Co-processing of wastes in cement kiln is emerging as one of the environment friendly alternative disposal method in the recent years. Distillery spent wash has high organic content and dissolved inorganic solids which require careful handling and proper disposal to avoid damage to the environment. Presently it is being used on to land to provide nutrient value, though it contaminates both the ground water and surface water sources, as most often it is practiced in non-scientific manner. The adverse effect of spent wash disposal, via bio-composting is magnified during the rainy season. Concentration of spent wash in multiple effect evaporators and its subsequent incineration is also being practiced. However, it is not found technically and economically feasible in majority of cases. Hence, Central Pollution Control Board (CPCB) proposed, co-processing of concentrated spent wash in cement kiln.
There are around 400 distillery units in India, with a total production capacity of about 3800 million litres of alcohol. Average generation of spent wash is around 8-12 litres / litre of alcohol produced, depending on continuous or batch process and quality of molasses used etc.
Thus the co-processing of spent wash concentrate in cement kiln has following benefits:
While in case of incineration, residuals require to be disposed suitably.
A typical physico-chemical characteristics of distillery spent wash is depicted at Annexure- I.
The production of cement in India is about 200 Million Tonnes per annum. The country, therefore, has potential to utilize spent wash concentrate from the distilleries for co-processing in cement industry.
Based on satisfactory performance of trial run, CPCB has granted regular permission for Co-processing of few categories of wastes and 25 cement manufacturing units in various States have already started co-processing of permitted wastes. Further, trial studies are undertaken for various other wastes.
Despite of co-processing having inherent advantages, a careful & scientific study of trial run for spent wash with potential to damage environment during transportation, handling, storage and processing was done. The desired handling, transport and storage applicable to distillery spent wash have been described in the following sub-sections.
Distillery spent wash is not categorized as a hazardous waste, still co- processing of the same needs to be handled in an environmentally sound manner, avoiding the possibilities of environment contamination. These guidelines includes standard methodology for submission of application for streamlining the entire processing mechanism taking all essential safeguards along with the delivery of approvals in a reasonable time frame.
"Occupier" in relation to any factory or premises, means a person who has, control over the affairs of the factory or the premises and includes in relation to spent wash;
The occupier shall take all adequate steps while handling spent wash to:
(a) Contain contaminants and prevent leakages/spillages and limit their consequences on the environment; and
(b) Provide persons working on the site with the training, equipment and necessary information.
The concerned distillery shall obtain separate permission from SPCB/PCC for co processing of spent wash concentrate in the prescribed formats. All other consents/authorization under the relevant acts shall also be valid for the industry.
The spent wash shall be collected, stored and co-processed only in the cement industries that have obtained necessary permission from the State Pollution Control Board/ Pollution Control Committee for the purpose in the prescribed format (Annexure II & III).
Safe transportation of spent wash to the site for co-processing in cement industry is a collective responsibility of the waste generator and processor as provided at Annexure - IV.
The occupier /co-processor/ cement industry may store the permitted quantity of spent wash concentrate for co-processing and shall maintain a record of transfer, storage and co-processing of such wastes and make these records available for inspection
The detailed storage requirements for spent wash concentrate have been provided at Annexure IV.
Different feed points can be used to inject the spent wash concentrate into the cement production process. The most common ones are:
- Main burner at the rotary kiln outlet end
- Pre-calciner
Fig. : A typical controlled injection system for spent wash parallel to that of pulverized coal, via the diesel firing line provided for start up of the kiln
Appropriate feed points have to be selected according to the physical & chemical characteristics of the spent wash used.
The findings of the trial runs at M/s Rajashree Cement Plant, Gulbarga, Karnataka and M/s Wadi Cement Works, Gulbarga, Karnataka suggest that disposal of spent wash concentrate through co-processing route is suitable and preferred way. The typical proximate analysis, ultimate analysis, chemical analysis and heavy metals and volatiles in spent wash are given at Annexure V. Co-processing of spent wash does not seem to influence clinker / cement quality or change kiln behavior subject to it when fed in limited and controlled low proportion of 3 - 5% of heat/coal substitution. Further trial runs may be attempted for co-processing of higher percentages.
Co-processing plants shall be designed, equipped, built and operated in such a way that the gas resulting from the co-processing is raised in a controlled and homogeneous fashion and even under the most un-favorable conditions, to a temperature of 950°C with a residence time of two seconds.
Co-processing plants shall operate in an automatic system to prevent spent wash feed, whenever emission monitoring show that any emission limits value is exceeded due to disturbances or failures of air pollution control devices.
Co-processing plants shall be designed, equipped, built and operated in such a way as to prevent emission into the air giving rise to significant ground level air pollution; in particular; exhaust gases shall be discharged in a controlled fashion by means of a stack, the height of which is calculated in such a way as to safeguard human health and the environment.
The management of the co- processing plant shall be in the hands of a skilled person, competent to manage the concentrated spent wash in an environmentally sound manner
The dust emission is the main pollutant emanated from cement industry which is unlikely to change during co-processing of spent wash with moisture content. Generally cement kilns are equipped with Electro Static Precipitator or Bag House to control the particulate matter emission. Any acidic gases formed during co-processing are likely to be scrubbed by the raw material (lime stone) being of an alkaline nature and are incorporated into the cement clinker. However, cement industry has to ensure compliance of particulate matter emission standards during co-processing as prescribed in consent conditions issued by SPCB/PCC. For other pollutants i.e. HCl, SO2, CO, TOC, NOx, Cd + Tl + their compounds, Hg and its compounds, Sb + As + Pb + Co + Cr + Zn + Cu + Mn + Ni + V + their compounds, the emission during co-processing should not exceed the base line emissions i.e.; during pre co-processing phase of trial run.
The emission standards for particulate matter prescribed for cement kiln by the concerned State Pollution Control Board shall be applicable during co-processing in cement kiln also. For other pollutants i.e. HCl, SO2, CO, TOC, NOx, Cd + Tl + their compounds, Hg and its compounds, Sb + As + Pb + Co + Cr + + Zn + Cu + Mn + Ni + V + their compounds, the emission during co-processing should not exceed the base line emissions i.e.; during pre co-processing phase of trial run.
The continuous measurement of particulate matter emission shall be carried out at co-processing plant and the emission data shall be submitted to SPCB/PCC as well as CPCB. As per directions of SPCB monitoring of other parameters will be done by the cement plant.
General Physico-Chemical characteristics of distillery spent wash
| Sl. No. | Characteristics | Value |
| 1 | Colour | Dark brown |
| 2 | Odour | Unpleasent burnt sugar |
| 3 | Specific gravity(g/cc) | 1.2 |
| 4 | pH | 3.80 |
| 5 | EC(dS/m) | 43 |
| 6 | TDS(mg/L) | 91700 |
| 7 | TSS (mg /L) | 26560 |
| 8 | TS (mg/L) | 118260 |
| 9 | BOD (mg/L) | 43000 |
| 10 | COD (mg/L) | 128000 |
| 11 | Organic Carbon (%) | 3.7 |
| 12 | Nitrogen (mg/L) | 1460 |
| 13 | Phosphorus (mg/L) | 326 |
| 14 | Potassium (mg/L) | 14300 |
| 15 | Sodium (mg/L) | 356 |
| 16 | Calcium (mg/L) | 6800 |
| 17 | Magnesium (mg/L) | 4384 |
| 18 | Chloride (mg/L) | 10650 |
| 19 | Sulphate (mg/L) | 3000 |
| 20 | Copper (mg/L) | 2.8 |
| 21 | Manganese (mg/L) | 9.2 |
| 22 | Iron (mg/L) | 24.6 |
| 23 | Zinc (mg/L) | 7.8 |
| 24 | Carbonates (mg/L) | Nil |
| 25 | Bicarbonates (mg/L) | 1530 |