Tero Luukkonen

Peracids in water treatment: A critical review

ABSTRACT Peracids have gained interest in the water treatment over the last few decades. Peracetic acid (CH3CO3H) has already become an accepted alternative disinfectant in wastewater disinfection whereas performic acid (CHO3H) has been studied much less, although it is also already commercially available. Additionally, peracids have been studied for drinking water disinfection, oxidation of aqueous (micro)pollutants, sludge treatment, and ballast water treatment, to name just a few examples. The purpose of this review paper is to represent comprehensive up-to-date information about the water treatment applications, aqueous reaction mechanisms, and disinfection by-product formation of peracids, namely performic, peracetic, and perpropionic acids.

Sulphate removal over barium-modified blast-furnace-slag geopolymer

Blast-furnace slag and metakaolin were geopolymerised, modified with barium or treated with a combination of these methods in order to obtain an efficient SO4(2-) sorbent for mine water treatment. Of prepared materials, barium-modified blast-furnace slag geopolymer (Ba-BFS-GP) exhibited the highest SO4(2-) maximum sorption capacity (up to 119mgg(-1)) and it compared also favourably to materials reported in the literature. Therefore, Ba-BFS-GP was selected for further studies and the factors affecting to the sorption efficiency were assessed. Several isotherms were applied to describe the experimental results of Ba-BFS-GP and the Sips model showed the best fit. Kinetic studies showed that the sorption process follows the pseudo-second-order kinetics. In the dynamic removal experiments with columns, total SO4(2-) removal was observed initially when treating mine effluent. The novel modification method of geopolymer material proved to be technically suitable in achieving extremely low concentrations of SO4(2-) (<2mgL(-1)) in mine effluents.

Comparison of organic peracids in wastewater treatment: Disinfection, oxidation and corrosion

The use of organic peracids in wastewater treatment is attracting increasing interest. The common beneficial features of peracids are effective anti-microbial properties, lack of harmful disinfection by-products and high oxidation power. In this study performic (PFA), peracetic (PAA) and perpropionic acids (PPA) were synthesized and compared in laboratory batch experiments for the inactivation of Escherichia coli and enterococci in tertiary wastewater, oxidation of bisphenol-A and for corrosive properties. Disinfection tests revealed PFA to be a more potent disinfectant than PAA or PPA. 1.5 mg L(-1) dose and 2 min of contact time already resulted in 3.0 log E. coli and 1.2 log enterococci reduction. Operational costs of disinfection were estimated to be 0.0114, 0.0261 and 0.0207 €/m(3) for PFA, PAA and PPA, respectively. Disinfection followed the first order kinetics (Hom model or S-model) with all studied peracids. However, in the bisphenol-A oxidation experiments involving Fenton-like conditions (pH = 3.5, Fe(2+) or Cu(2+) = 0.4 mM) peracids brought no additional improvement to traditionally used and lower cost hydrogen peroxide. Corrosion measurements showed peracids to cause only a negligible corrosion rate (<6 μm year(-1)) on stainless steel 316L while corrosion rates on the carbon steel sample were significantly higher (<500 μm year(-1)).

Removal of ammonium from municipal wastewater with powdered and granulated metakaolin geopolymer

ABSTRACT Ammonium removal from municipal wastewater poses challenges with the commonly used biological processes. Especially at low wastewater temperatures, the process is frequently ineffective and difficult to control. One alternative is to use ion-exchange. In the present study, a novel ion-exchanger, metakaolin geopolymer (MK-GP), was prepared, characterised, and tested. Batch experiments with powdered MK-GP indicated that the maximum exchange capacities were 31.79, 28.77, and 17.75 mg/g in synthetic, screened, and pre-sedimented municipal wastewater, respectively, according to the Sips isotherm (R2 ≥ 0.91). Kinetics followed the pseudo-second-order rate equation in all cases (kp2 = 0.04–0.24 g mg−1 min−1, R2 ≥ 0.97) and the equilibrium was reached within 30–90 min. Granulated MK-GP proved to be suitable for a continuous column mode use. Granules were high-strength, porous at the surface and could be regenerated multiple times with NaCl/NaOH. A bench-scale pilot test further confirmed the feasibility of granulated MK-GP in practical conditions at a municipal wastewater treatment plant: consistently <4 mg/L could be reached even though wastewater had low temperature (approx. 10°C). The results indicate that powdered or granulated MK-GP might have practical potential for removal and possible recovery of from municipal wastewaters. The simple and low-energy preparation method for MK-GP further increases the significance of the results.

Optimization of the metakaolin geopolymer preparation for maximized ammonium adsorption capacity

Abstract Geopolymers are functional materials that can be used in various environmental applications such as adsorbents in pollutant removal from wastewaters. Metakaolin geopolymer (MK-GP) has been proven to be especially suitable for ammonium (NH4+) removal. In this research, the optimal reagent and raw material ratios in the preparation of MK-GP in terms of NH4+ adsorption capacity were investigated. The response surface methodology based on the face-centered central composite design was used to optimize the levels of three factors: the amounts of hydroxide, silicate, and metakaolin. In addition, the effect of Na or K as the charge-balancing cation was studied. Empirical models were fitted to the experimental data using multiple linear regression. The significance of the models was confirmed by means of analysis of variance. Optimal NH4+ removal efficiency was achieved when the amounts of hydroxide and silicate were maximized, the amount of metakaolin was minimized, and Na-based reagents were used. These trends are most likely a result of optimized conversion of metakaolin into MK-GP.

Performance of Steel Fiber-Reinforced High-Performance One-Part Geopolymer Concrete

The high CO2 emissions of ordinary Portland cement (OPC) production have led to increasing the efforts on developing eco-efficient alternative binders. Geopolymers are inorganic binders proposed as an alternative to OPC, which are mainly based on aluminosilicate by-products and alkali activators. Higher utilization of industrial waste materials, such as ceramic manufacturing waste, could be enabled by geopolymers. In ceramic industry, around 30% of raw materials end up in waste streams, and therefore, an attempt is made to recycle these materials. The ceramic wastes are rich in silicate and aluminate and have therefore high potential to be used in the geopolymeric concrete. In the present paper, the porcelain ceramic waste was used as 10% of total binder weight in substituting ground-granulated blast-furnace slag (GGBFS). The results showed that the resulting binders have comparatively high compressive strength (≥60 MPa) and show brittle behavior, which is typical to inorganic binders with no fiber reinforcement. Microsteel fibers were used to improve the flexural performance of these binders at three different fibers by mass of binder (0.5%, 1%, and 1.5%). After curing, mechanical performances were investigated by measuring the compressive and flexural strength. The results showed that the addition of steel fibers significantly improved the flexural behavior. In addition, it was revealed that these fiber-reinforced binders had a deflection hardening behavior due to the bridging action of steel fibers.

How to tackle the stringent sulfate removal requirements in mine water treatment—A review of potential methods

ABSTRACT Sulfate (SO42‐) is a ubiquitous anion in natural waters. It is not considered toxic, but it may be detrimental to freshwater species at elevated concentrations. Mining activities are one significant source of anthropogenic sulfate into natural waters, mainly due to the exposure of sulfide mineral ores to weathering. There are several strategies for mitigating sulfate release, starting from preventing sulfate formation in the first place and ending at several end‐of‐pipe treatment options. Currently, the most widely used sulfate‐removal process is precipitation as gypsum (CaSO4·2H2O). However, the lowest reachable concentration is theoretically 1500 mg L−1 SO42‐ due to gypsums solubility. At the same time, several mines worldwide have significantly more stringent sulfate discharge limits. The purpose of this review is to examine the process options to reach low sulfate levels (< 1500 mg L−1) in mine effluents. Examples of such processes include alternative chemical precipitation methods, membrane technology, biological treatment, ion exchange, and adsorption. In addition, aqueous chemistry and current effluent standards concerning sulfate together with concentrate treatment and sulfur recovery are discussed. HighlightsGypsum precipitation can reach 1500 ppm SO42‐ but many mines have stricter limits.Several technologies for attaining low SO42‐ level (even near 0 ppm) are available.Sulfur chemicals can be recovered from sulfate.