19 Evaluation and Optimization of the Treatment Scheme …
201
supernatant was then mixed with the rest of the wastewater sources and directed to
biological treatment.
In the third alternative the process wastewaters combined with cooling water were
first applied to chemical treatment without being plain settled and then mixed with
domestic wastewater in the equalization tank before the biological treatment.
In the fourth alternative all wastewaters generated from the plant were first plain
settled for 2 h and then treated chemically prior biological treatment.
Plain settling was conducted in Imhoff cones of 1 L volume, settling was observed
for 2 h. Settling time was extended to 4 h in the first alternative since no chemical
treatment was applied. The performance of the plain settling was determined by
measuring COD and TSS.
Chemical treatment tests were implemented using a laboratory jar test equipment.
Considering that all process effluents contained metal components, pH value was set
to the optimum value of 9 from the original pH with caustic lime. All jar test experiments were conducted applying a sequence of 1 min stirring at 120 rpm for coagulation, 15 min stirring at 30 rpm for flocculation and 30 min settling. FeSO 4 and FeCl 3
were used as coagulants together with the nonionic and anionic polyelectrolytes to
increase the precipitation yield.
FeCl 3 and FeSO 4 were used as coagulants in chemical treatment as summarized
together with their dosages in Table 19.3. pH was adjusted with the addition of caustic
lime up to 9–9.5. Only the third alternative was practiced with FeCl 3 at 1200 mg/L
but with two different polyelectrolyte addition. The chemical treatment in the second
and fourth alternatives were conducted with both coagulants at a dosage range of
500–800 mg/L.
Biological treatability studies were conducted in fill and draw activated sludge
reactors. The volume of the reactors was selected as 2 L. The reactors were operated
at a sludge age of 6 day and a hydraulic retention time of 1 day. Nitrogen and
phosphorus requirement for biological activity were supplied by the addition of
domestic wastewater.
19.2.4 Analytical Procedures
All conventional parameters except COD were analyzed in accordance with Standard Methods (APHA 2005) COD measurements were conducted by following the
procedure in ISO 6060 (1986). pH estimation was conducted as defined in ISO 10523
(2008) by using a digital pH/millivolt meter. Treatability studies and all analysis were
performed at room temperature.
201
supernatant was then mixed with the rest of the wastewater sources and directed to
biological treatment.
In the third alternative the process wastewaters combined with cooling water were
first applied to chemical treatment without being plain settled and then mixed with
domestic wastewater in the equalization tank before the biological treatment.
In the fourth alternative all wastewaters generated from the plant were first plain
settled for 2 h and then treated chemically prior biological treatment.
Plain settling was conducted in Imhoff cones of 1 L volume, settling was observed
for 2 h. Settling time was extended to 4 h in the first alternative since no chemical
treatment was applied. The performance of the plain settling was determined by
measuring COD and TSS.
Chemical treatment tests were implemented using a laboratory jar test equipment.
Considering that all process effluents contained metal components, pH value was set
to the optimum value of 9 from the original pH with caustic lime. All jar test experiments were conducted applying a sequence of 1 min stirring at 120 rpm for coagulation, 15 min stirring at 30 rpm for flocculation and 30 min settling. FeSO 4 and FeCl 3
were used as coagulants together with the nonionic and anionic polyelectrolytes to
increase the precipitation yield.
FeCl 3 and FeSO 4 were used as coagulants in chemical treatment as summarized
together with their dosages in Table 19.3. pH was adjusted with the addition of caustic
lime up to 9–9.5. Only the third alternative was practiced with FeCl 3 at 1200 mg/L
but with two different polyelectrolyte addition. The chemical treatment in the second
and fourth alternatives were conducted with both coagulants at a dosage range of
500–800 mg/L.
Biological treatability studies were conducted in fill and draw activated sludge
reactors. The volume of the reactors was selected as 2 L. The reactors were operated
at a sludge age of 6 day and a hydraulic retention time of 1 day. Nitrogen and
phosphorus requirement for biological activity were supplied by the addition of
domestic wastewater.
19.2.4 Analytical Procedures
All conventional parameters except COD were analyzed in accordance with Standard Methods (APHA 2005) COD measurements were conducted by following the
procedure in ISO 6060 (1986). pH estimation was conducted as defined in ISO 10523
(2008) by using a digital pH/millivolt meter. Treatability studies and all analysis were
performed at room temperature.