Bioelectrochemical systems for enhanced removal of nitrate from water with a low electron donor concentration
Date
2022-07-06
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Abstract
Kõrge 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.
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.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
sewage, water pollution, water treatment, nitrates, wetlands, wetland sewage treatment systems, wastewater treatment, water quality, bioelectrochemistry