Difference in calcium ion precipitation between free and immobilized Halovibrio mesolongii HMY2

Biomineralization has become a research focus in wastewater treatment due to its much lower costs compared to traditional methods.However,the low sodium chloride(NaCl)-tolerance of bacteria limits applications to only water with low NaCl concentrations.Here,calcium ions in hypersaline wastewater(10%NaCl)were precipitated by free and immobilized Halovibrio mesolongii HMY2 bacteria and the differences between them were determined.The results show that calcium ions can be transformed into several types of calcium carbonate with a range of morphologies,abundant organic functional groups(C-H,C-O-C,C=O,etc),protein secondary structures(β-sheet,α-helix,3_(10)helix,andβ-turn),P=O and S-H indicated by P2p and S2p,and more negativeδ^(13)C_(PDB)(‰)values(-16.8‰to-18.4‰).The optimal conditions for the immobilized bacteria were determined by doing experiments with six factors and five levels and using response surface method.Under the action of two groups of immobilized bacteria prepared under the optimal conditions,by the 10^(th)day,Ca^(2+)ion precipitation ratios had increased to 79%-89%and 80%-88%with changes in magnesium ion cencentrations.Magnesium ions can significantly inhibit the calcium ion precipitation,and this inhibitory effect can be decreased under the action of immobilized bacteria.Minerals induced by immobilized bacteria always aggregated together,had higher contents of Mg,P,and S,lower stable carbon isotope values and less well-developed protein secondary structures.This study demonstrates an economic and eco-friendly method for recycling calcium ions in hypersaline wastewater,providing an easy step in the process of desalination.

Enrichment of Cd^(2＋) from water with a calcium alginate hydrogel filtration membrane

A new method was developed for effective enrichment of Cd2+ ions from water with a calcium alginate(CaAlg) hydrogel filtration membrane. First, the CaAlg hydrogel filtration membrane was prepared without a pore-forming agent. This membrane was used to remove Cd^(2+) via ion exchange with Ca^(2+), and the Cd^(2+) was preserved in the CaAlg hydrogel. Then, the CaAlg hydrogel containing Cd^(2+) was soaked in a sodium citrate solution, and the hydrogel was fully dissolved. The removal rate of the CaAlg filtration membrane reached almost 100% within 120 min when the Cd^(2+) concentration was under 1 mg/L. Factors affecting the removal rate were investigated, such as NaAlg concentration, operating pressure, operating time and the initial concentration of Cd^(2+). The effects of initial Cd^(2+) concentration, pressure and filtration time on the enrichment factor were also investigated. The results show that the enrichment factor reached 87.3 when the pressure was 0.18 MPa and the filtration time was 240 min. Different enrichment factors could be achieved by adjusting the operating pressure and filtration time.