Hydrothermal carbonization of sewage digestate at wastewater treatment works: Influence of solid loading on characteristics of hydrochar, process water and plant energetics

Nowadays the sludge treatment is recognized as a priority challenge to the wastewater industry due to the increasing volumes produced and tighter environmental controls for its safe disposal. The most cost-effective process for sewage sludge is the anaerobic digestion but raw digestate still contains high levels of organic matter that can be transformed into an energy carrier by using processes like Hydrothermal Carbonization (HTC). In this work, the influence of solid loading (2.5, 5.0, 10.0, 15.0, 17.5, 20.0, 25.0 and 30.0% solids w/w) on the composition of hydrochar and process water was studied, together with an evaluation of product yields, solubilisation of organic carbon and biomethane potential of process waters from HTC processing (250 °C, 30- minute reaction time). Hydrochar yields ranged from 64 to 88%wt, whereas the concentration of soluble organic carbon increased from 2.6 g/L in the raw digestate to a maximum of 72.3 g/L in the process water following HTC at the highest solid loading. Furthermore, process modelling with Aspen Plus shows that the integration of AD with HTC to wastewater treatment works provides a significant positive energy balance when process water and hydrochar are considered as fuel sources for cogeneration

Evaluation and comparison of product yields and bio-methane potential in sewage digestate following hydrothermal treatment

In recent years, sewage sludge management has been considered one of the biggest concerns in the wastewater industry for the environmental impacts linked to its high content of pollutants. Hydrothermal Treatments are a good option for converting wet biomass such as sewage sludge into high-value products. The digestate following anaerobic treatment of sewage sludge has high organic matter content despite initial conversion into biogas and is normally spread on land or composted; however, this does not fully harness its full potential. In fact, the digestate is a potential feedstock for hydrothermal processing and this route may produce higher value products. In this study, the potential of hydrothermal processing as a novel alternative to treat the digestate has been be evaluated. The effect of temperatures is evaluated with respect to product yields, biomethane potential and solubilisation of organic carbon. Three different temperatures were evaluated: 160, 220 and 250 °C at 30 min reaction time. The hydrochar yields obtained were 73.42% at 220 °C, 68.79% at 250 °C and 56.75% at 160 °C treatment. The solubilisation of carbon was increased from 4.62% in the raw feedstock to 31.68%, 32.56% and 30.48% after thermal treatments at 160, 220 and 250 °C, respectively. The thermal treatment enhanced the potential methane production in all products up to 58% for both, the whole fraction (hydrochar + processed water) and processed waters. The Boyle’s and Buswell’s equation were used to calculate theoretical methane yields for all hydrothermal products. Theoretical methane yields were compare with experimental data from biomethane potential (BMP) tests and it was found that the Boyle’s equation had closer agreement to BMP values

Integration of Hydrothermal Carbonisation and Anaerobic Digestion for the Energy Valorisation of Grass

The integration of hydrothermal carbonisation (HTC) and anaerobic digestion (AD) can overcome some of the disadvantages of thermal or biological processing alone. This study aims to investigate integrated HTC-AD across a range of integration strategies and HTC processing temperatures (150 °C, 200 °C and 250 °C) to improve the energy conversion efficiency (ECE) of grass, compared to AD alone. The separation of hydrochars (HCs) for combustion and process waters (PWs) for digestion appears to be the most energetically feasible HTC-AD integration strategy, compared to HC or HTC-slurry AD. Hydrochars represent the greater energy carrier with between 81–85% of total energy output. The ECE of grass was improved from 51% to 97% (150 °C), 83% (200 °C) and 68% (250 °C) through integrated HTC-AD. Therefore, lower HTC processing temperatures yield more favourable energetics. However, higher HTC temperatures favour more desirable HC properties as a combustion fuel. The hydrochar produced at 250 °C (HC-250) displayed the highest HHV (25.8 MJ/kg) and fixed carbon: volatile matter ratio (0.47), as well as the greatest reduction in slagging and fouling potential (ash flow temperature > 1550 °C). Overall, integrated HTC-AD is an effective energy valorisation strategy for grass. A compromise exists between the quality of hydrochar and the energetic balance. However, at 250 °C the process remains energetically feasible (EROI = 2.63)

An assessment of road-verge grass as a feedstock for farm-fed anaerobic digestion plants

Cuttings from road-verge grass could provide biomass for energy generation, but currently this potential is not exploited. This research assessed the technical, practical and financial feasibility of using grass harvested from road verges as a feedstock in farm-fed anaerobic digestion (AD) plants. The methane potential (191 mL CH4 gDM−1) and digestion characteristics of verge grass were similar to those of current farm feedstocks; indicating suitability for AD. Ensiling had no significant impact on the biomethane generated. Testing co-digestions of verge grass with current farm feedstocks showed enhanced methane yields, suggesting that verge grass could be a valuable addition to AD feedstock mixes. In a case study of the UK county of Lincolnshire, potential volumes and locations of verge grass biomass were estimated, with capacities and locations of existing AD plants, to assess the potential to supply practical grass volumes. Grass harvesting costs were modelled and compared with other feedstock costs. Finally, the attitudes of AD operators to using verge grass were investigated to understand whether a market for verge grass exists. In a small survey all operators were willing to use it as a feedstock and most were prepared to pay over the estimated harvesting cost. If verge grass was legally recognised as a waste product it could be attractive to AD operators especially where financial incentives to use waste feedstocks are in place. In rural areas, verge grass could be harvested and co-digested by existing farm-fed AD plants, potentially reducing the cost of road verge maintenance and increasing biodiversity

National inventory of emergency departments in Singapore

Background: Emergency departments (EDs) are the basic units of emergency care. We performed a national inventory of all Singapore EDs and describe their characteristics and capabilities. Methods: Singapore EDs accessible to the general public 24/7 were surveyed using the National ED Inventories instrument ( http://www.emnet-nedi.org). ED staff members were asked about ED characteristics with reference to calendar year 2007. Results: Fourteen EDs participated (100% response). All EDs were located in hospitals, and most (92%) were independent departments. One was a psychiatric ED; the rest were general EDs. Among general EDs, all had a contiguous layout, with medical and surgical care provided in one area. All but two EDs saw both adults and children; one ED was adult-only, and the other saw only children. Six were in the public sector and seven in private health-care institutions, with public EDs seeing the majority (78%) of ED patients. Each private ED had an annual patient census of 60,000. They received 98% of ambulances and had an inpatient admission rate of 30%. Two public EDs reported being overcapacity; no private EDs did. For both public and private EDs, availability of consultant resources in EDs was high, while technological resources varied. Conclusion: Characteristics and capabilities of Singapore EDs varied and were largely dependent on whether they are in public or private hospitals. This initial inventory establishes a benchmark to further monitor the development of emergency care in Singapore

Investigating the association between obesity and asthma in 6- to 8-year-old Saudi children:a matched case-control study

Background: Previous studies have demonstrated an association between obesity and asthma, but there remains considerable uncertainty about whether this reflects an underlying causal relationship. Aims: To investigate the association between obesity and asthma in pre-pubertal children and to investigate the roles of airway obstruction and atopy as possible causal mechanisms. Methods: We conducted an age- and sex-matched case–control study of 1,264 6- to 8-year-old schoolchildren with and without asthma recruited from 37 randomly selected schools in Madinah, Saudi Arabia. The body mass index (BMI), waist circumference and skin fold thickness of the 632 children with asthma were compared with those of the 632 control children without asthma. Associations between obesity and asthma, adjusted for other potential risk factors, were assessed separately in boys and girls using conditional logistic regression analysis. The possible mediating roles of atopy and airway obstruction were studied by investigating the impact of incorporating data on sensitisation to common aeroallergens and measurements of lung function. Results: BMI was associated with asthma in boys (odds ratio (OR)=1.14, 95% confidence interval (CI), 1.08–1.20; adjusted OR=1.11, 95% CI, 1.03–1.19) and girls (OR=1.37, 95% CI, 1.26–1.50; adjusted OR=1.38, 95% CI, 1.23–1.56). Adjusting for forced expiratory volume in 1 s had a negligible impact on these associations, but these were attenuated following adjustment for allergic sensitisation, particularly in girls (girls: OR=1.25; 95% CI, 0.96–1.60; boys: OR=1.09, 95% CI, 0.99–1.19). Conclusions: BMI is associated with asthma in pre-pubertal Saudi boys and girls; this effect does not appear to be mediated through respiratory obstruction, but in girls this may at least partially be mediated through increased risk of allergic sensitisation

The Cultivation of Water Hyacinth in India as a Feedstock for Anaerobic Digestion: Development of a Predictive Model for Scaling Integrated Systems

A novel, integrated system is proposed for the cultivation and co-digestion of the invasive macrophyte water hyacinth (WH) with cow manure (CM) for the production of biogas for cooking in rural India. This study investigates the pre-treatment approaches and performs a techno-economic analysis of producing biogas in fixeddome digesters as a replacement for liquefied petroleum gas (LPG). Methodologies have been developed for the cultivation of WH collected from wild plants in the Indrayani River, Pune, India. Cultivation trials were performed in 350 litre tanks using water, which was nutrient fed with CM. Cultivation trials were performed over a 3 week period, and growth rates were determined by removing and weighing the biomass at regular time intervals. Cultivation results provided typical yields and growth rates of biomass, allowing predictions to be made for cultivation scaling. Samples of cultivated WH have been co-digested with CM at a 20:80 ratio in 200 L anaerobic digesters, allowing for the prediction of bio-methane yields from fixed-dome anaerobic digesters in real world conditions, which are commonly used in the rural locations of India. A calculator has been developed, allowing us to estimate the scaling requirements for the operation of an integrated biomass cultivation and anaerobic co-digestion unit to produce an equivalent amount of biogas to replace between one and three LPG cylinders per month. A techno-economic analysis of introducing WH into fixed-dome digesters in India demonstrated that the payback periods range from 9 years to under 1 year depending on the economic strategies. To replace between one and three LPG cylinders per month using the discussed feedstock ratio, the cultivation area of WH required to produce sufficient co-feedstock ranges within 10–55 m2

Synthetic Peptides Mimic gp75 from Paracoccidioides brasiliensis in the Diagnosis of Paracoccidioidomycosis

Paracoccidioidomycosis (PCM) is a systemic granulomatous disease, endemic in Latin America, caused by the thermal dimorphic fungus Paracoccidioides brasiliensis. Although some fungal antigens have already been characterized and used for serological diagnosis, cross-reactions have been frequently observed. Thus, the examination of fungal forms in clinical specimens or isolation of P. brasiliensis by culture is still the most frequent method for the diagnosis of this mycosis. In this study, a random peptide phage display library was used to select mimotopes of P. brasiliensis, which were employed as antigens in an indirect enzyme-linked immunosorbent assay. The protective monoclonal antibody against experimental PCM (anti-gp75) was used as molecular target to screen a phage display library. That approach led to a synthetic peptide named P2, which was synthesized and tested against PCM patients’ sera to check whether it was recognized. There was significant recognition of P2 by sera of untreated PCM patients when compared with normal human sera. Sera from treated PCM group, patients with other mycosis or co-infected with HIV had much lower recognition of P2 than untreated patient group. The test showed a sensitivity of 100 and 94.59% of specificity in relation to human sera control. These data indicate a potential use of P2 as diagnostic tool in PCM. Its application for serological diagnosis of PCM may contribute to the development and standardization of simpler, faster and highly reproducible immunodiagnostic tests at low cost