CC BY
122
y^K 621.863.2
SMELLS IN DRAINAGE SYSTEMS AND PREVENTION METHODS OF
THEIR SPREADING
E.M. Voronova, ass. professor, K.U. Cheremnih, master, V.A. Urchenko,
professor
Summary. The chemical composition of the gaseous compounds formed at transportation of sewage by networks of drainage systems is considered. The most optimal prevention methods of gaseous emissions spreading from networks of drainage systems are offered.
Keywords: pollution, air pool, sewer network (collector), dangerous gaseous, compounds, microbiological processes, biological method, cleaning.
Introduction
In modem cities one of the factors influencing on deterioration of the condition of the environment is air pollution. Motor transport and large power engineering enterprises are the basic sources of pollution. However emissions of polluting substances happen at the enterprises of the municipal economy dealing with sewage disposal too. Volatile compounds which are emitted include a whole complex of various substances of both inorganic and organic origin representing health hazards for people. Besides in the process of increased requirements to residing comfort in modern cities an increasing attention is not only given to safetis air but also to the presence of substances (odorants) in it forming unpleasant smells even in concentrations not representing any threat for health. Compounds of the reduced sulfur belong to such evilsmelling substances (hydrogen sulfide, light mercaptans) nitrogen containing organic substances aromatic hydrocarbons ammonia etc.
Therefore the purpose of the given work is to reveal the most ecologically dangerous compounds in drainage systems of gaseous emissions and the methods preventing their spreading.
Smells in drainage systems
Abroad researches of the chemical composition of drainage systems of gaseous emissions and also of structure of gases above sewage disposal constructions is widely conducted during the long period of time applying the advanced gas analysis methods. Foreign authors divide the compounds polluting the atmosphere of collectors into 4 groups (tabl. 1) [1]:
1) carbon dioxyde;
2) hydrocarbons and thir chlor derivatives;
3) hydrogen sulphide;
4) smelling gases and pairs such as mercaptans aminos aldehydes etc.
Table 1 Typical structure of the atmosphere of sewer collectors
№ n/n Connection The order of volume concentration
1 Carbon dioxide 0,2-1,2 %
2 Hydrocarbons and thir chlor derivatives
a. Hydrocarbons, mainly aliphaticheskie C6-C14, C8-C12 (gasolines) < 500 ppm
b. Chlor derivatives of hydrocarbons, mainly treechlor etilen, dichlor ethylene, tetrachlorid carbon 10-100 ppm
3 Hydrogen sulphide 0,2-10 ppm
4 Odorous gases and pairs
a. Sulphide (mainly mercaptan, dimethyl sulfide, some methyl mercaptan) 10-50 ppb
b. Aminos (mainly trimethyl amine and dimethyl amine, some diethyl amine) 10-50 ppb
c. Aldehydes (mainly oil aldehyde) 10-100 ppb
The distribution of substances into groups depends not only on their chemical nature but also on their concentration. The authors of this classification have not considered the presence of inorganic nitrogen containig compounds such as ammonia, nitrogen oxide in gaseous emissions from drainage systems though their concentration in the gas-air environment
of collectors surpasses maximum concentration limit for a working zone.
The content of gases depends on sewage composition being different for different collectors even within one settlement. Therefore with the purpose of receiving average indices of statistical processed data received from different sites of Kharkiv has been conducted. These data are given in tabl. 2.
Table 2 Chemical compounds in drainage systems of gas emissions in Kharkiv and their origin
The greatest problems for ecological safety and operational reliability of water removal are caused by the presence of hydrogen sulphide in emissions from drainage systems. They are caused by this gas toxic influence on a human being (a class of danger) the ratio of the exceeded emission concentration of the given substance to the maximum concentration limit excess frequency at regular control and also the quantity of network sites on which excesses are present. Besides hydrogen sulphide initiates corrosion and destruction of water removal concrete pipelines because of which their operational durability decreases by 5-10 times. Hydrogen sulphide can be smelled by a person in the concentration of nearby 0,001 ppm (a threshold of sensitivity of a smell concentration).
But the whole number of both inorganic and organic gaseous compounds carbon oxide, carbon dioxide, metane formaldehyde etc also create an ecologically dangerous loading on the atmosphere [3].
If we are able to establish the ties between the origin of the gases formed the kind of sewage and also the concrete physical conditions of sewage transportation
it will allow us to discover methods of the given problem solution. Therefore the following stage was to solve the problem of gaseous compounds origin in water removal networks. While solving this problem we based on the existing data of genesis of similar sulfur-, nitrogen-, and carbon gaseous compounds in biosphere. A sewer collector was considered as a technogenic ecosystem which includes three phases: liquid (transported sewage) gaseous (the atmosphere of a collector) firm (concrete of the arch) and spontaneously generated microbiocenoses. The chemical composition of sewage and concentration of some compounds in them is essentially changed at transportation by the networks because of various microbiological and chemical transformations of the initial substances forming gaseous compounds too. As the data of the scientific and technical literature and the results of our own researches testify the basic source of compounds in the atmosphere of the collector (a gaseous phase) is the microbiological processe in transported sewage - a water phase of the ecosystem. As experimental researches have shown the reduction of sulfates being the basic source of H2S in sewer networks is caused by the microbiological processes carried out by immobilised microbiocenoses. Gaseous microbic metabolites are emitted from sewages into the atmosphere of a collector and are partially dissolved either directly in the condensate of moisture on the arch of the construction or in aerosols of the pipeline which are later condensed on the arch. On firm surfaces the dissolving gaseous compounds initiate the development of the microbiological processes causing the most active microbiological aggression sulfur acide. This aggression causes an active concrete sewer pipelines corrosion drastically reducing their operational durability [4].
Evil-smelling substances emissions from sewer networks at the adverse wind directions leads to complaints from the population living in adjoining areas. This problem demands an engineering decision by introducing special disposal systems. Therefore nowadays for gas emissions cleaning a wide spectrum of chemical physicomechanical, physicochemical and biological methods partially replacing and mutually supplementing each other is used [2]. The results of the researches carried out have allowed to reveal the advantages of modern biological gas emissions cleaning before other methods especially concerning large discharges of emissions and also the highly concentrated emissions. The advantages
include the following:
• influence of polluting substances on all the components;
• absence of the necessity to replace the filtering substances for many years;
• removal of all the substances formed as a result of cleaning in the liquid phase;
• the opportunity of full automation;
• high stability to any fluctuations of the pollution concentration.
Com- pounds Gas emissions conce- ntration Frequency rate of excess of maximum concentration limit Microbiolo- gical processes
CO2, 06. % 0,1-3,5 < 7 Mineraliza- tion
CO, Mr/M3 0-25 < 1,4 Mineraliza- tion
CH4, 06. % 0,2-6,0 < 3 Methane genesis
H2S, Mr/M3 0-100 < 10 Sulphale- reduction, rotting
SO2, Mr/M3 5-30 < 3 Chemical oxidation AMC h H2S
AMC, Mr/M3 (1-4) 10-4 < 102 Rotting
NH3, Mr/M3 0-5,0 < 4 Ammonifi- cation
NOx, Mr/M3 0-5,0 < 4 Denitrifica- tion
The most productive system is the system of biological cleaning - a biofilter with an irrigated layer «Bioreactor TM» [2]. At the time of contact of 4-7 seconds they provide the highest efficiency of cleaning: for hydrogen sulphide and mercaptans it is more than 99 %; for ammonia it is more than 95 %. In such biofilter (fig. 1) the polluted air first passes through a disk dampener then it passes as a descending stream through some layers of fibrous polymeric loading on which a microbiological consortium is placed and further it passes through a drop catching device and then it is emitted out into the atmosphere. Each layer of loading is irrigated with a recycling liquid through sprayers.
1 - dampener; 2 - case; 3 - sprayers; 4 - biocatalyst; 5 - drop chipper; 6 - bottom tank; 7 - rough filter; 8 - thin filter; 9 - grid
Figure 1 The scheme of the biofilter with the irrigating sphere «Bioreactor TM»
At the same time biological cleaning of gaseous emissions as well as any biotechnology is sensitive to violations of conditions for carrying out of the given cleaning process namely to insufficient air humidity, breaks in air supplies in winter, at insufficient heating and at the absence of alkalining and so on. But all these reasons make the biological method optimal for cleaning of big volumes of gaseous emissions in drainage systems and on sewage disposial constructions.
Conclusions:
1. Gaseous compounds in drainage systems emissions have a complex chemical composition including both organic and inorganic sulfur, nitrogen and carbon compounds.
2. The most ecologically dangerous compounds in gaseous emissions from drainage systems are hydrogen sulphides. These compounds are the most dangerous ones for operational durability of concrete pipelines of drainage systems.
3. The source of hydrogen sulphide and other organic and inorganic substances in gaseous emissions from drainage systems are the microbiological processes
carried out by microorganisms of the biofilm which is immobilised on the arch parts of sewer pipelines.
4. The most effective method of drainage systems gaseous emissions dusposal is the biological one. The most productive is the system of biological cleaning -the biofilter with the irrigated layer of «Bioreactor ТМ».
Reference:
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Рецензент: доц. к.т.н. Анисимова С.В.
