Method of treating waste liquid from production plant for hydrocarbons or oxygen-containing compounds

1. A method for treating a formaldehyde-containing waste liquid, comprising the steps of:

subjecting formaldehyde in the liquid to chemical treatment to form a resulting waste liquid;

treating the resulting waste liquid, while being aerated, by using a membrane bioreactor that is comprised of a microorganism or enzyme and a separation membrane to form a treated waste liquid;

filtrating the treated waste liquid to form a filtrated waste liquid; and

sterilizing the filtrated waste liquid to form a sterilized and filtrated waste liquid.

2. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein the membrane bioreactor is provided with activated sludge.

3. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein the chemical treatment is conducted by converting formaldehyde to formic acid.

4. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein the filtrating is reverse osmosis filtration.

5. The method for treating the formaldehyde-containing waste liquid according to claim 1 , further comprising the step of adding a mineral or fertilizer after the sterilizing step.

6. The method for treating the formaldehyde-containing waste liquid according to claim 1 , additionally comprising the step of reclaiming the sterilized and filtrated waste liquid.

7. The method for treating the formaldehyde-containing waste liquid according to claim 6 , wherein the formaldehyde-containing waste liquid is formed as a byproduct during the production of dimethyl ether from a hydrocarbon via methanol, or during the production of liquid fuel oil from natural gas via synthetic gas.

8. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein at least part of the formaldehyde is converted to methanol or formic acid.

9. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein the microorganism or enzyme of the membrane reactor is sensitive to the formaldehyde concentration.

10. The method for treating the formaldehyde-containing waste liquid according to claim 1 , wherein the initial formaldehyde concentration in the waste liquid is between 100 mg/l and 200 mg/l.

11. The method for treating the formaldehyde-containing waste liquid according to claim 6 , wherein the membrane bioreactor is provided with activated sludge.

12. The method for treating the formaldehyde-containing waste liquid according to claim 6 , wherein the chemical treatment is conducted by converting at least a portion of the formaldehyde to formic acid.

13. The method for treating the formaldehyde-containing waste liquid according to claim 6 , wherein the filtrating is reverse osmosis filtration.

14. The method for treating the formaldehyde-containing waste liquid according to claim 6 , further comprising the step of adding a mineral or fertilizer to the resulting liquid, after the sterilizing step.

15. A method for treating a formaldehyde-containing waste liquid, comprising the steps of:

converting formaldehyde in a waste liquid to at least one other substance to lower the formaldehyde concentration in the waste liquid and forming a resulting formaldehyde-containing waste liquid; and

treating the resulting formaldehyde-containing waste liquid, while being aerated, by using a membrane bioreactor that is comprised of a microorganism or enzyme and a separation membrane.

16. The method for treating the formaldehyde-containing waste liquid according to claim 15 , wherein the membrane bioreactor is provided with activated sludge.

17. The method for treating the formaldehyde-containing waste liquid according to claim 15 , wherein the chemical treatment is conducted by converting formaldehyde to formic acid.

18. The method for treating the formaldehyde-containing waste liquid according to claim 15 , further comprising the step of filtrating after the treating step with the membrane bioreactor.

19. The method for treating the formaldehyde-containing waste liquid according to claim 18 , wherein the filtrating is reverse osmosis filtration.

20. The method for treating the formaldehyde-containing waste liquid according to claim 18 , further comprising the step of sterilizing after the filtrating step.

21. The method for treating the formaldehyde-containing waste liquid according to claim 20 , further comprising the step of adding a mineral or fertilizer after the sterilizing step.