Bioelektrokeemilised süsteemid nitraadi võimendatud eraldamiseks väikse elektronidoonori sisaldusega veest

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKõrge nitraadi (NO3) sisaldus pinna- ja põhjavees on suuresti seotud intensiivse põllumajandusega. Kõrge NO3 sisaldus joogivees võib olla inimestele ohtlik, põhjustades näiteks methemoglobineemiat või seedetrakti vähki. Seetõttu on oluline leida erinevaid lahendusi, et NO3 seotud reostust vähendada. Üks protsess, mille käigus NO3 on võimalik eemaldada on denitrifikatsioon. Selle protsessi käigus kasutavad mikroorganismid NO3 elektronakseptorina, just nagu inimesed kasutavad hingamiseks hapniku. Põhja- või pinnavees on denitrifikatsioon aga takistatud, kuna elektrondoonorite, näiteks orgaaniliste süsinikühendite, kontsentratsioon on väike. Väitekirja põhieesmärk oli hinnata, kas mikrobioloogilist elektrosünteesi reaktorit (MESR) on võimalik kasutada NO3 redutseerimise tõhustamiseks, madala elektrondoonorite kontsentratsiooni korral. MESR-i elektroodidele rakendatakse elektrivoolu, et muuta elektronid mikroorganismidele kättesaadavaks ja seeläbi toetada denitrifikatsiooni. Katsete läbiviimiseks valmistati kahe-kambriline MESR ja jälgiti selles toimuvaid protsesse 38 päeva jooksul. Tulemustest selgus, et MESR-i kasutamisel suurenes NO3 redutseerimiskiirus kaks korda, saavutades ärastuskiiruse 1,4 mgN-NO3/(L×päevas) ning samal ajal vähenes ka kasvuhoonegaaside emissioon. Kuna kahe-kambrilise MESR-i kasutamine põhjustas kõrvalekallet neutraalsest pH-st, siis otsustati teostada teine katsete seeria ühekambrilise MESR-ga. Teine katse kestis kokku 612 päeva ja selle käigus prooviti läbi erinevaid tööelektroodi potentsiaale ning optimaalse potentsiaali juures saavutati NO3 redutseerimiskiirus 3,8±1,2 mgN-NO3/(L×päevas). Seejuures jäi ka lahuse pH neutraalseks. Erinevate tööelektroodi potentsiaalide proovimisel leiti, et MESR-i võib kasutada ka teiste lämmastikuringega seotud protsesside, näiteks dissimilatoorse nitraadi redutseerimine ammooniumiks või nitrifikatsiooni, läbiviimiseks. Tulemuste põhjal võib väita, et MESR on paljutõotav tehnoloogia erinevate mikroobsete protsesside toetamiseks ning seetõttu on MESR-i võimalik kasutada väga erinevatel viisidel.High nitrate (NO3) concentration in surface water and groundwater is related mainly to intensive agricultural practices. A high level of NO3 in drinking water can be harmful to humans, causing methemoglobinemia or digestive tract cancer. Therefore, it is necessary to find solutions to reduce NO3 pollution. One process by which NO3 can be removed is denitrification. In this process, microorganisms use NO3 as an electron acceptor, just as humans use oxygen for breathing. However, denitrification is hindered in the ground- or surface water as the concentration of electron donors, i.e., organic compounds, is low. The main goal of the dissertation was to evaluate if the microbial electrosynthesis reactor (MESR) can be used to enhance NO3 removal at low electron donor concentrations. An electric current is applied to the MESR electrodes to make the electrons available to the microorganisms and thereby support denitrification. For experiments, a two-chamber MESR was constructed and operated for 38 days. During the investigation, the MESR was able to increase the NO3 removal rate twice to 1.4 mgN-NO3/(L×day) while lowering the greenhouse gas emissions. However, the two-chamber MESR caused pH to shift, so an experiment with single chamber MESR was conducted. Different working electrode potentials were tested during the second experiment, which lasted for 612 days. The MESR was able to reduce 3.8±1.2 mgN-NO3/(L×day), and the pH of the solution also remained neutral on the optimal potential. While trying different working electrode potentials, it was found that the MESR can also be used to enforce other nitrogen-cycle-related processes, i.e., dissimilatory nitrate reduction to ammonium or nitrification. The results show that the MESR is a promising technology to support different microbial processes and the field of application of MESR is diverse.https://www.ester.ee/record=b550745

Single-chamber microbial electrosynthesis reactor for nitrate reduction from waters with a low-electron donors’ concentration : from design and set-up to the optimal operating potential

Funding Information: This research was supported by the Estonian Research Council (grant numbers PSG631, PSG714, PRG352) and by the European Union (EU) through the European Regional Development Fund: Centre of Excellence EcolChange, TK 141 Advanced materials and high-technology devices for energy recuperation systems (grant number 2014-2020.4.01.15-0011), the University of Tartu Feasibility Fund (grant number PLTOMARENG51), and the European Structural and Investment Funds.Peer reviewedPublisher PD

Effect of cathode material and its size on the abundance of nitrogen removal functional genes in microcosms of integrated bioelectrochemical-wetland systems

Funding Information: Funding: This study was supported by the Estonian Research Council (PUTJD715, IUT2-16, PRG352 and PRG676); the EU through the European Regional Development Fund (Centre of Excellence EcolChange, Estonia) and by the European Structural and Investment Funds. The financial support from The French National Research Agency (ANR-17-CE04-0004) is gratefully acknowledged. The financial support from the International mobility support for PhD students–DrEAM (University of Lorraine) is gratefully acknowledged.Peer reviewedPublisher PD

Treatment Efficiency of Diffuse Agricultural Pollution in a Constructed Wetland Impacted by Groundwater Seepage

Diffuse agricultural pollution degrades water quality and is one of the main causes of eutrophication; therefore, it is important to reduce it. Constructed wetlands (CW) can be used as an effective measure for water quality improvement. There are two possible ways to establish surface flow CWs, in-stream and off-stream. We studied treatment efficiency of the in-stream free surface flow (FSW) Vända CW in southern Estonia from March 2017 until July 2018. The CW consists of two shallow-water parts planted with cattail (Typha latifolia). According to our analyses, the CW reduced total phosphorus (TP) and phosphate (PO4-P) by 20.5% and 16.3%, respectively, however, in summer, phosphorus removal was twice as high. We saw significant logarithmic correlation between flow rates and log TP and log PO4-P removal efficiency (rs = 0.53, rs = 0.63, p < 0.01 respectively). Yearly reduction of total organic carbon was 12.4% while total inorganic carbon increased by 9.7% due to groundwater seepage. Groundwater inflow also increased the concentration of total nitrogen in the outlet by 27.7% and nitrate concentration by 31.6%. In-stream FWS CWs are a promising measure to reduce diffuse pollution from agriculture; however, our experience and literature data prove that there are several factors that can influence CWs’ treatment efficiency

In situ measurements with CPC micro-actuators using SEM

Comparative measurements of carbon-polymer composite micro-actuators based on room temperature ionic liquid electrolyte were carried out in situ (1) in vacuum using a state-of-the-art scanning electron microscope, (2) in an oxygen-free atmosphere under ambient pressure, and (3) under ambient environment. The fabricated micro-actuators sustained their actuation performance in all three environments, revealing important implications regarding their humidity-dependence. SEM observations demonstrate high stroke actuation of a device with submillimeter length, which is the typical size range of actuators desirable for medical or lab-on-chip applications