RU2153921C2 - Method of cleaning waste gases from biologically decomposed contaminants - Google Patents

Abstract

FIELD: cleaning of waste gases. SUBSTANCE: method is used in production processes ejecting into atmosphere of oxygen-free waste gases for cleaning the latter. Oxygen-free waste gases are cleaned from biologically decomposed contaminants by washing of flow of waste gases to be cleaned with aqueous suspension of activated sludge under strict anaerobic conditions. Invention provides for reduction of power consumption and working expenditures in cleaning of oxygen-free waste gases from biologically decomposed contaminants. EFFECT: higher efficiency.

Description

 The invention relates to a technology for the purification of oxygen-free gas emissions.

 In some cases, industrial polluted gas emissions do not contain oxygen (air). For example, in the production of antibiotics at the last stage, the drug powder is washed with acetone and, in order to avoid obtaining an explosive mixture, it is dried with a heated inert gas - nitrogen. The resulting gas mixture of nitrogen with acetone vapor is released into the atmosphere.

 Purification of oxygen-free gas emissions from various impurities is carried out by absorption of the impurity with solid porous (adsorption) or liquid (absorption) absorbers. Both of these methods include the subsequent stages of desorption and therefore are characterized by the extreme complexity of technological schemes and significant energy costs (Rodionov A.I. et al. Environmental protection engineering, M., Chemistry, 1989, pp. 65 - 155).

 Reducing energy costs is achieved by using biological treatment. Biological methods of removing contaminants are widely recognized as the most cost-effective and environmentally friendly.

 SU 287904 A, 03/03/1970 describes a method for purifying oxygen-containing gas emissions from biodegradable contaminants by oxidizing them by aeration of an aqueous suspension of activated sludge with a stream of purified gas. In this method, biodegradable impurities, as well as oxygen from the stream of gas to be purified, are absorbed by an aqueous suspension of activated sludge and then oxidized to carbon dioxide and water by the aerobic biocenosis of activated sludge as a result of its vital activity.

 To use the described method for the purification of oxygen-free gas emissions, significant energy consumption will be required to pump an additional air stream (aeration) through the aqueous suspension of activated sludge, which is necessary to provide activated sludge with oxygen. In addition, this method is characterized by significant operating costs associated with the need for continuous selection and disposal of increasing biomass of excess activated sludge. In the process of aerobic treatment, from 1 to 1.5 kg of activated sludge biomass is formed for each removed kilogram of biological oxygen consumption (conventional unit for the mass of contaminants), the disposal of which is difficult due to the high moisture content of the sludge and its low water removal properties.

 The invention is aimed at reducing energy consumption, reducing operating costs in the selection and disposal of increasing biomass of activated sludge when cleaning oxygen-free gas emissions from biodegradable contaminants.

 This is achieved by the fact that washing is carried out under strictly anaerobic conditions.

 Example 1

Activated sludge taken from urban wastewater treatment plants with a volume of 15 l with a dry matter concentration of 5.3 g / l was loaded into a glass column with an inner diameter of 150 mm and a height of 1000 mm. Nitrogen gas with acetone vapor was fed into the column below. The nitrogen flow rate of 6.7 l / min, the concentration of acetone during the experiment varied in the range of 3 - 5.5 g / m ³ . For aeration of activated sludge, air was additionally supplied from below to the column with a flow rate of 7.5 l / min. Installation in continuous aerobic treatment functioned for 64 days. The degree of purification from acetone was 88 - 97%.

 At the same time, the concentration of activated sludge in dry matter monotonically increased from 5.3 to 20 g / l, and activated sludge acquired a gummy consistency with a significant content of polysaccharides.

 Example 2

The process conditions for purifying nitrogen gas from acetone vapor are similar in all process conditions in Example 1, except that no additional air was supplied to the column. The process of purifying the nitrogen stream from acetone vapor and biodegradation of acetone by the activated sludge biocenosis in the column were carried out under strictly anaerobic conditions. When changing the initial concentration of acetone in nitrogen in the range of 3 - 5.5 g / m ^{3, the} degree of purification was 85 - 96%. The concentration of activated sludge during the experiment practically did not change. The presence of methane was noted in the gas stream at the outlet of the column.

 When washing the stream of cleaned gas emissions with an aqueous suspension of activated sludge, contaminants from the gas stream are absorbed by the suspension of activated sludge. Then, in the suspension of activated sludge, the same processes proceed as in the treatment of contaminated wastewater.

 For the degradation of pollution, two types of biological processes are used: a) aerobic processes in which microorganisms use dissolved oxygen introduced into a suspension of activated sludge due to its aeration; b) anaerobic processes in which microorganisms do not have access to free dissolved oxygen.

 In anaerobic metabolic processes, microorganisms use carbon from organic pollutants simultaneously as an electron donor, and they oxidize to carbon dioxide (one of the components of biogas), and as an electron acceptor, which ultimately leads to methane (the main component of biogas), as the most strongly reduced of carbon-containing compounds existing in nature.

 When choosing between aerobic and anaerobic processes, biodegradation of pollutants is usually in favor of the former, since at present they are better studied and more widely used. However, anaerobic biodegradation processes of pollution have a number of significant advantages. Firstly, the disadvantage of aerobic technologies is the significant energy consumption for aeration of a suspension of activated sludge, i.e. to provide it with dissolved oxygen. Secondly, much less biomass of excess sludge is formed in anaerobic processes. In aerobic forms from 1 to 1.5 kg of sludge biomass, while in anaerobic ones it is almost an order of magnitude less - only 0.1 - 0.2 kg of biomass or for each removed kilogram of biological oxygen consumption (conventional unit of pollution mass). Excess activated sludge obtained in aerobic processes has high humidity (90 - 99.7%) and has a very low water-giving capacity, which leads to the high cost of its processing. A significantly lower increase in activated sludge biomass in anaerobic processes, which also has good water-removing properties, practically eliminates the problems of processing and disposal of excess sludge.

Claims (1)

 The method of purification of oxygen-free gas emissions from biodegradable contaminants, which consists in washing the stream of purified gas emissions with an aqueous suspension of activated sludge under strictly anaerobic conditions.