Energy & Environment

An important application for the pure oxygen supplied by SOL is 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 advantage of the use of pure oxygen, compared with the use of air, comes both from shorter treatment times which means the plant can be smaller, and, with the same treatment tank volume, an increase in the reduction of the organic fraction and so less residual sludge for disposal, and 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 reach 40% in a plant using pure oxygen: the main reason for this is that, with pure oxygen, the amount of gas introduced is much smaller 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.