Net Energy Recovery Research Articles

Energy recovery of residual yeast via hydrothermal liquefaction with multi-cycle reuse of the post-HTL wastewater and subsequent anaerobic digestion

Coupling hydrothermal liquefaction (HTL) with anaerobic digestion (AD) could be an interesting alternative for the energetic reuse of residual yeast derived from ethanol production, generating two valuable biofuels to diversify the global energy matrix. A central composite rotational design 23 optimized residual yeast HTL. The independent variables were temperature (300–400 °C), retention time (30–60 min), and solid content (5–12 wt%). The principal response variable was bio-oil yield. Three recirculation cycles of post-HTL wastewater (PHW) into the HTL reaction were investigated to enhance the energy recovery. The methanogenic potential of PHWs from recirculation cycles was then determined at mesophilic temperatures. During HTL, the bio-oil yield remained constant, while the volume of PHW decreased with recirculation cycles. The organic matter and total nitrogen present in the PHW were reduced until Cycle 2. The highest energy recovery in HTL was achieved at Cycle 0. However, the highest energy recovery in AD was attained at AD-Cycle 2, showing an approximately ∼14 % increase compared to AD-Cycle 0 (no recirculation). The total energy recovery for HTL-AD was higher in both Cycle 0 and Cycle 2, with Cycle 0 being more advantageous regarding net energy recovery from the products. In contrast, Cycle 2 offered more significant energy recovery and sustainability benefits.

Resource-efficient nitrogen and salinity removal in a synergistic partial nitritation-anammox bioelectrochemical system

We investigated the performance of a two-stage partial-nitritation-anammox biocathode integrated microbial desalination cell (TNiAmoxMDC) for concurrent nitrogen removal, desalination, and bioelectricity generation at different aeration rates in the nitritation chamber. The TNiAmoxMDC system achieved a maximum total nitrogen removal rate of 50.4 ± 8.2 g-TN/m3/d with 300 mW/m2 of maximum power production utilizing 500 mg/L of glucose chemical oxygen demand (COD) in the anode. The organic removal in the anode chamber showed a good fit to first order reaction model with a rate constant of 0.036 h−1. The biocatalytic activity of anammox bacteria in the biocathode produced a current density of 0.7 A/m2 in the absence of oxygen. More than 98% of the salinity was removed at a rate of 1.48 mg/h. The energy consumption values for nitrogen removal at aeration rates of 0.7, 2.2, and 10 ml/min were 0.022, 0.55, and 0.20 kWh/kg-N, respectively. The maximum energy produced by the TNiAmoxMDC was 0.0157 kWh/m3. Excluding the energy consumption by the system, the net energy recovery was 0.0023 kWh/m3 at an airflow rate of 10 ml/min. Thus, the integration of the partial nitritation-anammox process with microbial desalination cell (MDC) provides energy-and resource-efficient synergy for bioelectrochemical wastewater treatment.

Hydrothermal but Not Mechanical Pretreatment of Wastewater Algae Enhanced Anaerobic Digestion Energy Balance due to Improved Biomass Disintegration and Methane Production Kinetics

This study used pilot-scale high-rate algae ponds to assess algal–bacteria biomass productivity and wastewater nutrient removal as well as the impact of mechanical and hydrothermal pretreatments on biomass disintegration, methane production kinetics, and anaerobic digestion (AD) energy balance. Mechanical pretreatment had a minor effect on biomass disintegration and methane production. By contrast, hydrothermal pretreatment significantly reduced particle size and increased the solubilized organic matter content by 3.5 times. The methane yield and production rate increased by 20–55% and 20–85%, respectively, with the highest values achieved after pretreatment at 121 °C for 60 min. While the 1st-order and pseudo-1st-order reaction equation models fitted methane production from untreated biomass best (R2 > 0.993), the modified Gompertz sigmoidal-type model provided a superior fit for hydrothermally pretreated algae (R2 ≥ 0.99). The AD energy balance revealed that hydrothermal pretreatment improved the total energy output by 25–40%, with the highest values for volume-specific and mass-specific total energy outputs reaching 0.23 kW per digester m3 and 2.3 MW per ton of biomass volatile solids. Additionally, net energy recovery (energy output per biomass HHV) increased from 20% for untreated algae to 32–34% for hydrothermally pretreated algae, resulting in net energy ratio and net energy efficiency of 2.14 and 68%, respectively.

Improved net energy recovery in a sludge anaerobic digestion process by coupling an electrochemical system: electrode material and its impact on suspended microbial community.

Despite its great potential to recover energy from waste sludge, anaerobic digestion (AD) still needs to solve issues such as slow hydrolysis and H2 inhibition. This study investigated the effects of coupling microbial electrolysis cell (MEC) with AD on the CH4 yield. Results and analysis show that the CH4 yield was significantly improved in MEC-AD reactors by two factors, i.e., enhanced and accelerated hydrolysis and acidogenesis, and enrichment of hydrogenotrophic methanogens in suspended culture. Compared with graphite rod and carbon fiber brush, carbon felt (CF) as an electrode showed the best performance in terms of net energy output. The CH4 yield of MEC-AD-CF was 40.2 L CH4/kg VS, 92.3% higher than in the control group, and the VS removal rate was also increased by 47.2%. Acetoclastic methanogens were dominant in the control AD reactor, while the relative abundance of Methanobacterium, which is electroactive and known as hydrogenotrophic methanogen, increased to 24.6% in MEC-AD with CF as electrodes.

Net zero greenhouse emissions and energy recovery from food waste: manifestation from modelling a city-wide food waste management plan

Food waste (FW) being a major solid waste component and of degradable nature is the most challenging to manage and mitigate greenhouse gas emissions (GHEs). Policymakers seek innovative approaches to achieve net zero objectives and recover resources from the FW which requires a comparative and holistic investigation of contemporary treatment methods. This study assessed the lifecycle of six alternative scenarios for reducing net GHEs and energy use potential from FW management in a metropolis, taking Hong Kong as a reference. In both impact categories, the business-as-usual (landfilling) was the worst-case scenario. The combined anaerobic digestion and composting (ADC) technique was ranked best in the global warming impact but was more energy intensive than anaerobic digestion with sludge landfilling (ADL). Incineration ranked second in net GHEs but less favourable for energy recovery from FW alone. The proposed integration of FW and biological wastewater treatment represented an enticing alternative. Integration by co-disposal and treatment with wastewater (CoDT-WW) performed above average in both categories, while anaerobic co-digestion with sewage sludge (AnCoD-SS) ranked fourth. The sensitivity analysis further identified critical parameters inherent to individual scenarios along with biogenic carbon emission and sequestration, revealing their significance on the magnitude of GHEs and scenarios’ ranking. Capacity assessment of the studied treatment facilities showed a FW diversion potential of ∼60% while reducing the net GHEs by ∼70% compared to the base-case, indicating potential of net zero carbon emissions and energy footprint by increasing treatment capacity. From this study, policymakers can gain insights and guidelines for low-carbon urban infrastructure development worldwide.

Comparative study on the treatment of swine wastewater by VFCW-MFC and VFCW: Pollutants removal, electricity generation, microorganism community

Swine wastewater, characterized by high organic and nutrient content, poses significant environmental challenges. This study aims to compare the effectiveness of two treatment technologies, namely Vertical Flow Constructed Wetland-Microbial Fuel Cell (VFCW-MFC) and Vertical Flow Constructed Wetland (VFCW), in terms of pollutant removal, electricity generation, and microorganism community dynamics. The results showed that the average removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen (TN), total phosphorus (TP) and sulfadiazine antibiotics (SDZ) by VFCW-MFC were as high as 94.15%, 95.01%, 42.24%, 97.16% and 82.88%, respectively, which were all higher than that by VFCW. Both VFCW-MFC and VFCW have good tolerance to SDZ. In addition, VFCW-MFC has excellent electrical performance, with output voltage, power density, coulombic efficiency and net energy recovery up to 443.59 mV, 51.2 mW/m3, 52.91% and 2.04 W/(g·s), respectively, during stable operation. Moreover, the microbial community diversity of VFCW-MFC was more abundant, and the species abundance distribution in cathode region was more rich and even than in anode region. At phylum level, the dominant microorganisms in VFCW-MFC included Proteobacteria, Bacteroidota, Firmicutes and Actinobacteriota, which showed good degradation effect on SDZ. Proteobacteria and Firmicutes are also involved in electricity production. Chloroflexi, Proteobacteria and Bacteroidota play a major role in nitrogen reduction.

Enhanced co-digestion of sewage sludge and food waste using novel electrochemical anaerobic membrane bioreactor (EC-AnMBR)

Membrane fouling remains a big challenge hindering the wide-application of anaerobic membrane bioreactor (AnMBR) technology. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) was developed by coupling electrochemical regulation to enhance co-digestion of sewage sludge and food waste and mitigate membrane fouling. The highest methane production (0.12 ± 0.02 L/Lreactor/day) and net energy recovery (31.82 kJ/day) were achieved under the optimum conditions of 0.8 V, hydraulic retention time of 10 days and solids retention time of 50 days. Electrochemical regulation accelerated the mineralization of high-molecular-weight organics and reinforced the membrane antifouling ability by inducing electrostatic repulsive force and electrochemical oxidation. Besides, symbiotic relationships among functional microorganisms (Spirochaetes, Methanolinea, etc.) were enhanced, improving the hydrolysis and methanogenesis processes of complex organics and the long-term stability. This study confirms the technical feasibility of EC-AnMBR in treating high-solid biowastes, and provides the fundamental data to support its application in real-world scenarios.

Influence of evapotranspiration on wastewater treatment and electricity generation performance of constructed wetland integrated microbial fuel cell

Evapotranspiration (ET) is a natural phenomenon of water loss through plants, which can influence the treatment performance of constructed wetlands integrated with microbial fuel cells (CW-MFC). The influence of ET on the electrochemical performance and treatment performance of CW-MFC in an actual field with real wastewater has never been studied in detail. Thus, this research aims to explore the effects of water loss ascribed by ET on different performance indicators of a CW-MFC fed with municipal wastewater in actual field conditions, for instance, voltage and power generation, internal resistance, and wastewater treatment. During the first 48 h of the operation of CW-MFC, a significant drop in the water level by 336 mm (from 15 mm to 351 mm from the top surface) in the cathode electrode zone due to ET was recorded. This water loss at the cathode enhanced cathodic reduction kinetics by increasing the oxygen saturation at the cathode, thereby improving the voltage generation from 182.5 ± 12.5 mV (first 6 h when the cathode was more water-saturated) to 800 ± 13.47 mV (after 48 h when the cathode was air-saturated due to loss of water), which corresponds to the current and power density of 85.71 mA/m3 and 25.71 mW/m3, respectively. Together with this significant coulombic efficiency (CE) and net energy recovery (NER) of 11.95 % and 2.44 Wh/kg·COD was achieved. The internal resistance of CW-MFC was also noted to decrease from 1000 Ω in the first 6 h to 700 Ω at the end of 48 h. After 48 h of the observation period, the CW-MFC could achieve chemical oxygen demand (COD), ammonium, and phosphate removal efficiency of 80 ± 7.98 %, 73.17 ± 5.01 %, and 75.60 ± 1.65 %, respectively. This study demonstrates a substantial effect on the performance of CW-MFC due to ET water loss in the actual field. Thus, ET is a critical aspect and worth considering for large-scale implementation of CW-MFCs, especially in tropical regions or with dense plantations.

Evaluating the Potential of Renewable Energy Sources in a Full-Scale Upflow Anaerobic Sludge Blanket Reactor Treating Municipal Wastewater in Ghana

Wastewater management remains a major challenge in developing countries due to the lack of adequate infrastructure, making the need for economically viable and efficient technologies that can be sustained by emerging economies imperative. The upflow anaerobic sludge blanket (UASB) reactor represents an efficient and low-cost technology that produces by-products from which valuable resources can be recovered. This study assessed the energy recovery potential in the form of electricity from biogas and sludge by-products produced by a full-scale UASB reactor. Biogas production rate and composition were monitored to determine the biogas energy recovery potential. Dehydrated sludge from sludge drying beds was likewise quantified and characterised for its elemental composition, immediate composition, gross calorific value and net calorific value to estimate sludge energy recovery potential. The average daily biogas production was found to be 611 ± 275 Nm3/d, with 65% methane in the biogas output. Average sludge dry matter production was determined to be 358.24 TS kg/d. The net energy recovery potential was estimated to be 534.1 MWh/yr, 36% more than the yearly energy demand (392.7 MWh/yr) of the entire plant. Conservative energy recovery at a UASB-based municipal wastewater treatment facility could serve as a self-supply energy option to support its operations.

Biocrude oil production from a self-settling marine cyanobacterium, Chroococcidiopsis sp., using a biorefinery approach

Although the whole microalgal biomass is typically used as a feedstock for hydrothermal liquefaction (HTL), the conversion of a primary metabolite (i.e., carbohydrate) to biocrude is very low. In this study, a self-settling cyanobacterium (i.e., Chroococcidiopsis sp.) was used to understand the effect of carbohydrate removal, as a pretreatment, on the net energy recovery from the residual biomass. The optimum biocrude yields from pretreated and control biomass were 50.2% (350 °C) and 41.3% (300 °C), respectively. For the temperature range studied, the biocrude yield from the pretreated biomass was higher compared to that obtained from the control feedstock. Further, maximum alkane formation of 42.7 and 23.3% occurred for pretreated and control biomass, respectively, at 325 °C. Total organic carbon and total nitrogen values in the aqueous phase liquid obtained from pretreated biomass were at least 1.31 and 1.23 times lower when compared to the corresponding values obtained from control biomass. When APL was recycled as a source of nutrients, it reduced the biomass yield (24.1%) and pigment content (68.4%) in Chroococcidiopsis sp. Further, a model was developed to understand how the cellular carbohydrate content would affect the net energy recovery for the proposed biorefinery route.

In-Situ Steam Generation Using Mist Water-Air Injection as Enhanced Oil Recovery and Energy Efficiency Process: Kinetic Modeling and Numerical Simulation Approach

Summary In the current energy transition era, oil exploitation and especially the development of heavy oil reservoirs are facing big challenges to overcome the possible limitations in terms of economy (oil price), energy efficiency, and carbon footprint. Particularly, thermal enhanced oil recovery processes need to be re-evaluated in an attempt to harness the injected and produced energy. In that sense, Ecopetrol is evaluating new strategies to optimize the current steam injection process using different hybrid technologies from laboratory to field scale. One of the most attractive initiatives is evaluating the in-situ steam generation using mist water-air injection. This process involves simultaneous air and water injection into the formation through a set of nozzles. It looks to use part of the in-situ oil as a fuel, using the reservoir not only as a tank of energy but also as a steam generator. The main contribution of the technique concerning conventional steam generation is the use of the heat from the combustion of the residual oil to generate an in-situ steam front to transfer the uncontacted oil. This is reflected in reduced carbon dioxide (CO2) emissions, reduced fuel and water requirements, and increased oil production and net energy recovery. This article describes the methodology, results, history matching, and kinetic modeling of experimental evaluations and the upscaling of the experimental observations to a representative sector model from a Colombian heavy oil field. Results are described in terms of incremental oil recovery, energy efficiency, and carbon intensity compared with the baseline (a traditional steamflooding scenario). The technology of in-situ steam generation using mist waterair injection led to benefits in terms of better energy use and reducing the external fuel dependency for steam generation at the surface. Additionally, it was possible to identify improvements in incremental oil recovery (around 90%), energy efficiency (about 10 times less energy required to produce 1 m3 of oil), and reduction in carbon intensity (up to 91%) considering as baseline a conventional steamflooding scenario. These results will be key input parameters for designing and commissioning future applications in the Colombian fields.

Pollutant Removal and Energy Recovery from Swine Wastewater Using Anaerobic Membrane Bioreactor: A Comparative Study with Up-Flow Anaerobic Sludge Blanket

Due to its high content of organics and nutrients, swine wastewater has become one of the main environment pollution sources. Exploring high-efficient technologies for swine wastewater treatment is urgent and becoming a hot topic in the recent years. The present study introduces anaerobic membrane bioreactor (AnMBR) for efficient treatment of swine wastewater, compared with up-flow anaerobic sludge blanket (UASB) as a traditional system. Pollutant removal performance, methanogenic properties, and microbial community structures were investigated in both reactors. Results showed that by intercepting particulate organics, AnMBR achieved stable and much higher chemical oxygen demand (COD) removal rate (approximately 90%) than UASB (around 60%). Due to higher methanogenic activity of anaerobic sludge, methane yield of AnMBR (0.23 L/g-COD) was higher than that of UASB. Microbial community structure analysis showed enrichment of functional bacteria that can remove refractory organic matter in the AnMBR, which promoted the organics conversion processes. In addition, obvious accumulation of acetotrophic and hydrotrophic methanogens in AnMBR system was recorded, which could broaden the organic matter degradation pathways and the methanogenesis processes, ensuring a higher methane yield. Through energy balance analysis, results concluded that the net energy recovery efficiency of AnMBR was higher than that of UASB system, indicating that applying AnMBR for livestock wastewater treatment could not only efficiently remove pollutants, but also significantly enhance the energy recovery.

Comparative life-cycle assessment of pyrolysis processes for producing bio-oil, biochar, and activated carbon from sewage sludge

This study aimed to determine the feasibility of pyrolysis scenarios as sewage sludge treatment processes through cradle-to-gate life-cycle assessment and additional energy consumption, carbon emission, and economic benefit analyses, considering circular economy principles. The examined pyrolysis scenarios include slow pyrolysis with various residence times to produce activated carbon (AC) or biochar and fast pyrolysis to produce bio-oil, all with internal gas energy recovery. The functional unit (FU) in this study comprises 1000 kg of dried sludge entering the pyrolysis reactor. The overall evaluation and new product application routes address gaps in current studies on sludge treatment via pyrolysis. Environmentally, the bio-oil (-0.31 kg CO2-eq/kg FU) and biochar (-0.05 kg CO2-eq/kg FU) scenarios show considerable improvement over contemporary pyrolysis and other conventional sludge treatment methods. The AC scenarios have higher toxicity but lower carbon emissions (1.50–1.70 kg CO2-eq/kg FU) than contemporary AC production processes. Chemical reagent usage has significant effects on the environmental burden of AC production processes. The biochar and bio-oil pyrolysis scenarios achieve net energy recovery through product applications. Although the AC scenarios still require energy input, this demand can be significantly reduced by optimising moisture removal processes. Operating cost analysis indicates that the examined pyrolysis scenarios are potentially profitable. Primary product yield and market value are significant factors determining the net profit of these pyrolysis scenarios, but further assessment of capital costs is required. This study shows that bio-oil and biochar pyrolysis are eco-friendly sewage sludge treatment methods.

Quality assessment of bio-oil and biochar from microwave-assisted pyrolysis of corn stover using different adsorbents

Biofuels in the form of bio-oil and biochar have been produced by microwave heating of corn stover. Different adsorbents such as silicon carbide (SiC) and activated carbon (AC) with different ratios (10%, 20%, and 30%) to corn stover are investigated with the aims of enhancing the absorption of the microwave, maximizing the yields of the desirable products i.e. bio-oil followed by biochar as well as improving their qualities. Use of both the adsorbents improved the heating performance through increase in the maximal temperature and heating rate by 170 °C and 36 °C/min respectively compared to without adsorbent. Use of AC increased the yield of bio-oil up to 45 wt% while SiC increased the gas yields up to a maximum value of 48 wt%. The better physical properties such as 37%, 5.3, 2.9 mPa s, and 1 g/mL for water content, pH, viscosity and density respectively of bio-oil were obtained when using AC as an adsorbent. Also, use of AC helped in producing bio-oils which contained higher carbon and hydrogen contents as well as high calorific value (17 MJ/kg). Similarly, use of AC increased the contents of hydrocarbons and phenols in the bio-oil up to 36% and 28% respectively with low oxygen-containing compounds (2%). Also, use of AC produced the biochar having cleanest pores that were almost free of carbon-like impurities with a higher surface area of the pore (105.2 m2/g). In addition, biochar having low ash content, high carbon content, and calorific value (28 MJ/kg) were achieved. The net energy recovery with respect to raw corn stover was calculated to be of maximum value i.e., 55% when using AC. The AC and SiC were reused for further runs of the experiments (5 times) with few changes in the heating behavior and the yields of the pyrolytic products.

Application of biogas recirculation in anaerobic granular sludge system for multifunctional sewage sludge management with high efficacy energy recovery

This study investigated the possibility of biogas recirculation-driven anaerobic granular sludge system for sewage sludge treatment, aiming to develop an energy sufficient and multifunctional anaerobic digestion (AD) system for sewage sludge with biogas upgrading, sludge stabilization and self-aggregation. Results show that biogas recirculation could enhance the CH4 production rate by 31–44% and shorten the lag-phase duration to 0.08–0.2 day with simultaneous increment of CH4 content (> 83% in this study). The reason is mainly associated with the stronger interspecies electron transfer under the biogas recirculation condition. In addition, 37–40% better dewaterability of the digested sludge was achieved, implying the occurrence of self-aggregation of microbial cells induced by biogas recirculation. Energy balance analysis reflects that this sewage sludge treatment system could enhance the net energy recovery by 78–85%. Moreover, almost no obvious influence was noticed on the seed granules’ compositionand properties. These findings suggest that the biogas recirculation-driven anaerobic granular sludge system could be a promising alternative for sewage sludge treatment, which can improve biogas quality and sludge dewaterability simultaneously towards sludge self-aggregation with no addition of other chemicals.

Design of a Tandem Compressor for the Electrically-Driven Turbocharger of a Hybrid City Car

Within a broader national project aimed at the hybridization of a standard city car (the 998 cc Mitsubishi-derived gasoline engine of the Smart W451), our team tackled the problem of improving the supercharger performance and response. The originally conceived design innovation was that of eliminating the mechanical connection between the compressor and the turbine. In the course of the study, it turned out that it is also possible to modify both components to extract extra power from the engine and to use it to recharge the battery pack. This required a redesign of both compressor and turbine. First, the initial configuration was analyzed on the basis of the design data provided by the manufacturer. Then, a preliminary performance assessment of the turbocharged engine allowed us to identify three “typical” operating points that could be used to properly redesign the turbomachinery. It was decided to maintain the radial configuration for both turbine and compressor, but to redesign the latter by adding an inducer. For the turbine, only minor modifications to the nozzle guide vanes (NGV) and rotor blades shape were deemed necessary, while a more substantial modification was in order for the compressor. Fully 3-D computational fluid dynamics simulations of the rotating machines were performed to assess their performance at three operating points: the kick-in point of the original turbo (2000 rpm), the maximum power regime (5500 rpm), and an intermediate point (3500 rpm) close to the minimum specific fuel consumption for the original engine. The results presented in this paper demonstrate that the efficiency of the compressor is noticeably improved for steady operation at all three operating points, and that its choking characteristics have been improved, while its surge line has not been appreciably affected. The net energy recovery was also calculated and demonstrated interesting returns in terms of storable energy in the battery pack.

Microbial fuel cells: Devices for real wastewater treatment, rather than electricity production

For last two decades, various microbial fuel cells have been studied to treat real wastewater and simultaneously produce electricity. The performance of 106 MFCs using real wastewater were summarized and grouped according to reactor design (size, shape, and whether single chamber), installation type, operating mode, and wastewater type. Most studies operated MFCs with mini size (<1 L) (57%), box shape (50%), single-chamber (60%), chamber-type (94%), operated under continuous flow mode (67%) with non-domestic wastewater (66%). Their maximum power production and net energy recovery were as low as ~165 W/m3 and ~1.1 kWh/kgCOD, respectively. However, most MFC studies (75/106) using real wastewater achieved higher than 60% of COD removal efficiencies. In addition, recent MFC studies reported successful treatment of nutrients (nitrogen and phosphorus) and antibiotics as well as organics. The review on MFCs using real wastewater suggests that MFC is more proper to apply for wastewater treatment rather than energy production.

Evidence of solution-diffusion-with-defects in an engineering-scale pressure retarded osmosis system

An engineering-scale seawater reverse osmosis-pressure retarded osmosis (SWRO-PRO) system was designed and deployed to evaluate the energy recovery during seawater desalination through salinity gradient energy. Experimental data on energy recovery and consumption were collected from a PRO system composed of up to five 4040 spiral-wound membrane elements, utilizing freshwater and RO concentrate to drive permeation. During experimental testing, specific energy recoveries as high as 0.14 kW h/m3 were achieved; however, energy consumption due to pressure losses in the system reduced the net specific energy recovery to a maximum of −0.07 kW h/m3. A 100% increase in energy recovery or 50% decrease in energy consumption would be necessary to yield a positive net energy recovery. Also, a combined approach of simultaneously increasing energy recovery and decreasing energy consumption would be a more desirable path for SWRO-PRO to become an energy positive technology. Experimental data were then paired with modeling software utilizing a solution-diffusion-with-defects model to demonstrate the presence and extent of defects in the membrane structure that allow for pressure-driven pore flow. The solution-diffusion-with-defect model explains the lower than expected water permeability and salt rejection often seen in experimental PRO results. Integrating this model into future software will allow for more accurate simulation of larger systems and aid in investigations of PRO scale-up.

Effect of methanol-organosolv pretreatment on anaerobic digestion of lignocellulosic materials

Lignocellulosic materials are the most abundant biomass on the planet, representing a great opportunity for energy valorisation. This work investigated the effect of methanol-organosolv pretreatment on the methane production from hazelnut skin (HS), spent coffee grounds (SCG), and almond shell (AS). The pretreatment on the three lignocellulosic materials was performed at 130, 160, and 200 °C for 60 min using a 50% (v/v) methanol solution, with and without the addition of sulfuric acid as a catalyst. The biomethane potential of raw and pretreated substrates was evaluated under wet-mesophilic conditions in batch reactors, achieving 17.3 (±32.3), 293.4 (±46.6), and 23.2 (±9.6) mL CH4/g VS for HS, SCG, and AS, respectively. The methanol-organosolv pretreatment was particularly effective on HS, increasing its biomethane potential up to 310.6 (±22.2) CH4/g VS. On the contrary, all pretreatment conditions were ineffective on SCG and AS in terms of cumulative methane production. Among the three substrates, only HS showed significant composition changes due to the pretreatment, with the lignin content decreasing from 39.66 to 34.73% and the amount of bioavailable sugars increasing. An energy assessment confirmed the pretreatment efficacy on HS, with a maximum net positive energy recovery of 1.35 kWh/kg VS.

Critical analytical parameters for faecal sludge characterisation informing the application of thermal treatment processes

Thermal processes for the treatment of faecal sludge such as pyrolysis or combustion offer complete destruction of pathogens, whilst allowing for energy and nutrient recovery. The development of such processes is currently constrained by a lack of knowledge on thermally relevant faecal sludge characteristics. This study investigated thirty faecal sludge samples from three sanitation technologies (ventilated improved pit latrines (VIP), urine diverting dry toilets (UD), septic tanks (ST)) and compared these by non-parametric statistical analysis. A focus was placed on parameters necessary for thermal process development and recoverable nutrient concentrations. The relevant characteristics ranged widely within technology groups. Calorific values and ash concentrations of 2.1–25.7 MJ/kg and 9.5–88.4% were observed for STs, of 9.2–13.9 MJ/kg and 40.9–61.5% for VIPs and of 3.9–18.1 MJ/kg and 18.8–81.3% for UDs. These two parameters show a strong linear inverse correlation and determine the minimum dewatering requirements from which a net energy recovery may be possible. Results suggest that more than 90% of samples can meet these requirements following commonly used dewatering technologies. A comparison across technologies provided strong evidence that the faecal sludge source significantly influences sludge composition, emphasized by higher median ratios of fixed carbon to volatile matter in VIPs (0.23) and UDs (0.23) compared to STs (0.15). The sanitation technology also influenced recoverable nutrient concentrations, with phosphorus and potassium concentrations generally ranging between 5.8–49.2 g/kg and 1.4–26.1 g/kg respectively. Compared to STs, median concentrations of phosphorus and potassium in VIPs were 3.4 and 3.8 times higher respectively, and 3.0 and 8.8 times higher in UDs. The findings highlight the importance of considering the faecal sludge source in the development of thermal treatment processes. This study provides critical knowledge to further develop such processes through modelling, experimental and scaled approaches.