Gravity membrane filtration in water and wastewater treatment schemes (a review)

Summary

Gravity membrane filtration technology involves the use of flat polymer ultrafiltration and microfiltration membranes with pore sizes from several nanometers to several hundred nanometers submerged in water at 40-100 cm, i.e. operating under a hydrostatic head of 40–100 mbar as a driving force of the membrane filtration in deadlock mode. The bacterial community of the source water induces the formation of a biofilm layer on the membrane surface. At the same time, the presence of eukaryotes in the biofilm layer that are characterized by predatory behavior produces a kind of “biological purification” effect that provides for decreasing the filtration resistance of the biofilm due to the formation of voids and development of its heterogeneity. As a result of the dynamic development of such a system, its sustainability and relative continuity of the permeate flow at the level of 2–10 l/(m2·h) are achieved. Sustainable water flow in the gravity membrane filtration mode is maintained for many months without cleaning the membrane. The system ensures the removal of organic substances and pathogenic microorganisms from water. Different-scale testing of the gravity membrane filtration system has been carried out: for decentralized river water treatment, for stormwater and gray wastewater treatment in local treatment systems to produce water suitable for non-potable consumption, in wastewater treatment for safe discharge, and for seawater pretreatment before desalination. Currently, examples of the practical application of this filtration system are known.

Key words

ultrafiltration , water treatment , organic substances , pathogens , gravity membrane filtration , deadlock mode

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Sanitary regulation and sanitary control – the basis of ensuring water body safety

Summary

Water safety is provided with two complementary processes: sanitary regulation and sanitary control of water bodies. The task of sanitary regulation is setting safety requirements to biological, chemical and physical indices. Sanitary representative microorganisms include representatives of obligatory microflora of human and homoiotherm organisms that allow estimating the degree of biogeneous pollution. These are Escherichia coli (collibacillus), fecal streptococcus (enterococcus), sulfite-reducing clostridia spores, Proteus, thermophilic microorganisms, coliphages (bacterial viruses) etc. Sanitary index is reflecting the presence and amount of one or another sanitary representative microorganism in a specified sample size taken from the water body under investigation. Qualitative sanitary index reflects and regulates the absence or presence of specified microorganisms in a specified sample size. Quantitative sanitary index is the concentration of specified (unknown) microorganisms in the specified sample size. Index figure reflects the degree of fecal contamination of the water body (Escherichia coli, Enterococcus faecalis, coliphages). Indicator figure reflects the efficiency of disinfection processes and technologies and points at possible presence of pathogens with different tolerance (Clostridium perfringens, coliphages). World Health Organization recommends distinguishing between two types of microbiological monitoring: for estimating water treatment efficiency; for identifying fecal pollution and presence of pathogens.

Key words

potable water , water object , sanitary and epidemiological requirements , pathogens , sanitary index