MEDEIROS, Ú. T. P.; http://lattes.cnpq.br/6478394140113089; MEDEIROS, Úrsula Thaís de Paula.
Resumen:
The energy requirement for aeration is normally the largest factor of
operational costs in activated sludge systems. In order to treat the industrial effluent
generated at the Petrochemical Complex at Camacari CETREL installed an aeration
capacity of more than 5 MW. Since the operational costs are high, the possibility of
reduction of energy consumption without adverse effects on the effluent quality or the
sludge properties was evaluated. Among the parameters defining the effluent quality, the
concentrations of organic matter, suspended solids and ammonium are the most important
ones, as these have limits imposed by the environmental authority (CRA, Regional
Environmental Council). The most important sludge properties are the metabolic capacity
in the degradation of substrates (organic matter and ammonium) and the sludge
settleability.
One possibility to reduce costs is to reduce the concentration of dissolved
oxygen in the mixed liquor. Aeration theory affirms that the energy required for aeration is
proportional with the oxygen deficit, i.e. the difference between the saturation
concentration of dissolved oxygen and its value at any time in the liquid phase. Thus, the
lower the DO concentration, the lower the energy requirement for aeration. However, it is
necessary to verify the effect of the DO reduction on the quality of the effluent and the
sludge.
In an experimental investigation three pilot scale systems were operated,
while different DO concentrations were maintained in each system. The DO concentration
was maintained at the desired levels (3,0, 1,5-2,5 e 0,5-1,5 mg//) with the aid of
respirometers. The influence of the DO concentrations on the effluent quality was observed
during the experimental investigation. The respirometers were also used to assess the
biological quality of the sludges. The influence on settleability was evaluated from data of
the sludge volume index (SVI) of the three sludges. The heterotrophic sludge activity can be estimated from the oxygen uptake
rate (OUR) as follows: after determining the OUR in the absence of substrate (i.e. the
endogenous respiration rate), substrate is added in abundance so that the sludge starts to
consume oxygen at maximum rate, both for endogenous respiration (which remains
unchanged) and for its exogenous demand to metabolize the extra cellular material. The
proportion between the maximum (with abundant substrate) and the minimum OUR
(without substrate) is indicative for the metabolic capacity of the sludge. The same method
can also be used to evaluate the autotrophic (nitrifying) sludge activity: in this case an
ammonium salt (for example NH4CI) is added in abundance and the OUR related to this
addition is measured.
The results of the investigation showed that down to a DO concentration of
1 mg// there was no significant influence of this parameter on the effluent quality, or on the
biological or mechanical sludge properties, with 83% removal of COD, 99% removal of
TSS and ammonia, and LVI at 34ml.g"1.
