A review of nature-based solutions for resource recovery in cities

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 specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future

Improvement of anaerobic digestion of municipal wastewatertreatment plant sludges and lignocellulosic substrates in biogas production

Namen doktorske disertacije je izboljšati tvorbo metana z mehanskimi in encimskimi predobdelavami substratov. Za anaerobno presnovo različnih substratov in določevanje biometanskega potenciala smo uporabili napravo Automatic Methane Potential Test System (AMPTS II). AMPTS II je analitična naprava laboratorijske skale, ki omogoča meritve ultra nizkih hitrosti tvorbe biometana, proizvedenih med anaerobno presnovo biološko razgradljivih substratov. Donosnost bioplinskih elektrarn je omejena na konkretne primere, ki jih je težko posplošiti na zbrane podatke v literaturi, saj ti zajemajo različno modificirane substrate, ki so jim zmanjšali velikost delcev ali jih kemično predobdelali in s tem posledično spremenili njihove lastnosti in energetski prirastek. Zato za konkretne odločitve na bioplinarnah potrebujemo podatke, ki izhajajo iz inokuluma konkretne bioplinske naprave in substrate v takem stanju, kot se jih dozira v anaerobne reaktorje na realnem modelnem merilu. Z nadgradnjo komercialnega sistema AMPTS II iz 0,5 l velikosti na 5 l modelno merilo smo razvili in validirali napravo za eksperimente, kjer lahko uporabljamo realni inokulum iz realne bioplinske naprave in realne substrate v takšni obliki kot jih dozirajo v anaerobne reaktorje na bioplinarnah. Na 5 l pilotnem modelnem merilu smo ocenili biometanski donos 24 substratom, ki so bili v trdni in tekoči obliki in jih primerjali z že obstoječimi objavljenimi podatki. Z dodajanjem različnih aditivov v obliki encimov in mikroorganizmov v proces anaerobne presnove, smo ocenili vpliv na nastajanje metana in izboljšali tvorbo metana. S kombinacijo različnih substratov, ki so jih sestavljali papirniško blato iz Kraft procesa, dehidrirano papirniško blato, biološki odpadki in lignocelulozni substrat, smo v šaržnih sistemih optimizirali tvorjenje metana. V semi-kontinuiranih procesih, kjer smo uporabili dehidrirano papirniško blato iz Palome, smo testirali vpliv delovanja encimov na tvorjenje metana, kjer smo dosegli občutno povečanje tvorbe metana, v naslednjem semi-kontinuiranem procesu pa smo testirali ultrazvočno predobdelavo blata iz ČN v kombinaciji z dodajanjem hidrolitskih encimov. Spremljali smo tudi delovanje bioplinske elektrarne (BPE) Vučja vas v obdobju 5 mesecev, ko je sestava vhodnih substratov nihala. S tehniko T-RFLP smo preučili vpliv encimov in čas inkubacije na strukturo bakterijske in arhejske združbe. Z uporabo programske opreme STATISTICA smo predvideli optimalne kombinacije substratov pri šaržnem načinu delovanja.The aim of this doctoral dissertation was to improve the production of methane by mechanical and enzymatic pretreatments of organic substrates. For anaerobic digestion of different substrates and determination of biomethane potential, Automatic Methane Potential Test System (AMPTS II) device was used. AMPTS II is an analytical laboratory scale device used in measurements of ultra low speed production of biomethane produced during the anaerobic digestion of biodegradable substrates. Although biogas yields of biogas plants arelimited to the specific substrates, methane yields are difficult to generalize from the collected data in published literature due to different modifications of substrates, including particle size reduction or chemical pretreatment all affecting their properties and energy recovery. Therefore, for biogas plant decision making the data need to be derived from inoculum of concrete biogas plant and substrates in such a condition as to be dosed in anaerobic reactors on real industrial scale. By upgrading commercial system AMPTS II from 0.5 liters to 5 liters, a pilot scale device was developed and validated for such real-scale experiments mirroring anaerobic reactors at the biogas plant. On 5 liter pilot scale biomethane yield of 24 substrates in solid or liquid form was assessed and compared with existing published data. By adding a variety of additives in the form of enzymes and micro-organisms in the process of anaerobic digestion, the impact on the production of methane and enhancement of the production of methane was evaluated. A combination of different substrates from paper mill sludge from Kraft process, a dehydrated paper mill sludge, bio-waste and lignocellulosic substrate an optimization of methane production in batch mode was conducted. The effects of the addition of hydrolytic enzymes on the production of methane from dehydrated paper mill sludge from Paloma was further tested in semi - continuous experiments. Significant improvements were detected. In the next following semi - continuous experiments an ultrasonic pre-treatment of sludge from the treatment plant in combination with the addition of hydrolytic enzymes was tested. In addition, the operation of the biogas plant Vučja vas was monitored for a period of 5 months during the substrate fluctuation period. Using T- RFLP technique the effects of enzyme and incubation time on the structure of bacterial and archeae consortium were assessed. By using software STATISTICA an optimal combinations of substrates in a batch mode were determined

Possibility of using waste edible oil for biogas production

Anaerobna presnova je proces, s katerim lahko iz organsko razgradljivih odpadnih snovi ponovno pridobimo energijo v obliki bioplina. Nekontrolirano odlaganje biološko razgradljivih odpadkov je za okolje lahko zelo obremenjujoče. V Sloveniji letno proizvedemo večje količine odpadnega jedilnega olja, ki bi ga lahko izkoristili za proizvodnjo bioplina. V tej študiji smo izvedli meritve metanskega potenciala odpadnega jedilnega olja v šaržnem eksperimentu. V pilotnem semikontinuirnem eksperimentu smo ocenili primernost odpadnega jedilnega olja za uporabo v anaerobnih reaktorjih na čistilni napravi. Rezultati študije kažejo, da je količina jedilnega olja, ki ga dnevno lahko doziramo v anaerobne reaktorje, omejena, saj močno vpliva na stabilnost procesa anaerobne presnove in na proizvodnjo bioplina. Izkazalo se je, da je najbolj optimalna obremenitev anaerobnega reaktorja z jedilnim oljem znašala med 1,6 in 2,4 g OS/L inokuluma. Takrat je proces anaerobne presnove deloval stabilno, produkcija bioplina je bila največja. Pri večji obremenitvi je prišlo do velikih nihanj v sistemu, zmanjšanja pH, povečanja hlapnih maščobnih kislin, povišanih vrednosti KPK na iztoku iz reaktorja in bistveno zmanjšane proizvodnje bioplina.Anaerobic digestion is a process by which energy from organically degradable waste can be recovered in the form of biogas. The uncontrolled disposal of such organic waste is very burdensome to the environment. In Slovenia, large quantities of waste edible oils are produced every year, which could be used for biogas production. In this study, we investigated the methane potential of waste edible oil in a batch reactor. Further in the pilot scale in a semi-continuous experiment we evaluated the use of waste edible oil in anaerobic digesters of wastewater treatment plant. The results show that the quantity of oil per day that is fed into the anaerobic reactor is limited due to the process\u27s instability and lower biogas production. The optimal daily organic loading of waste edible oil was between 1.6 and 2.4 g VS/L inoculum. During these conditions, the process of anaerobic digestion was stable and methane production was highest. At higher organic loading, the process became unstable, pH was reduced, volatile fatty acids increased, COD at the outflow of reactor increased, and biogas production was significantly reduced

Risks to the individual and the environment in biogas production

V Sloveniji se število bioplinskih naprav zadnja leta ne spreminja. Drugod v Evropi se število bioplinskih enot povečuje, posledično se proizvodnja bioplina in biometana veča, povečuje pa se tudi verjetnost nesreč, kot so razlitje digestata, eksplozije plina in podobno. Zaradi visokih koncentracij dušika in fosforja je nenadzorovano razlitje digestata nevarno za okolje ter podtalnico. Slabo vzdrževanje opreme, tehnične napake merilnikov in nezadostno izobraževanje operaterjev bioplinskih naprav povečujejo tveganja za nastanek nesreč.In the recent years, the number of biogas plants in Slovenia has remained unchanged. However, elsewhere in Europe, the number of biogas plants is increasing, and so is the production of biogas and biomethane, together with the likelihood of the occurrence of various accidents such as digestate spills, gas explosions and the like. Due to the high concentrations of nitrogen and phosphorus, an uncontrolled digestate spill poses a risk to the environment and to groundwater. Poor maintenance of technical equipment, technical errors in measuring devices, and inadequate training of biogas plant operators increase the likelihood of the occurrence of accidents

On the effect of aeration on laser ranging measurements of free water surface

Aerated flows pose both challenges and opportunities in the measurement of free water surface. In this study, an amplitude-modulated continuous wave scanning LIDAR device was used to measure a distance from the device sensor to the water column surface subjected to different degrees of aeration, while reference measurements were performed by high-speed imaging. Different aeration conditions were generated by variation of the air flow rate supplied to the liquid and by using perforated plates with different hole arrangements. The LIDAR device was shown to produce level readings consistently below visible water levels. The measurement error of the LIDAR method is largely determined by the volume fraction of air in water and was lowest at about 0.1 air volume fraction. The error increases linearly until a very high air volume fraction (i.e., above 0.55), while the LIDAR method also performs poorly in unaerated water. Although the measurement uncertainty of L IDAR in the range of aerated water is by at least an order of magnitude higher than in the case of measuring dry solid surfaces, the method is viable for free surface measurement under low to moderate aeration conditions that don’t produce excessive foaming.Aerirani tokovi predstavljajo izziv in priložnost pri merjenju proste vodne površine. V tej študiji je bila naprava LIDAR uporabljena za merjenje razdalje od senzorja naprave do površine vodnega stolpca, izpostavljenega različnim stopnjam prezračevanja, medtem ko so bile referenčne meritve opravljene s slikanjem z veliko hitrostjo. Različni pogoji prezračevanja so bili ustvarjeni s spreminjanjem hitrosti pretoka zraka, ki se dovaja v tekočino, in z uporabo perforiranih plošč z različno razporeditvijo lukenj. Pokazalo se je, da je naprava LIDAR izmerila višino gladine pod vidno gladino vode. Merilna napaka metode LIDAR je v veliki meri odvisna od prostorninskega deleža zraka v vodi in je bila najmanjša pri približno 0,1 prostorninskega deleža zraka. Napaka linearno narašča do zelo visokega volumskega deleža zraka (tj. nad 0,55), metoda LIDAR pa se slabo obnese tudi v vodi brez zraka. Čeprav je merilna negotovost metode LIDAR v območj u prezračevane vode vsaj za red velikosti večja kot pri merjenju suhih trdnih površin, je metoda primerna za merjenje prostih površin v pogojih nizke do zmerne ozračenosti, ki ne povzročajo prekomernega penjenja

A Review on Rotary Generators of Hydrodynamic Cavitation for Wastewater Treatment and Enhancement of Anaerobic Digestion Process

The issue of ever-increasing amounts of waste activated sludge (WAS) produced from biological wastewater treatment plants (WWTPs) is pointed out. WAS can be effectively reduced in the anaerobic digestion (AD) process, where methanogens break down organic matter and simultaneously produce biogas in the absence of oxygen, mainly methane and CO2. Biomethane can then be effectively used in gas turbines to produce electricity and power a part of WWTPs. Hydrodynamic cavitation (HC) has been identified as a potential technique that can improve the AD process and enhance biogas yield. Rotary generators of hydrodynamic cavitation (RGHCs) that have gained considerable popularity due to their promising results and scalability are presented. Operation, their underlying mechanisms, parameters for performance evaluation, and their division based on geometry of cavitation generation units (CGUs) are presented. Their current use in the field of wastewater treatment is presented, with the focus on WAS pre/treatment. In addition, comparison of achieved results with RGHCs relevant to the enhancement of AD process is presented

Vpliv surovega glicerola iz proizvodnje biodizla in vsebnosti njegovih elementov v sledovih na proizvodnjo biometana v šaržnem eksperimentu: modeliranje kot korak k enakovredni rutinski primerjavi rezultatov

In this study, crude glycerol from the biodiesel industry was tested as a co-substrate in biogas production. To investigate the influence of crude glycerol and the underlying trace element (TE) content on the efficiency of biomethane production, a batch experiment using Automatic Methane Potential Test System (AMPTS II) was carried out. The single addition of crude glycerol significantly contributed only to the total content of K (14.4%), Si (17.3%), and P (11.6%), whereas the contributions of other metals were within the range of other substrates. The addition of crude glycerol increased biomethane production, however, its utilization beyond 1% of total volume resulted in prolonged lag phase and final cessation of biomethane production. The negative effects of inorganic salts present in crude glycerol were reflected in progressively diminishing parts of glycerol and methanol being utilized in its anaerobic digestion, posing serious problems for daily routine use. A nonlinear least square regression analysis was performed to fit the Gompertz, Logistic, Transfer, and Richards models to biomethane production. The most suitable model was the Richards model, exhibiting the best fit to the experimental curves for complex substrates. Glycerol fractions remaining after biodiesel production have to be pre-tested for their negative effects on the content of TEs and inorganic salts, lag phase in biogas production, before they are used as co-substrates in biogas production phase.V študiji smo za proizvodnjo biometana kot kosubstrat uporabili surovi glicerol iz industrije proizvodnje biodizla. Da bi raziskali vpliv surovega glicerola in vsebnosti osnovnih elementov v sledovih (TE) na učinkovitost proizvodnje biometana, smo izvedli šaržni poskus z uporabo Automatic Methane Potential Test System (AMPTS II). Enkratno doziranje surovega glicerola je pomembno prispevalo le k skupni koncentraciji K (14,4 %), Si (17,3 %) in P (11,6 %), medtem ko so bili prispevki drugih elementov v sledeh v območju koncentracij drugih substratov. Z dodajanjem surovega glicerola se je povečala proizvodnja biometana, a ko je njegova uporaba presegla 1 % celotne prostornine, smo zaznali dolgotrajno lag-fazo in končno prenehanje proizvodnje biometana. Negativni učinki anorganskih soli, prisotnih v surovem glicerolu, so se odražali v postopnem zmanjševanju koncentracije glicerola in metanola, ki so se razgradili v procesu anaerobne presnove, to pa predstavlja resne težave pri vsakdanji rutinski uporabi surovega glicerola. Izvedena je bila analiza nelinearne regresije najmanjših kvadratov z uporabo modelov Gompertz, Logistic, Transfer in Richards za kumulativno proizvodnjo metana. Najprimernejši model je bil Richards, ki se je najbolj prilegal eksperimentalno izmerjenim krivuljam kompleksnih substratov. Frakcije glicerola, ki ostanejo po proizvodnji biodizla, je treba predhodno preizkusiti zaradi negativnih učinkov, ki jih lahko povzročajo TE, anorganske soli in lag-faze, preden se lahko uporabijo kot kosubstrati za pridobivanje bioplina

Meritve kompleksne topografije vodne gladine z uporabo fotorametrijske metode

This paper presents a photogrammetry-based system for capturing turbulent aerated flow topography in a laboratory environment, especially for complex hydraulic phenomena character-ised by turbulent, non-stationary, and non-homogeneous aerated flows. It consists of ten high-resolution cameras equipped with monochromatic sensors and custom-built LED lights, all synchronised for accurate data acquisition. Post processing involves Structure-from-Motion and Multi-View Stereo techniques to calculate exterior and interior orientation parameters that ensure accurate alignment within a desired coordinate system, and conversion to point clouds. The proposed method showed great potential for capturing free water surface topography of turbulent aerated flows with high spatial and temporal resolution over the entire field of view of the cameras. Due to the unique capabilities of this system, direct comparisons with existing benchmarks were not possible. Instead, average free water surface profiles were derived from selected control cross sections, using 2D LIDAR measurements for verification. Both the LIDAR and photogrammetry averaged profiles showed remarkably good agreement, with deviations within ±20 mm. Validation showed that photogrammetry can be used to measure the complex aerated turbulent free water surface. In this way, this approach, involving consecutive image dataset acquisition at predefined intervals, is proving to be a valuable tool for observing, visualising, analysing, investigating, and gaining a comprehensive understanding of the dynamics of the free water surface

A Review on Methods for Measurement of Free Water Surface

Turbulent free-surface flows are encountered in several engineering applications and are typically characterized by the entrainment of air bubbles due to intense mixing and surface deformation. The resulting complex multiphase structure of the air–water interface presents a challenge in precise and reliable measurements of the free-water-surface topography. Conventional methods by manometers, wave probes, point gauges or electromagnetic/ultrasonic devices are proven and reliable, but also time-consuming, with limited accuracy and are mostly intrusive. Accurate spatial and temporal measurements of complex three-dimensional free-surface flows in natural and man-made hydraulic structures are only viable by high-resolution non-contact methods, namely, LIDAR-based laser scanning, photogrammetric reconstruction from cameras with overlapping field of view, or laser triangulation that combines laser ranging with high-speed imaging data. In the absence of seeding particles and optical calibration targets, sufficient flow aeration is essential for the operation of both laser- and photogrammetry-based methods, with local aeration properties significantly affecting the measurement uncertainty of laser-based methods