Chemical Pre-Treatment of Sewage - A Cost-Benefit Method
377
All experiments were performed in 1-1 glass cylinders with a Kemira flocculator
device (Kemira 1990). This flocculator can handle up to 6 glass cylinders. Each
glass cylinder has a stirrer with an individual motor equipped with a tachometer.
The coagulants were mixed with the wastewater (taken from the effluent of the
grit chamber) for 1 min at 350 rpm. Coagulation was carried out in 10 min at 20
rpm. The samples were allowed to settle for 20 min.
In the laboratory tests, different iron(III) and aluminum salts were applied. They
were as follows: Prefloc [iron(III)-sulfate], BOPAC (poli-aluminum-chloride),
FeCh'6H20 and Ah(S04kI8H20. The next parameters were analyzed: pH;
chemical oxygen demand (CODer); total phosphorus (TP); ortho-phosphate (P04P); sludge volume; ammonium-nitrogen
The dissolved parts of the organic pollutants as CODer and BODs were also
analyzed. The terms dissolved CODer and dissolved BODs mean the CODer and
BODs values measured in the filtrate of a 0.45-)lm pore size membrane filter.
Two wastewater treatment plants were selected for analyzing the possibility of
chemical pretreatment as an upgrading method.
5 Results
5.1 N1 Wastewater Treatment Plant
The Nl Waste Water Treatment Plant is an activated sludge-treatment plant with a
mean capacity of 12 000 m 3 day-l. The plant consists of bar screens, grit chamber,
circular primary sedimentation tanks, aeration tanks, and secondary sedimentation
tanks. The treatment plant will receive wastewater (10 000 m 3 day-l) from another
treatment plant, which will be closed in the near future. This, and the present
problems, the low removal rate of ammonium-nitrogen and BODs make it
necessary to improve the pollutant removal capacity of the treatment plant.
The possibility of upgrading the plant with chemical pretreatment was examined
and compared to another alternative without chemical addition. Besides sufficient
organic matter removal, chemical pretreatment gives good removal efficiency also
for phosphorus. As Hungary wishes to join the European Union, more stringent
regulations (effluent standards) are to be introduced. Basically, the whole of the
country belongs to the watershed of the River Danube, meaning that if the whole
tributary of the Black Sea is considered as a sensitive area in the future, total
phosphorus concentration in wastewater effluents (discharged to surface
waterbodies) should not exceed 1 mgrl. This strict regulation might make it
necessary to use chemicals for phosphorus removal.
377
All experiments were performed in 1-1 glass cylinders with a Kemira flocculator
device (Kemira 1990). This flocculator can handle up to 6 glass cylinders. Each
glass cylinder has a stirrer with an individual motor equipped with a tachometer.
The coagulants were mixed with the wastewater (taken from the effluent of the
grit chamber) for 1 min at 350 rpm. Coagulation was carried out in 10 min at 20
rpm. The samples were allowed to settle for 20 min.
In the laboratory tests, different iron(III) and aluminum salts were applied. They
were as follows: Prefloc [iron(III)-sulfate], BOPAC (poli-aluminum-chloride),
FeCh'6H20 and Ah(S04kI8H20. The next parameters were analyzed: pH;
chemical oxygen demand (CODer); total phosphorus (TP); ortho-phosphate (P04P); sludge volume; ammonium-nitrogen
The dissolved parts of the organic pollutants as CODer and BODs were also
analyzed. The terms dissolved CODer and dissolved BODs mean the CODer and
BODs values measured in the filtrate of a 0.45-)lm pore size membrane filter.
Two wastewater treatment plants were selected for analyzing the possibility of
chemical pretreatment as an upgrading method.
5 Results
5.1 N1 Wastewater Treatment Plant
The Nl Waste Water Treatment Plant is an activated sludge-treatment plant with a
mean capacity of 12 000 m 3 day-l. The plant consists of bar screens, grit chamber,
circular primary sedimentation tanks, aeration tanks, and secondary sedimentation
tanks. The treatment plant will receive wastewater (10 000 m 3 day-l) from another
treatment plant, which will be closed in the near future. This, and the present
problems, the low removal rate of ammonium-nitrogen and BODs make it
necessary to improve the pollutant removal capacity of the treatment plant.
The possibility of upgrading the plant with chemical pretreatment was examined
and compared to another alternative without chemical addition. Besides sufficient
organic matter removal, chemical pretreatment gives good removal efficiency also
for phosphorus. As Hungary wishes to join the European Union, more stringent
regulations (effluent standards) are to be introduced. Basically, the whole of the
country belongs to the watershed of the River Danube, meaning that if the whole
tributary of the Black Sea is considered as a sensitive area in the future, total
phosphorus concentration in wastewater effluents (discharged to surface
waterbodies) should not exceed 1 mgrl. This strict regulation might make it
necessary to use chemicals for phosphorus removal.