Comparison of direct-flow and displacement biofiltration in decentralized water treatment devices
Abstract
At present, a serious issue is the contamination of groundwater by nitrates. The peculiarity of these substances consists in the difficulty of removal and the need to use expensive technologies. The health risk is the most essential to the population of regions with a lack of centralized water supply and low incomes. This work has been aimed at the evaluation of the effectiveness of decentralized purification of nitrate-contaminated water by the methods of direct flowing and piston (displacement) biofiltration. Despite the existing warnings, biofiltration is an effective and economic means of water denitrification. The combined use of biofiltration with available, proven, and effective methods of post-treatment of the filtrate, for example, bubble-film extraction and UV sterilization, provides high-quality tap water at sites where there is no centralized water supply. In this paper, denitrification has been studied by the direct-flowing and displacement biofiltration methods in the specially designed small-sized filtration devices of the "Point of use" type with the use of heterotrophs and autotrophs as agents of denitrification reactions. Heterotrophic denitrification is preferred in small-sized devices due to the rate of the process, which is an order of magnitude higher than autotrophic denitrification does. The results of studies of biofilter, with the optimal structure of the filtration bed, allow one to recommend the use of the piston biofiltration, as an alternative to direct flowing mode. This alternative has the following advantages. The consumer has the opportunity to periodically feed big portions of water contaminated with nitrates into the biofilter and simultaneously receive an equal portion of purified water that meets the sanitary and hygienic standards. A regular supply of water portions for denitrification ensures normalization of biofouling activity inside the biofiltration bed, which increases the stability of the biofilter action and eliminates the need for special dosing and flushing devices. In this mode of operation, the biofilter can run for a long time without clogging. The design of the created biofilters is simple, standardized parts, components, and materials, including easily recyclable ones, can be used for their assembly
Keywords
denitrification; biological reactor; displacement filtration; environmental friendliness; economy
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