Marika E Kokko

Tampere University | UTA · Faculty of Engineering and Natural Sciences

Methanol is a promising feedstock for the bio-based economy as it can be derived from organic waste streams or produced electrochemically from CO2. Acetate production from CO2 in microbial electrosynthesis (MES) has been widely studied, while more valuable compounds such as butyrate are currently attracting attention. In this study, methanol was us...

This book comprises six chapters prepared by the COST Action Circular City (https://circular-city.eu/). The Action aims to establish a network of researchers and stakeholders testing the hypothesis that: ‘A circular flow system that implements nature-based solutions (NBS) for managing nutrients and resources within the urban biosphere will lead to...

Biological hydrogen methanation (BHM) is a biocatalytic process for biogas upgrading. Integrating ex-situ BHM processes into biogas facilities has the advantage of using inoculum, CO2, and nutrients directly from anaerobic digestion (AD) processes to enhance CH4 productivity. This study investigated the potential of biowaste digestate as an inoculu...

Background Bacillus subtilis is generally regarded as a ubiquitous facultative anaerobe. Oxygen is the major electron acceptor of B. subtilis, and when oxygen is absent, B. subtilis can donate electrons to nitrate or perform fermentation. An anode electrode can also be used by microorganisms as the electron sink in systems called anodic electro-fer...

Background: Bacillus subtilis is generally regarded as a ubiquitous facultative anaerobe. Oxygen is the major electron acceptor of B. subtilis, and when oxygen is absent, B. subtilis can donate electrons to nitrate or perform fermentation. An anode electrode can also be used by microorganisms as the electron sink in systems called anodic electro-fe...

At conventional wastewater treatment plants (WWTPs), reject waters originating from the dewatering of anaerobically digested sludge contain the highest nitrogen concentrations within the plant and thereby have potential for realising nitrogen recovery in a reusable form. At the same time, nitrogen removal from reject waters has potential to reduce...

The possibility of producing hydrogen and methane from sedimented pulp and paper mill waste fibre was explored for the first time in a double-stage process. Hydrogen and methane production was compared in batch experiments under four different conditions: two-stage hydrogen and methane production under (i) mesophilic (37 °C) and (ii) thermophilic (...

The analysis of microplastics in complex environmental samples requires the use of chemicals to reduce the organic matrix. This procedure should be evaluated in terms of the preservation of the microplastic's integrity, typically done with pristine reference microplastics. However, real microplastics are most likely degraded due to weathering, so p...

The use of pyrolysis process to valorize digestate from anaerobic digestion (AD) of municipal sewage sludge for biochar production was piloted in a central biogas plant. The pyrolysis also generates pyrolysis liquid with high organics and nutrient contents that currently has no value and requires treatment, which could potentially be done in AD. As...

The pulp and paper industrýs mixed sludge represents waste streams with few other means of disposal than incineration. Hydrothermal carbonization (HTC) could be advantageous for the sludge refinement into value-added products, thus complementing the concept of pulp and paper mills as biorefineries. Laboratory HTC was performed on mixed sludge (at 3...

The extraction of microplastics from complex environmental matrices, such as sewage sludge, has proven challenging because of their high organic content. A common procedure for the extraction of microplastics from sludge involves conducting a chemical digestion to reduce the amount of organic matter in the sample, followed by a density separation o...

Contamination detection in drinking water is crucial for water utilities in terms of public health; however, current online water quality sensors can be unresponsive to various possible contaminants consisting of particulate and dissolved content or require a constant supply of reagents and sample preparation. We used a two-line test environment co...

Cathodic biofilms have an important role in CO2 bio-reduction to carboxylic acids and biofuels in microbial electrosynthesis (MES) cells. However, robust and resilient electroactive biofilms for an efficient CO2 conversion are difficult to achieve. In this review, the fundamentals of cathodic biofilm formation, including energy conservation, electr...

Recycling vital macronutrients, such as nitrogen, from wastewaters back to fertiliser use is becoming essential to ensure sustainable agricultural practices. Technologies developed for such purposes are typically evaluated for their capacity to recover nutrients; however, the presence of contaminants of emerging concern (CECs) in these waste-derive...

Biological hydrogen methanation (BHM) is a biocatalytic process for biogas upgrading. Integrating ex-situ BHM processes into biogas facilities has the advantage of using inoculum, CO2, and nutrients directly from anaerobic digestion (AD) processes to enhance CH4 productivity. This study investigated the potential of biowaste digestate as an inoculu...

Distinct microbial assemblages evolve in anaerobic digestion (AD) reactors to drive sequential conversions of organics to methane. The spatio-temporal development of three such assemblages (granules, biofilms, planktonic) derived from the same inoculum was studied in replicated bioreactors treating long-chain fatty acids (LCFA)-rich wastewater at 2...

Swelling bentonites, planned to be installed around spent nuclear fuel canisters made of copper/cast iron in geological repositories, contain organic matter. Organic matter can act as substrates for microorganisms, such as sulfate-reducing microorganisms (SRM), which produce sulfide, a copper corrosion agent. Thus, it is important to study the quan...

Reject waters from the dewatering of anaerobically digested municipal sewage sludge are nitrogen-rich (ca. 1 gNH4-N L⁻¹) wastewater streams. They account for up to 25% of the total nitrogen load of wastewater treatment due to their internal recirculation within treatment plants. In this study, nitrogen was effectively removed and recovered from rea...

There is an urgent need for more sustainable living and urban governance as natural resources are gradually being depleted and are deteriorating as a result of linear production/consumption patterns, which threatens our well-being (Bifulco et al. 2016; Liedtke et al. 2012; Voytenko et al. 2016). One of the reasons for the deterioration of natural r...

Source-separated urine is a natural liquid fertilizer used by humanity for millennia. Urine use in modern nutrient recycling can be hindered by high relative salinity, non-optimal macro-nutrient ratio, presence of pathogens, and organic micropollutants. In this study, an electrochemical system was used to oxidize and concentrate synthetic urine int...

Source-separated urine can enable efficient nutrient recycling, but the removal of the organic fraction that is required to ensure a safe nutrient product typically also removes the nitrogen in urine (present as total ammonium nitrogen, TAN). In this study, a reagent-free pH control method was used with a two-chamber electrochemical cell with a bor...

This study aimed to assess the role of hydrothermal carbonisation (HTC) in digestate processing in centralised biogas plants receiving dewatered sludge from regional wastewater treatment plants and producing biomethane and fertilisers. Chemically conditioned and mechanically dewatered sludge was used as such (total solids (TS) 25%) or as diluted (1...

In nature as well as in industrial microbiology, all microorganisms need to achieve redox balance. Their redox state and energy conservation highly depend on the availability of a terminal electron acceptor, for example oxygen in aerobic production processes. Under anaerobic conditions in the absence of an electron acceptor, redox balance is achiev...

With the growing demand for macronutrients, such as nitrogen, and environmental issues related to their production, there is increasing need for efficient nutrient recycling. Reject waters from the dewatering of anaerobically digested sewage sludge are potential sources for nutrient recovery due to their high ammonium nitrogen (NH4–N) concentration...

To enable and/or facilitate analysis of microplastics from environmental samples, a purification process is required to reduce the organic matter content. The development of such process has as one main concern, besides achieving efficient organic matter reduction, the preservation of the microplastics. In this study, a three-step method for sewage...

Sulfide formed by sulfate-reducing microorganisms (SRM) is a potential safety risk in the geological disposal of spent nuclear fuel (SNF) enclosed in copper canisters because it can corrode copper. The canisters will be isolated from the environment by surrounding them with compacted bentonite. This study shows experimentally that the organic matte...

Lipid-containing wastewaters, such as those arising from dairy processing, are frequently discharged at temperatures ≤ 20°C. Their valorization at low ambient temperatures offers opportunities to expand the application of high-rate anaerobic wastewater treatment toward achieving energy neutrality by minimizing the energy demand for heating. Lipid h...

The high volumes of sewage sludge produced have raised interests for simultaneous treatment and clean energy production, e.g. in the form of hydrogen. Pretreatment of sewage sludge is required to enhance microbial degradation and in turn hydrogen yield from sewage sludge. The potential of five substrate pretreatments, individually and in combinatio...

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this spe...

The utilization of foul condensate (FC) collected from a Kraft pulp mill for the anaerobic production of volatile fatty acids (VFA) was tested in upflow anaerobic sludge blanket (UASB) reactors operated at 22, 37 and 55°C at a hydraulic retention time (HRT) of ∼75 h. The FC consisted mainly of 11370, 500 and 592 mg/L methanol, ethanol and acetone,...

Start-up of bioelectrochemical systems (BESs) fed with brewery wastewater was compared at different adjusted anode potentials (-200 and 0 mV vs. Ag/AgCl) and external resistances (50 and 1000 Ω). Current generation stabilized faster with the external resistances (9 ± 3 and 1.70 ± 0.04 A/m3 with 50 and 1000 Ω, respectively), whilst significantly hig...

The microbial communities developed from a mixed-species culture in up-flow and flow-through configurations of thermophilic (55°C) microbial fuel cells (MFCs), and their power production from acetate, were investigated. The up-flow MFC was operated for 202 days, obtaining an average power density of 0.13 W/m3, and Tepidiphilus was the dominant tran...

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assess...

The inoculum source plays a crucial role in the anaerobic treatment of wastewaters. Lipids are present in various wastewaters and have a high methanogenic potential, but their hydrolysis results in the production of long chain fatty acids (LCFAs) that are inhibitory to anaerobic microorganisms. Screening of inoculum for the anaerobic treatment of L...

Human urine contributes approximately 80% of nitrogen and 50% of phosphorous in urban wastewaters while having a volume of only 1–1.5 L/d per capita compared to 150–200 L/d per capita of wastewater generated. There is interest to study source separation of urine and search methods to recover the nutrients form the urine. In this study, the objectiv...

Microbial electrochemical technologies (MET), also known as bioelectrochemical systems (BES), use microorganisms as biocatalysts to recover valuable resources like bioelectricity, hydrogen, nutrients, metals, and industrial chemicals from wastes and wastewaters. MET are therefore expected to play a key role in waste management and reduction of the...

The aim of this study was to determine an optimal anode material for electricity production and COD removal from xylose containing synthetic wastewater in an up-flow microbial fuel cell (MFC), and assess its suitability for treatment of thermomechanical pulping (TMP) wastewater with an enrichment culture at 37 °C. The anode materials tested include...

Anaerobic treatment of sedimented fibers collected from bottom of a bay that had been receiving pulp and paper mill wastewater for about 70 years were studied for the first time in semi-continuously fed continuously stirred tank reactors (CSTR). Anaerobic treatment of the fiber sediment was shown to be feasible, without dilution and with nitrogen an...

Herein, a techno-economic and environmental performance evaluation (i.e. Life Cycle Assessment (LCA)) of a 45kW Microbial Electrolysis Cell (MEC) system is presented, in the context of industrial wastewater remediation. This system produces H2 and CO2 –suitable for downstream CH3OH synthesis – based on the bio-electrochemical conversion of chemical...

This study demonstrates (bio)electrochemical tetrathionate (S4O62 −) degradation with simultaneous elemental copper recovery from simulated acidic mining water. The effect of applied external voltage on anodic tetrathionate removal, cathodic copper removal and current density was studied using two-chamber flow-through bioelectrochemical (MEC) and a...

Over the last decade, there has been an ever-growing interest in bioelectrochemical systems (BES) as a sustainable technology enabling simultaneous wastewater treatment and biological production of, e.g. electricity, hydrogen, and further commodities. A key component of any BES degrading organic matter is the anode where electric current is biologi...

Since the 1980s, the pulp and paper industry in Finland has resulted in the accumulation of fibres in lake sediments. One such site in Lake Näsijärvi contains approximately 1.5 million m³ sedimented fibres. In this study, the methane production potential of the sedimented fibres (on average 13% total solids (TS)) was determined in batch assays. Fur...

Aerobic wastewater management is energy intensive and thus anaerobic processes are of interest. In this study, a microbial fuel cell was used to produce electricity from xylose which is an important constituent of lignocellulosic waste. Hydraulic retention time (HRT) was optimized for the maximum power density by gradually decreasing the HRT from 3...

Microbial electrolysis cells (MECs) are an attractive future alternative technology to generate renewable hydrogen and simultaneously treat wastewaters. The thermodynamics of hydrogen evolution in MECs can be greatly improved by operating the cathode at acidic pH in combination with a neutral pH microbial anode. This can easily be achieved with aci...

The effect of poised anode potential on electricity production and tetrathionate degradation was studied in two-chamber flow-through electrochemical (ES) and bioelectrochemical systems (BES). The minimum anode potential (vs. Ag/AgCl) for positive current generation was 0.3 V in BES and 0.5 V in the abiotic ES. The anode potential required to obtain...

To prevent uncontrolled acidification of the environment, reduced inorganic sulfur compounds (RISCs) can be bioelectrochemically removed from water streams. The long-term stability of bioelectricity production from tetrathionate (S4O62-) was studied in highly acidic conditions (pH <2.5) in two-chamber fed-batch microbial fuel cells (MFCs). The maxi...

In bioelectrochemical systems (BES), the catalytic activity of anaerobic microorganisms generates electrons at the anode which can be used, for example, for the production of electricity or chemical compounds. BES can be used for various purposes, including wastewater treatment, production of electricity, fuels and chemicals, biosensors, bioremedia...

The results on the effects of different anode potentials on current densities, coulombic efficiencies and microbial communities are contradictory and have not been studied with xylose, an important constituent of lignocellulosic materials. In this study, the effects of different anode potentials (+0.2, 0 and -0.2V vs. Ag/AgCl) on current generation...

Inorganic sulfur compounds, such as tetrathionate, are often present in mining process and waste waters. The biodegradation of tetrathionate was studied under acidic conditions in aerobic batch cultivations and in anaerobic anodes of two-chamber flow-through microbial fuel cells (MFCs). All four cultures originating from biohydrometallurgical proce...

An exoelectrogenic culture was enriched on 1.0 g/L xylose from a compost sample in two-chamber microbial fuel cells (MFCs). Electricity production was optimized by changing mixing type, external resistance, xylose concentration and pH. Furthermore, the changes in microbial communities after each optimization step were monitored with PCR-DGGE. Elect...

Changes in temperature, pH, moisture, C/N ratio, and bacterial community were monitored in Istanbul full-scale composting plant. C/N ratio steadily decreased during composting and final mature compost products had a C/N ratio of less than 20. During the composting process, temperature was mostly above 55 °C and decreased to mesophilic conditions in...

Conifer and birch pulp fermentation to hydrogen and methane was studied using dry and wet pulps with a compost enrichment culture at a pH range from 6 to 9. Hydrogen was produced at each pH, whilst methane was produced at all other pH values except pH 6 with dry conifer pulp and pH 9. Hydrogen and methane yields were generally higher with birch tha...

Anaerobic hydrogen producing mesophilic and thermophilic cultures were enriched and studied from an intermediate temperature (45 °C) hot spring sample. H2 production yields at 37 °C and 55 °C were highest at the initial pH of 6.5 and 7.5, respectively. Optimum glucose, iron and nickel concentrations were 9 g/l, 25 mg/l and 25 mg/l both at 37 °C and...

Concentrated acid hydrolysis of cellulosic material results in high dissolution yields. In this study, the neutralization step of concentrated acid hydrolysate of conifer pulp was optimized. Dry conifer pulp hydrolysis with 55 % H(2)SO(4) at 45 °C for 2 h resulted in total sugar yields of 22.3-26.2 g/L. The neutralization step was optimized for sol...

In this study, grass silage was used both as a source of bacteria and as a substrate for dark fermentative hydrogen production. Silage is produced by lactic acid fermentation controlled by end point pH (<4.0). In this study, the fermentation of silage was successfully continued and directed to hydrogen production by neutralizing the pH. Highest hyd...

Dark fermentative hydrogen production by a hot spring culture was studied from different sugars in batch assays and from xylose in continuous stirred tank reactor (CSTR) with on-line pH control. Batch assays yielded hydrogen in following order: xylose > arabinose > ribose > glucose. The highest hydrogen yield in batch assays was 0.71 mol H2/mol xyl...

Cellulosic plant and waste materials are potential resources for fermentative hydrogen production. In this study, hydrogen producing, cellulolytic cultures were enriched from compost material at 52, 60 and 70°C. Highest cellulose degradation and highest H(2) yield were 57% and 1.4 mol-H(2) mol-hexose(-1) (2.4 mol-H(2) mol-hexose-degraded(-1)), resp...

Elevated temperatures (52, 60 and 65 °C) were used to enrich hydrogen producers on cellulose from cow rumen fluid. Methanogens were inhibited with two different heat treatments. Hydrogen production was considerable at 60 °C with the highest H2 yield of 0.44 mol-H2 mol-hexose−1 (1.93 mol-H2 mol-hexose-degraded−1) as obtained without heat treatment a...