19 Evaluation and Optimization of the Treatment Scheme …
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19.3 Results and Discussion
19.3.1 Plain Settling
Plain settling experiments were focused to evaluate the behavior of the settleable
organics under two different settling time. The process wastewaters were separately
applied to 2 and 4 h settling to understand the effect of settling time on the performance of COD and TSS removal. In 2 h settling the removal efficiency was measured
as 35% for COD and 85% for TSS, where they only be increased up to 40% and
90% when the settling time was expanded to 4 h, respectively. Regarding the observation that the doubling in settling time did not reflect any remarkable difference
for process wastewaters, the third and fourth alternatives were only applied to 2 h
settling coupled with chemical treatment. The performance of 2 h settling for other
alternatives was noticed as the same obtained for the process wastewaters.
19.3.2 Chemical Treatment
Chemical treatment was designed first for process wastewaters as in the second
alternative and then a combination with cooling water as in the third alternative and
finally with the addition of domestic wastewaters as in the fourth alternative.
The performance of chemical treatment if only applied to process wastewaters
indicated that 700 mg/L FeSO 4 resulted a better quality in terms of TSS (90%) and
COD (70%) than other dosages and FeCl 3 application. The results indicated that TSS
and COD removal together with the metal removal were satisfactory to be discharged
into the common wastewater treatment plant.
The combination of process wastewater and cooling water was chemically treated
by using only a single coagulant FeCl 3 at a higher dosage of 1200 mg/L FeCl 3 together
with two different polyelectrolytes. The reason using higher dosage was directly due
to not applying plain settling. 1 mg/L anionic polyelectrolyte was more effective
than 3 mg/L nonionic polyelectrolyte, with a removal yield of 95% for TSS, 70% for
COD and 90% for oil-grease.
The results related to chemical precipitation of all wastewaters clearly indicated
that best removal was again achieved with FeSO 4 application, but at a slightly higher
dosage (800 mg/L) than in the second alternative as a consequence of the increased
amount of wastewater to be treated. The removal efficiencies were observed to be 95%
for TSS, 70% for COD and 90% for oil and grease. Table 19.4 shows the performance
obtained from chemical treatment by the application of different coagulants.
A general evaluation of the pretreatment step prior biological treatment revealed
that only a COD removal of 38% and a TSS removal of 86% were achieved in the
first alternative, whereas these removal efficiencies were almost doubled for COD
removal (78%) and slightly higher for TSS removal (95%) in the second alternative.
203
19.3 Results and Discussion
19.3.1 Plain Settling
Plain settling experiments were focused to evaluate the behavior of the settleable
organics under two different settling time. The process wastewaters were separately
applied to 2 and 4 h settling to understand the effect of settling time on the performance of COD and TSS removal. In 2 h settling the removal efficiency was measured
as 35% for COD and 85% for TSS, where they only be increased up to 40% and
90% when the settling time was expanded to 4 h, respectively. Regarding the observation that the doubling in settling time did not reflect any remarkable difference
for process wastewaters, the third and fourth alternatives were only applied to 2 h
settling coupled with chemical treatment. The performance of 2 h settling for other
alternatives was noticed as the same obtained for the process wastewaters.
19.3.2 Chemical Treatment
Chemical treatment was designed first for process wastewaters as in the second
alternative and then a combination with cooling water as in the third alternative and
finally with the addition of domestic wastewaters as in the fourth alternative.
The performance of chemical treatment if only applied to process wastewaters
indicated that 700 mg/L FeSO 4 resulted a better quality in terms of TSS (90%) and
COD (70%) than other dosages and FeCl 3 application. The results indicated that TSS
and COD removal together with the metal removal were satisfactory to be discharged
into the common wastewater treatment plant.
The combination of process wastewater and cooling water was chemically treated
by using only a single coagulant FeCl 3 at a higher dosage of 1200 mg/L FeCl 3 together
with two different polyelectrolytes. The reason using higher dosage was directly due
to not applying plain settling. 1 mg/L anionic polyelectrolyte was more effective
than 3 mg/L nonionic polyelectrolyte, with a removal yield of 95% for TSS, 70% for
COD and 90% for oil-grease.
The results related to chemical precipitation of all wastewaters clearly indicated
that best removal was again achieved with FeSO 4 application, but at a slightly higher
dosage (800 mg/L) than in the second alternative as a consequence of the increased
amount of wastewater to be treated. The removal efficiencies were observed to be 95%
for TSS, 70% for COD and 90% for oil and grease. Table 19.4 shows the performance
obtained from chemical treatment by the application of different coagulants.
A general evaluation of the pretreatment step prior biological treatment revealed
that only a COD removal of 38% and a TSS removal of 86% were achieved in the
first alternative, whereas these removal efficiencies were almost doubled for COD
removal (78%) and slightly higher for TSS removal (95%) in the second alternative.