Potential and limitations of alum or zeolite addition to improve the performance of a submerged membrane bioreactor

Abstract

In this study, alum and natural zeolite were added to a submerged membrane bioreactor (MBR) not only to reduce membrane fouling but also to increase the removal of nitrogen and phosphorus. Alum addition reduced significantly the rising rate of suction pressure and also resulted in stable and better COD removal. Although phosphorus removal was more than 90% by chemical precipitation, nitrification inhibition was observed. With the addition of natural zeolite, membrane permeability was greatly enhanced by the formation of rigid floc that had lower specific resistance than that of the control activated sludge floc. In particular, the nitrification efficiency was over 95% even at N-shock loading due to the ion-exchange capacity of zeolite. The mechanisms for improved membrane permeability through alum or zeolite addition were discussed in detail.

Effect of alum on nitrification during simultaneous phosphorous removal in anoxic/oxic reactor

“…For the alum dosage 59.18 mg/L it was 84~82% from then it was decreased in a step wise manner for successive higher dosage and it fell to a value of 74~76% for the alum dosage (97.13 mg/L). Lee et al [22] have used alum in the MBR reactor to improve its performance and found out that the addition of alum significantly reduced the suction pressure of the membrane but increased the effluent nitrogen level. Fig.…”

Performance of bioferric-submerged membrane bioreactor for dyeing wastewater treatment

“…1 Reactor. This indicated that adding Fe(OH) 3 to SMBR could mitigate the membrane fouling effectively.…”

“…The membrane fouling causes permeating flux decline, requiring frequent membrane cleaning and even replacing, which increases the maintenance and operating costs of SMBR. Many attempts such as intermittent operation, jet aeration, air and water backwashing, dosing zeolite, O 3 , alum or powder activated carbon have been employed to reduce the membrane fouling [1][2][3][4]. However, membrane fouling in SMBR is still one of the major drawbacks for their wide application.…”

“…Iron salt or ferric hydroxide (Fe(OH) 3 ) is often used as flocculant to improve the sludge's filterability on surplus sludge disposal. Adding iron salt or iron hydroxide to CAS processes named as bioferric process or to biofilm processes can also improve the systems' performance such as enhancing removal efficiency and reducing surplus sludge discharge [5][6][7].…”

“…Raw water supplied to the two systems was pumped from the same storage tank. Fe(OH) 3 floc was added to the No. 2 bioreactor twice per week to maintain iron weight at approximately 5% of mixed liquor suspended solids (MLSS) contained in the bioreactor.…”