38 research outputs found
Chemical aspects of peracetic acid based wastewater disinfection
Peracetic acid (PAA) has been studied for wastewater disinfection applications for some 30 years and has been shown to be an effective disinfectant against many indicator microbes, including bacteria, viruses, and protozoa. One of the key advantages compared to, e.g., chlorine is the lack of harmful disinfection by-products. In this paper a pilot-scale study of PAA-based disinfection is presented. Indicator microbes (E. coli, total coliforms and coliphage viruses) as well as chemical parameters (pH, oxidation-reduction potential (ORP), chemical and biochemical oxygen demand (COD and BOD), and residual PAA and hydrogen peroxide) were studied. The main aim of this investigation was to study how these selected chemical parameters change during PAA treatment. Based on the results, disinfection was efficient at C·t values of 15 to 30 (mg·min)/l which equals to a PAA dose of 1.5 to 2 mg/l and a contact time of 10 to 15 min. In this concentration area changes in pH, COD and BOD were negligible. However, hydrogen peroxide residues may interfere with COD  measurements and apparent COD can be higher than the calculated  theoretical oxygen demand (ThOD). Additionally PAA or hydrogen peroxide residues interfere with the BOD test resulting in BOD values that are too low. Residual PAA and ORP were found to correlate with remaining amounts of bacteria.Keywords: tertiary wastewater disinfection, peracetic acid, total coliform, E. coli, coliphage
Cold temperature represses daily rhythms in the liver transcriptome of a stenothermal teleost under decreasing day length
The climate-change-driven increase in temperature is occurring rapidly and decreasing the predictability of seasonal rhythms at high latitudes. It is therefore urgent to understand how a change in the relationship between photoperiod and temperature can affect ectotherms in these environments. We tested whether temperature affects daily rhythms of transcription in a cold-adapted salmonid using high-throughput RNA sequencing. Arctic char (Salvelinus alpinus) from a subarctic population were reared at a high and a low temperature (15 and 8 degrees C) for 1 month under natural, decreasing day length during late summer. Liver transcriptomes were compared between samples collected in the middle and towards the end of the light period and in the middle of the dark period. Daily variation in transcription was lower in fish from the low temperature compared with strong daily variation in warm-acclimated fish, suggesting that cold temperatures dampen the cycling of transcriptional rhythms under a simultaneously decreasing day length. Different circadian clock genes had divergent expression patterns, responding either by decreased expression or by increased rhythmicity at 15 degrees C compared with 8 degrees C. The results point out mechanisms that can affect the ability of fish to adapt to increasing temperatures caused by climate change
Biodegradation studies of recycled vegetable oils, surface-active agents, and condensing wastewaters
Abstract
Biodegradation is an aerobic or anaerobic degradation reaction where bacteria use organic materials as an energy source. In the aerobic biodegradation reaction, bacteria need oxygen as an electron acceptor, whereas an anaerobic reaction takes place in the absence of oxygen. Compounds degrade totally or partially, and produce simple inorganic species, such as CO2, CH4, NH3, NO3â, and H2O, as well as by-products that may be non-biodegradable and/or toxic.
In this thesis, the biodegradability of recycled vegetable oils, surface-active agents, and condensing waters from the process of wood drying were studied using the manometric respirometric BOD OxiTop method. The biodegradation of organic compounds was measured under the standard conditions (OECD 301F), and also in other matrices, such as different waters and soils. These are very different environments with respect to the biodegradation reaction in nature. The main differences in waters and soils are their organic and inorganic nutrient contents, bacteria strains, and temperatures.
The BOD OxiTop method is based on automatic pressure detection in a closed reactor vessel. Oxygen is consumed and carbon dioxide is formed in the aerobic reaction. The pressure decrease is detected after the carbon dioxide is adsorbed into a NaOH pellet or solution. The pressure change is dependent on oxygen consumption. The degree of biodegradation is calculated from the BOD value of the sample.
The studied recycled vegetable oils were found to be 60â83% biodegradable, and the added surface-active agent did not affect their biodegradation. Biodegradation of tall oil soaps was also examined in sand, topsoil, groundwater, and surface water, as well as under OECD 301F standard conditions. Tall oil soaps were proven to be 50â85% biodegradable. Concrete solvent agent (CSA) was also proven to be 78â83% biodegradable under standard conditions. Another detergent, cetyltrimethylammonium bromide (CTAB), was found to be toxic, whereas Triton X-100 biodegraded by only 6% in solution. Biodegradation of the soil matrix was found to be enhanced with added surface-active agents. This can be explained by better wetting of small pores with surface-active agents, as compared to the behavior of pure water. The biodegradation of the matrix occurred even with toxic surface-active agents. Organic pollutants of wastewaters from the process of wood drying were 25â61% biodegradable during a 28-day period, and were proven to be quite pure when considering the carbon content of the samples. Based on these results, the disposal into drainage of condensing waters from wood drying may be regarded as safe, which from an economical viewpoint is a very important conclusion.TiivistelmĂ€
Biohajoavuus on luonnollinen aerobinen tai anaerobinen hajoamisprosessi, jossa bakteerit kĂ€yttĂ€vĂ€t orgaanista materiaalia energian lĂ€hteenĂ€. Aerobisessa reaktiossa bakteerit tarvitsevat happea elektronien vastaanottajaksi, kun taas anaerobinen reaktio tapahtuu hapettomissa olosuhteissa. Yhdisteet hajoavat joko tĂ€ysin tai osittain sekĂ€ tuottavat yksinkertaisia epĂ€orgaanisia yhdisteitĂ€, kuten CO2, CH4, NH3, NO3â tai H2O. Reaktiossa voi myös muodostua sivutuotteita, jotka voivat olla biohajoamattomia ja/tai toksisia.
TÀssÀ työssÀ on tutkittu kierrÀtettyjen kasviöljyjen, pinta-aktiivisten aineiden sekÀ jÀtevesien sisÀltÀmien orgaanisen aineksien biohajoavuuksia kÀyttÀen manometristÀ respirometristÀ BOD OxiTop-menetelmÀÀ. Biohajoavuutta mitattiin standardiolosuhteiden (OECD 301F) lisÀksi muissakin olosuhteissa, kuten erilaisissa maissa ja vesissÀ. NÀmÀ ovat kaikki hyvin erilaisia ympÀristöjÀ luonnossa tapahtuville biohajoavuusreaktioille. PÀÀasialliset erot ovat sekÀ orgaanisten ettÀ epÀorgaanisten ravinteiden mÀÀrÀssÀ, bakteerikannoissa ja lÀmpötilassa.
BOD OxiTop-menetelmÀ perustuu automaattiseen paineen muutoksen havainnointiin suljetussa astiassa. Aerobisessa reaktiossa kuluu happea ja muodostuu hiilidioksidia, joka imeytetÀÀn NaOH-pelletteihin tai -liuokseen ja tÀstÀ muodostuu alipaine. Paineen muutokset muunnetaan hapenkulutuksen arvoiksi, joista lasketaan biohajoavuusaste.
Tutkittujen kierrĂ€tettyjen kasviöljyjen biohajoavuusasteet vaihtelivat vĂ€lillĂ€ 60â83 %, eikĂ€ lisĂ€tty pinta-aktiivinen aine vaikuttanut kyseisten ekoöljyjen biohajoavuuteen. MĂ€ntysaippuoiden biohajoavuus tutkittiin standardiolosuhteiden lisĂ€ksi hiekassa, mullassa, pohjavedessĂ€ sekĂ€ pintavedessĂ€. Niiden biohajoavuusasteet vaihtelivat vĂ€lillĂ€ 50â85 %. Betoninpesuaineen biohajoavuusaste standardiolosuhteissa oli 78â83 %. Kahdesta tutkituista pinta-aktiivisista aineista setrimoniumbromidi (CTAB) oli myrkyllinen liuosolosuhteissa eikĂ€ tĂ€ten biohajonnut ja Triton X-100 biohajosi vain 6 %. Pinta-aktiivisen aineen lisÀÀminen maahan aiheutti matriisina kĂ€ytetyn maan biohajoamisen. TĂ€mĂ€ voitiin selittÀÀ siten, ettĂ€ pintajĂ€nnityksen laskemisen jĂ€lkeen neste voi paremmin tunkeutua maan pieniin huokosiin ja nĂ€in tuoda hajoamatonta orgaanista ainesta ja uusia bakteereita biohajoavuuskĂ€yttöön. TĂ€mĂ€ ilmiö havaittiin myös myrkyllisen pinta-aktiivisen aineen lisĂ€yksen jĂ€lkeen. JĂ€tevesien sisĂ€ltĂ€mĂ€t orgaaniset ainekset hajosivat 25â61 % 28 pĂ€ivĂ€n aikana ja niiden havaittiin olevan hiilen mÀÀrĂ€n huomioon ottaen hyvin puhtaita. TĂ€ssĂ€ tutkimuksessa saatujen tulosten perusteella tutkitut puunkuivauksen kondenssivedet voidaan laskea viemĂ€riin, mikĂ€ on erittĂ€in tĂ€rkeĂ€ tulos ekologiselta ja taloudelliselta kannalta katsottuna
Effect of some process parameters on the main properties of activated carbon produced from peat in a lab-scale process
Abstract
Activated carbons (ACs) are widely used in different industrial processes as adsorbents for pollutant removal or as catalytic material support. The parameters and methods of activation can vary, and they affect the final characteristics of ACs, e.g., specific surface area, pore size distribution, and surface functional groups. The results of this study show that microporosity and mesoporosity can be modified, variating these parameters. ACs from Northern Finland Region peat have been prepared through physical activation with steam. The process has been evaluated using the design of experiment approach. Different parameters have been considered as factors, including holding time, oven temperature, heating rate, steam flow, nitrogen flow, kiln rotation, and biomass initial mass. Based on these factors, several responses characterizing the porosity and the elemental analysis of ACs have been selected. All the data collected have been processed statistically using the Fractional Factorial Resolution IV design linear model in a screening configuration fitted with a partial least squares regression using MODDE 9.1 by Umetrics Software
Peracetic acid for conditioning of municipal wastewater sludge:hygienization, odor control, and fertilizing properties
Abstract
Peracetic acid (PAA) is an environmentally friendly disinfectant and oxidizer used in several water and wastewater treatment applications. In the present study, PAA was utilized for the conditioning of municipal wastewater sludge before thickening and dewatering. It was shown that PAA can effectively prevent odor formation (i.e., HâS and NHâ) and provide hygienization (using E. coli and Salmonella as indicators). Phytotoxicity can be prevented by controlling the amount PAA-conditioned sludge that is mixed in the soil to be fertilized. The required PAA dose for hygienization was relatively high (480âŻmg 100% PAA perL sludge) but the results indicated that other sludge stabilization processes are not necessarily required. Therefore, the proposed process involving PAA could be feasible in cases where limited land area is available for sludge processing or quick conditioning of sludge is required
Removal of metals by sulphide precipitation using NaâS and HSâ»-solution
Abstract
Precipitation of metals as metal sulphides is a practical way to recover metals from mine water. Sulphide precipitation is useful since many metals are very sparingly soluble as sulphides. Precipitation is also pH dependent. This article investigates the precipitation of metals individually as sulphides and assesses which metals are precipitated as metal hydroxides by adjustment of the pH. The precipitation of different metals as sulphides was studied to determine the conditions under which the HSâ» solution from the sulphate reduction reaction could be used for precipitation. HâS gas and ionic HSâ» produced during anaerobic treatment could be recycled from the process to precipitate metals in acidic mine drainage (AMD) prior to anaerobic treatment (Biological sulphate reduction), thereby recovering several metals. Precipitation of metals with HSâ» was fast and produced fine precipitates. The pH of acid mine water is about 2â4, and it can be adjusted to pH 5.5 before sulphide precipitation, while the precipitation, on the other hand, requires a sulphide solution with pH at 8 and the sulphide in HSâ» form. This prevents HâS formation and mitigates the risk posed from the evaporation of toxic hydrogen sulphur gas. This is a lower increase than is required for hydroxide precipitation, in which pH is typically raised to approximately nine. After precipitation, metal concentrations ranged from 1 to 30 ÎŒg/L