about 1,025 million liters of alcohol, India produced about 15 liters of effluent is produced per liter of alcohol, India produced about 15,375 million liters of distillery effluent during 1990-91. The effluent is foul smelling, dark brown coloured and has a very high BOD (Biochemical Oxygen Demand – a measure of pollution).

The most damaging effect of distillery effluent on a water stream is caused by high concentration of readily decomposable organic matters present in the effluent which case rapid depletion of the oxygen content of water and render it totally unit for propagating aquatic life and for drinking and other purposes. The receiving stream assumes an unsightly appearance. The colour persists over a long stretch in the stream and gives an impression that the stream is highly polluted.

As on 8/7/91, India had 212 distilleries (about 10% of the distilleries are considered to be non-functional/bottling units). Of the above, 44 distilleries had completed and 49 distilleries had started the construction of Effluent Treatment Plants (ETPs). It is reported that several units are doing spade work prior to commencement of construction of ETPs.

4. The Importance of the Alcohol Industry

In 1931, India had 29 sugar factories which produced about 1.2 lakh tonnes of sugar and about 50,000 tonnes of molasses. The number of sugar factories increased dramatically to 135 by 1935-36 taking sugar production to 9.34 lakh tonnes and molasses production to 3.36 lakh tonnes. The country was not prepared for such a sudden increase in the production of molasses. This was one of the factors which induced the Government to encourage alcohol production using molasses. Thus, molasses which was considered a waste during the early years of the Indian sugar industry became a valuable by-product used in the manufacture of alcohol. In the absence of distillery industry, it is difficult to comprehend the extent of environmental damage that would have been caused by molasses. Without the distillery industry the Indian sugar industry could not have grown to its present size.

The distillery industry plays an important role in the Indian economy by providing alcohol. As on 31/3/91, India had 212 distilleries with an installed capacity of 1933 million liters of alcohol per annum. The production of alcohol has been showing a steady increase over the years. During 1990-91, India produced 1,025 million liters of alcohol. India’s sugar production is expected to increase to 17 million tonnes by the end of the current decade (13.3 million tonnes during 1991-92). The expected corresponding rise in molasses output will help to improve alcohol availability considerably.

Of the total alcohol output, about 50 to 52 percent is utilized for industrial purposes and the balance is utilized for potable purposes.

The importance of alcohol as a feedstock for the manufacture of organic chemicals has been steadily improving. The current foreign exchange scarcity together with the mounting crude oil import bill is likely to further increase the reliance on alcohol for the manufacture of organic chemicals.

The estimated demand for some of the important organic chemicals (alcohol route) by the turn of the century and the resultant overall demand for alcohol are follows:

2-thyl Hexanol 52,500 tonnes
N-butanol 46,700 tonnes
Vinyl Acetate 44,000 tonnes
Styrene 120,000 tonnes
Acetone 64,700 tonnes
Alcohol

 

2,000 million liters


 

For the State Governments, alcohol is an important source of revenue. Between 12 to 14 percent of the States own revenues come from the State excise duties levied on potable alcohol. In addition, on inter-state sales, Central sales tax and various kinds of fees are also levied                                                                                                                                                                          Back


 

5. Effluent Generation

The wastewater (effluent) generated in a distillery is of two types viz. process wastewater and non-process wastewater. The non-process wastewater is comparatively pure and as such can be recycled. The process wastewaters of a distillery consist of fermenter sludge, spent lees and spent wash. Spent less is usually recycled. Fermenter Sludge has a higher Biochemical Oxygen Demand (BOD) and a lower volume as compared to spent wash. It is advisable to dewater fermenter sludge and dispose it off without mixing it with spent wash as it will increase the BOD of the receiving stream.

The amount of effluent (wastewater) generated in a distillery depends upon the extent of process water used and the technology adopted for the manufacture of alcohol. Most of the Indian distilleries are of the conventional batch type in which about 15 KL of spent wash is produced per KL of alcohol. In the modern continuous type distillery, spent wash generation is of the order of 10 to 12 KL/KL of alcohol (5 to 6 KL/KL of alcohol if a reboiler is used).

6. Characteristics of Indian Distillery Effluent

Alcohol can be produced from a number of substrates such as cane molasses, beet molasses, starchy substances. The characteristics of spent wash depend upon the substrate used, quality of the substrate and the manufacturing process adopted. In India, alcohol is primarily produced from cane molasses. The cane molasses spent wash has a higher BOD level as compared to beet molasses spent wash and as such more difficult to treat as compared to beet molasses spent wash. Among countries using cane molasses for the production of alcohol, the Indian cane molasses and, in turn, spent wash are the worst in quality with respect to environmental parameters. He spent wash produced by the Indian distilleries is one of the most difficult distillery effluents to treat.

Spent wash has a temperature of about 90C to 100C with a smell of burnt sugar. It is highly acidic (pH between 4.3 and 5.3) and dark brown in colour. It contains a high percentage of dissolved organic and inorganic matter with a BOD in the range of 45,000 to 60,000 mg/l.

7. The Requirements of Effluent Quality (After Treatment)

Under the The Environmental (Protection) Act, the Government has specified Minimum National Standards (MINAS) for different industries taking into account the characteristics of the effluent and the minimum acceptable quality of the treated effluent. The standards for the distillery industry stipulate that the treated effluent should have a pH in the region of 5.5-9.0, maximum BOD level of 30 mg/I for disposal into inland surface waters and 100 mg/l for disposal on land. It also states that all efforts should be made to remove colour and unpleasant odour as far as practicable.

8. Technologies For the Treatment of Distillery Effluent

Industrial effluents may be treated by a number of methods, either singly or in combination. The selection of the effluent treatment route or approach is dependent upon:-

- Effluent characteristics (before treatment)
- Requirements of effluent quality (after treatment)
- Other factors such as operating economics, initial/capital cost, land and power requirement, ease of operations etc.

In general, physico-chemical treatment of distillery spent wash has met with litter success. There have been some attempts to use spent wash as substrate for yeast growth or for biochemical production. It is reported that the remaining BOD content after using spent wash for yeast growth or biochemical production is still high necessitating further treatment which would be difficult as all easily degradable organics are already consumed.

Concentration of spent wash and its usage as an animal feed additive is a common practice among countries producing alcohol from beet molasses (Europe, North America). This practice has not found acceptance because Indian spent wash contains a higher percentage of inorganic substance which produce a laxative effect if the consumption of feed is not closely monitored. Besides, in Indian conditions, the cost of concentration of spent wash is prohibitive.

The following technologies have been discussed in detail:

  •   Anaerobic Lagooning
  •   Methane Recovery Processes (Biomethanation)
  •   Incineration Processes
  •   Composting
  •   Effluent Treatment with Aquaculture
  •   Vermifilter Process
  •   DIEG Process
  •   Hydrolysis and concentration

9. World Trends

Anaerobic digestion (biomethanation/methane recovery processes), concentration of spent wash for usage as a animal feed ingredient, concentration followed by incineration, land application, composting etc. are the common methods of treating distillery spent wash in different parts of the World.                                                                                                  Back


10. Assessment of Options

The options available for the treatment of distillery effluent have been compared using a set of evaluation criteria relevant in the Indian context. The details are presented in the Table give below.

11. Observations and Recommendation

As of now, there is no adverse technological gap between India and the rest of the World in the area of distillery effluent treatment. This observation has been corroborated by the majority of respondents to the survey.

The recommendations are as follows:

(A) After the methane recovery process, the effluent is subjected to secondary treatment usually by aerobic processes. The incremental cost of operating aerobic process reduced considerably the savings generated by the methane recovery process. The methane recovery process can become an attractive economic proposition for the distilleries, and thus induce speedier implementation of newer ETPs, if the aerobic process is avoided or replaced by a more economical proposition. Several eminent scientists have recommended utilization of spent wash for irrigation purposes after primary treatment by methane recovery process.. a study ha to be carried out to ascertain the suitability of spent wash for irrigation.

Assessment of Options

Technologies

Criteria Methane Recovery Incineration (Sparnnihilator) Composting (Bioearth)

End result

- BOD(mg/l)


- Colour problem

- Odour nuisance

~1,000


Continues

Nil

~2,500
(condensate)

Nil

Nil

Claimed to be <30

Nil

Nil

Land requirement 2-3 acres <0.5 acres 25-30 acres
Capital cost ~Rs. 2.60 crores ~Rs. 3.75 crores ~Rs. 1.50 crores
Cost of operations Least High (Note 1)
Power requirement High High Nominal
Indigenous avbity of Eqpmt/know-how Yes Yes (Note 2)
Ease of operation Same degree as composting Comparatively more difficult Same degree as methane recovery
Manpower requirement Nominal Nominal High


Note:
1. The Economics of composting depend upon availability of press mud and saleability of compost at a good price.
2. Aerotiller is presently imported-expected to be indigenized in the near future.
3. Methane recovery process includes secondary treatment by aerobic processes.
4. The value are for a 50 KLPD distillery.
5. Capital cost excludes cost of land.
6. Please refer to chapters 5 & 8 for details.


(B) There are no proven viable processes for the recovery of potash from ash- a by-product of the incineration process. The economics of the incineration process would improve considerably if a suitable process is identified for recovering potash from ash.

(C) Composting (Bioearth) can become a viable effluent treatment route if(i) the cost of culture is brought down to reasonable levels (ii) the compost is popularized and sold at a higher price. A study is required to evaluate the beneficial effects of using compost produced from spent wash.

(D) The rising input costs and fiscal imposts have adversely affected the health of the distillery industry. The capital cost of an ETP is quite high. It is almost same or more than that of the main plant. Many of the distilleries are small and old. The Government should do away with all types of taxes and excise duties on ETPs so as to reduce the capital cost ETPs. Common effluent treatment facilities should be set up for treating the effluents of smaller units.

(E) The present scheme of allowing high depreciation on effluent treatment plants can be of immediate benefit to profitable units. For units which are financially weak incentives should be provided in the form of lowering of promoter’s margins, longer repayment period, lower interest rates etc.

(F) At least one model plant of each type of effluent treatment system in the country should be designed as demonstration plant. This will help in the improvement of technologies, removing apprehension regarding different technologies in the minds of the Government agencies and the industry. The results noted at such demonstration projects could act as guidelines in laying down the effluent standards and estimating the cost of effluent treatment while revising the price of alcohol.


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