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Distilleries can be categorized as highly polluting industries generating large volumes of wastewater known as spent wash. Elimination of pollutants and colour from distillery effluent is becoming increasingly important, as such effluent leads to extensive soil and water pollution due to its high BOD and COD content and the presence of toxic materials such as phenolic compounds.
Distillery wastewater can also have a very low pH. Distilleries generate wastewater at various stages in the process, such as distillation, condenser cooling, fermenter cooling, fermentation and washing stages. The most significant amounts of this effluent is produced at distillation and condenser cooling stages. The characteristics of the wastewater generated depend on the feed stock used.
Distilleries are agro-based industries, which utilize agricultural products such as sugar cane juice, sugar cane molasses, sugar beet molasses, corn, wheat, cassava, rice, barley as raw materials due to the big volume of effluent and presence of certain recalcitrant compounds, the treatment of this stream is rather challenging by conventional methods.
Distillery effluent is characterized by dark brown color, acidic pH, high temperature, low dissolved oxygen (DO), high biochemical oxygen demand (BOD) and chemical oxygen demand (COD) Raw distillery wastewater has the characteristics such as pH 4.0–4.6; chemical oxygen demand 85,000–110,000 ppm; total dissolved solids 85,000–110,000 ppm and biological oxygen demand 25,000–35,000 ppm. Distillery effluent also contains significant amount of phenols (7,202 mg/L), chlorides (7,997 mg/L), sulphates (1,100 mg/L), nitrates, phosphates (1,625 mg/L) and heavy metals.
Water plays a key role in distillery industry. It is used in every step of the technological lines, including cleaning and washing, disinfection, heating and cooling. Water requirements are significant and reuse is often viable by implementing ultrafiltration and reverse osmosis steps.
The three major categories according to their origin and composition are:
- Processing water: Processing water is formed in special coolers and condensers, as well as condensates from evaporation. In general, processing waters lack pollutants and, after minimal pretreatment, they can be reused or discharged together with stormwater. Water reuse is possible, typical applications are hot water and steam production as well as membrane cleaning.
- Cleaning wastewater: Cleaning wastewater usually comes from washing equipment which is in direct contact with the distilled products. It also includes product spillage, pressing and CIP effluents or equipment malfunction and even operational errors. These effluents are in large quantities and are highly polluted, thus requiring further treatment.
- Sanitary wastewater: Sanitary wastewater is found in lavatories, shower rooms, etc. Sanitary wastewater is similar in composition to municipal wastewater and is generally piped directly to sewage works, but it can be used as a nitrogen source for unbalanced dairy effluents before a secondary aerobic treatment.