Selenium bio-recovery (removal) from wastewater to low ppb levels
Although selenium (Se) is a an essential micronutrient for animals and humans, it becomes toxic at slightly higher intake levels than metabolically needed. Recovery (removal) of Se from wastewater provide a solution for both securing the Se supply and decreasing Se pollution. To achieve this, bio-crystallization is attractive interms of sustainability, cost and is suitable for treating dilute and variable Se-laden wastewaters. The objective of this project is to find an optimal operation method to remove/recover Se in wastewater down to 5 ppb.
- The large volume of wastewater makes it hard to design an efficient process to reach the strict discharging limits of Se-laden wastewater, especially at low temperature.
- The Se products in a bio-system are usually attached to biomass or suspended in the effluent, challenging the solid-liquid separation process and thus leading to higher operational.
Thus, the aims of this project are:
- To remove 0.42mg Se/L to less than 5ug Se/L at 5-15°C
Figure 1. A two-reactor system to remove selenate at 5- 15°C
2. To obtain recoverable Se particles from concentrated selenate waste streams at high bioconversion rates.
Figure 2. Recoverable crystalized Se particles from the continuous bio-reactor
Adding a minute amount (mg/L) of Sulphur or Sulphate might help the kinetics of selenate reduction process by providing HS- to react with the bio-produced selenite to SeS2, which can be further bio-reduced to larger-sized crystal elemental selenium.
Figure 3. Possible principle of bio crystallization