Removing heavy metal ions from wastewater in the process
of tertiary treatment with a new sorbent based on modified clays

Summary

The concentrations of heavy metal ions present in municipal and industrial wastewater after biological treatment often exceed the maximum permissible values set for fishery water bodies. Sorption on activated carbon is a popular method in wastewater tertiary treatment practice. However, activated carbon is rather expensive and ineffective in removing heavy metal ions. Lately zeolites that provide for meeting MPC_fishery waterbodies in tertiary treatment have been used; however, their sorption capacity is low. In ordert to reduce the cost of tertiary treatment brand new sorption materials that are free from shortcomings of activated carbon and zeolites, widely used and affordable are required. The results of studying the removal of heavy metal ions from the model multicomponent solution with the use of new sorbents based on modified clays and peat from the Samara Region are presented. The activation was executed by thermal method. For the enhanced removal of copper, iron, manganese, zinc and lead ions from effluents the sorbent prepared from two clay types and peat in equal ratio with polyvinil acetate emulsion as a bonding agent turned to be most efficient. The required contact time of sorbent and solution was 90 minutes. For aluminium removal a sorbent prepared from two clay types, peat,wood ash and polyvinil acetate can be used with 150 minutes contact time with the solution. Sorbents prepared on the basis oft he Samara Region clays provide for meeting MPC_fishery waterbodies in the process of removing copper, iron, manganese, zinc, lead and aluminium from municipal and industrial effluents after biological treatment.

Key words

wastewater aftertreatment , sorbent , heavy metal ions , modified clay , sorption kinetics

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