Removing heavy metals from effluents with natural and modified clay-containing sorbents

Summary

The results of studies of the sorption of heavy metal ions by clay-containing sorbents from plating effluents are presented. The purpose of the tests carried out in a pilot plant was developing a process scheme for the removal of heavy metal ions from effluents and extraction of the spent sorbent in a precoat cartridge filter with a layer of perlite. The materials used in the tests were as follows: thermally modified sorbent based on natural material, i. e., modified clay, as well as mixed sorbent consisting of montmorillonite, peat and dolomite in a ratio of 5:4:1 without heat treatment. The studies were carried out on eight ions of heavy metals in the low concentration range typical for the effluent coming for tertiary treatment after sedimentation with pH adjustment. The main process parameters of tertiary treatment were: pH 8; the duration of the sorbent contact with the effluent was 90 min, the dose of sorbents was 1–1.6 g/l. The separation of the spent sorbent from the effluent was executed in two stages – sedimentation and filtration in a precoat cartridge filter. The addition of Aqua-AuratTM-30 coagulant with a dose of 40 mg/l as Al₂O₃ provided for reducing the concentration of suspended solids in the clarified effluent supplied to the precoat filters to 8 mg/l for modified clay and 15 mg/l for the mixed sorbent. The specific productivity of the alluvial layer was 23 m³/(h·m²), the specific load of the suspension on the filter surface was 850 g/m² for modified clay, and 680 g/m² for mixed sorbent. The estimated duration of the filtration phase of the alluvial layer while using preliminary chemical sedimentation was 4.6 and 2 h for the modified clay and mixed sorbent, respectively. The efficiency of removing heavy metal ions from effluents was provided at the level of the maximum permissible concentration for fishery water bodies.

Key words

wastewater , sorption , heavy metals , modified clay , dolomite , montmorillonite , peat , precoat filter

Common problems at water treatment facilities and ways to address them

Summary

Due to the anthropogenic factors, the quality of surface water is subject to rapid, mainly negative, changes; therefore, water treatment plants not always can meet the standards of the drinking water quality. Currently, many water treatment facilities are in need of upgrade, re-technologization and even reconstruction. In addition, significant changes in the actual water supply by the water facilities (decreasing, as a rule) do not always produce a positive effect on the technical and economic indicators of the water treatment facilities. Problems arising during the operation of the water treatment facilities at all stages of surface water purification – microfiltration, chemical treatment, mixing with chemicals and flocculation, sedimentation, filtration and wash water treatment are summarized. The methods used by MY PROJECT JSC in its projects to address such problems as the lack of the treatment efficacy, overspending of chemicals, short filter cycle, large water losses for process needs, discharge of untreated wash water, high purification cost are considered.

Key words

sedimentation tank , microfiltration , rapid filter , mechanical mixing chamber , flocculation chamber , zeolites , reconstruction of water treatment facilities , dolomite