Modern methods of slime waste disposal utilized by wastewater treatment plants were analyzed. Domestic and foreign experience in the application of silver clusters in reducing pathogenic and conditionally pathogenic microorganisms inhabiting the waste sludge was studied. The main mechanisms of bactericidal and bacteriostatic effects silver clusters are capable of exerting on microorganisms were considered. Strains of microorganisms with the ability to recycle organic and inorganic substances present in the waste sludge into ecologically pure humus fertilizer in the course of their vital activity were selected. The effects of different concentrations of silver clusters on growth and development of the microorganisms decomposing organic compounds (Microbacterium terregens BSB-570, Streptococcus termophilus St5, Lactobacillus sp. 501 (2A4), Rhodococcus erythropolis, Bacillus fastidiosus, Arthrobacter sp. (Arthrobacter paraffineus) ATCC 15591, etc.), as well as on the Escherichia coli bacteria chosen as a model organism, were studied. For the first time, decomposers modified with silver clusters, i.e. resistant to high concentrations of silver clusters, able not only to grow, but also to reproduce normally and, consequently, to recycle the waste sludge, were obtained. Bacteriostatic and bactericidal concentrations of silver clusters with respect to decomposers and optimal concentration, at which the useful microorganisms are able to grow and reproduce actively and the pathogenic Escherichia coli die, were determined.
silver clusters, nano-silver, destruction, pathogen, ion, nanoparticles, sludge, waste
Today, problems of environment protection and rational nature management, as well as improvement of ecological safety, are considered to be of paramount importance worldwide. Wastes formed in the process of industrial wastewater treatment belong to the most abundant contaminants of practically all components of the environment (surface and ground waters, soil, vegetative cover, and atmospheric air). These sediments, differing by chemical and physical properties, are called slimes. Very often, they are harmful for living organisms and the environment.
Most often, slimes formed in the course of wastewater treatment are buried at the industrial waste disposal sites upon slime treatment with bonding cement, bitumen, glass, or polymers. However, these waste disposal sites pose serious danger for the environment. Self-purification of the contaminated areas without human interference lasts for decades; besides, the inherent capacity of the environment for self-restoration decreases each year. Consequently, the problem of maximally efficient slime purification, which would take into account contaminant composition, economic, and ecological factors, becomes urgent .
In most cases, due to the lack in sufficient amount of specialized waste disposal sites meeting the requirements of construction norms and rules of the Russian Federation 2.01.28-85, the factories are forced to store wastes on their territories, often without adhering to the burial rules, which leads to soil and surface water contamination due to dissolving of slimes under the effects of atmospheric factors.
The amount of accumulated wastes and new wastes produced each year is so high that the slimes hold the first place in the extent of negative effect they produce on the environment and man, leaving behind such factors as noise, radioactive wastes, chemical fertilizers, and oil spills.
In most slimes, in addition to various organic and inorganic compounds, considerable amount of pathogenic microorganisms is contained. This natural slime microflora—thermotolerant сoliform bacteria, Escherichia coli, Chlostridium perfringens, Salmonella enteriditis, Salmonella virchow, etc.—poses a great danger, as it possesses the ability to excrete toxic compounds affecting human body.
The aim of the work was to study the effect of silver clusters on microorganisms capable of waste decomposing in the course of their vital activity and on E. coli to determine antipathogen activity of silver clusters. The study was conducted to develop new microbiological method of waste slime purification and processing under conditions of Siberian Federal District.
E. coli was chosen as a model organism since this rod-like bacterium is one of the best studied prokaryotic microorganisms and one of the most important subjects in biotechnology and microbiology. E. coli is well adapted to growth and proliferation under laboratory conditions .