Wastewater Treatment Review

Leading Technologies is a reel to reel electronics plating company located in the Pittsburgh, PA area.

The waste water treatment plant has undergone a transformation from being an overhead cost to Leading Technologies of $164,450/year (chemistry and sludge disposal) to the current revenue generating department of $1,674/year (chemistry and sludge disposal costs). Besides the huge cost savings to the company, the environment now has approximately 480 tons less F006 sludge being generated to landfill each year as all of the current 40 tons of sludge being generated is recycled.

The following is a chronological story of how a determined waste water manager, Ron Zidian, with the help of outside consultant, Dean Schmelter, has changed the waste water treatment plant chemistries, and many of the past practices that were utilized to treat the 140 GPM (average) waste water stream flow through stream.

The chemistry program that was being run (until 1/18/96) to treat both the flow through system and batch treatment consisted of the following:

• Ferrous for metal Precipitation and Coagulation
• Lime for pH adjustment/Precipitant
• Flocculent for Enhanced Liquid Solid Separation

The total cost for the chemistry sludge hauling and disposal was at an annual amount of $164,450/yr. (see chart below). The chemistry program was inconsistent in controlling the amount of chemistry needed to Precipitate/Coagulate the metals in the waste stream and generated more solids than the system could separate from the water. Production was actually stopped often so the wastewater treatment could catch up with the sludge/solid loading that the system had generated. In addition, there were turbidity problems and solids carrying over in the clarifier were a common occurrence. The flow through system consisted of a 1 stage cyanide oxidation reaction, a 3 stage tank (pH adjust coagulation/pH adjust precipitation /flocculation) and a slant plate clarifier. The cyanide destruct system was undersized for the flow and cyanide complexing of metals in the waste water system was a real problem.

Extensive bench testing was done by Water Specialists to establish an alternate chemistry program that would accomplish the following:

• Reduce the sludge volume
• Consistently lower the solids being discharged from the plant
• Concentrate the metals in the sludge to a reclaimable value

In October 1996 a trial with Water Specialists chemistry was run. The trial was stopped, as turbidity was inconsistent. After careful evaluation, some mechanical and chemical injection changes were made and a second trial was scheduled.

Before the trial was resumed, exceptional care was taken to wash out all the wastewater equipment so no chemistry contamination would occur. In addition, a sludge recycle or reseeding system was installed and an ORP controller to automatically feed the metal precipitant based on demand.

Once again, the trial failed as the cyanide complexed metals couldn’t be fully broken and due to the increase in production and dump schedules. A batch treatment system to work in conjunction with the flow through system was initiated with existing tanks. The taking of heavy cyanide liquors out of the flow waste stream and putting them into the batch system was piped. The ORP original controller was undependable and was repaired at the ORP controller manufacturer. In addition, a 2nd ORP controller was added to the treatment system to control large spikes of metal with a second precipitant pump.

The wastewater treatment manager and Water Specialists went back to the drawing board. Batch treating these baths was an advantage for two reasons. First, the high cyanide was diverted from the flow through system. Second, pressing the batch could be done when the batch was completed – not limited to time retention as in the flow through system.

Over the next few months, the Water Specialists chemistry in the flow through system was optimized so crystal clear water was always produced with almost non detectable levels (to a 99.99% efficiency) of all metals separated by the flow through system (Cu, Ni, Ag).

Segregating the waste streams to separately batch the Nickel, Silver, and Copper was the concurrently undertaken. When the volumes of Copper or Nickel or Silver reached a previously planned set point, the batch would be treated with a chemistry combination that would be estimated in a 1 Liter sample that was bench tested.

Thus, to segregate and batch treat separate waste streams enabled Leading Technologies to go from paying for their sludge generated to be paid for their separate waste sludges as the metal content in the waste sludges were now nigh enough that metal recovery/recycling generated a pay back. In addition, the amount paid Leading Technologies over the course of a year is also listed. Chart below.

In the flow through system, the recycling of sludge to concentrate the metals in the waste has also increased the Silver content to the point that the sludge is now worth money as the metal content is high enough for the smelter to recover.