Minna Pirilä

Removal of aqueous As(III) and As(V) by hydrous titanium dioxide.

Dissolved arsenic in drinking water is a global concern as it causes serious health problems. The purpose of this research was to study the applicability of an industrial intermediate product, a mixture of titanium hydroxide and titanium dioxide for removing aqueous arsenic. The material is common, inexpensive, and non-toxic, making it an attractive choice for drinking water purification. The kinetics and equilibrium of removing both primary inorganic arsenic forms, As(III) and As(V), were studied by separate batch experiments. The tested material functioned well in removing both of these arsenic forms. The apparent values for Langmuir monolayer sorption capacities were 31.8 mg/g for As(III) and 33.4 mg/g for As(V) at pH 4. The studied TiO(2) performed the best in acidic conditions, but also reasonably well in other pH conditions.

Production of Activated Carbon from Cocoa (Theobroma cacao) Pod Husk

Activated carbons were obtained from cocoa pod husk using two different initial particle sizes (ranges 0.25 – 0.50mm and 0.50 – 1.00mm), three chemical activation agents (K2CO3, KOH and ZnCl2) and carbonization under nitrogen atmosphere during two hours at three different temperatures (500°C, 650°C and 800°C). The prepared activated carbons were characterized using Brunauer–Emmett–Teller (BET) and Langmuir surface areas, pore volume, average pore size, bulk density, moisture, ash content, and yield. The five best activated carbons were selected for further experiments according to the chemical activation agent used, high BET surface area, high pore volume and low ash content. Additionally, content of impurities, carbon content and FE-SEM micrographs were determined for these five best activated carbons. As adsorption tests were also carried out with these samples. Results of the experiments show that cocoa pod husk is a material that can be used to produce activated carbon by chemical activation and ZnCl2 showed to be the best chemical activation agent based on the highest BET surface area (780 m2/g in the best case) and pore volume (0.58 m3/g in the best case), the lowest ash content (6.14% in the best case), and the highest carbon content (86.1% in the best case), compared with others chemicals. Carbons activated by ZnCl2 are capable to adsorb As(V), getting As(V) removal levels up to 80% in less than 1 hour in the experimental conditions applied (initial pH 6-7, activated carbon concentration 0.1 g/l and 0.5 g/l, initial As concentration 100 ppb).

Photocatalytic Degradation of Organic Pollutants in Wastewater

Even today the efficient treatment of industrial wastewaters is not evident. The effluents may contain large amounts of harmful organic compounds that are not easily removed with conventional methods. This study focuses on the photocatalytic treatment of four organic pollutants originated from different types of industry. The pollutants are diuron (herbicide), p-coumaric acid (agro-industrial wastewater), bisphenol A and phthalic anhydride (plasticizers), which all are widely used and cause significant health and environmental problems. To get deeper understanding, the photocatalytic degradation of the model molecules was studied both in synthetic solutions and in industrial wastewater matrix over TiO2 P25 in two different batch photoreactors under UV-A irradiation. The effects of catalyst loading, pH and initial concentration were studied. To gain understanding on the reactivity of molecules and costs of treatment, the kinetic modelling and energy modelling were compared and the specific applied energy (ESAE) was estimated. ESAE is proposed as a useful value to estimate the energy needed to degrade one mole of pollutant and further to calculate the operating costs to treat the wastewater. Of the model pollutants, diuron was removed the most efficiently and its removal consumed the least amount of energy in terms of the specific applied energy. Bisphenol A was found to be the most difficult to be removed by photocatalysis. The industrial wastewater matrix affected negatively the removal results.

Photocatalytic Degradation of Butanol in Aqueous Solutions by TiO2 Nanofibers

Removal of butanol from aqueous solutions was studied using both custom made and commercial TiO2 photocatalysts. The custom made photocatalytic materials were nanofibers of titanium dioxide doped with nitrogen and subsequently decorated with nanoparticles of platinum or palladium. Pd-decorated photocatalysts were found to be highly efficient in the degradation of butanol under UV-A irradiation compared to Pt-decorated nanofibers or to commercial Degussa P25.

Adsorption of As(V), Cd(II) and Pb(II), in multicomponent aqueous systems using activated carbons

  This paper studies the use of two activated carbon samples made of cocoa pod husk (CPH-AC) and one commercial activated carbon sample in the adsorption of As(V), Cd(II) and Pb(II) from multicomponent synthetic solutions and from the Puyango-Tumbes River water, a river located in northwest Peru. The characterization of the activated carbon samples was conducted. The CPH-AC samples exhibited a specific surface area (SBET) between 709 and 1117 m2/g and a pH point of zero charge (pHPZC) between 4.4 ± 0.2 and 5 ± 0.2, while the commercial material gave an SBET value of 775 m2/g and a pHPZC value of 7.6 ± 0.1. All the evaluated samples displayed the capacity to adsorb As(V), Cd(II) and Pb(II) from both aqueous systems. The adsorption efficiency for Pb was outstanding reaching the value of 89%. A pseudo-second order kinetic model was satisfactorily applied for most of the activated carbon samples.