Liquid purification or separation – Processes – Chemical treatment
Patent
1997-03-17
1998-11-17
Woo, Jay H.
Liquid purification or separation
Processes
Chemical treatment
210759, 210760, 210903, 159 473, C02F 172, C02F 178
Patent
active
058371486
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for eliminating inorganic and/or oxidizable nitrogen compounds from industrial wastewater and simultaneously using the nitrogen compounds contained in the wastewater as valuable industrial materials.
In 1986, 13% of the nitrogen input of 790,000 t N/a in the Federal Republic of Germany came directly from industry (Wieting, J.; Wolf., P.; Wasser Boden 10(1990), pp. 646-648). Nitrogen compounds endanger water ecology primarily through eutrophication by the ammonium, nitrite, and nitrate introduced. The intake of these substances in the diet via groundwater so affected significantly increases the risk of cancer for example owing to the carcinogenic effect of nitrosamines. For this reason, efforts are being made to keep the concentration of these materials as low as possible. Thus far, biological treatment methods, namely nitrification and denitrification, have been used for this purpose. Here, the end product of the reaction is elemental nitrogen which escapes into the atmosphere. The drawback of these treatment methods is that industrially valuable substances such as nitrate and ammonium are unavailable for industrial use. Moreover, this method leads to sludge formation with additional disposal problems.
In many chemical reaction processes such as the manufacture of nitric acid esters such as glycerol trinitrate, ethylene glycol dinitrate, etc. or nitro aromatics, e.g. trinitrotoluene, nitrobenzene, etc. appear in the subsequent product washings and in the wastewater from NO.sub.x washing, which contain high levels of nitrates and other nitrogen compounds. These normally acid wastewaters are generally neutralized with sodium hydroxide solution or milk of lime before going to the sewage treatment plant. The nitrates and nitrites produced by neutralization, together with the other nitrogen-containing compounds, are not only wasted in this process but they are also a burden on the biological sewage treatment plants and outlet channels.
Biological purification of such wastewater has become a particular financial problem for industry because of the high level of inorganic nitrate because the cost burden of wastewater treatment continues to increase through cost assumption of investment outlays by disposal associations, rising sewer fees and charges, and proportional operating costs.
BRIEF DESCRIPTION OF THE FIGURE
FIG. 1 shows a flow chart of how nitrogen compounds are eliminated from industrial wastewater and recovered for industrial use in accordance with an embodiment of the invention. Wastewater is processed through oxidation, absorption, neutralization and evaporation steps to obtain nitrogen compounds which may be recycled for industrial use.
The goal of the present invention was to produce a method for eliminating inorganic and/or oxidizable nitrogen compounds in industrial wastewater while simultaneously using the nitrogen compounds contained in the wastewater as materials useful for industry.
According to the invention, the inorganic nitrate is eliminated by extracting the nitrate portion from the wastewater as a recyclable material. This is achieved by neutralizing the acid wastewater to a pH of approximately 7 by adding sodium hydroxide solution or ammonia, preferably ammonia, as a neutralizer. The neutralized solution is then evaporated. When ammonia is used as a neutralizer, both ammonia gas and ammonia solution or ammonia water can be used as a neutralizer according to the invention. The advantage of ammonia gas is that it is easy to procure and does not contribute additional water to the neutralization reaction. It is disadvantageous that the neutralization container must be kept completely gastight and increased expenditure overall of MSR (measurement, control, and regulation) technology is necessary. An ammonia solution or ammonia water is relatively unproblematic on the other hand and can be handled safely. The circumstance that the parts of the plant also used for neutralization with sodium hydroxide solution can also be used when ammonia solution or ammonia
REFERENCES:
patent: 4971777 (1990-11-01), Firnhaber et al.
patent: 5167834 (1992-12-01), Gallup
patent: 5182027 (1993-01-01), Gallup et al.
patent: 5183577 (1993-02-01), Lehmann
Danzmann Erich
Muskulus Bernd
Neitzert Bernd
Trautmann Wilhelm-Heinrich
Zips Frank
Dynamit Nobel Atkiengesellschaft
Morrison Betsey J.
Woo Jay H.
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