Typen talteenotto hydrolysoituneesta virtsasta energiaomavaraisen elektrokonsentraation avulla

Nutrients, especially the most widely used macronutrients nitrogen, phosphorus and potassium, are essential for sufficient food production to feed the constantly growing human population. However, fertiliser production deals with scarce, non-renewable raw-materials and high energy consumption, which is why more efficient nutrient recovery and re-use from human waste streams should be encouraged. Human urine is an especially interesting source for nutrient recovery since it contains most of the nutrients consumed and excreted by humans. This study focused on utilising bioelectrochemistry for nitrogen recovery from source-separated urine. The reactor design was a combination of microbial fuel cell and electrodialysis technology. The aim was to optimise the performance of both the anode and the cathode of the reactor towards a power-free nutrient recovery method. On the anodic side, the target was to enrich an acidophilic electroactive consortium, which would be able to enhance the nitrogen recovery as well as make more complete use of the high buffering capacity of urine. Of the three studied pH – 5.5, 6.5 and 7.5 – the highest one, 7.5, proved to be the most suitable one for the enriched culture, resulting in a maximum current density of 16 A m‑2 at Ewe = 0 V vs. SHE. On the cathodic side, an air-cathode using carbon cloth as the electrode material, carbon nanoparticles as the catalyst layer and commercial PTFE spray as diffusion layers was developed. Of the different layer materials tested, the best performance was obtained using acid-pre-treated nitrogen-doped carbon nanotubes as the catalyst and four layers of WD-40 PTFE spray as the diffusion layers. With this combination, an onset potential of +0.1 V vs. SHE for the reduction reaction was obtained and the maximum current reached in a cyclic voltammetry test was 25 A m‑2 at -0.6 V vs. SHE. When the best performing anode and cathode were combined in a reactor, current densities in the range of 1–2 A m‑2 were obtained at short circuit. When the cell voltage was increased to 0.5 V, the current production approximately doubled, but further increase in cell voltage did not have a notable effect on the current density obtained. Based on the preliminary studies, higher current densities should have been obtained, which indicates that further optimisation in the reactor configuration and operation is needed

Modelling and techno-economic assessment of (bio)electrochemical nitrogen removal and recovery from reject water at full WWTP scale

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 energetic and chemical demands of the WWTP due to a reduced nutrient load to the activated sludge process. In recent years, (bio)electrochemical methods have been extensively studied for nitrogen recovery from reject waters in laboratory-scale but not yet implemented in real WWTP environments, particularly due to concerns about the need for large capital investments. This study assessed the techno-economic feasibility of retrofitting a (bio)electrochemical nitrogen removal and recovery (NRR) unit into the reject water circulation line of a full-scale WWTP through modelling. Data from laboratory-scale (bio)electroconcentration ((B)EC) experiments was used to construct a simple, semi-empirical model block integrated into the Benchmark Simulation Model No. 2 (BSM2) simulating a generalised WWTP. The effects of nitrogen removal from the reject water on both the effluent quality and operational costs of the WWTP were assessed and compared to the BSM2 performance without an NRR unit. In all studied scenarios, the effluent quality index was improved by 4–11%, while both the aeration (7–19% decrease) and carbon (24–71%) requirements were reduced. The additional energy consumed by the NRR unit increased the total operational cost index by >18%, but the revenue assumed for the generated nutrient product (20 EUR kgN−1) was enough to make the BEC-NRR scenarios at realistically low current densities (1 and 5 A m−2) economically attractive compared to the control. A sensitivity analysis revealed that electricity price and nutrient product value had the most notable effects on the feasibility of the NRR unit. The results suggest a key factor in making (bio)electrochemical NRR economically viable is to reduce its electricity consumption further, while the anticipated increases in nitrogen fertiliser prices can help accelerate the adoption of these methods in larger scale.publishedVersionPeer reviewe

Fate of pharmaceuticals and PFASs during the electrochemical generation of a nitrogen-rich nutrient product from real reject water

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-derived nutrient products must not be overlooked. In this study, nitrogen was recovered from real anaerobically digested municipal sewage sludge reject water using a novel set-up combining membrane-based electroconcentration (EC) with electrochemical advanced oxidation processes (EAOPs). Simultaneously, the fate of five spiked pharmaceuticals (carbamazepine, ciprofloxacin, diclofenac, erythromycin and metoprolol) as well as ten indigenous perfluoroalkyl substances (PFASs) was investigated. The EC-EAOP system was effective in up-concentrating nitrogen ca. 13 times to a final concentration of 12.7 ± 0.8 g L−1 in the nutrient product. At the same time, no up-concentration was observed for the pharmaceuticals and their concentrations in the recovered concentrated remained at ≤ 3.4 ± 1.3 µg L−1. The EAOPs were the main transformation mechanism for all the pharmaceuticals at 33–88% efficiency, while diclofenac also notably adsorbed in the system (30 ± 1.4%). Out of the ten studied PFASs, only three were found in the recovered nutrient concentrate, albeit at very limited concentrations of ≤ 0.024 ± 0.013 µg L−1. The EAOPs were found to degrade longer-chain PFASs into their shorter-chain counterparts. The low contaminant concentrations in the nutrient product pose a reduced risk for soil contamination compared to, e.g., biosolids that are more typically used as fertilisers.publishedVersionPeer reviewe

Nitrogen Recovery from Digested Sewage Sludge Reject Waters Using (Bio)Electroconcentration

Typpi on yksi tärkeistä makroravinteista, jota käytetään laajasti lannoitteena maataloudessa sen reaktiivisissa muodoissa, kuten ammoniumtyppenä (NH4-N). Reaktiivisen typen tuottamiseen liittyy kuitenkin vakavia ympäristöongelmia, kuten kaasumaisia päästöjä ja vesistöjen rehevöitymistä reaktiivisen typen kertyessä ympäristöön. Näiden ympäristöongelmien lieventämiseksi jo olemassa olevaa reaktiivista typpeä tulisi kierrättää ja käyttää uudelleen entistä tehokkaammin. Jopa 30% lannoitteena käytetystä typestä päätyy lopulta yhdyskuntien jätevesiin. Keskitetyillä jätevedenpuhdistamoilla kaikista typpirikkaimpia virtoja ovat rejektivedet, jotka syntyvät mädätetyn jätevesilietteen kuivausprosessissa. Tämä väitöstyö tutki typen talteenottoa näistä rejektivesistä konsentroituun ravinnetuotteeseen sekä biologisesti katalysoidun että puhtaasti elektrokemiallisen elektrokonsentraation avulla. Laboratoriomittakaavan laitteistojen toimintaparametreja optimoitiin typen talteenoton maksimoimiseksi, mikä johti parhaimmillaan 88% talteenottotehoon. Ammoniumtypen tehokkaan talteenoton lisäksi elektrokonsentraatiosysteemi onnistui estämään erilaisten orgaanisten epäpuhtauksien, tarkemmin sanottuna valittujen lääkeaineiden ja perfluorattujen alkyyliyhdisteiden, päätymisen ravinnetuotteeseen. Samanaikaisesti elektrokemialliset hapetusprosessit hajottivat suurimman osan näistä epäpuhtauksista. Rejektivedestä tapahtuvan typen talteenoton vaikutuksia koko jätevedenpuhdistamon toimintaan arvioitiin mallinnuksen kautta. Mallinnuksen yhteydessä suoritettu taloudellinen tarkastelu paljasti, että (bio)elektrokonsentraation vielä toistaiseksi korkea sähkönkulutus tekee siitä pääsääntöisesti taloudellisesti kannattamatonta suuren mittaluokan sovelluksissa. Teknologian optimoinnin lisäksi typpilannoitteiden odotettavissa oleva hinnannousu sekä jätevedenpuhdistamoiden päästörajoitusten jatkuva kiristyminen todennäköisesti vaikuttavat merkittävästi siihen, kuinka nopeasti tutkittu typen talteenottomenetelmä saadaan taloudellisesti kannattavaksi. Ravinnetuotteen typpipitoisuus ja simulointien perusteella arvioidut jätevedenpuhdistamon mittakaavassa realistiset saannot osoittavat, että potentiaalinen markkina tuotteelle voisi löytyä ei-syötävien kasvien kotiviljelyyn tarkoitetuista nestemäisistä lannoitteista.Nitrogen is one of the key macronutrients vastly used as a fertiliser in agriculture in its reactive forms, such as ammonium nitrogen (NH4-N). Reactive nitrogen production, however, is associated with serious environmental issues, including gaseous emissions and eutrophication of water ecosystems due to reactive nitrogen accumulation in the environment. The key in mitigating these environmental issues is to recover and recycle the already existing reactive nitrogen more efficiently. Up to 30% of the nitrogen used in fertilisers ends up at municipal wastewater treatment plants (WWTPs), where reject waters originating from the dewatering of the anaerobically digested sewage sludge are the most nitrogen-rich streams. This doctoral thesis studied the recovery of NH4-N from these reject waters into a concentrated nutrient product using both biologically catalysed and purely electrochemical electroconcentration applications. The operational parameters were optimised in laboratory experiments to maximise the NH4-N recovery efficiency, which peaked at 88% with the electrochemical approach. In addition to efficiently recovering the NH4-N in a reusable form, the electroconcentration system was also found to effectively prevent contaminants of emerging concern (CECs), namely selected pharmaceuticals and perfluoroalkyl substances, from concentrating into the nutrient product. At the same time, electrochemical advanced oxidation processes facilitated the disintegration of the majority of the CECs. The effects of NH4-N recovery from reject water on the operation of a full WWTP were assessed through modelling. The accompanying economic analysis revealed that the still high electricity consumption of the (bio)electroconcentration system is the bottleneck in making its larger-scale implementation economically viable. In addition to technical improvements, the anticipated increases in nitrogen fertiliser prices and tightening of WWTP effluent limits for both nitrogen and CECs can help in making the proposed NH4-N recovery method feasible in the upcoming years. The NH4-N content of the product (ca. 1–2 w/v-%) generated in laboratory-scale and its simulated production rates at a full WWTP scale suggest a potential market could be found in the liquid fertilisers for non-edible plant cultivation in households

Typen talteenotto hydrolysoituneesta virtsasta energiaomavaraisen elektrokonsentraation avulla

Nutrients, especially the most widely used macronutrients nitrogen, phosphorus and potassium, are essential for sufficient food production to feed the constantly growing human population. However, fertiliser production deals with scarce, non-renewable raw-materials and high energy consumption, which is why more efficient nutrient recovery and re-use from human waste streams should be encouraged. Human urine is an especially interesting source for nutrient recovery since it contains most of the nutrients consumed and excreted by humans. This study focused on utilising bioelectrochemistry for nitrogen recovery from source-separated urine. The reactor design was a combination of microbial fuel cell and electrodialysis technology. The aim was to optimise the performance of both the anode and the cathode of the reactor towards a power-free nutrient recovery method. On the anodic side, the target was to enrich an acidophilic electroactive consortium, which would be able to enhance the nitrogen recovery as well as make more complete use of the high buffering capacity of urine. Of the three studied pH – 5.5, 6.5 and 7.5 – the highest one, 7.5, proved to be the most suitable one for the enriched culture, resulting in a maximum current density of 16 A m‑2 at Ewe = 0 V vs. SHE. On the cathodic side, an air-cathode using carbon cloth as the electrode material, carbon nanoparticles as the catalyst layer and commercial PTFE spray as diffusion layers was developed. Of the different layer materials tested, the best performance was obtained using acid-pre-treated nitrogen-doped carbon nanotubes as the catalyst and four layers of WD-40 PTFE spray as the diffusion layers. With this combination, an onset potential of +0.1 V vs. SHE for the reduction reaction was obtained and the maximum current reached in a cyclic voltammetry test was 25 A m‑2 at -0.6 V vs. SHE. When the best performing anode and cathode were combined in a reactor, current densities in the range of 1–2 A m‑2 were obtained at short circuit. When the cell voltage was increased to 0.5 V, the current production approximately doubled, but further increase in cell voltage did not have a notable effect on the current density obtained. Based on the preliminary studies, higher current densities should have been obtained, which indicates that further optimisation in the reactor configuration and operation is needed

Anaerobic digestion of 30−100-year-old boreal lake sedimented fibre from the pulp industry : Extrapolating methane production potential to a practical scale

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. Furthermore, the methane production from solid (on average 20% TS) and liquid fractions of sedimented fibres after solid-liquid separation was studied. The sedimented fibres resulted in fast methane production and high methane yields of 250 ± 80 L CH4/kg volatile solids (VS). The main part (ca. 90%) of the methane potential was obtained from the solid fraction of the sedimented fibres. In addition, the VS removal from the total and solid sedimented fibres was high, 61–65% and 63–78%, respectively. The liquid fraction also contained a large amount of organics (on average 8.8 g COD/L), treatment of which also has to be considered. The estimations of the methane production potentials in the case area showed potential up to 40 million m3 of methane from sedimented fibres.acceptedVersionPeer reviewe

Efficient nitrogen removal and recovery from real digested sewage sludge reject water through electroconcentration

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 real reject water using a novel electrochemical setup combining electroconcentration and stripping. High nitrogen removal (≤ 94 ± 0.7%) and recovery (≤ 87 ± 8.5%) efficiencies from real reject water were obtained while simultaneously reducing the influent nitrogen concentration of 913 ± 14 mgNH4-N L−1 to 57 ± 6.7 mgNH4-N L−1 in the effluent. Most of the nitrogen recovery took place via electroconcentration into a liquid concentrate (≤ 82 ± 5.7%), while stripping contributed little to the removal and recovery (≤ 5 ± 2.8%). The reported removal and recovery efficiencies are the highest to date for a system utilising three-chamber electroconcentration. Furthermore, the concept of cation load ratio (the ratio between applied current density and cation loading rate) was introduced as a more precise parameter than the widely used and simpler NH4-N load ratio for predicting the performance of a (bio)electrochemical nutrient removal and recovery system.publishedVersionPeer reviewe

Optimising nitrogen recovery from reject water in a 3-chamber bioelectroconcentration cell

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 (ca. 1 gNH4-N L−1) and low volume (ca. 1% of incoming sewage). In this study, a 3-chamber bioelectroconcentration cell was used for NH4-N recovery into a liquid concentrate from both synthetic and real reject water. NH4-N recovery efficiency and rate were optimised based on NH4-N loading rate, varying from 1.4 to 9.4 gNH4-N L−1 d−1 with synthetic reject water. The obtained NH4-N recovery efficiencies are the highest reported to date for bioelectroconcentration, peaking at 75.5 ± 4.6% (recovery rate of 728 ± 117 gN m−3 d−1) at loading rate 1.9 gNH4-N L−1 d−1. A loading rate of 2.9 gNH4-N L−1 d−1 led to the most optimal ratio between NH4-N recovery efficiency (68.2 ± 11.6%) and recovery rate (965 ± 66 gN m−3 d−1), with NH4-N up-concentrated 7.4 ± 0.9 times to 7483 ± 625 mg L−1 in the concentrate. With real reject water, NH4-N recovery efficiency of 53.2 ± 4.0% and recovery rate of 556 ± 37 gN m−3 d−1 were obtained at loading rate 2.5 gNH4-N L−1 d−1, with a specific energy consumption of 6.1 ± 1.1 kWh kgN−1. 16S rRNA amplicon analysis showed the dominance of phyla Bacteroidetes and Firmicutes in the anodic biofilms, with a significant change in the enriched microbial communities after transitioning from synthetic to real reject water. This study indicates the potential of bioelectroconcentration for nitrogen recovery from reject water without the need for an external organic carbon source or other chemical additions.publishedVersionPeer reviewe