Biological wastewater treatment generates huge amounts of waste sludge which need to be dewatered
and eventually dried to minimize transportation and incineration costs. A characteristic feature of sludge
in this context is that it turns into a sticky substance during its drying process inducing fouling problems
in the drying installation. At the wastewater treatment plant of Monsanto in Antwerp, Belgium, one
enclosed centrifuge-dryer system is used to dry the sludge. In the past, this installation had to be shut
down regularly due to dryer fouling problems. To avoid these operational problems, a binary logistic
regression analysis is presented in this research based on a 5-year database, resulting in an empirical
model for the evaluation of the dryer fouling risk as a function of the sludge feed characteristics. The
model inputs are the sludge volume index (SVI) and the dosing of clay additive and tertiary (flotation)
sludge, the latter containing polyaluminumchloride (PACl), to the sludge feed of this particular system.
By exploiting the knowledge captured by this model, the derived control strategy is based on the value
of the SVI. Whenever the SVI is high the original high clay dosing to the feed needs to be maintained.
At moderate SVI values, implying an intrinsically better sludge dewaterability, the strategy dictates a
reduction in the clay dosing to the sludge feed to have a reduced sludge solids dryness after dewatering,
thereby avoiding that the sludge exhibits its most sticky phase when passing the most fouling sensitive
part of the dryer. When the SVI is lower than 50 mL/g the control strategy states that conditioning of the
sludge with PACl is required to mask the stickiness instead of postponing it, avoiding that the stickiness
of the sludge already hampers the dewatering stage of the process.
Biological wastewater treatment generates huge amounts of waste sludge which need to be dewateredand eventually dried to minimize transportation and incineration costs. A characteristic feature of sludgein this context is that it turns into a sticky substance during its drying process inducing fouling problemsin the drying installation. At the wastewater treatment plant of Monsanto in Antwerp, Belgium, oneenclosed centrifuge-dryer system is used to dry the sludge. In the past, this installation had to be shutdown regularly due to dryer fouling problems. To avoid these operational problems, a binary logisticregression analysis is presented in this research based on a 5-year database, resulting in an empiricalmodel for the evaluation of the dryer fouling risk as a function of the sludge feed characteristics. Themodel inputs are the sludge volume index (SVI) and the dosing of clay additive and tertiary (flotation)sludge, the latter containing polyaluminumchloride (PACl), to the sludge feed of this particular system.By exploiting the knowledge captured by this model, the derived control strategy is based on the valueof the SVI. Whenever the SVI is high the original high clay dosing to the feed needs to be maintained.At moderate SVI values, implying an intrinsically better sludge dewaterability, the strategy dictates areduction in the clay dosing to the sludge feed to have a reduced sludge solids dryness after dewatering,thereby avoiding that the sludge exhibits its most sticky phase when passing the most fouling sensitive
part of the dryer. When the SVI is lower than 50 mL/g the control strategy states that conditioning of the
sludge with PACl is required to mask the stickiness instead of postponing it, avoiding that the stickiness
of the sludge already hampers the dewatering stage of the process.
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