In this process, phenol and thiocyanate were "eaten" (oxidized to carbon dioxide and water) by bacteria at a bio-oxidation plant. The treated water was then sent to the City of Bethlehem's municipal sewage treatment plant where the remaining ammonia was "eaten" by a yet another strain of bacteria and made safe to discharge into the Lehigh River.
The standard bio-oxidation plant for treating coke-making wastewater was developed by Bethlehem Steel beginning in the late 1950s and the full-scale plant was installed in the summer of 1962--a "first" in the United States. In developing the facility, researchers took bacteria from a local creek contaminated with phenol and cultured them for their ability to remove phenol. Later, mutant bacteria were introduced to maintain stability.
Until the facility was closed in the late 1990s, mutant bacteria arrived freeze dried and were rehydrated and cultured (fed milk whey) before being introduced into an aeration basin at their most active stage of life.
The bio-oxidation plant operation consisted of four main units: a large treated weak-liquor holding tank, a mix box, a rectangular aeration basin, and a pair of round clarifier ponds.
Before bio-oxidation actually began, process water was held at the treated weak liquor holding tank to equalize possible fluctuation of ammonia so that it does not adversely affect the rate of phenol oxidation. Process water was water used in cokemaking. From a holding tank, process water flowed to a mix box where an antifoam agent, phosphoric acid (a nutrient required by the bacteria), and dilution water were added. At this stage, process water was ready to begin bio-oxidation.
In starting bio-oxidation, the treated process water entered a rectangular aeration basin outfitted with eight spinning mixers called surface aerators. These acted like giant egg beaters to stir the process water and increase its oxygen content, which encouraged the bacteria to "eat" (break down) phenol and thiocyanate. As the bacteria increased in number (flocculated), they formed a bacterial cell mass called sludge.
Both the sludge and water flowed from the aeration basin to clarifiers where sludge settled out and was recycled back to the aeration pond. A side stream of excess sludge and effluent discharged to the city's sewage treatment plant where the remaining ammonia was "eaten" by a different strain of bacteria and was made safe to discharge into the Lehigh River.
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