Metals biological treatment

Clarifiers typically are used in chemical precipitation and biological treatment processes to remove precipitated metal soHds and suspended biological soHds. To prevent the sludge blanket from becoming too thick or heavy, part of the sludge blanket is removed continuously or intermittently from the system and thickened prior to disposal. 

Heavy Metals Removal. Heavy metals should be removed prior to biological treatment or use of other technologies which generate sludges to avoid comingling metal sludges with other, nonhazardous sludges. 

Alternative 1 consists of preliminary treatment for heavy metals removal with the primary concern being iron removal (Figure 8.3). The levels of iron observed in the groundwater at this site would be very detrimental to the downstream treatment processes. This pretreated water would then be used for cooling tower makeup water followed by biological treatment. This approach would be the easiest and cheapest alternative. This combined process should provide effective removal of BTEX. 

The use of filtration to polish biological treatment system effluent has become more popular in recent years because of more stringent discharge requirements. The 1977 EPA survey of petroleum refineries indicated that 27 of 259 plants used filtration as part of the existing treatment scheme and 16 others planned to install filtration systems in the near future [5]. Filtration can improve effluent quality by removing oil, suspended solids, and associated BOD and COD, and carryover metals that have already been precipitated and flocculated. Improved effluent filtration in one recent instance helped a Colorado refinery to meet the newly adopted discharge toxicity requirements [49]. 

There are six primary in-plant control methods for removal of priority pollutants and pesticides in pesticide manufacturing plants. These methods include steam-stripping, activated carbon adsorption, chemical oxidation, resin adsorption, hydrolysis, and heavy metals separation. Steam-stripping can remove volatile organic compounds (VOCs) activated carbon can remove semi volatile organic compounds and many pesticides and resin adsorption, chemical oxidation, and hydrolysis can treat selected pesticides [7]. Heavy metals separation can reduce toxicity to downstream biological treatment systems. Discussion of each of these methods follows. 

Organic pollutants are generally found to be reduced to insignificant levels (<10 p-g/L) by biological treatment. Most metals are also found to be reduced across biological treatment they are generally at very low levels in the treated effluent. However, significant metal concentrations may be found in some treated effluent. 

At emulsion crumb rubber facilities, a well-operated biological treatment facility permits compliance with BPT limitations and reduces organic toxic pollutant levels. Toxic metals that may not be reduced include chromium, cadmium, copper, selenium, and mercury. Tables 16 and 17 show pollutant removal efficiencies at two emulsion cmmb plants. 

Metal precipitation and removal may also be used as a pretreatment step prior to a snbseqnent treatment for removal of other contaminants. Examples of their downstream process inclnde ultraviolet oxidation, air stripping, and biological treatment (D16512I, p. 5-6). 

Pintail Systems, Inc. s, spent-ore bioremediation technology includes two main treatment processes. The first process involves the biological treatment of cyanide wastes using indigenous bacteria, which are isolated from contaminated sites and cultured in large quantities for full-scale applications. The second process involves metal biomineralization in which biological processes are adapted to immobilize soluble and leachable metals. 

Cost Component Soil Wash Biological Treatment Metals Removal Total... 

Table 1 presents a detailed breakont of the costs for the hypothetical treatment of 22,000 tons of contaminated soil using the soil recycle treatment train (D10059U, p. 21). The hypothetical case cost estimate is based on a fines content of 16.5%. The estimated cost per ton is sensitive to the percent of fines present. This occnrs becanse the metals removal and/or biological treatment capacity can limit the utilization rate of the wash plant (D10059U, p. 21). 

U.S. Filter s powdered activated carbon treatment (PACT ) is a sorption system used to treat water contaminated with organics, inorganics, dyes, and metals. PACT combines biological treatment and powdered activated carbon (PAC) adsorption in one unit to attain treatment standards not readily attainable with these treatments independently. 

Barth, E. F., Ettinger, M. B., Salotto, B. V. McDermott, G. N. (1965). Summary report on the effects of heavy metals on the biological treatment processes.Joumal Water Pollution Control Federation, 37, 86—96. 

Lester, J. N. (1987). Biological treatment. In Heavy Metals in Wastewater and Sludge Treatment Processes Treatment and Disposal, Vol. 2,ed.J.N. Lester, pp. 15-40. New York CRC Press. 

E.F. Barth, M.B. Ettinger, B.V. Salotto, G.N. McDermott, Summary report on the effects of heavy metals on die biological treatment processes, J. WPCF 37 (1965) 86-96. 

Although removal of organic and microbiological pollutants from waters has been thoroughly studied, less attention has been paid to the transformation of metal or metalloid ions in species of lower toxicity or more easily isolated. Metals in their various oxidation states have infinite lifetimes, and chemical or biological treatments present severe restrictions or are economically prohibitive. Removal of these species is carried out, generally, by precipitation, electrolysis, chemical oxidation, adsorption, or chelation, all of them presenting drawbacks. 

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