Littérature scientifique sur le sujet « Hydrothermal carbonization, sewage sludge, food waste, energy recovery »

This paper is about the conversion of wet waste stream into valuable products via thermal processing. Hydrothermal carbonization of sewage sludge was carried out at 200°C and 2.1 MPa in a closed reactor for 1–6 h. Main products were in solid and liquid phases. The resulting hydrochar was shown to have H/C and O/C ratios moving towards natural lignite, improved energetic content, and adsorption property in terms of iodine number. The aqueous solution was found to contain high concentration of plant food nutrients, especially nitrogen and potassium. They may be desirable for subsequent fuel and chemical production as well as applications in agriculture. The study shows that valuable products can be generated successfully from sewage sludge using hydrothermal carbonization.

In this study, the growing scientific field of alternative biofuels was examined, with respect to hydrochars produced from renewable biomasses. Hydrochars are the solid products of hydrothermal carbonization (HTC) and their properties depend on the initial biomass and the temperature and duration of treatment. The basic (Scopus) and advanced (Citespace) analysis of literature showed that this is a dynamic research area, with several sub-fields of intense activity. The focus of researchers on sewage sludge and food waste as hydrochar precursors was highlighted and reviewed. It was established that hydrochars have improved behavior as fuels compared to these feedstocks. Food waste can be particularly useful in co-hydrothermal carbonization with ash-rich materials. In the case of sewage sludge, simultaneous P recovery from the HTC wastewater may add more value to the process. For both feedstocks, results from large-scale HTC are practically non-existent. Following the review, related data from the years 2014–2020 were retrieved and fitted into four different artificial neural networks (ANNs). Based on the elemental content, HTC temperature and time (as inputs), the higher heating values (HHVs) and yields (as outputs) could be successfully predicted, regardless of original biomass used for hydrochar production. ANN3 (based on C, O, H content, and HTC temperature) showed the optimum HHV predicting performance (R2 0.917, root mean square error 1.124), however, hydrochars’ HHVs could also be satisfactorily predicted by the C content alone (ANN1, R2 0.897, root mean square error 1.289).

Municipal sewage sludge is the residual material produced as a waste of municipal wastewater purification. It is a sophisticated multi-component material, hard to handle. For many years, it has been landfilled, incinerated, and widely used in agriculture practice. When unproperly discharged, it is very polluting and unhealthy. The rapidly increasing global amount of municipal sewage sludge produced annually depends on urbanization, degree of development, and lifestyle. Some diffused traditional practices were banned or became economically unfeasible or unacceptable by the communities. In contrast, it has been established that MSS contains valuable resources, which can be utilized as energy and fertilizer. The objective of the review was to prove that resource recovery is beneficially affordable using modern approaches and proper technologies and to estimate the required resources and time. The open sources of information were deeply mined, critically examined, and selected to derive the necessary information regarding each network segment, from the source to the final point, where the municipal sewage sludge is produced and disposed of. We found that developed and some developing countries are involved with ambitious and costly plans for remediation, the modernization of regulations, collecting and purification systems, and beneficial waste management using a modern approach. We also found that the activated sludge process is the leading technology for wastewater purification, and anaerobic digestion is the leading technology for downstream waste. However, biological technologies appear inadequate and hydrothermal carbonization, already applicable at full scale, is the best candidate for playing a significant role in managing municipal sewage sludge produced by big towns and small villages.

The aim of the paper was to summarize and discuss current research trends in biomass thermal treatment (torrefaction process). Quantitative analyses were carried out, in which the main countries, research units and scientists were indicated. The analysis showed a clear upward trend in number of publications after 2010. Most scientists on selected topics come from China, USA, Canada, South Korea, Republic of China, Poland (Web od Science—Core Collection (WoS-CC) and Scopus databases). Quantitative analysis also showed that the most relevant WoS-CC categories in the summary are: Energy Fuels, Engineering Chemical, Agricultural Engineering, Biotechnology Applied Microbiology and Thermodynamics and Scopus Subject area: Energy, Chemical Engineering, Environmental Science, Engineering and Chemistry. Thematic analysis included research topics, process parameters and raw materials used. Thematic groups were separated: torrefaction process (temp.: 150–400 °C), hydrothermal carbonization process (HTC) (temp: 120–500 °C), pyrolysis process (temp.: 200–650 °C) and gasification and co-combustion process (temp.: 350–1600 °C). In the years 2015–2019, current research topics were: new torrefaction technologies (e.g., HTC), improvement of the physico-mechanical, chemical and energetic properties of produced fuel as well as the use of torrefied biomass in the process of pyrolysis, gasification and co-combustion. The raw materials used in all types of biomass thermal treatment were: energy crops, wood from fast-growing and exotic trees, waste from the agri-food industry, sewage sludge and microalgae.

Very little is known about how products derived from the hydrothermal carbonization (HTC) of municipal waste affect the availability and uptake of nitrogen in plant nutrition. This study examined the effects of 60% sewage sludge and 40% food waste HTC products, i.e., biochar (BC) and process water (PW), as nitrogen sources on garden cress growth and quality. A fertilization program using four nitrogen doses [(control), 9, 12, and 15 kg da−1 N] and BC, PW, chemical nitrogen (CN), and their combinations were used in a pot experiment conducted under greenhouse conditions. The highest nitrogen dose often produced better results in terms of plant growth and quality. Additionally, fertilization with PW+CN and BC+CN at the highest nitrogen dose significantly improved plant height, plant fresh and dry weight, and root dry weight parameters of garden cress over the previous treatments. The highest stem diameter, number of leaves, and plant area values were obtained in the 15 kg da−1 N dose PW+BC application. The vitamin C content in cress decreased with the increasing levels of CN. The highest vitamin C content was obtained with 15 kg N da−1 PW fertilization. BC+PW and CN fertilization applications improved chlorophyll a, b, and the total contents of garden cress leaves. Moreover, the nitrate (NO3) concentration of cress increased with CN doses while it decreased in all BC and PW administrations. The 9, 12, and 15 kg N da−1 doses of PW+CN and the 15 kg N da−1 dose of BC+CN yielded the highest agricultural nitrogen utilization efficiency (ANUE) values. Plant nutrient content was positively affected in all fertilization applications, except for Na and Cl. However, it was determined that BC+CN fertilizer application improved plant nutrient uptake. Surprisingly, PW+CN treatment at the lowest nitrogen dosage resulted in the highest soil organic matter and total nitrogen content. In conclusion, it has been determined that biochar and process water have a synergistic effect with CN to increase plant growth by improving nitrogen efficiency, but their application alone without CN is insufficient to meet the nitrogen requirement.

The goal of this paper is to review current impacts of human activities on the deep-sea floor ecosystem, and to predict anthropogenic changes to this ecosystem by the year 2025. The deep-sea floor ecosystem is one of the largest on the planet, covering roughly 60% of the Earth's solid surface. Despite this vast size, our knowledge of the deep sea is poor relative to other marine ecosystems, and future human threats are difficult to predict. Low productivity, low physical energy, low biological rates, and the vastness of the soft-sediment deep sea create an unusual suite of conservation challenges relative to shallow water. The numerous, but widely spaced, island habitats of the deep ocean (for example seamounts, hydrothermal vents and submarine canyons) differ from typical deep-sea soft sediments in substrate type (hard) and levels of productivity (often high); these habitats will respond differently to anthropogenic impacts and climate change. The principal human threats to the deep sea are the disposal of wastes (structures, radioactive wastes, munitions and carbon dioxide), deep-sea fishing, oil and gas extraction, marine mineral extraction, and climate change. Current international regulations prohibit deep-sea dumping of structures, radioactive waste and munitions. Future disposal activities that could be significant by 2025 include deep-sea carbon-dioxide sequestration, sewage-sludge emplacement and dredge-spoil disposal. As fish stocks dwindle in the upper ocean, deep-sea fisheries are increasingly targeted. Most (perhaps all) of these deep-sea fisheries are not sustainable in the long term given current management practices; deep-sea fish are long-lived, slow growing and very slow to recruit in the face of sustained fishing pressure. Oil and gas exploitation has begun, and will continue, in deep water, creating significant localized impacts resulting mainly from accumulation of contaminated drill cuttings. Marine mineral extraction, in particular manganese nodule mining, represents one of the most significant conservation challenges in the deep sea. The vast spatial scales planned for nodule mining dwarf other potential direct human impacts. Nodule-mining disturbance will likely affect tens to hundreds of thousands of square kilometres with ecosystem recovery requiring many decades to millions of years (for nodule regrowth). Limited knowledge of the taxonomy, species structure, biogeography and basic natural history of deep-sea animals prevents accurate assessment of the risk of species extinctions from large-scale mining. While there are close linkages between benthic, pelagic and climatic processes, it is difficult to predict the impact of climate change on deep-sea benthic ecosystems; it is certain, however, that changes in primary production in surface waters will alter the standing stocks in the food-limited, deep-sea benthic. Long time-series studies from the abyssal North Pacific and North Atlantic suggest that even seemingly stable deep-sea ecosystems may exhibit change in key ecological parameters on decadal time scales. The causes of these decadal changes remain enigmatic. Compared to the rest of the planet, the bulk of the deep sea will probably remain relatively unimpacted by human activities and climate change in the year 2025. However, increased pressure on terrestrial resources will certainly lead to an expansion of direct human activities in the deep sea, and to direct and indirect environmental impacts. Because so little is known about this remote environment, the deep-sea ecosystem may well be substantially modified before its natural state is fully understood.

AbstractPhosphorus (P) recovery from P-rich residues is crucial to sustain food and industrial demands globally, as phosphate rock reserves are being depleted. The aim of this study is to investigate the speciation and recovery of P from hydrochars (HC) of a metal-bearing sewage sludge (SS) produced by hydrothermal carbonization (HTC). We here focus on extractions by acid leaching as P cannot be directly recovered by HTC due to insoluble metal-P compounds. Acid leaching of SS and HCs was investigated using H2SO4 and HCl over a range of leaching times, and explained in terms of how composition affects P and metal release efficiency. HTC at 180, 215 and 250 °C showed that P remained immobilized (> 75% of total P) in the HCs. More than 95% was present as inorganic P, and was the direct consequence of the double addition of iron salts in the wastewater treatment plant. Leaching experiments in 2.5 M acid solutions showed that a near complete release of P could be achieved in HCs, while it was only incomplete in SS (up to 85%). Lower acid concentrations were ineffective for total P recovery. Treatment temperature exceeding 180 °C however decreased P release rates, such that total removal took at least 2 h of reaction time instead of a few minutes. On the other hand, acid leaching transferred more than 70% of iron, manganese, copper and zinc into the leachate, necessitating a post-treatment purification process. This work therefore reveals that HC produced at low HTC temperatures could offer promising avenues for time- and energy-efficient P recovery from SS. Graphic Abstract

Sewage sludge (SS), which is the main by-product of a Water Resources Recovery Facility (WRRF), is produced worldwide in large amounts. The rapid population growth, together with the progressive urbanization, has led to the generation of an increasing amount of SS, which is expected to continuously increase in the next future (up to an annual production of 150 – 200 million tons on a dry basis by 2050). Further, the production of other wastes, such as food waste (FW), are going to increase in the coming years. In fact, more than 2 billion tons of municipal waste have been generated worldwide and the production is estimated to increase by 70% to 2050. Sewage sludge and food waste must be properly disposed of using the best available technologies, in accordance with the current legislation and the circular economy principles. Both wastes can be generally treated via composting, anaerobic digestion (AD), incineration, and landfilling. However, all these treatments suffer from various limitations (e.g., long treatment time, pre-treatments, and inhibition). Therefore, thermochemical technologies, such as hydrothermal carbonization (HTC), are becoming increasingly attractive to treat different types of wet biomasses (such as SS, and FW). Indeed, HTC is able to transform the feedstock in three fractions: a solid fraction (hydrochar, HC), a liquid phase (process water, PW), and a small gaseous phase. This aim of this work was to investigate the application of HTC to treat SS or FW. In particular, the carbonization of SS has been extensively studied (Chapter 1 – 5), whereas only Chapter 6 has been devoted to the treatment of FW through HTC. Chapter 1 studies the influence of HTC reaction conditions (i.e., temperature, time, and solid content) on products (HC and PW) characteristics. Secondary SS derived from San Colombano WRRF (Florence, Italy) was collected and further treated via HTC by changing the operating conditions. Both HC and PW were characterized, pointing out that there was a relationship between HTC conditions and products characteristics. Further, the dewaterability of SS after HTC treatment was tested, showing better filtration performance than raw sludge. Chapter 2 investigates the recovery of phosphorous (P) from HC by acid leaching. Two acids (HNO3, and H2SO4) were tested, using both process water derived from SS carbonization and demineralized water as solution. Phosphorous yield (P yield) and ash content were selected as responses, with the goal to find the optimal conditions to maximize P yield while minimizing ash content. H2SO4 favoured P yield, but at the same time increased ash content in HC after leaching. In Chapter 3, three possible valorization pathways of PW derived from HTC on SS are proposed. Six SS samples (three anaerobically digested, and three aerobically stabilized) were collected from six WRRFs in Tuscany (Italy). The potential applications of PW as fertilizer on soils, as a substrate in AD, and as an effluent to be recirculated into the WRRF were further investigated. Process water was studied both in terms of chemical characterization and of biodegradability in anaerobic and aerobic conditions. The result was that PW has potential for a future use in soils, and that a correlation between anaerobic and aerobic biodegradability can be found. Chapter 4 is focused on the continuous anaerobic treatment of HTC-derived PW of the digested SS. For this purpose, an upflow anaerobic sludge blanket reactor (UASB) was set up for continuous treatment of PW. The reactor was first started up with only glucose, and subsequently a progressively increasing percentage of PW was added, reaching the 100 % of PW after 113 Days. Various parameters were monitored over time (e.g., biogas volume and composition, chemical oxygen demand (COD), and volatile fatty acids). A soluble COD removal up to 73 % was observed, while a specific CH4 production equal to 202 (33) mL STP CH4 g-1CODfed was achieved. Chapter 5 addresses the integration between the existing SS treatment line of San Colombano WRRF and HTC through Life Cycle Assessment analysis. HC was assumed to be energetically valorized as a solid fuel, while different treatments were proposed for PW (recirculation into the WRRF, or anaerobic digestion). In addition, phosphorous recovery from HC was also included in two of five Scenarios. Results showed that more environmental benefits occurred when including HTC into the SS treatment line (excluding three impact categories). Phosphorous recovery negatively affected the environmental performances of the proposed configurations, indicating that this process should be optimised. Finally, Chapter 6 investigates the application of HTC on FW. HC was chemically characterized, and since its properties resulted to fulfil the requirements of ISO/TS 17225-8, its application as biofuel was proposed. Further, PW was used as substrate in AD. The process was monitored over time in terms of soluble COD, total ammonia nitrogen, pH, alkalinity, and volatile fatty acids. The trend of recalcitrant compounds before and after AD was studied, observing that AD promoted the removal of specific refractory compounds. In addition, an energetic and economical balance of the process was carried out, evaluating the benefits produced by HTC technology.