Wet reclamation of sodium silicate used sand and biological treatment of its wastewater by Nitzschia

The massive amount of sodium silicate in the used sand was a pollution source,especially in the waste water from the wet reclamation of used sand.A new process of wet reclamation by biologically treating the waste water produced during the wet reclamation process of used sand was studied in the paper.In the work,the precultivation of N.palea was performed firstly,and three different scrubbing solutions:(1) tap water,(2) modified medium for N.palea,and (3) filtrate of the broth treated by N.palea for 15 days,were used.The results of the primary investigation show that a de-skinning ratio of 90％ is obtained when using the scrubbing solution containing modified medium for N.palea at the ratio 1:2 of sand and scrubbing solution,and the maximal concentrations of Na+ and SiO32- are 1.49 g·L-1 and 0.51 g·L-1,respectively.The results of the optimal biomass,pH value decrease and Na+ and SiO32- consumption indicate the optimal incubation conditions are at the irradiance of 5,000 lux and 25 ℃.Using the filtrate of the broth treated by N.palea for 15 days as the scrubbing solution directly,a de-skinning ratio of 93％ isthe highest compared to the results of the tap water and the modified medium for N.palea.In the biological process using N.palea,less water is used and little wastewater is produced,which is advantageous to the purpose of green manufacturing and environmental protection.