This paper deals with the long-term operation of a full-scale municipal membrane bioreactor, focusing mainly on the membrane section. The ultrafiltration chamber, equipped with 12 130 m2 of submerged hollow-fiber membranes, was installed after an existing alternating oxic/anoxic bioreactor. Attention is paid to a number of practical details, from the effectiveness of different sieves to the impact of the operating parameters on the membrane performances; finally, data of the energy consumptions and items of the operating costs are presented. Starting from the pretreatments, while the wedge wire sieve (openings ) 1 mm) involved the visible accumulation of fibers and trash in the filtration chamber, the punched holes (holes diameter ) 1.5 mm) involved less than 100 milligrams of dry trash per liter of mixed liquor, demonstrating that they suited the following membrane system. Moving on to the off-line equalization basin, a volume of one-fifth of the bioreactor was sufficient to cope with the normal fluctuations of the municipal inloadings. As for the membrane section, a net flux of 26 LMH and chemical maintenance cleaning in place once a week with only hypochlorite (around 300 mgCl L-1) was a sustainable practice to keep the long-term permeability (adjusted at 20 °C) stable in the range 220-240 LMH bar-1. Under this operating protocol, increases of specific aeration for membrane scouring from 0.12 to 0.19 Nm3 m-2 h-1 did not lead to permeability gains that might justify the increased power requirements. This evidence allows us to conclude that 0.12 Nm3 m-2 h-1 was sustainable for the normal operation of the hollow-fiber membranes. Irreversible membrane fouling (permeability decrease up to 150-160 LMH bar-1) was observed because of irregular discharges of municipal landfill leachate, which, from one side, caused a drastic deflocculation of the activated sludge (sludge volume index (SVI) increased from 110 up to 250 mL gMLSS) and, from the other side, involved a probable incoming of recalcitrant compounds that might have acted as foulants. The power requirements of the whole treatment facility were always lower than 0.6 kWh m-3 thanks to the general good utilization of the air supplied. The specific operating costs related to the energy consumptions and chemicals purchase were in the range 0.06-0.08 euro m-3.

Operation and Maintenance of full-scale Municipal Membrane Biological Reactors: a detailed overview on a case study

PAVAN, Paolo;
2007-01-01

Abstract

This paper deals with the long-term operation of a full-scale municipal membrane bioreactor, focusing mainly on the membrane section. The ultrafiltration chamber, equipped with 12 130 m2 of submerged hollow-fiber membranes, was installed after an existing alternating oxic/anoxic bioreactor. Attention is paid to a number of practical details, from the effectiveness of different sieves to the impact of the operating parameters on the membrane performances; finally, data of the energy consumptions and items of the operating costs are presented. Starting from the pretreatments, while the wedge wire sieve (openings ) 1 mm) involved the visible accumulation of fibers and trash in the filtration chamber, the punched holes (holes diameter ) 1.5 mm) involved less than 100 milligrams of dry trash per liter of mixed liquor, demonstrating that they suited the following membrane system. Moving on to the off-line equalization basin, a volume of one-fifth of the bioreactor was sufficient to cope with the normal fluctuations of the municipal inloadings. As for the membrane section, a net flux of 26 LMH and chemical maintenance cleaning in place once a week with only hypochlorite (around 300 mgCl L-1) was a sustainable practice to keep the long-term permeability (adjusted at 20 °C) stable in the range 220-240 LMH bar-1. Under this operating protocol, increases of specific aeration for membrane scouring from 0.12 to 0.19 Nm3 m-2 h-1 did not lead to permeability gains that might justify the increased power requirements. This evidence allows us to conclude that 0.12 Nm3 m-2 h-1 was sustainable for the normal operation of the hollow-fiber membranes. Irreversible membrane fouling (permeability decrease up to 150-160 LMH bar-1) was observed because of irregular discharges of municipal landfill leachate, which, from one side, caused a drastic deflocculation of the activated sludge (sludge volume index (SVI) increased from 110 up to 250 mL gMLSS) and, from the other side, involved a probable incoming of recalcitrant compounds that might have acted as foulants. The power requirements of the whole treatment facility were always lower than 0.6 kWh m-3 thanks to the general good utilization of the air supplied. The specific operating costs related to the energy consumptions and chemicals purchase were in the range 0.06-0.08 euro m-3.
2007
46
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10278/18113
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