Precoagulation has been widely used by low pressure membrane filtration (LPMF) plants to reduce membrane fouling and increase natural organic matter (NOM) removal. Formation of aluminum and aluminum-NOM moieties plays a fundamental role in this important engineering process. This study comprehensively investigated the mechanisms of aluminum-NOM species formation during precoagulation and their impacts on LPMF performance. The results show that, at low alum doses, humic substances (HS) and Al species reacted to form small Al(OH)3(am)-HS colloids. Increases in alum dose resulted in sequential transitions of the Al-HS moieties to larger particles and eventually precipitates. Compared to waters containing only naturally occurring organic colloids (OC) or HS, the coexistence of OC and HS facilitated the formation of Al-HS precipitates, thereby increasing the removal of HS by 7-15%, but the removal of OC was decreased by 3-20%. Interestingly, these transitions in Al-HS moieties did not affect membrane fouling. Both short-term and long-term filtration results demonstrate that OC, rather than the Al(OH)3(am)-HS colloids, primarily caused membrane fouling. These findings highlight the dynamics of particulate Al-NOM formation during precoagulation and its relationship with membrane fouling, which can be utilized to optimize the operation of integrated precoagulation-LPMF systems.

Aluminum-humic colloid formation during pre-coagulation for membrane water treatment: Mechanisms and impacts

248th National Meeting (2014)

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