Heikki Särkkä

Bioprospective of Sorbus aucuparia leaf extract in development of silver and gold nanocolloids.

At the present time the bioprospective field is a dynamic area of research. The rapid biosynthesis of silver and gold nanoparticles without using toxic chemicals is reported here. Sorbus aucuparia is omnipresent in Europe. The aqueous leaves extract of the plant were used as reducing agent for the synthesis of silver and gold nanoparticles from their salt solutions. The synthesized nanoparticles were spherical, triangular and hexagonal in shape with an average size of 16 and 18nm for silver and gold, respectively. Different extract quantities, metal concentrations, temperatures and contact times were investigated to find their effect on nanoparticles synthesis. The resulting silver and gold nanoparticles were characterized by transmission electron microscopy (TEM), UV-vis spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). The concentration of residual silver and gold ions was measured by Inductively Coupled Plasma (ICP) spectroscopy. Silver and gold nanoparticle suspensions gave maximum UV-vis absorbance at 446 and 560nm, respectively. The XRD data illustrated characteristic diffraction patterns of the elemental silver and gold phases and the average size of the crystallites were estimated from the peak profiles by Scherrer method. FTIR spectra of the leaf extract before and after the development of nanoparticles were determined to allow identification of possible functional groups responsible for the conversion of metal ions to metal nanoparticles.

Electrochemical inactivation of paper mill bacteria with mixed metal oxide electrode

In this study electrochemical inactivation of selected bacteria living in paper mill circulating waters was investigated. Three aerobic bacteria species (Deinococcus geothermalis, Pseudoxanthomonas taiwanensis and Meiothermus silvanus) were inactivated effectively (>2 log) at a mixed metal oxide (MMO) electrode in 3 min. The influence of parameters, such as current density and initial pH or chloride concentration of synthetic paper machine water (SPW) on the inactivation efficiency were studied. Increasing current density and initial chloride concentration of SPW increased the inactivation rate but change of pH value did not have significant influence on the inactivation rate. It was observed that inactivation was mainly due to the electrochemically generated chlorine/hypochlorite. Electrochemical oxidation showed good performance for inactivation these primary biofilm forming bacteria species with improved current efficiency by higher initial chloride concentrations.

Precipitation of dissolved sulphide in pulp and paper mill wastewater by electrocoagulation

The precipitation of dissolved sulphide ions by electrocoagulation was studied at laboratory scale using pulp and paper mill wastewaters. Concentrations of dissolved organic carbon and phosphorus were analysed before and after the electrocoagulation process to examine the suitability of the process for treatment of sulphide odour from pulp and paper mill wastewater. The electrochemical cell used in this study was constructed from monopolar dissolving iron electrodes. The dissolved iron concentration was directly proportional to the applied electric charge (C/L) at the tested current densities. Electrochemically produced ferrous iron (Fe2+) precipitated dissolved sulphide ions efficiently. Electricity consumption of the treatment was 4–8 C/mg S2− while iron consumption was 1.1–2.2 mg/mg S2− during the initial phase of the sulphide precipitation when the applied electric charge was 10–60 C/L. When 60 C/L was applied, 88% of dissolved sulphides and 40% of phosphorus was precipitated. The reduction in DOC was low during the sulphide precipitation. According to these results, electrocoagulation can precipitate dissolved sulphides effectively and thereby reduce sulphide odours of pulp and paper mill wastewaters.

Electrochemical oxidation of sulphides in paper mill wastewater by using mixed oxide anodes.

In this study, the electrochemical oxidation technique was used to oxidize sulphides present in paper mill wastewater. Inactivation of anaerobic bacteria in wastewater was also investigated. Sulphide oxidation was effective during the experiments, and the best efficiency was achieved by the smallest current density used. One of the main oxidants of sulphides during the experiments was oxygen. Anaerobic bacteria were better inactivated with higher initial chloride concentration in wastewater because of electrochemically generated chlorine/hypochlorite. Dissolved oxygen, redox potential and pH values of the wastewater increased because of electrochemically generated oxygen‐based oxidants and oxidation reactions occurring on the anode. In general, it can be said that sulphide removal was successful in the present study.

Incorporating Submerged MBR in Conventional Activated Sludge Process for Municipal Wastewater Treatment: A Feasibility and Performance Assessment

A pilot-scale submerged membrane bioreactor (MBR) was incorporated in a conventional activated sludge (CAS) process for more than 100 days in order to assess the feasibility and performance on the municipal wastewater treatment. After a stabilization period of 50 days, the MBR unit was operated under various temperatures (21 ± 4°C), mixed liquor suspended solids (MLSS) concentrations (14000 ± 1800 mg L-1 ), and different aeration intensities (3 to 6 m3 h-1). No significant deterioration in membrane flux was observed while operating with high biomass concentration. From the results, the removal of total suspended solids (TSS), chemical oxygen demand (COD), total phosphorus (TP) were enhanced using MBR. However, due to some limiting operational conditions, the total nitrogen (TN) removal was less efficient in MBR than in CAS. The MBR unit was 100% effective in removing E. coli and enterococcus, as well as noroviruses and adenovirus, making it more efficient than CAS. Also, the removal of most of the trace organic compounds (TrOCs) including personal care products, pharmaceuticals, steroid hormones and perfluorinated compounds were enhanced after the incorporation of MBR to CAS, as well as for many heavy metals in MBR.

NOM Removal by Electrochemical Methods

Electrochemical techniques such as electrocoagulation (EC) and electrooxidation (EO) have proved their efficiency in the removal of humic acid (HA), coliform, and algae from surface waters. Many investigations have also been conducted with synthetic wastewaters. EC combined with membrane filtration hybrid systems can increase natural organic matter (NOM) removal rates remarkably. In EO technology, electrolysis efficiency is strongly linked to electrode composition. Efficiency could be increased by changing the reactor design, using commercial electrodes, and exploring the semiconducting properties of oxide mixtures. Electrochemical methods may present an attractive alternative to other NOM removal techniques, such as conventional coagulation and chemical oxidation methods, for natural waters. Surface water treatment with EC can produce high-quality water for either potable or industrial use. This technology appears to remove some toxic pollutants from wastewater and could be used as a pretreatment in combination with some other purification technology. Boron-doped diamond (BDD) anodes have proved effective in HA removal from aqueous solutions and potentially their total mineralization.