Flue gas scrubber water for nitrogen supply in biological pulp and paper mill wastewater treatment
Keskinen, Päivi (2021)
Keskinen, Päivi
2021
Ympäristö- ja energiatekniikan DI-ohjelma - Programme in Environmental and Energy Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2021-10-18
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202109287315
https://urn.fi/URN:NBN:fi:tuni-202109287315
Tiivistelmä
Wood industry produces air emissions and high amounts of wastewater which are treated in different ways. Biological activated sludge treatment is commonly used in pulp and paper industry wastewater treatment. Pulp and paper industry wastewaters usually lack nutrients and urea is most often used as nutrient supply to ensure efficient treatment process. Pulp and paper industry air emissions, including nitrogen oxides, can be treated by wet scrubbers. Wet scrubbers applied in nitrogen oxides removal produce scrubber water containing nitrogenous compounds and this scrubber water is also treated in some way. In this study was examined if scrubber water could be used as a nitrogen supply in biological activated sludge treatment of pulp and paper mill wastewater. As an alternative method for scrubber water treatment denitrification was also examined.
Two laboratory-scale activated sludge reactors were operated simultaneously in common activated sludge operational conditions for 149 days. Pulp and paper mill wastewater was used as an influent and synthetic scrubber water was used as a nitrogen supply. Reactor 1 was supplied with scrubber water containing nitrate and nitrite. Reactor 2 was supplied with scrubber water containing nitrate, nitrite and urea. Impact of varying concentrations of nitrate, nitrite and urea on reactor performance were examined around 2‒3 weeks at a time. First three supplementation phases ran with total nitrogen supply of 3 mg/L in influent and the last two phases with total nitrogen supply of 29.5 mg/L in influent.
Efficient chemical and biological oxygen demand removal (around 80 % and 98 %, respectively) were obtained in both reactors and dissolved nitrogen did not accumulate in the effluent. However, in reactor 1 decreased sludge flocculation, decreased sludge settling properties and elevated total soluble solids concentration of effluent was noticed in comparison to performance of reactor 2. During the last two supplementation phases (nitrogen supply 29.5 mg/L in influent), a significant increase in the presence of filamentous bacteria occurred in both reactors.
Denitrification as an alternative scrubber water treatment method was studied with batch bottle assay. Synthetic scrubber water containing 1000 mg/L of nitrate and five different concentrations between 0 and 2000 mg/L of chloride was used. Methanol was used as an electron donor with carbon to nitrogen ratio 1.7 and a denitrifying sludge sample of a municipal wastewater treatment plant was used as a source of microorganisms. Complete denitrification was obtained at 35 °C within 110 hours regardless of chloride concentration.
According to the study, flue gas scrubber water could only partially replace conventional nitrogen supplements in pulp and paper mill wastewater treatment as urea was found to be important to sludge quality. Further studies may be needed to study more carefully the effect of nitrate and nitrite on activated sludge quality and settling properties. Denitrification could be used as an alternative nitrogen removal method for flue gas scrubber water if it contains inhibitive compounds under threshold concentrations known for denitrification. Detailed analysis of flue gas scrubber water of pulp and paper mills would give useful information for future studies.
Two laboratory-scale activated sludge reactors were operated simultaneously in common activated sludge operational conditions for 149 days. Pulp and paper mill wastewater was used as an influent and synthetic scrubber water was used as a nitrogen supply. Reactor 1 was supplied with scrubber water containing nitrate and nitrite. Reactor 2 was supplied with scrubber water containing nitrate, nitrite and urea. Impact of varying concentrations of nitrate, nitrite and urea on reactor performance were examined around 2‒3 weeks at a time. First three supplementation phases ran with total nitrogen supply of 3 mg/L in influent and the last two phases with total nitrogen supply of 29.5 mg/L in influent.
Efficient chemical and biological oxygen demand removal (around 80 % and 98 %, respectively) were obtained in both reactors and dissolved nitrogen did not accumulate in the effluent. However, in reactor 1 decreased sludge flocculation, decreased sludge settling properties and elevated total soluble solids concentration of effluent was noticed in comparison to performance of reactor 2. During the last two supplementation phases (nitrogen supply 29.5 mg/L in influent), a significant increase in the presence of filamentous bacteria occurred in both reactors.
Denitrification as an alternative scrubber water treatment method was studied with batch bottle assay. Synthetic scrubber water containing 1000 mg/L of nitrate and five different concentrations between 0 and 2000 mg/L of chloride was used. Methanol was used as an electron donor with carbon to nitrogen ratio 1.7 and a denitrifying sludge sample of a municipal wastewater treatment plant was used as a source of microorganisms. Complete denitrification was obtained at 35 °C within 110 hours regardless of chloride concentration.
According to the study, flue gas scrubber water could only partially replace conventional nitrogen supplements in pulp and paper mill wastewater treatment as urea was found to be important to sludge quality. Further studies may be needed to study more carefully the effect of nitrate and nitrite on activated sludge quality and settling properties. Denitrification could be used as an alternative nitrogen removal method for flue gas scrubber water if it contains inhibitive compounds under threshold concentrations known for denitrification. Detailed analysis of flue gas scrubber water of pulp and paper mills would give useful information for future studies.