Air Backwash Efficiency on Organic Fouling of UF Membranes Applied to Shellfish Hatchery Effluents

Abstract

Among all the techniques studied to overcome fouling generated in dead-end filtration, the injection of air during backwashes proved to be the most effective. Indeed, shear stress engendered by the two-phase flow enhanced particle removal on membrane surface. This work aims to study the injection of air to drain the membranes before backwash. Firstly, the efficiency of this backwash procedure was evaluated during the ultrafiltration of seawater on a semi industrial pilot plant using different operating conditions. Then, the treatment of seawater, doped with oyster gametes to simulate the filtration of shellfish hatchery effluents, was performed to confirm the hydraulic performance of the air backwash. Indeed, the release of gametes, expulsed by exotic bivalves in the natural environment, could be a risk for the biodiversity preservation. The impact of air backwash on the integrity of oocytes and spermatozoa was identified using flow cytometry and microscopic analyses. When oyster gametes were added, their retention by ultrafiltration was validated. The impact of air backwash on these species viability was a significant information point for the implementation of this process on shellfish production farms.

Ultrafiltration: A solution to recycle the breeding waters in shellfish production

“…This cleaning procedure has a significative impact on the stability of the process facing this pollution. These results justify the choice of increasing the AB frequency in the case of harder filtration conditions and confirm the conclusion obtained in a previous study on the efficiency of air backwash to eliminate fouling generated by the filtration of seawater and an effluent containing biological material from oysters (Cordier et al, 2018b).…”

“…Their MWCO was 0.02 µm and initial permeability 1000 L.h -1 .m -2 .bar -1 . The membrane module of a total area of 8 m² has been integrated into a semi industrial pilot Figure 1 (Moll et al, 2007), able to treat 20 m 3 .d -1 (Cordier et al, 2018b).…”

“…Indeed, flux is affected by the water temperature and must be normalized to a standard temperature to account viscosity fluctuations with this parameter. Filtration conditions, permeate flux (L.h -1 .m -2 ) and filtration time (min), were pre-selected according to the literature (Guilbaud et al, 2019(Guilbaud et al, , 2018) and previous studies (Cordier et al, 2018a(Cordier et al, , 2018b.…”

Optimization of Air Backwash Frequency during the Ultrafiltration of Seawater

“…The system includes the classical backwash (CB), air backwash (AB) and chemical cleaning (CEB). As mentioned here before, the CB is the injection of permeate from permeate side to feed side (inverse of filtration mode) with a flow rate of 2.5 m 3 h −1 [15,16] and AB air injection inside fibers to discharge water to outside until to drain all fibers when the pressure reached 0.3 bar. The air is supplied with an air compressor.…”

“…In this paper, a semi-industrial UF pilot was used to study the efficiency of new air backwash in two steps (i.e., the novelty of this paper) and its frequency during the seawater treatment: Air backwash (AB) consists (i) to inject air in membrane module before (ii) a classical backwash. In the case of specific effluent this new backwash shows high performances [15,16]. In this paper, the ultrafiltration of seawater, generally used as pretreatment, is operated.…”