October 29, 2013 Artis ROBALDS Heavy metal removal from wastewater by peat

1.What is biosorption? Peat as a biosorbent. 2.What type of peat is used and what metals are removed from polluted waters? 3.Factors influencing the sorption performance. 4.Instrumental tools used in the research of biosorption. 5.Modification of peat.

Based on the literature studies and our research results, a range of subjects are covered, including: 1.What is biosorption and what are biosorbents? Removal mechanisms 2.Peat as a biosorbent. Different types of studies 3.What type of peat is used and what metals are removed? 4.Factors influencing the sorption performance 5.Instrumental tools used in the research of biosorptiom 6.Modification of peat 7.Utilization, regeneration or reuse of peat. + example of Thallium(I) sorption by peat

Peat is a natural material formed from the partial decomposition of mosses, sedges, grasses, shrubs, or trees in waterlogged conditions. All peatlands, such as bogs and fens, are composed primarily of peat.

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Many industrial effluents are contaminated with heavy metals (e.g. lead, copper, cadmium, zinc, chromium). These pollutants are highly toxic, non biodegradable and may be cancerogenic. Sorption of metals onto biological materials (biosorption), including peat, is well-recognized as a alternative to “traditional” wastewater treatments processes. Compared to “traditional” techniques (such as precipitation, ion exchange and reverse osmosis), biosorption offers the advantages of low cost, good efficiency and it does not produce sludge of high metal content.

Insecticides and pesticides Medical diagnostics Special glasses Corrosian resistant alloys Electrical and electronic equipment Manufacture of cement Metal mining and ore processing Smelting of non-ferrous metals Combustion of coal

Definition: Biosorption may be simply defined as the removal of substances from solution by biological material.* Biosorption processes are used not only to remove heavy metals from polluted waters, but also to recover precious metals (such as gold or palladium). * Gadd, G. M. (2009). Biosorption: critical review of scientific rationale, environmental importance and significance for pollution treatment. Journal of Chemical Technology & Biotechnology, 84(1), 13–28.

Title=biosorption; WoS database Michalak, I., Chojnacka, K., Witek-Krowiak, A. (2013). State of the art for the biosorption process – a review. Applied biochemistry and biotechnology, 170(6), 1389–416.

Dried water hyacinth roots Seaweed Tea leaves Yeast biomass Sawdust Olive stones Fish scales Soybean hulls Oil-palm fibers Coconut shells Moss Rice hulls Chitin Animal bones Bacteria Fungi Algae

Peat can be used for wastewater treatment of polluted waters because: + Natural characteristics of peat ensure high removal efficiencies + Little pretreatment is required + It is inexpensive and available in large quantities There is a need to explore new areas, where peat could be used

There are at least three major points to consider when choosing the metal for biosorption studies to focus on: 1. metal toxicity (direct health threat); 2. metal costs (recovery interests); 3. how representative the metal may be in terms of its behavior (scientific studies).

15 Calcium, Titanium, Zirconium, Barium, Chromium, Iron, Manganese, Cobalt, Nickel, Copper, Zinc, Aluminum, Lead, Silver, Cadmium, Mercury, Thallium

1. Leachate from landfills 2. Mine drainage 3. Industrial effluents 4. Drinking water? Millions of people are drinking water that are contaminated with heavy metals!

 Peat with a low degree of decomposition for the production of sorbents should be used, because it exhibits higher porosity, specific surface area, and more developed structure.  However, very often little information is provided on type of peat used.

Sorption performance of peat has been evaluated in different types of studies: 1)In natural condition, e.g., in peatlands 2)In laboratory batch scale studies 3)In laboratory column studies 4)In pilot scale studies 5)In full scale systems, such as constructed wetlands

Sorption performance of peat has been evaluated in different types of studies: 1)In natural condition, e.g., in peatlands 2)In laboratory batch scale studies 3)In laboratory column studies 4)In pilot scale studies 5)In full scale systems, such as constructed wetlands

There is a big gap between laboratory studies and application of biosorbents in full scale systems However, studies show that peat can be used as an effective sorbent in so called constructed wetlands Potential application in full scale systems

Eifert, W.H. (2000). Constructed Wetlands: An Overview of the Technology. In: Proceedings of Peconic River Remedial Alternatives Workshop.

Factory producing fertilizers and industrial chemicals Perth, Australia

Batch scale laboratory studies

Pretreatment of peat Modification of peat Determination of sorption capacity, depending on:  Type of peat used  Initial metal concentration  Contact time between sorbent and sorbate  pH of the solution  Ionic strength  Temperature Characterization of peat sample (before and after the sorption)

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Peat are usually mixed with fixed volumes of solutions of metal ions of different concentrations, until equilibrium, that is saturation, has been reached.

1 g of peat was mixed with 80 ml of aqueous solution containing different concentrations of Tl(I) ions, using capped bottles (100 ml). Samples were shaken on a rotary shaker with a constant speed of 140 rpm for 24 h. The suspensions were filtered and the concentration of Tl(I) in the filtrates as well as in the initial solutions was determined.

The factors that influence the biosorption process can be grouped as: 1.Physical and chemical properties of metal ions (i.e., molecular weight, ionic radius, oxidation state) 2.Properties of biosorbent (i.e., the structure of the biomass surface) 3.The experimental conditions (i.e., pH, temperature, concentration of biosorbent, the concentration of sorbate) Factors influencing the sorption performance

Instrumental tools used A number of analytical techniques have been used in research of biosorption  Some are mandatory  Some are simple and low cost tools  Some are expensive and seldom used

Determine metal concentration in aqueous phase Atomic absorption spectroscopy (AAS) Visual confirmation of surface morphology of the biosorbent Scanning electron microscope (SEM) Crystallographic structure and chemical composition of metal bound on the biosorbent X-ray diffraction (XRD) analysis Determine active sites of the biosorbent Fourier transformed infrared spectroscopy (FT-IR); Characterize thermal stability of the biosorbent Thermogravimetric analysis (TGA)

Peat can be modified in order to reduce several deficiencies, which are:  Low chemical stability  Low mechanical strength  Tendency of peat particles to expand or shrink Modification can include chemical (e.g., washing with acids) and physical processes (e.g., grinding, boiling). However, modification costs are seldom mentioned in the research reports. Modification of peat

More focus should be put on: 1)Economic analyses are required to obtain the overall cost of the sorbent and biosorption process 2)The process is still in laboratory-scale, which should be brought to commercialization 3)The fate of exhausted biosorbent remains relatively unanswered 4)Cooperation between scientists, as multidisciplinary skills are needed Future trends and chalanges in this type of studies?

1.Eifert, W.H. (2000). Constructed Wetlands: An Overview of the Technology. In: Proceedings of Peconic River Remedial Alternatives Workshop. 2.Gadd, G. M. (2009). Biosorption: critical review of scientific rationale, environmental importance and significance for pollution treatment. Journal of Chemical Technology & Biotechnology, 84(1), 13–28. 3.Magri, M.E., Zaguini, J.G., Barão, L.Z., Haiml, C., Sezerino, H., Philippi, L.S. (2012). Operation Of Constructed Wetlands For Sludge Dewatering With Effluent Recirculation: Characteristics Of Effluent Produced and Accumulated Sludge. In: Proceedings of the 13th international conference Wetland systems for eater pollution control (Volume II). Perth, Australia, Michalak, I., Chojnacka, K., Witek-Krowiak, A. (2013). State of the art for the biosorption process – a review. Applied biochemistry and biotechnology, 170(6), 1389–1416. References

This study was supported by European Social Fund within the project "Support for Doctoral Studies at University of Latvia".