MEMORANDUM 

TO: Ron Jordan, EPA 

 Jezebele Alicea, EPA 

FROM: Liz Sabol, ERG 

 TJ Finseth, ERG 

 

DATE: 23 April 2012 

SUBJECT: Summary of Performance Data Requested from Vendors for Chemical 

Precipitation Systems with Organosulfide Addition and Biological Treatment 

1. INTRODUCTION/BACKGROUND 

ERG contacted General Electric (GE) and Nalco to request pilot-, bench-, and/or full-scale 

performance data for chemical precipitation systems operating with organosulfide addition and 

biological treatment (GE only). ERG specifically requested performance data for dissolved mercury 

to determine the affect of organosulfide addition in chemical precipitation systems for the treatment 

of high dissolved mercury concentrations in FGD wastewater. In addition to dissolved mercury, 

ERG also requested performance data for total mercury, selenate, and other metals, as available. 

This memorandum summarizes the performance data and information received from GE based on 

studies of biological treatment and GE and Nalco based on studies of chemical precipitation 

systems with organosulfide addition. 

2. GE BIOLOGICAL TREATMENT – SELENATE AND OTHER MISCELLANEOUS METALS

[CBI has been removed from this section.] 

3. GE CHEMICAL PRECIPITATION WITH ORGANOSULFIDE ADDITION – DISSOLVED AND 

TOTAL MERCURY

[CBI has been removed from this section.] 

4. NALCO CHEMICAL PRECIPITATION WITH ORGANOSULFIDE ADDITION – TOTAL AND 

DISSOLVED MERCURY 

Nalco provided raw data from a full scale evaluation of Nalmet 1689 at a power plant FGD 

wastewater treatment facility. At this particular site, the FGD wastewater from 2 units/FGD 

scrubbers is processed through a single FGD wastewater treatment process. Unit 1 scrubber purge 

dissolved mercury concentrations ranged from 1,500 to 12,000 ppt. Unit 2 scrubber purge 

dissolved mercury concentrations range from 1,400 ppt to 20,000 ppt. Total mercury effluent 

concentrations range from 92 to 421 ppt. See Appendix C (monitoring data) for the specific 

concentration data. 
Memorandum 

23 April 2012 

Page 2 

Attachment CH-904, “Nalco Helps Wisconsin Power Plant Reduce Mercury Emissions” (included 

in Appendix C), is a summary of the FGD wastewater at the Wisconsin power plant where the raw 

data described above was collected. The FGD wastewater influent mercury concentration is 

approximately 10,000 ppt. Through chemical treatment using a sulfide-based coagulant (i.e., TMT15), the plant was able to achieve 75% removal of the mercury, which was not enough to meet 

discharge requirements (1,500 ppt). As a result, the organosulfide based coagulant/flocculant 

Nalmet was used to lower mercury discharges. Because Nalmet is a polymer, coagulation and 

flocculation occur simultaneously. The addition of Nalmet creates large floc particles which settle 

quickly and therefore, do not readily carry over into the effluent. Coupled with filtration, mercury 

concentrations could be reduced to the parts per trillion (430 ppt as shown in CH-904) level without 

further coagulation. 

Attachment R-917, “Chemical Treatment Technology for Effective Heavy Metals Removal from 

FGD Scrubber Wastewater” (included in Appendix C), provides data on three case studies. Case 

Studies 1 and 3 provide information on mercury removal and Case Study 2 focuses on selenium 

removals. In Case Study 1, low-level mercury testing shows 48% better removal of soluble mercury 

with the organosulfide treatment over ferric chloride alone. In Case Study 3, the addition of 30 ppm 

of NALMET gave 90% reduction of soluble mercury. In Case Study 2, the goal of the treatment 

plan was to determine a chemical addition that would remove all of the insoluble selenium as well 

as some of the soluble selenium in the selenite or selenide form. According to the study, the best 

results were obtained using Nalmet 1689 in conjunction with Nalco 8130 and Nalco 71307. This 

combination (without filtration) provided over 80 % removal of total selenium (100 % of the 

insoluble and 8 % of the soluble selenium). With filtration and Nalmet, Nalco 8130, Nalco 71307 

treatment combination, over 90 % removal of total selenium (100 % of the insoluble and 53 % of 

the soluble selenium) was achieved.

Attachment CH-1080, “Improved Mercury Removal from FGD Wastewater with Nalco NALMET 

Technology” (included in Appendix C), is another case study of a plant installing a new FGD 

wastewater treatment plant to remove solids and metals from the FGD blowdown as part of a 

retrofit FGD scrubber project. This FGD wastewater treatment plant utilizes a high rate solids 

contact clarifier/thickener which combines coagulation, flocculation and settling in two conjoined 

vessels. To achieve lower mercury levels in the effluent than original system operations, 

organosulfide was added to the treatment process. Results of this jar testing showed that the 

optimum treatment for mercury removal was a combination of Nalco 8130, a proprietary coagulant 

blend, and Nalmet 1689 technology, achieving an average mercury concentration of 31 ppt. 

Nalco stated that in wastewater treatment, 90+ percent removal of dissolved mercury can be 

achieved if influent concentrations reaching 40,000 to 50,000 ppt. That means that 400-500 ppt in 

the effluent can be achieved with proper treatment and clarification without a final filtration step. 

Nalco noted that with a final filtration step, effluent concentrations below 100 ppt can be achieved. 

Additionally, if a system designed for 100-200 ppt dissolved mercury suddenly received a 

concentration of 40,000 ppt, the response of the system would depend on the dosage of chemistry 

used for mercury precipitation. 
Memorandum 

23 April 2012 

Page 3 

5. CHEMICAL PRECIPITATION WITH ORGANOSULFIDE SUMMARY 

[CBI has been removed from this section.]