•Three inocula have been tested systematically with four different substrates.•If inoculum’s origin impacts the performance in BMP test depend on the substrate.•Methane yield was not significantly ...influenced by the inoculum except for cellulose.•Degradation velocity was highest for the inoculum adapted to the substrate.
The impact of the inoculum’s origin on the methane yield in Biochemical Methane Potential (BMP) tests was investigated. The three most commonly applied inocula were chosen, originating from (i) a digester of a wastewater treatment plant, (ii) an agricultural biogas plant treating manure and energy crops, and (iii) a biowaste treatment plant. The performance of each inoculum was tested with four different substrates, namely sewage sludge, dried whole crop maize, food waste, and microcrystalline cellulose as a typical reference material. The results revealed that the choice of inoculum had no significant impact on the specific methane yield of the tested substrates except for cellulose. Still, the specific methane production rate was significantly influenced by the choice of the inoculum especially for sewage sludge, but also for food waste and cellulose, whereas it became clear that an inoculum adapted to a substrate is beneficial for a speedy digestion.
Wastewater treatment plants in many countries use anaerobic digesters for biosolids management and biogas generation. Opportunities exist to utilise the spare capacity of these digesters to co-digest ...food waste and sludge for energy recovery and a range of other economic and environmental benefits. This paper provides a critical perspective for full-scale implementation of co-digestion of food waste and wastewater sludge. Data compiled from full-scale facilities and the peer-reviewed literature revealed several key bottlenecks hindering full-scale implementation of co-digestion. Indeed, co-digestion applications remain concentrated mostly in countries or regions with favourable energy and waste management policies. Not all environmental benefits from waste diversion and resource recovery can be readily monetarised into revenue to support co-digestion projects. Our field surveys also revealed the important issue of inert impurities in food waste with significant implication to the planning, design, and operation of food waste processing and co-digestion plants. Other pertinent issues include regulatory uncertainty regarding gate fee, the lack of viable options for biogas utilisation, food waste collection and processing, impacts of co-digestion on biosolids reuse and downstream biogas utilisation, and lack of design and operation experience. Effort to address these bottlenecks and promote co-digestion requires a multi-disciplinary approach.
•Batch trials on co-digestion of raw sludge and food waste were performed.•Eleven mass-based mixtures from 5% to 30% were tested in four independent trials.•Methane yield raised linear with increased ...contribution of food waste.•Hydrolysis constants for lower share were higher than expected from mono-digestions.•Co-digestion is recommended due to higher methane yield and accelerated degradation.
Batch trials for co-digestion of raw sludge and food waste using eleven different mass-based mixtures were performed ranging from 5% to 30%. In contrast to conducting digestion trials as replicates in parallel as commonly done in previous studies, replications were performed successively in each trial to capture the variability in yield caused by a changing composition of the substrates. Trials were conducted four times with the same mixture ratios, but always using a fresh charge of inoculum, raw sludge and food waste. Data fitting was applied to assess the effect of the different mixtures on both the ultimate methane yield and the hydrolysis rate constant. The results revealed that with increasing contributions of food waste, the methane yield of the mixtures increased just due to its higher methane potential. The hydrolysis rate constant in the mixtures with a low contribution of food waste (up to 12.5% mass-based or 35% based on volatile solids) derived in batch experiments were higher than the one observed during the mono-digestion. Hence, co-digestion of food waste holds promise not only due to a higher methane yield, but in particular due to the accelerated methane production rate.
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•The Moosburg WWTP incorporates 65% by VS of co-substrates.•186% OLR increase from co-substrates resulted in 300% increase in CH4 production.•Solids accumulation of 5 m3/month from ...high ratio of food waste.•65% increase in nitrogen backload from co-substrate addition.•Alternative method for determining gate-fees proposed.
Anaerobic co-digestion (AcoD) is a key technology in reframing organic waste as a viable energy source. A lack of documented experience on full-scale AcoD at wastewater treatment plants (WWTPs) has created a bottleneck in AcoD implementation, which is further tightened by the focus of existing AcoD studies being on low co-substrate loading (<50%) and the obtainable benefits. This study aims to fill this gap by investigating the drawbacks and benefits of high-ratio co-substrate dosing of food and dairy wastes at the Moosburg WWTP (Germany) from 2014 to 2017. The Moosburg WWTP co-digests sewage sludge, food waste, and dairy wastes at a 35:47:18 ratio by volatile solids (organic loading rate (OLR) of 3.0 kgVS/(m3·day)). During the study period, this high co-substrate dosing increased the methane potential by 300 ± 50%. The corresponding high methane yield significantly increased the on-site electricity production, resulting in energy neutrality in 2014–2015. The corresponding economic gain from gate fees was 48,000 ± 5,000 € per year. The observed drawbacks included solids accumulation inside the digester (5 m3/month), high nitrogen backload (65% increase from co-substrate addition), reduced retention time (loss of 1.18 days/year from solids accumulation), and reduced dewaterability. The high nitrogen content in the centrate is treated by sequential batch reactors (SBRs), using lactose as the carbon source for denitrification. This study presents an alternative approach for determining gate fees based on the economic gains from inherent methane content, which identified waste milk, lactose and grease trap sludge as the most profitable co-substrates.
•The economic feasibility to co-digest sewage sludge and food waste was evaluated.•The higher electricity revenue offsets the higher cost in co-digestion scenarios.•Treating nutrient backloads in the ...sidestream was costlier than in the mainstream.•Biosolids disposal cost was the most important gross cost contributor.•Food waste gate fee had a noticeable impact on co-digestion economic feasibility.
The implementation of anaerobic membrane bioreactor as mainstream technology would reduce the load of sidestream anaerobic digesters. This research evaluated the techno-economic implications of co-digesting sewage sludge and food waste in such wastewater treatment plants to optimise the usage of the sludge line infrastructure. Three organic loading rates (1.0, 1.5 and 2.0 kg VS m−3 d−1) and different strategies to manage the additional nutrients backload were considered. Results showed that the higher electricity revenue from co-digesting food waste offsets the additional costs of food waste acceptance infrastructure and biosolids disposal. However, the higher electricity revenue did not offset the additional costs when the nutrients backload was treated in the sidestream (partial-nitritation/anammox and struvite precipitation). Biosolids disposal was identified as the most important gross cost contributor in all the scenarios. Finally, a sensitivity analysis showed that food waste gate fee had a noticeable influence on co-digestion economic feasibility.
•Thermophilic trickle bed reactor as a promising concept for biological methanation.•Productivity of 15.4m3CH4/(m3·d) with 98% CH4 in a non-pressurized reactor.•Significant impact of metabolic water ...production during dynamic operation.•pH and nutrient control are crucial for stable process performance.•Rapid adaption of mesophilic inoculum to thermophilic conditions after start-up.
In order to enhance energy efficiency of biological methanation of CO2 and H2, this study investigated the performance of a thermophilic (55°C) anaerobic trickle bed reactor (ATBR) (58.1L) at ambient pressure. With a methane production rate of up to 15.4m3CH4/(m3trickle bed·d) at methane concentrations above 98%, the ATBR can easily compete with the performance of other mixed culture methanation reactors. Control of pH and nutrient supply turned out to be crucial for stable operation and was affected significantly by dilution due to metabolic water production, especially during demand-orientated operation. Considering practical applications, inoculation with digested sludge, containing a diverse biocenosis, showed high adaptive capacity due to intrinsic biological diversity. However, no macroscopic biofilm formation was observed at thermophilic conditions even after 313days of operation. The applied approach illustrates the high potential of thermophilic ATBRs as a very efficient energy conversion and storage technology.
•Co-digestion of raw sludge and food waste was studied.•Results from batch trials were compared with full-scale experiences.•Mass balance of WWTP revealed a rise of 18% compared to batch tests.•Share ...of self-generated energy has more than doubled with 10% food waste.
The effects of co-digestion of food waste in a municipal wastewater treatment plant (WWTP) were studied in batch tests. The results obtained were compared with the mass balance of a digester at a full-scale WWTP for a one-year period without and with the addition of co-substrate. The specific methane yield calculated from the balance was 18% higher than the one in the batch tests, suggesting a stimulation of methane generation by co-digestion. It was hypothesized that this increase was caused by shifting the C/N ratio of raw sludge (8.8) to a more favourable ratio of the added food waste (17.7). In addition, potential benefits by adding food waste for energy autarky was investigated. While just 25% of the total energy demand of the plant could be recovered by biogas generation when no co-substrate was fed, this percentage has more than doubled when food waste was added at a ratio of 10% (w/w).
To evaluate a novel hydrophobic, non-diffractive, extended depth of focus (EDOF) intraocular lens (IOL) design in comparison to two monofocal aspheric lenses.
Inclusion criteria for this prospective, ...monocentric cohort study were opacification of the crystalline lens and patients' wishes for surgery. In the case of the EDOF IOL, patients asked for a presbyopia correction. All patients received surgery on both eyes. Corrected and uncorrected distance visual acuity (CDVA, UCDVA), uncorrected and distance corrected intermediate visual acuity (UIVA, DCIVA) and defocus curves (all monocular and binocular) were compared three months postoperatively.
Fifty-six eyes were implanted with an EDOF IOL (LuxSmart
TM
, Bausch & Lomb GmbH, Berlin, Germany), 50 eyes with a monofocal aspheric IOL: 32 eyes with a clear IOL (Polylens
®
AS 61, Polytech Domilens, Roßdorf, Germany), 16 eyes with a yellow IOL (iSert
®
251, Hoya Surgical Optics GmbH, Frankfurt, Germany). Three months postoperatively, UCDVA was comparable with the EDOF IOL, versus the monofocal IOL (P > 0.9). Binocular DCIVA in the EDOF IOL was significantly higher than in the monofocal IOL (P = 0.001). Monocular DCIVA better than 20/23 Snellen was achieved in 10% with the monofocal IOL and in 68% (P < 0.0001) with the EDOF IOL. Defocus curves showed a depth of focus at 20/23 Snellen of 1.6 vs. 0.83 diopters (D) in the EDOF IOL, vs. the monofocal IOL. No patient reported halos or starbursts in non-standardized questioning.
This non-diffractive EDOF IOL provided comparably high UCDVA and significantly higher DCIVA than the mono-focal lenses, causing only mild optical phenomena.
The three-dimensional surface imaging system is becoming more common in plastic surgeries. However, few studies have assessed three-dimensional periocular structures and surgical outcomes. This study ...aimed to propose a standardized three-dimensional anthropometric protocol for the periocular region, investigate its precision and accuracy, and determine the three-dimensional periocular anthropometric norms for young Caucasians.
Thirty-nine healthy young Caucasians (78 eyes) were enrolled. Three-dimensional facial images were obtained with a VECTRA M3 stereophotogrammetry device. Thirty-eight measurements in periocular regions were obtained from these images. Every subject underwent facial surface capture twice to evaluate its precision. A paper ruler was applied to assess its accuracy.
Sixty-three percent of measurements in linear distances, curvatures, angles, and indices were found to reach a statistically significant difference between sexes (p ≤ 0.05, respectively). Across all measurements, the average mean absolute difference was 0.29 mm in linear dimensions, 0.56 mm in curvatures, 1.67 degrees in angles, and 0.02 in indices. In relative error of magnitude, 18 percent of the measurements were determined excellent, 51 percent very good, 31 percent good, and none moderate. The mean value of the paper-ruler scale was 10.01 ± 0.05 mm, the mean absolute difference value 0.02 mm, and the relative error of magnitude 0.17 percent.
This is the first study to propose a detailed and standardized three-dimensional anthropometric protocol for the periocular region and confirm its high precision and accuracy. The results provided novel metric data concerning young Caucasian periocular anthropometry and determined the variability between sexes.
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•First application of real wastewater feed-streams in the CANDO process.•Long-term investigation of process performance and dynamics.•Comparison of different N2O harvesting ...strategies.•Mass-balance for the intended application concept on WWTPs.
A Coupled Aerobic-anoxic Nitrous Decomposition Operation (CANDO) was performed over five months to investigate the performance and dynamics of nitrogen elimination and nitrous oxide production from digester reject water under real feed-stream conditions. A 93% conversion of ammonium to nitrite could be maintained for adapted seed sludge in the first stage (nitritation). The second stage (nitrous denitritation), inoculated with conventional activated sludge, achieved a conversion of 70% of nitrite to nitrous oxide after only 12 cycles of operation. The development of an alternative feeding strategy and the addition of a coagulant (FeCl3) facilitated stable operation and process intensification. Under steady-state conditions, nitrite was reliably eliminated and different nitrous oxide harvesting strategies were assessed. Applying continuous removal increased N2O yields by 16% compared to the application of a dedicated stripping phase. These results demonstrate the feasible application of the CANDO process for nitrogen removal and energy recovery from ammonia rich wastewater.
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