Organic pollutants variation and antifouling enhancement with attapulgite clay addition in MBR treating micro-polluted surface water

Abstract

Membrane bioreactor (MBR) is widely used in water treatment, while attapulgite clay is a kind of hydrated magnesium aluminum silicate mineral, which has a perfect sorptive quality. In order to study the effect of attapulgite clay dosed to a MBR-attapulgite clay system, compared experiments between the conventional MBR and MBR-attapulgite clay system were carried out, and the basic performance of those two MBRs was investigated. The results demonstrated that both of MBRs could remove CODMn, ammonia, UV254, TOC, and turbidity successfully. The membrane fouling in MBR-attapulgite clay system was much slight than that in MBR system, which has a longer operation time (more than 35days) before backwashing with chemical solution. While particle size distribution (PSD) showed that fine particles in mixed liquor had a strong deposit tendency on the membrane surface and membrane foulants in MBR-attapulgite clay system had much smaller size than that in the MBR. Moreover, the Zeta potential of sludge mixture in MBR-attapulgite clay system was about 11–34% lower than that in MBR. FT-IR indicates that the structure and composition of the organic matter in the mixture liquor were changed with the dosing of attapulgite. Moreover, the types and content of organic matter were also reduced, which resulted in the slow membrane fouling rate. Excitation–emission matrix (EEM) analysis proved that membrane foulants, such as aromatic amino acids, protein, and natural dissolved organic matter are decomposed more effectively by biomass in MBR-attapulgite system for a more suitable conditions supplied by attapulgite clay. SEM and component analysis demonstrated that membrane surface was covered with compact gel layer formed by organic substances and inorganic elements, such as Ca, Fe, Mg, Mn, and Si. The organic foulants coupled the inorganic precipitation enhanced the formation of gel layer and thus caused membrane fouling in the MBR.