Recovery and reuse of alginate in an immobilized algae reactor.

The use of microalgae for nutrients removal from wastewater has attracted more attention in recent years. More specifically, immobilized systems where algae cells are entrapped in beads in a matrix of a polysaccharide such as alginate have shown a great potential for nutrients removal from wastewater to low levels with reduced retention times and hence smaller footprint. However, a significant operational cost in the up-scaling of alginate-immobilized algae reactors will be the gelling agent alginate. To reduce expenditure of this consumable a proof-of-concept is given for an alginate recycling method using sodium citrate as a dissolving agent. Using algae beads made from virgin and recycled alginate yielded comparable removal rates for both phosphorus and nitrogen compounds from wastewater. At labscale, an alginate recovery of approximately 70% can be achieved which would result in a net operational cost reduction of about 60%.

The impact of polymer selection and dose on the incorporation of ballasting agents onto wastewater aggregates.

Ballasted flocculation is an efficient high-rate sedimentation process getting more attention as an advanced P removal technology for levels below 0.1 mg/L. The process is well-known yet only very few studies have investigated the interactions, within the matrix of wastewater, of coagulant, polymer and ballast, especially when it comes to polymer doses and types which are, in the industry, rather based on recommendations than scientific evidence. In this work, the impact of anionic and cationic polymers has been investigated on P removal and floc properties. Anionic polymers showed to be superior to cationic ones when it comes to P removal and doses even as low as 0.01 mg/L yield better results than coagulant alone. There appears to be a "best-case" floc size with which very good P removal (>90%) can be achieved and flocs of sufficient strength can be generated.