Wastewater carbon

Other uses include chemical manufacture (especially soda ash), fire extinguishers, and pH control of wastewater. Carbon dioxide is also used as a fumigant for stored grain and has replaced ethylene dibromide in this application. 

In addition to advanced hltration, this chapter also discusses carbon adsorption. This is a unit operation that uses the active sites in powdered, granular, and hbrous activated carbon to remove impurities from water and wastewater. Carbon adsorption and hltration share some similar characteristics. For example, head loss calculations and backwashing calculations are the same. Carbon adsorption will be discussed as the last part of this chapter. 

For example, productivities are limited by the amount of carbon in the wastewater. Carbon dioxide or some other carbon source must be introduced if growth to the N or P limit is to be accomplished, which is desirable because this would allow the most effective use of waste nutrients for recycling to the Energy Plantation. Introduction of CO2 to the pond system in the amounts required appears to be cost-prohibitive. 

Environmental Considerations. Environmental problems in Ziegler chemistry alcohol processes are not severe. A small quantity of aluminum alkyl wastes is usually produced and represents the most significant disposal problem. It can be handled by controlled hydrolysis and separate disposal of the aqueous and organic streams. Organic by-products produced in chain growth and hydrolysis can be cleanly burned. Wastewater streams must be monitored for dissolved carbon, such as short-chain alcohols, and treated conventionally when necessary. 

The wastewater produced in this process consists mostly of water used in cleanup and propellant conveyance and sorting operations. Techniques such as the use of activated carbon and biological treatment are being investigated for the removal of solvents and dissolved organic compounds (143). 

The dependence of the oxidizabiUty of Mn on the degree of alkalinity is an important factor in some processes for the removal of manganese from water and wastewater. Manganese(Il) compounds are fairly stable, although the hydroxide and carbonate precipitated from alkaline solution tend to... 

Activated carbon adsorption generally uneconomical for removal of >1000 ppm contaminant from large stream unless bed regenerated steaming often easiest regeneration method but creates new wastewater problem usually 3—5 kg steam requited per kg of carbon for regeneration. 

Other burners are used for low capacity operations. A cascade or checker burner, ia which molten sulfur flows down through brick checkerwork countercurrent to a flow of air, is used ia small units with a sulfur trioxide converter to condition gases entering electrostatic precipitators at boiler plants operating on low sulfur coal. A small pan burner, which is fed with soHd, low carbon sulfur, is used to produce sulfur dioxide for solution ia irrigation water to control the pH and maintain porosity ia the soil. The same type of burner is used to disiafect wastewater ia this case sulfur dioxide is used iastead of chlorine. 

Carbon Adsorption. Carbon adsorption is a well estabflshed and widely used technology for the removal of organics from wastewaters and gaseous streams. Carbon adsorption is a proven technology for potable water treatment and capable of reducing organic concentrations to very low or nondetectable levels. 

Common examples of compounds that are amenable to carbon adsorption are aromatics (benzene, toluene) and chlorinated organics (trichloroethylene, trichloroethane [71-55-6, 75 -(9(9-j5y, tetrachloroethylene, polychlorinated biphenyls (PCBs), DDT /T(9-77-77, pentachlorophenol [87-86-5J. Compounds that are not adsorbed effectively by carbon include ethanol [64-17-5], diethylene glycol [111-46-6], and numerous amines (butylamine [109-73-9, 13952-84-6, 75-64-9], triethanolamine [102-71-6], cyclohexylamine [108-91-8], hexamethylenediamine [108-91-8] (1). Wastewater concentrations that are suitable for carbon adsorption are generally less than 5000 mg/L. 

Most carbon adsorption units use granular activated carbon (GAC). The powdered form of activated carbon (PAC) typically is less than 100 microns in diameter and may be used to reduce dioxins in incinerator emissions (2) and in the treatment of drinking water and wastewater treatment (see the section on "Activated Sludge"). 

GAC may be used in fixed or moving beds and in downflow or upflow mode. Eixed beds are operated in downflow mode and as such, provide some amount of soflds filtration however, influent soflds concentration must be kept low (less than 5 mg/L suspended soflds) to prevent rapid plugging of the bed. Entered soflds are periodically removed by backwashing. Upflow beds are more tolerant of soflds because they are fluidized and expanded by the wastewater entering at the bottom. In moving beds, the flow is countercurrent and makeup, fresh carbon is added continuously at the top of the unit while an equal amount of spent carbon is removed from the bottom. 

Table 3. Oxygen Demand and Organic Carbon of Industrial Wastewaters...

Fig. 1. Alternative wastewater treatment technologies, where GAC = granular activated carbon, PAC = powdered activated carbon, POTW = publicly owned treatment works, and RBC = rotating biological contactor (— ), wastewater return flows (—— ), sludge.

Anaerobic treatment is usually employed for high strength wastewaters. In anaerobic treatment, complex organics are broken down through a sequence of reactions to end products of methane gas, CH, and carbon dioxide, CO2 ... 

Design data are available for the specific organics on the EPA s priority pollutant Hst. For mixed wastewaters, a laboratory study is necessary to determine adsorption characteristics. Wastewater is contacted with a range of concentrations of powdered carbon and adsorption occurs, as graphed ia the form of a Freundhch Isotherm, shown ia Figure 19. 

Because several commercial carbons are available, a comparative isotherm study should be made for a wastewater to determine which carbon is the... 

Type of Industry Wastewater TOC or phenol, mg/L, or color index Average removal, % Carbon usage nkg/10 L... 

Recent air pollution regulations limit the amount of volatile organic carbon (VOC) that can be discharged from wastewater treatment plants. Benzene is a particular case in which air emission controls are required if the concentration of benzene in the influent wastewater exceeds 10 mg/L. 

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