Distillery spentwash reaching a stream before the monsoon

First, the load. 60 kilolitres per day at 45,000 mg per litre is 60 x 45,000 = 2,700,000 grams, that is 2,700 kg of BOD per day, equivalent to the sewage of a town of roughly 45,000-50,000 people. That is why 20 hectares cannot absorb it.

Second, the dilution available. A base flow of 0.1 cubic metres per second is 8,640 cubic metres per day. If the stream must meet a BOD of 20 mg per litre after mixing, with 2 mg per litre upstream:

(60 x C + 8,640 x 2) / 8,700 = 20

60C = 174,000 - 17,280 = 156,720, so C = about 2,610 mg per litre.

Required reduction = (45,000 - 2,610) / 45,000, that is about 94 percent.

Third, storage. The pipeline of 5,000 cubic metres holds only about 5 days of flow, so there is no buffer for a monsoon failure.

Conclusion: any talk of dilution is untenable. The stream would need an 8,640 cubic metre per day flow merely to dilute the load to the limit, and no such flow exists. The treatment target should be near-zero discharge rather than 94 percent removal.

Molasses spentwash is one of the strongest organic effluents produced in India, and the regulatory position for molasses-based distilleries is zero liquid discharge, so the scheme must be built around that rather than around a dilution formula.

Treatment train:

1. Segregation and flow control - separate cooling and wash water, which is clean, from the spentwash.
2. Anaerobic digestion (biomethanation) - removes 60-70 percent of COD and produces biogas that can replace bagasse or coal in the boiler, so it pays back part of its own cost.
3. Concentration - multiple-effect evaporation to a concentrate of about 30-40 percent solids, which is composted with press mud and boiler ash to make a saleable organic manure, or co-fired in the boiler.
4. Condensate polishing - the evaporated water is not clean; it needs aerobic treatment and polishing before reuse in cooling or washing.
5. Land application only of treated effluent at agronomic rates - calculated from soil potassium and nitrogen, on designated bunded land, and never in the monsoon.

The Board will require a revised consent application, a bank guarantee tied to compliance, an upgraded lagoon of at least 15 days' storage, continuous effluent quality monitoring and a zero-discharge undertaking. Dilution and night discharge are offences, not solutions.

Six weeks is enough to prevent a repeat of the fish kill, but only if the plan is modest and enforced.

Immediate actions:

• Stop all land application now; the 20 hectares is saturated and the first heavy rain will flush it to the stream.
• Bundle and re-line the spreading area so that any runoff is collected, and build a diversion drain between the field and the stream.
• Use the existing 5,000 cubic metre lagoon plus emergency tanker or co-processing contracts with a cement kiln or a common treatment plant to cover the monsoon months.
• If storage cannot be arranged, reduce production; a short shutdown is cheaper than prosecution and compensation.
• Desilt the stream and remove the decaying sludge that is still consuming oxygen.

Monitoring:

• Weekly DO, BOD, COD and pH at three points: upstream, the outfall and 2 km downstream.
• Groundwater sampling from three wells in the spreading area for COD, potassium and nitrate before and after monsoon.
• A continuous flow meter on the distillery outfall and a log of tanker movements.

Community measures: inform the two villages in writing, provide an alternative drinking water point if their wells are affected, and agree a compensation route before the monsoon, not after the next fish kill.