Abstract: Methods and apparatus for coding a digital data string to represent a sequence of acoustic frequencies to be transmitted as an acoustic signal by a genuine acoustic authentication device; related to providing for improving the rate of successfully detecting a valid data string contained in the acoustic signal transmitted by the device. Each of a plurality of groups of bits of the data string are coded to represent a respective frequency value set of one or more acoustic frequencies to be transmitted acoustically to represent the respective group of bits. The number of acoustic frequencies in a frequency value set is less than the number of bits in the respective group of bits that the frequency value set represents. For each of the plurality of groups of bits of the data string, the respective frequency value set is selected according to a predetermined frequency assignation pattern that provides for probabilistic transition coding used for error correction of the acoustic signal.

Abstract: An oil-water separator for use in a trench, which surrounds an oilfield. The separator is positioned in the ground such that an inlet conduit extends at about the same level as the bottom of the trench. The trench water is admitted into the housing, where it contacts a plurality of buoyant oil-absorbing members, causing the oil particles to adhere to the surface of the oil-absorbing members. An outlet conduit located downstream from the oil-absorbing members is connectable to a pump to cause the oil-free water to be pumped from the housing and diverted away from the trench.

Abstract: An oil-water separator for use in a trench, which surrounds an oilfield. The separator is positioned in the ground such that an inlet conduit extends at about the same level as the bottom of the trench. The trench water is admitted into the housing, where it contacts a plurality of buoyant oil-absorbing members, causing the oil particles to adhere to the surface of the oil-absorbing members. An outlet conduit located downstream from the oil-absorbing members is connectable to a pump to cause the oil-free water to be pumped from the housing and diverted away from the trench.