Ensuring safety standards in sewage sludge-derived biochar: Impact of pyrolysis process temperature and carrier gas on micropollutant removal.

The application of sewage sludge to agricultural land is facing increasing restrictions due to concerns about various micropollutants, including polycyclic aromatic hydrocarbons (PAHs), dioxins and furans (PCDD/Fs), polychlorinated biphenyls (PCBs), per- and poly-fluoroalkyl substances (PFAS), and heavy metals (HMs). As an alternative approach to manage this residue, the use of pyrolysis, a process that transforms sludge into biochar, a carbon-rich solid material, is being explored. Despite the potential benefits of pyrolysis, there is limited data on its effectiveness in removing micropollutants and the potential presence of harmful elements in the resulting biochar. This study aims to evaluate the impact of the temperature and the use of a carrier gas (N2) during a two-stage pyrolysis and cooling on micropollutant removal. Pilot-scale tests showed that a higher temperature (650 °C) and the use of a carrier gas (0.4 L/min N2) during the pyrolysis and the cooling process led to a reduction of PAHs, PCDD/Fs, PCBs and PFAS below their detection limits. As such, the generated biochar aligns with the guidelines set by the International Biochar Initiative (IBI) and the European Biochar Certificate (EBC) for all micropollutants, except for zinc and copper. Additional investigation is required to determine whether the micropollutants undergo destruction or transition into other pyrolysis end-products, such as the gas or liquid phase.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions.

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Multi-scale techno-economic assessment of nitrogen recovery systems for livestock operations.

Intensive livestock farming generates vast amounts of organic materials, which are an important source of nitrogen releases. These anthropogenic nitrogen releases contribute to multiple environmental problems, including eutrophication of water systems, contamination of drinking water sources, and greenhouse gas emissions. Nitrogen recovery and recycling are technically feasible, and there exists a number of processes for nitrogen recovery from livestock material in the form of different products. In this work, a multi-scale techno-economic assessment of techniques for nitrogen recovery and recycling is performed. The assessment includes a material flow analysis of each process, from material collection to final treatment, to determine nitrogen recovery efficiency, losses, and recovery cost, as well as an environmental cost-benefit analysis to compare the nitrogen recovery cost versus the economic losses derived from its uncontrolled release into the environment. The results show that transmembrane chemisorption process results in the lowest recovery cost, 3.4-10.4 USD per kilogram of nitrogen recovered in the range of studied processing scales. The recovery of nitrogen from livestock material through three technologies, i.e., transmembrane chemisorption, MAPHEX, and stripping in packed bed, reveales to be cost-effective. Since the economic losses due to the harmful effects of nitrogen into the environment are estimated at 32-35 USD per kilogram of nitrogen released, nitrogen recycling is an environmentally and economically beneficial approach to reduce nutrient pollution caused by livestock operations.

N, P, K recovery from hydrolysed urine by Na-chabazite adsorption integrated with ammonia stripping and (K-)struvite precipitation.

This study investigated the recovery of K+ along with NH4+-N and PO43--P from hydrolyzed urine by technical integration. The K adsorption capacities of biochar, clinoptilolite, artificial zeolite and chabazite were firstly compared. Due to the high K recovery efficiency and additional P recovery capacity, Na-chabazite was selected as the adsorbent in this study. Its kinetics and isotherm analysis indicated that the high molarity of NH4+-N seriously hindered the K adsorption onto Na-chabazite in synthetic hydrolyzed urine (SHU). However, this competition between NH4+ and K+ got diminished when their molarity is the same, i.e. in the SHU after ammonia stripping (ASSHU). Based on this key finding, Na-chabazite adsorption was integrated with ammonia stripping and struvite precipitation under different configurations. Simultaneous ammonia stripping was inadequate to diminish the competitive effect of NH4+ on K+ adsorption. Depending on the demand for fertilizer, two sequential configurations were recommended, respectively.

Construction, renovation and demolition (CRD) wastes contaminated by gypsum residues: Characterization, treatment and valorization.

Management of wastes resulting from construction, renovation and demolition (CRD) activities has become an important challenge for scientists. The recovery of gypsum residues from CRD waste is one of the solutions to minimize the impact of CRD operations on the environment. This review discusses the characteristics of CRD waste, different treatment and valorization methods for both CRD waste and extracted gypsum residues. Pre-treatment based on particle size separation is the most fundamental step in the process of extracting gypsum residues from CRD fine tailings. The subsequent application of a physical, chemical or biological decontamination approach on the gypsum residues could significantly improve its quality as compared to natural gypsum. The quality of the gypsum obtained affects its valorization potential in different sectors such as cement manufacturing, the sequestration of carbon dioxide and nutrients. The valorization strategy could help reducing emissions of greenhouse gases while producing by-products that can be reused in agriculture. As such, this review may provide guidance for more sustainable management of CRD and gypsum residues in the future.

Greenhouse gas emissions from inorganic and organic fertilizer production and use: A review of emission factors and their variability.

Fertilizers have become an essential part of our global food supply chain and are necessary to sustain our growing population. However, fertilizers can also contribute to greenhouse gas (GHG) emissions, along with other potential nutrient losses in the environment, e.g. through leaching. To reduce this environmental impact, tools such as life cycle assessments and decision support systems are being used to aid in selecting sustainable fertilization scenarios. These scenarios often include organic waste-derived amendments, such as manures, composts and digestates. To produce an accurate assessment and comparison of potential fertilization scenarios, these tools require emission factors (EFs) that are used to estimate GHG emissions and that are an integral part of these analyses. However, such EFs seem to be very variable in nature, thereby often resulting in high uncertainty on the outcomes of the analyses. This review aims to identify ranges and sources of variability in EFs to provide a better understanding of the potential uncertainty on the outcomes, as well as to provide recommendations for selecting EFs for future studies. As such, an extensive review of the literature on GHG emissions from production, storage, transportation and application of synthetic fertilizers (N, P, K), composts, digestates and manures was performed. This paper highlights the high variability that is present in emissions data and confirms the great impact of this uncertainty on the quality and validity of GHG predictions related to fertilizers. Variability in EFs stem from the energy source used for production, operating conditions, storage systems, crop and soil type, soil nutrient content, amount and method of fertilizer application, soil bacterial community, irrigation method, among others. Furthermore, a knowledge gap exists related to EFs for potassium fertilizers and waste valorization (anaerobic digestion/composting) processes. Overall, based on this review, it is recommended to determine EFs on a case by case basis when possible and to use uncertainty analyses as a tool to better understand the impact of EF variability.

Current state and potential valorisation of ship-generated organic waste in Quebec, Canada.

The Quebec residual materials management policy implies the banning of organic waste disposal or incineration from 2022 onwards. This policy also applies to domestic ship-generated organic waste. However, little is known about the current state of ship-generated organic waste management in the province of Quebec. This study aims to analyse the current situation and propose sustainable strategies for ship-generated organic waste valorisation in Quebec. Using the available data, it was attempted to estimate ship-generated waste quantities in Quebec, after which the current practices of domestic ship-generated organic waste management in Quebec and Europe were inventoried, along with international waste management practices. Five waste valorisation scenarios were then proposed and compared in terms of advantages and disadvantages, required equipment, and associated costs and revenues. It involves: 1) composting on board of the ship, 2) centralised composting, 3) composting at the port, 4) centralised biomethanation, and 5) biomethanation at the port. The current available data on ship-generated waste quantities in Quebec did, however, not allow selecting an optimal scenario. The information provided in this short communication can serve as a valuable basis to guide future research efforts and decision-making in this regard. Furthermore, the current management of international waste was found to be complex and costly, although biomethanation of such waste could offer a suitable and more sustainable solution. Finally, it was concluded that a good cooperation between ships and ports is crucial to the implementation of any sustainable waste valorisation strategy.

A review of mathematical models for composting.

Composting is a valuable method to treat and valorize organic waste. However, the process is defined by its dynamic nature and governed by a multitude of operating parameters. As such, mathematical modelling of the process offers a powerful tool to simulate and predict the variable outcomes of the process, allowing for its optimization. This can include improving efficiency, lowering costs and reducing environmental impact. To aid with the development of future models, we provide an up to date review and assessment on the state of the art of composting modelling. By reviewing 40 years of literature, this review paints the most complete picture of the field to date. This includes an analysis of trends in composting modelling: looking at the type of systems that are targeted, the aim of the models and the approaches to kinetics and mass and heat transfer. Regarding modelling approaches, we explore the fractionation of both substrates and microorganisms, the biological processes that can be included (disintegration, hydrolysis, uptake and death) and their kinetics (first-order, Monod-type), energy balances (biological generation, convection, conduction) and mass balances. We also provide a review of the results of sensitivity analyses performed on composting models, finding that models are most sensitive to microbial growth and death rates, as well as consumption rates and product yields. In the final portion of the review, we identify, explore, and provide guiding recommendations for work on emerging areas and areas requiring development in composting modelling (volume change, pH, maturation, artificial intelligence, etc.).

Developing successful environmental decision support systems: Challenges and best practices.

Environmental decision support systems (EDSSs), or DSS applied in the environmental field, have been developed for over 40 years now. However, most of these tools fail to find use or fall out of use extremely quickly. In the aim of aiding in the conception and development of practical and successful decision support systems, i.e. systems that can lead to positive outcomes, this review looks over the existing literature, both EDSS-centric and from broader decision-related fields, to highlight some of the most important challenges influencing the success and usability of these systems. In all, 13 major challenges facing EDSS development were identified and over 60 recommendations and best practices were provided to address these challenges. Though this paper is mainly focused on environmental decision support systems, most of the highlighted information and conclusions are applicable to the development of decision support systems in any field.

Management of ship-generated food waste and sewage on the Baltic Sea: A review.

The combination of increased maritime transportation and the sensitivity of the Baltic Sea makes it necessary to establish efficient, eco-friendly and profitable ship-generated waste management strategies. This study aims to identify best management practices for ship-generated nutrient-rich organic wastes, i.e. food waste and sewage, on the Baltic Sea. Ship-generated waste quantities and characteristics, maritime waste regulations, and disposal methods are reviewed and discussed according to the available literature for the Ports of Helsinki, Stockholm, Tallinn and Copenhagen Malmö, which are the most important and busiest ports on the Baltic Sea. Sorting onboard and separation of food waste from other waste sources such as sewage and grey water is a suitable solution that facilitates further treatment. However, this procedure demands special facilities and sufficient storage space. Aforementioned food waste can be delivered to port reception facilities (PRFs) and used to produce biogas at land. However, currently only food waste from ships operating in the EU may be used as input for biogas production, not international food waste. Grinding of food waste and discharge into the sea is still common practice. In addition, shipping companies can choose buffet type restaurants in order to reduce food waste generation. Grey wastewater is generally discharged into the sea, whereas sewage needs to be treated on board before discharge or delivered to PRFs for treatment. New MARPOL regulations for passenger ships on the Baltic Sea require advanced treatment of pollutant nutrients, nitrogen and phosphorus, before sewage discharge in order to combat eutrophication of this sensitive area.

Enzymatic reactions in the production of biomethane from organic waste.

Enzymatic reactions refer to organic reactions catalyzed by enzymes. This review aims to enrich the documentation relative to enzymatic reactions occurring during the anaerobic degradation of residual organic substances with emphasis on the structures of organic compounds and reaction mechanisms. This allows to understand the displacement of electrons between electron-rich and electron-poor entities to form new bonds in products. The detailed mechanisms of enzymatic reactions relative to the production of biomethane have not yet been reviewed in the scientific literature. Hence, this review is novel and timely since it discusses the chemical behavior or reactivity of different functional groups, thereby allowing to better understand the enzymatic catalysis in the transformations of residual proteins, carbohydrates, and lipids into biomethane and fertilizers. Such understanding allows to improve the overall biomethanation efficiency in industrial applications.

Optimization of P compounds recovery from aerobic sludge by chemical modeling and response surface methodology combination.

Phosphorus recovery has drawn much attention during recent years, due to estimated limited available quantities, and to the harmful environmental impact that it may have when freely released into aquatic environments. Struvite precipitation from wastewater or biological sludge is among the preferred approaches applied for phosphorus recovery, as it results in the availability of valuable fertilizer materials. This process is mostly affected by pH and presence of competitive ions in solution. Modeling and optimization of the precipitation process may help understanding the optimal conditions under which the most efficient recovery could be achieved. In this study, a combination of chemical equilibrium modeling and response surface methodology (RSM) was applied to this aim to aerobic sludge from a plant in Italy. The results identify optimum chemical parameters values for best phosphorus precipitation recovery and removal efficiencies, respectively. Identification of optimal conditions for process control is of great importance for implementing pilot scale struvite precipitation and achieve efficient phosphorus recovery.

Optimizing the configuration of integrated nutrient and energy recovery treatment trains: A new application of global sensitivity analysis to the generic nutrient recovery model (NRM) library.

This paper describes the use of global sensitivity analysis (GSA) for factor prioritization in nutrient recovery model (NRM) applications. The aim was to select the most important factors influencing important NRM model outputs such as biogas production, digestate composition and pH, ammonium sulfate recovery, struvite production, product purity, particle size and density, air and chemical requirements, scaling potential, among others. Factors considered for GSA involve: 1) input waste stream characteristics, 2) process operational factors, and 3) kinetic parameters incorporated in the NRMs. Linear regression analyses on Monte Carlo simulation outputs were performed, and the impact of the standardized regression coefficients on major performance indicators was evaluated. Finally, based on the results, the paper describes the original use of GSA to obtain insight in complex nutrient recovery systems and to propose an optimal nutrient and energy recovery treatment train configuration that maximizes resource recovery and minimizes energy and chemical requirements.

Evaluation of sustainable scrubbing agents for ammonia recovery from anaerobic digestate.

Organic acids (citric and acetic), chilled water, epsom and gypsum were tested for ammonia recovery from anaerobic digestate in a bench-scale stripping-scrubbing experimental setup. Citric acid was found to give excellent scrubbing performance equivalent to that of sulfuric acid but required double the acid dosage due to its partial dissociation characteristics. Acetic acid performed satisfactorily at low temperature and was susceptible to vaporization due to stripping effect in the scrubbing unit, while the other three scrubbing agents were found to be ineffective. Economic and safety comparisons among the acids demonstrated that citric acid could be feasible for full-scale applications given competitive material cost and an expended organic fertilizer market.

Life Cycle Assessment of Biofertilizer Production and Use Compared with Conventional Liquid Digestate Management.

Handling of digestate produced by anaerobic digestion impacts the environment through emission of greenhouse gases, reactive nitrogen, and phosphorus. Previous life cycle assessments (LCA) evaluating the extraction of nutrients from digestate using struvite precipitation and ammonia stripping did not relate synthetic fertilizer substitution (SFS) to nutrient use efficiency consequences. We applied an expanded LCA to compare the conventional management of 1 m3 of liquid digestate (LD) from food waste against the production and use of digestate biofertilizer (DBF) extracted from LD, accounting for SFS efficacy. Avoidance of CH4, N2O, and NH3 emissions from LD handling and enhanced SFS via more targeted use of nutrients in the versatile DBF product could generate environmental savings of up to 0.129 kg Sb eq, 4.16 kg SO2 eq, 1.22 kg PO4 eq, 33 kg CO2 eq, and 20.6 MJ eq per m3 LD, for abiotic resource depletion, acidification, eutrophication, global warming, and cumulative energy demand burdens, respectively. However, under worst-case assumptions, DBF extraction could increase global warming and cumulative energy demand by 7.5 kg CO2e and 251 MJ eq per m3 LD owing to processing inputs. Normalizing these results against per capita environmental loadings, we conclude that DBF extraction is environmentally beneficial.

Nutrient recovery from digested waste: Towards a generic roadmap for setting up an optimal treatment train.

This paper aims to develop a generic roadmap for setting up strategies for nutrient recovery from digested waste (digestate). First, a guideline-based decision-tree is presented for setting up an optimal bio-based fertilization strategy as function of local agronomic and regulatory criteria. Next, guidelines and evaluation criteria are provided to determine the feasibility of bio-based fertilizer production as function of the input digestate characteristics. Finally, a conceptual decision making algorithm is developed aiming at the configuration and optimization of nutrient recovery treatment trains. Important input digestate characteristics to measure, and essential factors for monitoring and control are identified. As such, this paper provides a useful decision-support guide for wastewater and residuals processing utilities aiming to implement nutrient recovery strategies. This, in turn, may stimulate and hasten the global transition from wastewater treatment plants to water resource recovery facilities. On top of that, the proposed roadmap may help adjusting the choice of nutrient recovery strategies to local fertilizer markets, thereby speeding up the transition from a fossil-reserve based to a bio-based circular nutrient economy.

Climate regulation, energy provisioning and water purification: Quantifying ecosystem service delivery of bioenergy willow grown on riparian buffer zones using life cycle assessment.

Whilst life cycle assessment (LCA) boundaries are expanded to account for negative indirect consequences of bioenergy such as indirect land use change (ILUC), ecosystem services such as water purification sometimes delivered by perennial bioenergy crops are typically neglected in LCA studies. Consequential LCA was applied to evaluate the significance of nutrient interception and retention on the environmental balance of unfertilised energy willow planted on 50-m riparian buffer strips and drainage filtration zones in the Skåne region of Sweden. Excluding possible ILUC effects and considering oil heat substitution, strategically planted filter willow can achieve net global warming potential (GWP) and eutrophication potential (EP) savings of up to 11.9 Mg CO2e and 47 kg PO4e ha-1 year-1, respectively, compared with a GWP saving of 14.8 Mg CO2e ha-1 year-1 and an EP increase of 7 kg PO4e ha-1 year-1 for fertilised willow. Planting willow on appropriate buffer and filter zones throughout Skåne could avoid 626 Mg year-1 PO4e nutrient loading to waters.

Environmental assessment of digestate treatment technologies using LCA methodology.

The production of biogas from energy crops, organic waste and manure has augmented considerably the amounts of digestate available in Flanders. This has pushed authorities to steadily introduce legislative changes to promote its use as a fertilising agent. There is limited arable land in Flanders, which entails that digestate has to compete with animal manure to be spread. This forces many anaerobic digestion plants to further treat digestate in such a way that it can either be exported or the nitrogen be removed. Nevertheless, the environmental impact of these treatment options is still widely unknown, as well as the influence of these impacts on the sustainability of Flemish anaerobic digestion plants in comparison to other regions where spreading of raw digestate is allowed. Despite important economic aspects that must be considered, the use of Life Cycle Assessment (LCA) is suggested in this study to identify the environmental impacts of spreading digestate directly as compared to four different treatment technologies. Results suggest relevant environmental gains when the digestate mix is treated using the examined conversion technologies prior to spreading, although important trade-offs between impact categories were observed and discussed. The promising results of digestate conversion technologies suggest that further LCA analyses should be performed to delve into, for instance, the appropriateness to shift to nutrient recovery technologies rather than digestate conversion treatments.