1. A method of biologically treating a spent caustic to provide a treated spent caustic, said method comprising the steps of:
(a) passing a spent caustic stream comprising water, alkali metal hydroxide and sulphide to a first bioreactor;
(b) biologically oxidising sulphide in the first bioreactor with sulphide-oxidising bacteria to form sulphur (S0) and sulphate to provide a partially oxidised spent caustic comprising sulphur (S0) and sulphate; and
(c) passing the partially oxidised spent caustic to a second bioreactor where at least a portion of the partially oxidised spent caustic is further oxidised with sulphide-oxidising bacteria to form sulphate from sulphur (S0) to provide a treated spent caustic comprising sulphate.
2. The method according to claim 1, wherein the first bioreactor and the second bioreactor are located in one vessel.
3. The method according to claim 2 wherein the partially oxidised spent caustic is substantially free of sulphide, comprising less than 10 mgl sulphide.
4. The method according to claim 3 wherein the redox potential of one or both of the first and second bioreactors is controlled at a value above \u2212300 mV versus a standard AgAgCl reference electrode.
5. The method according to claim 4 wherein the first and second bioreactors are operated as a continuous culture.
6. The method according to claim 5 wherein the sulphide-oxidising bacteria is of the general Thiobacillus, Thiomicrospira, and related organisms.
7. An apparatus for the biological treatment of a spent caustic comprising at least:
a first bioreactor having a first inlet for a spent caustic stream comprising water, alkali metal hydroxide and sulphide and a first outlet for a partially oxidised spent caustic stream comprising sulphate and sulphur (S0);
a second bioreactor having a first inlet connected downstream to the first outlet of the first bioreactor, and a first outlet for providing a treated spent caustic stream comprising sulphate;
wherein said first bioreactor comprises a first medium comprising a sulphide-oxidising bacteria which generates sulphur (S0) and sulphate from sulphide and said second bioreactor comprises a second medium comprising a sulphide-oxidising bacteria which generates sulphate from sulphur (S0).
8. The apparatus of claim 7 wherein the first outlet of the second bioreactor is connected to the first inlet of a separation device, which has a first outlet for a treated water stream.
9. The apparatus of claim 8 wherein the sulphide-oxidising bacteria is of a genera selected from the group consisting of Thiobacillus and Thiomicrospira.
10. The apparatus of claim 9 wherein one or both of the first and second bioreactors further comprise a redox device for controlling the redox potential of one or both of the first and second media.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A torque distribution control device for a four-wheel drive vehicle having an electromagnetic clutch for distributing to sub-drive wheels a torque transmitted from an engine to prime drive wheels and current apply means for applying a command electric current corresponding to a command torque to an electromagnetic coil of said electromagnetic clutch, said torque distribution control device comprising: command torque operation means for determining said command torque based on a vehicle speed, a throttle opening degree and a rotational speed difference between said prime drive wheels and said sub-drive wheels; and command torque limit processing means for limiting said command torque to an upper limit value therefor or below in dependence on an engine torque.
2. A torque distribution control device as set forth in claim 1, wherein said command torque operation means for determining said command torque is composed of pre-torque operation means for determining a pre-torque based on said vehicle speed and said throttle opening degree; compensation torque operation means for determining a compensation torque based on said rotational speed difference between said prime drive wheels and said sub-drive wheels and said vehicle speed; and addition means for calculating said command torque by the addition of said pre-torque to said compensation torque.
3. A torque distribution control device as set forth in claim 1, wherein said command torque limit processing means estimates said engine torque from at least the rotational speed of said engine and determines said upper limit value for said command torque based on said estimated engine torque.
4. A torque distribution control device as set forth in claim 3, wherein said command torque limit processing means estimates said engine torque from both of the rotational speed of said engine and said throttle opening degree.