Energy & Environment

Excess sludge treatment

An important application of the pure oxygen supplied by SOL, is the aerobic stabilisation of the excess sludge in biological plant: the excess activated sludge extracted from the oxidation and nitrification tanks is sent to special treatment tanks so that the only organic substrate available for feeding the bacterial population are the substances contained in the sludge. In these conditions, an endogenous respiration regime is created, so that bacterial activity leads to a substantial reduction in the quantity of the biodegradable solids initially suspended in the sludge, accompanied by effective stabilisation. The advantages of using pure oxygen rather than air, are the shorter treatment times, which means the plant can be smaller, an increase in the reduction of the organic fraction using the same size treatment tank, and so less residual sludge for disposal, together with the minimum environmental impact achieved by limiting gas emissions from the treatment tank.

The reduction of the quantity of suspended biodegradable solids is generally 20% for a plant using air, but can be as high as 40% in a plant using pure oxygen: the main reason for this is that with pure oxygen, the amount of gas introduced is much less than when using air, so the heat generated by bacterial activity is not lost by evaporation; as a result, the temperature of the liquid increases, favouring bacterial activity.

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