Experience of Modernization of Settling Tanks and Clarifiers at Water Treatment Stations

Summary

Methods of the modernization of different designs of flocculators, settling tanks and clarifiers based on the use of thin-layer, recirculating flocculation and thin-layer deposition are presented. Advantages of the design of thin-layer cellular blocks developed by the authors and produced by the EcoholdingClosed Company are shown. Results of the long term (over 10 years) operation of modernized settling facilities in the systems of communal and industry water treatment at different compositions of natural water and various methods of their treatment are presented.

Key words:

water treatment , modernization , intensification , flocculation , settling , thin-layer cellular blocks

Precipitation of dyes from spent solutions using magnesium-containing agents

Summary

Spent solutions generated in the process of skin dyeing make a significant negative contribution to the pollution of the total amount of wastewater of the enterprise; hence, the need arises for their local treatment to reduce the concentration of organic dyes before discharging into the total wastewater flow. The aim of the work was to study the possible use of magnesium-containing agents for the precipitation of dyes from local wastes. The experiments were conducted with simulated solutions of acid dyes that differed in molecular structure and the number of auxochrome groups to ensure the solubility of the dye and its adsorption by the dyeing material. Dyes were precipitated using magnesium-containing agents, i. e. suspension of magnesium hydroxide and magnesium oxide (MagPro), and for comparison, aluminium sulfate. The efficiency of the precipitation of dyes from solutions was evaluated by the amount of separated precipitate and the optical density of the supernatant. The effect of the precipitation agent consumption on the efficiency of removing dyes from the solution is shown. The results of the experiment provided for establishing the optimal consumption of precipitation agents for each of the dyes used. It was found that aluminum sulfate and MagPro were equally effective with respect to the direct brown solution. The acid black dye is predominantly precipitated with aluminum sulfate, while Luganyl brown NG is precipitated only with magnesium-containing agents. To precipitate dyes from local effluents with an equal precipitate yield, the consumption of MagPro agent is 10 times less than while using aluminum sulfate. MagPro is more effective in sedimentation and discoloration of local effluents after skin dyeing at pH above 12.

Key words

settling , aluminium sulphate , absorbency , local wastes , dyes , magnesium-containing agents , magnesium hydroxide , discoloration of solutions

Purification of local chrome-containing wastewater and recovery
of chrome compounds

Summary

Domestic and international experience in wastewater recycling and reuse at various stages of leather production shows that the effectiveness of the process solutions directly depends on the chemicals used. In the practice of Russian leather factories sodium carbonate is used to precipitate chromium compounds from solutions. The results of experimental studies of the recovery of spent chrome-containing solutions from the process of skin tanning with magnesium hydroxide suspension and sodium carbonate solution are presented. The conditions of spent chrome tanning liquor precipitation using magnesium hydroxide suspension were studied. The main parameters influencing the precipitation process are pH value and precipitation agent consumption. The high efficiency of using magnesium hydroxide suspension as a precipitation agent is explained by the higher precipitation rate and absence of chromium compounds in supernatant. The main characteristics of the generated sludge are determined. Chromic hydroxide generated as a result of using magnesium hydroxide suspension is characterized by the higher density and better filterability. The possible recovery of tannic chromium compounds from precipitated chromium hydroxide is shown when dissolved in sulfuric acid and reinforced with chrome tanning agent to the required concentration. Recommendations on the use of magnesium hydroxide suspension in the process of spent chrome tanning agent recovery have been developed. The technological advantages and economic efficiency of using magnesium hydroxide as compared to sodium carbonate solution are given.

Key words

settling , chrome-containing spent solutions , filtering capacity , chrome tanning agent , chromic oxide , magnesium hydroxide suspension

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