Impact of Calcium on the Membrane Fouling in Membrane Bioreactors

ISSN： 1938-6478

Source： Proceedings of the Water Environment Federation, Vol.2007, Iss.11, 2007-10, pp. : 6402-6416

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Abstract

Fouling in submerged membrane bioreactors (MBRs) was studied under two calcium levels (280 and 830 mg/L). Two MBRs were operated on synthetic municipal wastewater at a solids retention time (SRT) of 15 days, a control at a calcium level of around 35 mg/L and a test reactor at two calcium levels of 280 and 830 mg/L. Permeability, flux, extracellular polymeric substances (EPS), Ca²⁺ concentration and particle size distribution were measured regularly in both reactors to investigate the cause of membrane fouling. The test reactor showed 35% higher permeability than the control at 280 mg/L of calcium. However, at 830 mg Ca²⁺/L feed, the permeability in the test reactor stabilized at 0.15 LMH/kPa approximately 50% lower than the control. The lower membrane fouling rate in the Ca²⁺ fed MBR at an influent calcium concentration of ∼ 280 mg/L can be attributed to cationic bridges with EPS within the floc. Statistical analysis was used to specify the degree of influence of each of EPS type, calcium concentration in the sludge, and mean floc size on membrane permeability. Among all these variables, the calcium concentration in sludge was proven to affect the permeability most significantly. Thus, the reduction in membrane permeability at higher calcium concentration (∼ 830 mg/L) was the result of very high Ca²⁺ concentrations in the sludge that contributed to significant inorganic fouling