Treatment of wastewater from anaerobic digestion

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Courtesy of EVALED - Veolia Water Technologies

The Client

The customer is power plant which produces biogas from biomass and sewage farm, through anaerobic digestion and thermal recovery, located nearby Munich in Germany.

The Client’s needs

Biogas is produced by the fermentation of organic substances of animal and vegetal origin in absence of oxygen (anaerobic process). This process produces a stream called digestate which is an aqueous solution with a high conductivity and heavy metals. It contains also an high concentration of ammonia, nitric nitrogen, methane, phosphorous and BOD. Due to this specific chemical composition, often environmental regulations do not allow to spread it directly to the fields.

The solution provided

The vacuum and forced circulation evaporator EVALED EW 40000 has a capacity of about 40,000 litres of distillate a day and a specific electric energy consumption of 0,02 kWh per litre of distillate.

The evaporator exploits the heat supplied by the hot water from the cogeneration to evaporate the digestate, the waste produced by the fermentation. A circulation pump sends the water through the shell & tube heat exchanger where it is supplied with the heat necessary for boiling. The digestate flowing at high speed keeps cleaned the surface of the heat exchanger and reduces the maintenance requirements. Once heated, the digestate goes back to the boiling chamber, where it immediately boils (flash evaporation).

The results

The performance of the evaporation, in terms of distillate quality and volume reduction, is excellent.

The following table shows the characteristics of the distillate and the reduction of the pollution charge.

Treatment of wastewater from anaerobic digestion

The digestate is concentrated about five times. The concentrate of the EVALED® AC EW 40000 is then sent to a storage tank and then put in the digestors or used as organic fertilizer.

The digestate treatment solution provides a real economic benefit for the Client. This amounts to the recovery of all of their wastewater and, consequentially, to a zero liquid discharge to the sewer – representing a substantial saving for the company.

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